HG/T 20570.5-1995 Calculation of pump system characteristics and determination of relative installation height of equipment
Some standard content:
Calculation of pump system characteristics and determination of relative installation height of equipment HG/T20570.5-95 Prepared by: China Wuhuan Chemical Engineering Corporation Approved by: Ministry of Chemical Industry Implementation date: "September 1, 1996 Prepared by: China Wuhuan Chemical Engineering Corporation Audited by: Gong Jingde Wu Bingyong Wu Qiying Gong Renwei of the Process System Design Technology Center of the Ministry of Chemical Industry 1 Scope 1.0.1 This regulation applies to the piping system of centrifugal pumps and reciprocating pumps, proposes the calculation of pump system characteristics and pump calculation tables, and introduces the process system to ensure the pump Measures for normal operation and methods for determining the relative installation height of equipment. 1.0.2
The system characteristic calculation of centrifugal pumps is also applicable to rotor pumps and vortex pumps. 101
2 Piping system of pumps
2.0.1 Basic types of piping systems of pumps
2.0.1.1 The piping system of a pump is divided into suction piping and discharge piping. The suction piping and discharge piping include pipelines with constant diameter and flow rate, pipelines with variable diameter but constant flow rate, and branch pipelines (different pipe sections have different diameters and flow rates).
2.0.1.2 The suction piping is divided into two types: suction and injection. The accessories on the pipeline mainly include heat exchangers, filters, valves, pipe fittings, buffer tanks (for reciprocating pumps), etc. 2.0.1.3 The accessories of the discharge pipeline mainly include Including heat exchangers, furnaces, separators, control valves, flow meters, flow limiting orifice plates, nozzles, pipe fittings, buffer tanks (for reciprocating pumps), etc. 2.0.1.4 The piping system of any pump is any combination of the above suction and discharge piping conditions. 2.0.2 Selection of flow rate and pipe diameter of the pump piping system 2.0.2.1 The flow rate in the suction pipe of a centrifugal pump for water and liquids with similar physical properties to water is 1.5~2m/s (normal temperature), or 0.5~1.5m/s (70~110℃); the flow rate in the discharge pipe is 1.5~3m/s. The flow rate in the suction pipe of a reciprocating pump is 0.5~1.5m/s, and the flow rate in the discharge pipe is 1~2m/s.
2.0.2.2 The diameter of the pipeline is determined by the flow rate and the corresponding allowable pressure drop. 2.0.3 The pump Calculation of pressure drop in piping system 2.0.3.1 The pressure drop of the pump piping system includes the pressure drop of the pipeline (including pipe fittings), the pressure drop of the equipment inlet and outlet, the pressure drop of the control valve, the pressure drop of the equipment, the pressure drop of the flow meter, the pressure drop of the orifice plate, etc. 2.0.3.2 The pressure drop of the pipeline, the pressure drop of the equipment inlet and outlet, the pressure drop of the control valve, the pressure drop of the flow meter (orifice plate type), and the pressure drop of the flow limiting orifice plate shall be calculated according to the requirements of the process system professionals. The pressure drop of the equipment and the pressure drop of the flow meter (non-orifice plate type) shall be provided by the relevant professionals such as chemical process and automatic control. 2.0.3.3
2.0.4 Pressure drop control of the pump piping system 2.0.4.1 The pressure drop per unit length of the pump suction pipe and discharge pipe is generally determined by calculation. Some systems may be limited due to economic reasons and operational requirements. 2.0.4.2 The pressure drop of the pump suction pipeline is generally controlled within 20mm liquid column/(m pipe). When the temperature of the conveying liquid is higher than 70℃ or in a balanced state, it should be controlled within 6mm liquid column/(m pipe). 2.0.4.3 The control range of the pressure drop of the pump discharge pipeline varies with the flow rate, see the table below. 102
Flow rate m/h
34~110
Pressure drop per unit pipe length
0.35~1.38
0.23~0.92
2.0.4.4 The data mentioned in the table are all control ranges under normal circumstances. In actual use, attention should be paid to the fluid properties, operating conditions, installation location and pump type, and the flow rate and allowable pressure drop of the pump suction pipe and discharge pipe should be determined based on the principles of safety and economy. 103
3* Calculation of pump system characteristics
3.0.1 Calculation of the net positive suction head (NPSH) of the pump3.0.1.1 Definition of NPSHr and NPSHa and their relationship (1) The difference between the energy (static pressure energy and kinetic energy) of the unit mass of liquid at the pump inlet (the lowest pressure point) and the saturated vapor pressure head of the conveyed liquid at the working temperature is called the net positive suction head NPSH (Net Positive Suction Head) of the pump, also known as the cavitation margin of the pump. The net positive suction head of the pump is divided into the required net positive suction head (or the required value of the net positive suction head), marked as NPSHr (NPSHRequired) or NPSHR and the effective net positive suction head (or the effective value of the net positive suction head), marked as NPSHa (NPSHAvail-able) or NPSHA.
(2) To ensure the normal operation of the pump without cavitation, the net positive suction pressure head must be greater than a specified minimum value, which is called the net positive suction pressure head required by the pump (NPSHr). NPSHr is related to the type and structural design of the pump, and varies with the speed and flow rate of the pump. The smaller the NPSHr, the stronger the pump's ability to resist cavitation. NPSHr is generally measured and provided by the pump manufacturer. The measurement condition of NPSHr is based on the delivery of clean water at 20C. If there is no NPSHr provided by the pump manufacturer or the pumped fluid is different from the measurement condition of NPSHr, it can be calculated or corrected according to the formula in 3.0.1.2 of this regulation.
(3) After the equipment and pipeline configuration of the device are given, the net positive suction pressure head given to the pump by the pump suction system is called the effective net positive suction pressure head (NPSHa) of the pump system. NPSHa is only related to the device system and has nothing to do with the characteristics of the pump itself.
（4）To ensure that the pump can operate normally without cavitation, NPSHa must be greater than NPSHr, and in general, it must be at least 0.3m greater. For some conveying conditions (such as conveying liquids with a near boiling point), NPSHa should be 1.3NPSHr.
3.0.1.2 Calculation and correction of NPSHr
（1）Calculation of NPSHr
The NPSHr given by the pump manufacturer should be used as much as possible. When there is no NPSHr provided by the pump manufacturer, it can be estimated according to formula (3.0.1-1):
NPSHr=
Where NPSHr——the net positive suction pressure head required by the pump, m; n——the speed of the pump, r/min;
Va—the design flow rate of the pump, m/min;
(3.0.1--1)
——the suction specific speed of the pump, (m\/min)·(m)·(r). For general centrifugal pumps, regardless of the specific speed, the suction specific speed can be 1200, so the formula (3.0.1-1) can be simplified to NPSHr=7.86X10-5.n4/3.V2/3
For specially designed pumps, such as high-speed pumps, when NPSHa cannot be very large, the impeller must be specially designed, and its S value can actually reach 1500~1600, which should be considered when calculating NPSHr. (2) Correction of NPSHr
a. When the fluid transported by the pump is different from 20℃ clean water, NPSHr should be corrected according to formula (3.0.1-3): NPSHr=@·NPSHre
?-Correction coefficient of the required net positive suction pressure head relative to water; NPSHrw-
(3.0.1-3)
-The net positive suction pressure head required when transporting 20℃ clean water (that is, the NPSHr provided by the pump manufacturer), m.
b. When conveying Newtonian fluids such as oil and liquid medicine, viscous and corrosive liquids, non-Newtonian fluids such as slurries with solid particles uniformly distributed in liquids, and two-phase flow pulps with uneven distribution but whose flow can be approximately regarded as a simple combination of Newtonian and non-Newtonian fluids, etc., they have a tendency to be less prone to cavitation than conveying clean water, but their thermodynamic properties have not been fully mastered, the Φ value is difficult to determine and is less than 1, and NPSHr can be left uncorrected and used as an additional safety factor. c. When conveying hot water or non-viscous liquid hydrocarbons (viscosity is lower than water), the pump can operate at a net positive suction pressure head smaller than that required when conveying 20C clean water. Figure 3.0.1-1 is a correction diagram for estimating the NPSHr of the pump when conveying non-viscous liquid hydrocarbons. The value of ? is obtained based on the relative density and saturated vapor pressure of liquid hydrocarbons at the conveying temperature, and the NPSHr when conveying non-viscous liquid hydrocarbons is calculated. When the vapor pressure of hydrocarbons at the conveying temperature is lower than 100kPa, the value is equal to 1.
Figure 3.0.1-1
Relative density of hydrocarbons at the delivery temperature
Vapor of hydrocarbons at the delivery temperature
Gas pressure (MPa)
NPSHr correction diagram of pumps for transporting non-viscous hydrocarbons 1.0
3.0.1.3 Calculation of NPSHa and selection of related parameters (1) Calculation of NPSHa of centrifugal pumps
NPSHHa of centrifugal pumps can be calculated according to formula (3.0.1-4) to calculate: NPSHa
(AP +AP-)K?
NPSHa-——effective net positive suction pressure head of the pump, m; Pi—minimum normal working pressure of the container on the suction side of the pump, kPa; P—saturated vapor pressure of the liquid under pump inlet conditions, kPa; (3.0.1-4)
H,——vertical distance from the suction liquid surface to the top surface of the pump foundation, H is "10" when pouring, and H is "1" when sucking up, m;
AP,——pipe friction pressure drop under normal flow from the outlet of the suction container to the suction port of the pump (including pipe fittings, valves, etc.), kPa;
△P-—the sum of the equipment pressure drops on the pump suction pipeline under normal flow (including the equipment pipe mouth pressure drop), kPa;
—relative density of the liquid under pump inlet conditions; K—pump flow safety factor, which is the ratio of the design flow of the pump to the normal flow. (2) Calculation of NPSHa of reciprocating pumps
NPSHα of reciprocating pumps can be calculated according to formula (3.0.1-5): P-PH
(AP,·K+AP.)K?
(3.0.1-5)
H1nc--Acceleration loss of the suction pipeline of the reciprocating pump (its calculation is shown in formula 3.0.1-6).m; Kace-pulsation loss coefficient of the reciprocating pump.
The meanings of other symbols are the same as those of formula (3.0.1-4). Since the reciprocating pump intermittently sucks (discharges) liquid periodically, the liquid inlet (discharge) flow rate also changes periodically, which causes the friction loss to change and generates acceleration loss. a. Friction loss variation
(a) When a buffer tank (or other buffer device also called pulse attenuator or air tank) is not installed on the pump suction (discharge) pipeline, the pipeline friction loss should be calculated according to the constant flow condition, and the flow rate used is the design flow rate of the pump multiplied by ① Theoretically, H, should mean the vertical distance from the suction liquid surface to the center of the pump shaft (impeller), but in engineering design, when calculating the system characteristics of the pump, the geometric dimensions of the pump are usually unknown. For the convenience of engineering calculation, when calculating the system characteristics of the pump, H1 is taken as the vertical distance from the suction liquid surface to the top surface of the pump foundation. The same applies to H and H, involved later in this regulation. 106
The pulse loss coefficient of the reciprocating pump in Table 3.0.1-1. Reciprocating pump pulse loss coefficient (Kace)
single acting
Table 3.0.11
double acting
When a buffer tank is installed on the pump suction (discharge) pipe, regardless of the type of pump, the pulse loss coefficient is 1.2, that is, when calculating the friction loss, the flow rate used is 1.2 times the design flow rate of the pump. b. Acceleration loss
When a buffer tank is not installed on the pump suction pipe, the acceleration loss is calculated according to formula (3.0.1-6): L·Va.R·C
Acceleration loss of the reciprocating pump suction pipe, m liquid column; straight length of the pump suction pipe, m;
Va-the design flow rate of the pump, m/h;
C-pump type coefficient (see Table 3.0.1-2)
Di-inner diameter of the pump suction pipe, mm;
-liquid correction coefficient (see Table 3.0.1-3): (3.0.1-6)
-number of reciprocating times of the reciprocating pump, min-1. When the pump reciprocating times are unknown, for reciprocating pumps driven directly by steam, R is 20min-1; for reciprocating pumps driven by electric motors or steam turbines, R is 350min-1 (b)
When no buffer tank is installed on the pump discharge pipeline, the acceleration loss is calculated according to formula (3.0.1-7): Ha - 36L·Va·RC
Acceleration loss of the reciprocating pump discharge pipeline, m liquid column; Lz - straight length of the pump discharge pipeline, m; Dz - inner diameter of the pump discharge pipeline, mm.
The meanings of other symbols are the same as those of formula (3.0.1--6). (3.0.1-7)
Reciprocating pump type coefficient (C)
Single-acting electric pump or
Turbine driven pump
Double-acting electric pump or
Turbine driven pump
Table 3.0.1-2
Steam directly driven
Reciprocating pump
If the steam driven pump is driven by crank and flywheel, the "C\ value" of the electric pump or turbine driven pump can be used. Liquid correction factor (K)
Fluid name
Most hydrocarbons
Amines, water, ethylene glycol
Table 3.0.1-3
When a buffer tank is installed on the suction (discharge) pipeline, the acceleration loss between the pump and the buffer tank is calculated according to formula (c)
(3.0.1-6) and formula (3.0.1-7), The acceleration loss between the suction (discharge) container and the buffer tank is taken as 10% of the value calculated according to formula (3.0.1-6) and formula (3.0.17), and then the acceleration losses of the two sections of the pipeline are added together to obtain the total acceleration loss of the suction (discharge) pipeline. (3) Notes on NPSHa calculation
a. When determining the suction loss, please note:
(a) The pipe diameter is the inner diameter:
(b) The flow rate is the design flow rate of the pump. If the normal flow rate is used for calculation, each loss must be multiplied by the square of the flow safety factor;
(c) For several key pumps running in parallel during normal operation, the effective net positive suction pressure head should be estimated when a pump is suddenly damaged. This value is usually reduced; 108
(d) When the suction side container elevation is determined by the required net positive suction pressure head, the total friction loss of the suction pipeline should not exceed 0.6m liquid column:
(e) When the suction side container elevation is not determined by the required net positive suction pressure head, the total friction loss of the suction pipe may exceed 0.6m liquid column. The recommended practice is to determine the diameter of the suction pipe and the pump inlet pipe according to the control unit pressure drop of 0.23~0.46kPa/m.
b. The working pressure of the suction side container is the lowest working pressure that normally occurs. .c. The liquid level elevation "L" of the suction side container should be the lowest normal situation. When the chemical process professional does not provide it, please refer to Figure 3.0.1-2. d. The saturated vapor pressure of the pump inlet liquid should be the value at the highest normal operating temperature. e. The acceleration loss calculation formula for reciprocating pumps is applicable to inelastic and shorter suction pipes. In short, to calculate the NPSHa of the pump, the data under the most unfavorable conditions that normally occur should be selected for calculation to ensure To ensure that the pump does not cavitate and can operate reliably. L
Bottom tangent
Vertical container bottom outlet pipe
Bottom tangent
Horizontal container outlet pipe
Top of vertical pipe
Horizontal container vertical outlet pipe
Vertical container lateral outlet pipe
Bottom tangent
Tower bottom outlet pipe or head discharge pipe
0.15m~0.3m above the pipe mouth
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the suction side of the pump (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to obtain the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not have a safety margin, which is included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Pump NPSHa safety margin
Pump types and uses
Boiler feed water pumps and boiler feed water circulation pumps, horizontal condenser hot condensate pumps
Vacuum tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower check pumps and liquid delivery temperatures between 15.5~ Pumps for CO stripping towers and the like between 205℃ and 300℃ Pumps for other purposes, such as pumps for raising the NPSHa of containers
Pumps for conveying balanced liquids and liquids at vapor partial pressure
Pumps for conveying non-equilibrium liquids
Note①:
Explanation (Note*)
Table 3.0.1-
Safety margin
When calculating NPSHa, the submerged liquid column head above the suction nozzle of the suction cooling water pump should not be included.——The vertical distance from the suction liquid surface to the top surface of the pump foundation, H is taken as "10" during filling, and H is taken as "-" m during suction;
AP, the friction pressure drop of the pipeline (including pipe fittings, valves, etc.) under normal flow rate from the outlet of the suction container to the suction port of the pump, kPa;
△P-—The sum of the equipment pressure drops on the pump suction pipeline under normal flow rate (including the pressure drop of the equipment pipe mouth), kPa;
—Relative density of the liquid under the pump inlet conditions; K is the pump flow safety factor, which is the ratio of the design flow rate of the pump to the normal flow rate. (2) Calculation of NPSHa of reciprocating pumps
NPSHα of reciprocating pumps can be calculated according to formula (3.0.1-5): P-PH
(AP,·K+AP.)K?
(3.0.1-5)
H1nc--Acceleration loss of the suction pipeline of the reciprocating pump (its calculation is shown in formula 3.0.1-6).m; Kace-pulsation loss coefficient of the reciprocating pump.
The meanings of other symbols are the same as those of formula (3.0.1-4). Since the reciprocating pump intermittently sucks (discharges) liquid periodically, the liquid inlet (discharge) flow rate also changes periodically, which causes the friction loss to change and generates acceleration loss. a. Friction loss variation
(a) When a buffer tank (or other buffer device also called pulse attenuator or air tank) is not installed on the pump suction (discharge) pipeline, the pipeline friction loss should be calculated according to the constant flow condition, and the flow rate used is the design flow rate of the pump multiplied by ① Theoretically, H, should mean the vertical distance from the suction liquid surface to the center of the pump shaft (impeller), but in engineering design, when calculating the system characteristics of the pump, the geometric dimensions of the pump are usually unknown. For the convenience of engineering calculation, when calculating the system characteristics of the pump, H1 is taken as the vertical distance from the suction liquid surface to the top surface of the pump foundation. The same applies to H and H, involved later in this regulation. 106
The pulse loss coefficient of the reciprocating pump in Table 3.0.1-1. Reciprocating pump pulse loss coefficient (Kace)
single acting
Table 3.0.11
double acting
When a buffer tank is installed on the pump suction (discharge) pipe, regardless of the type of pump, the pulse loss coefficient is 1.2, that is, when calculating the friction loss, the flow rate used is 1.2 times the design flow rate of the pump. b. Acceleration loss
When a buffer tank is not installed on the pump suction pipe, the acceleration loss is calculated according to formula (3.0.1-6): L·Va.R·C
Acceleration loss of the reciprocating pump suction pipe, m liquid column; straight length of the pump suction pipe, m;
Va-the design flow rate of the pump, m/h;
C-pump type coefficient (see Table 3.0.1-2)
Di-inner diameter of the pump suction pipe, mm;
-liquid correction coefficient (see Table 3.0.1-3): (3.0.1-6)
-number of reciprocating times of the reciprocating pump, min-1. When the pump reciprocating times are unknown, for reciprocating pumps driven directly by steam, R is 20min-1; for reciprocating pumps driven by electric motors or steam turbines, R is 350min-1 (b)
When no buffer tank is installed on the pump discharge pipeline, the acceleration loss is calculated according to formula (3.0.1-7): Ha - 36L·Va·RC
Acceleration loss of the reciprocating pump discharge pipeline, m liquid column; Lz - straight length of the pump discharge pipeline, m; Dz - inner diameter of the pump discharge pipeline, mm.
The meanings of other symbols are the same as those of formula (3.0.1--6). (3.0.1-7)
Reciprocating pump type coefficient (C)
Single-acting electric pump or
Turbine driven pump
Double-acting electric pump or
Turbine driven pump
Table 3.0.1-2
Steam directly driven
Reciprocating pump
If the steam driven pump is driven by crank and flywheel, the "C\ value" of the electric pump or turbine driven pump can be used. Liquid correction factor (K)
Fluid name
Most hydrocarbons
Amines, water, ethylene glycol
Table 3.0.1-3
When a buffer tank is installed on the suction (discharge) pipeline, the acceleration loss between the pump and the buffer tank is calculated according to formula (c)
(3.0.1-6) and formula (3.0.1-7), The acceleration loss between the suction (discharge) container and the buffer tank is taken as 10% of the value calculated according to formula (3.0.1-6) and formula (3.0.17), and then the acceleration losses of the two sections of the pipeline are added together to obtain the total acceleration loss of the suction (discharge) pipeline. (3) Notes on NPSHa calculation
a. When determining the suction loss, please note:
(a) The pipe diameter is the inner diameter:
(b) The flow rate is the design flow rate of the pump. If the normal flow rate is used for calculation, each loss must be multiplied by the square of the flow safety factor;
(c) For several key pumps running in parallel during normal operation, the effective net positive suction pressure head should be estimated when a pump is suddenly damaged. This value is usually reduced; 108
(d) When the suction side container elevation is determined by the required net positive suction pressure head, the total friction loss of the suction pipeline should not exceed 0.6m liquid column:
(e) When the suction side container elevation is not determined by the required net positive suction pressure head, the total friction loss of the suction pipe may exceed 0.6m liquid column. The recommended practice is to determine the diameter of the suction pipe and the pump inlet pipe according to the control unit pressure drop of 0.23~0.46kPa/m.
b. The working pressure of the suction side container is the lowest working pressure that normally occurs. .c. The liquid level elevation "L" of the suction side container should be the lowest normal situation. When the chemical process professional does not provide it, please refer to Figure 3.0.1-2. d. The saturated vapor pressure of the pump inlet liquid should be the value at the highest normal operating temperature. e. The acceleration loss calculation formula for reciprocating pumps is applicable to inelastic and shorter suction pipes. In short, to calculate the NPSHa of the pump, the data under the most unfavorable conditions that normally occur should be selected for calculation to ensure To ensure that the pump does not cavitate and can operate reliably. L
Bottom tangent
Vertical container bottom outlet pipe
Bottom tangent
Horizontal container outlet pipe
Top of vertical pipe
Horizontal container vertical outlet pipe
Vertical container lateral outlet pipe
Bottom tangent
Tower bottom outlet pipe or head discharge pipe
0.15m~0.3m above the pipe mouth
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the suction side of the pump (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to obtain the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not have a safety margin, which is included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Pump NPSHa safety margin
Pump types and uses
Boiler feed water pumps and boiler feed water circulation pumps, horizontal condenser hot condensate pumps
Vacuum tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower check pumps and liquid delivery temperatures between 15.5~ Pumps for CO stripping towers and the like between 205℃ and 300℃ Pumps for other purposes, such as pumps for raising the NPSHa of containers
Pumps for conveying balanced liquids and liquids at vapor partial pressure
Pumps for conveying non-equilibrium liquids
Note①:
Explanation (Note*)
Table 3.0.1-
Safety margin
When calculating NPSHa, the submerged liquid column head above the suction nozzle of the suction cooling water pump should not be included.——The vertical distance from the suction liquid surface to the top surface of the pump foundation, H is taken as "10" during filling, and H is taken as "-" m during suction;
AP, the friction pressure drop of the pipeline (including pipe fittings, valves, etc.) under normal flow rate from the outlet of the suction container to the suction port of the pump, kPa;
△P-—The sum of the equipment pressure drops on the pump suction pipeline under normal flow rate (including the pressure drop of the equipment pipe mouth), kPa;
—Relative density of the liquid under the pump inlet conditions; K is the pump flow safety factor, which is the ratio of the design flow rate of the pump to the normal flow rate. (2) Calculation of NPSHa of reciprocating pumps
NPSHα of reciprocating pumps can be calculated according to formula (3.0.1-5): P-PH
(AP,·K+AP.)K?
(3.0.1-5)
H1nc--Acceleration loss of the suction pipeline of the reciprocating pump (its calculation is shown in formula 3.0.1-6).m; Kace-pulsation loss coefficient of the reciprocating pump.
The meanings of other symbols are the same as those of formula (3.0.1-4). Since the reciprocating pump intermittently sucks (discharges) liquid periodically, the liquid inlet (discharge) flow rate also changes periodically, which causes the friction loss to change and generates acceleration loss. a. Friction loss variation
(a) When a buffer tank (or other buffer device also called pulse attenuator or air tank) is not installed on the pump suction (discharge) pipeline, the pipeline friction loss should be calculated according to the constant flow condition, and the flow rate used is the design flow rate of the pump multiplied by ① Theoretically, H, should mean the vertical distance from the suction liquid surface to the center of the pump shaft (impeller), but in engineering design, when calculating the system characteristics of the pump, the geometric dimensions of the pump are usually unknown. For the convenience of engineering calculation, when calculating the system characteristics of the pump, H1 is taken as the vertical distance from the suction liquid surface to the top surface of the pump foundation. The same applies to H and H, involved later in this regulation. 106
The pulse loss coefficient of the reciprocating pump in Table 3.0.1-1. Reciprocating pump pulse loss coefficient (Kace)
Single acting
Table 3.0.11
Double acting
When a buffer tank is installed on the pump suction (discharge) pipe, regardless of the type of pump, the pulse loss coefficient is 1.2, that is, when calculating the friction loss, the flow rate used is 1.2 times the design flow rate of the pump. b. Acceleration loss
When a buffer tank is not installed on the pump suction pipe, the acceleration loss is calculated according to formula (3.0.1-6): L·Va.R·C
Acceleration loss of the reciprocating pump suction pipe, m liquid column; straight length of the pump suction pipe, m;
Va-the design flow rate of the pump, m/h;
C-pump type coefficient (see Table 3.0.1-2)
Di-inner diameter of the pump suction pipe, mm;
-liquid correction coefficient (see Table 3.0.1-3): (3.0.1-6)
-number of reciprocating times of the reciprocating pump, min-1. When the pump reciprocating times are unknown, for reciprocating pumps driven directly by steam, R is 20min-1; for reciprocating pumps driven by electric motors or steam turbines, R is 350min-1 (b)
When no buffer tank is installed on the pump discharge pipeline, the acceleration loss is calculated according to formula (3.0.1-7): Ha - 36L·Va·RC
Acceleration loss of the reciprocating pump discharge pipeline, m liquid column; Lz - straight length of the pump discharge pipeline, m; Dz - inner diameter of the pump discharge pipeline, mm.
The meanings of other symbols are the same as those of formula (3.0.1--6). (3.0.1-7)
Reciprocating pump type coefficient (C)
Single-acting electric pump or
Turbine driven pump
Double-acting electric pump or
Turbine driven pump
Table 3.0.1-2
Steam directly driven
Reciprocating pump
If the steam driven pump is driven by crank and flywheel, the "C\ value" of the electric pump or turbine driven pump can be used. Liquid correction factor (K)
Fluid namebzxZ.net
Most hydrocarbons
Amines, water, ethylene glycol
Table 3.0.1-3
When a buffer tank is installed on the suction (discharge) pipeline, the acceleration loss between the pump and the buffer tank is calculated according to formula (c)
(3.0.1-6) and formula (3.0.1-7), The acceleration loss between the suction (discharge) container and the buffer tank is taken as 10% of the value calculated according to formula (3.0.1-6) and formula (3.0.17), and then the acceleration losses of the two sections of the pipeline are added together to obtain the total acceleration loss of the suction (discharge) pipeline. (3) Notes on NPSHa calculation
a. When determining the suction loss, please note:
(a) The pipe diameter is the inner diameter:
(b) The flow rate is the design flow rate of the pump. If the normal flow rate is used for calculation, each loss must be multiplied by the square of the flow safety factor;
(c) For several key pumps running in parallel during normal operation, the effective net positive suction pressure head should be estimated when a pump is suddenly damaged. This value is usually reduced; 108
(d) When the suction side container elevation is determined by the required net positive suction pressure head, the total friction loss of the suction pipeline should not exceed 0.6m liquid column:
(e) When the suction side container elevation is not determined by the required net positive suction pressure head, the total friction loss of the suction pipe may exceed 0.6m liquid column. The recommended practice is to determine the diameter of the suction pipe and the pump inlet pipe according to the control unit pressure drop of 0.23~0.46kPa/m.
b. The working pressure of the suction side container is the lowest working pressure that normally occurs. .c. The liquid level elevation "L" of the suction side container should be the lowest normal situation. When the chemical process professional does not provide it, please refer to Figure 3.0.1-2. d. The saturated vapor pressure of the pump inlet liquid should be the value at the highest normal operating temperature. e. The acceleration loss calculation formula for reciprocating pumps is applicable to inelastic and shorter suction pipes. In short, to calculate the NPSHa of the pump, the data under the most unfavorable conditions that normally occur should be selected for calculation to ensure To ensure that the pump does not cavitate and can operate reliably. L
Bottom tangent
Vertical container bottom outlet pipe
Bottom tangent
Horizontal container outlet pipe
Top of vertical pipe
Horizontal container vertical outlet pipe
Vertical container lateral outlet pipe
Bottom tangent
Tower bottom outlet pipe or head discharge pipe
0.15m~0.3m above the pipe mouth
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the suction side of the pump (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to obtain the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not have a safety margin, which is included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Pump NPSHa safety margin
Pump types and uses
Boiler feed water pumps and boiler feed water circulation pumps, horizontal condenser hot condensate pumps
Vacuum tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower check pumps and liquid delivery temperatures between 15.5~ Pumps for CO stripping towers and the like between 205℃ and 300℃ Pumps for other purposes, such as pumps for raising the NPSHa of containers
Pumps for conveying balanced liquids and liquids at vapor partial pressure
Pumps for conveying non-equilibrium liquids
Note①:
Explanation (Note*)
Table 3.0.1-
Safety margin
When calculating NPSHa, the submerged liquid column head above the suction nozzle of the suction cooling water pump should not be included.1-4). Since the reciprocating pump intermittently sucks (discharges) liquid periodically, the liquid inlet (discharge) flow rate also changes periodically, which causes the friction loss to change and generates acceleration loss. a. Friction loss change
(a) When a buffer tank (or other buffer device, also known as a pulse attenuator or air tank) is not installed on the pump suction (discharge) pipeline, the pipeline friction loss should be calculated according to the constant flow condition. The flow rate used is the design flow rate of the pump multiplied by ① In theory, H, should mean the vertical distance from the suction liquid surface to the center of the pump shaft (impeller). However, in engineering design, when calculating the system characteristics of the pump, the geometric dimensions of the pump are usually unknown. For the convenience of engineering calculations, when calculating the system characteristics of the pump, H1 is taken as the vertical distance from the suction liquid surface to the top surface of the pump foundation. The same applies to H and H, which are involved later in this regulation. 106
The pulse loss coefficient of the reciprocating pump in Table 3.0.1-1. Reciprocating pump pulse loss coefficient (Kace)
Single acting
Table 3.0.11
Double acting
When a buffer tank is installed on the pump suction (discharge) pipe, regardless of the type of pump, the pulse loss coefficient is 1.2, that is, when calculating the friction loss, the flow rate used is 1.2 times the design flow rate of the pump. b. Acceleration loss
When a buffer tank is not installed on the pump suction pipe, the acceleration loss is calculated according to formula (3.0.1-6): L·Va.R·C
Acceleration loss of the reciprocating pump suction pipe, m liquid column; straight length of the pump suction pipe, m;
Va-the design flow rate of the pump, m/h;
C-pump type coefficient (see Table 3.0.1-2)
Di-inner diameter of the pump suction pipe, mm;
-liquid correction coefficient (see Table 3.0.1-3): (3.0.1-6)
-number of reciprocating times of the reciprocating pump, min-1. When the pump reciprocating times are unknown, for reciprocating pumps driven directly by steam, R is 20min-1; for reciprocating pumps driven by electric motors or steam turbines, R is 350min-1 (b)
When no buffer tank is installed on the pump discharge pipeline, the acceleration loss is calculated according to formula (3.0.1-7): Ha - 36L·Va·RC
Acceleration loss of the reciprocating pump discharge pipeline, m liquid column; Lz - straight length of the pump discharge pipeline, m; Dz - inner diameter of the pump discharge pipeline, mm.
The meanings of other symbols are the same as those of formula (3.0.1--6). (3.0.1-7)
Reciprocating pump type coefficient (C)
Single-acting electric pump or
Turbine driven pump
Double-acting electric pump or
Turbine driven pump
Table 3.0.1-2
Steam directly driven
Reciprocating pump
If the steam driven pump is driven by crank and flywheel, the "C\ value of the electric pump or turbine driven pump can be used. Liquid correction factor (K)
Fluid name
Most hydrocarbons
Amines, water, ethylene glycol
Table 3.0.1-3
When a buffer tank is installed on the suction (discharge) pipeline, the acceleration loss between the pump and the buffer tank is calculated according to formula (c)
(3.0.1-6) and formula (3.0.1-7), The acceleration loss between the suction (discharge) container and the buffer tank is taken as 10% of the value calculated by formula (3.0.1-6) and formula (3.0.17), and then the acceleration losses of the two sections of the pipeline are added together to obtain the total acceleration loss of the suction (discharge) pipeline. (3) Notes on NPSHa calculation
a. When determining the suction loss, please note:
(a) The pipe diameter is the inner diameter:
(b) The flow rate is the design flow rate of the pump. If the normal flow rate is used for calculation, each loss must be multiplied by the square of the flow safety factor;
(c) For several key pumps running in parallel during normal operation, the effective net positive suction pressure head should be estimated when a pump is suddenly damaged. This value is usually reduced; 108
(d) When the suction side container elevation is determined by the required net positive suction pressure head, the total friction loss of the suction pipeline should not exceed 0.6m liquid column:
(e) When the suction side container elevation is not determined by the required net positive suction pressure head, the total friction loss of the suction pipe may exceed 0.6m liquid column. The recommended practice is to determine the diameter of the suction pipe and the pump inlet pipe according to the control unit pressure drop of 0.23~0.46kPa/m.
b. The working pressure of the suction side container is the lowest working pressure that normally occurs. .c. The liquid level elevation "L" of the suction side container should be the lowest normal situation. When the chemical process professional does not provide it, please refer to Figure 3.0.1-2. d. The saturated vapor pressure of the pump inlet liquid should be the value at the highest normal operating temperature. e. The acceleration loss calculation formula for reciprocating pumps is applicable to inelastic and shorter suction pipes. In short, to calculate the NPSHa of the pump, the data under the most unfavorable conditions that normally occur should be selected for calculation to ensure To ensure that the pump does not cavitate and can operate reliably. L
Bottom tangent
Vertical vessel bottom outlet pipe
Bottom tangent
Horizontal vessel outlet pipe
Top of vertical pipe
Horizontal vessel vertical pipe outlet
Vertical vessel lateral outlet pipe
Bottom tangent
Tower bottom outlet pipe or head discharge pipe
0.15m~0.3m above the pipe mouth
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the suction side of the pump (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to obtain the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not have safety margins, which are included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Pump NPSHa safety margin
Pump types and uses
Boiler feed water pumps and boiler feed water circulation pumps, horizontal condenser hot condensate pumps
Vacuum tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower check pumps and liquid delivery temperatures between 15.5~ Pumps for CO stripping towers and the like between 205℃ Pumps for other purposes, such as pumps for raising the NPSHa of vessels
Pumps for conveying balanced liquids and liquids at vapor partial pressure
Pumps for conveying non-equilibrium liquids
Note①:
Explanation (Note*)
Table 3.0.1-
Safety margin
In calculating NPSHa, the submerged liquid column head above the suction nozzle of the suction cooling water pump should not be included.1-4). Since the reciprocating pump intermittently sucks (discharges) liquid periodically, the liquid inlet (discharge) flow rate also changes periodically, which causes the friction loss to change and generates acceleration loss. a. Friction loss change
(a) When a buffer tank (or other buffer device, also known as a pulse attenuator or air tank) is not installed on the pump suction (discharge) pipeline, the pipeline friction loss should be calculated according to the constant flow condition. The flow rate used is the design flow rate of the pump multiplied by ① In theory, H, should mean the vertical distance from the suction liquid surface to the center of the pump shaft (impeller). However, in engineering design, when calculating the system characteristics of the pump, the geometric dimensions of the pump are usually unknown. For the convenience of engineering calculations, when calculating the system characteristics of the pump, H1 is taken as the vertical distance from the suction liquid surface to the top surface of the pump foundation. The same applies to H and H, which are involved later in this regulation. 106
The pulse loss coefficient of the reciprocating pump in Table 3.0.1-1. Reciprocating pump pulse loss coefficient (Kace)
single acting
Table 3.0.11
double acting
When a buffer tank is installed on the pump suction (discharge) pipe, regardless of the type of pump, the pulse loss coefficient is 1.2, that is, when calculating the friction loss, the flow rate used is 1.2 times the design flow rate of the pump. b. Acceleration loss
When a buffer tank is not installed on the pump suction pipe, the acceleration loss is calculated according to formula (3.0.1-6): L·Va.R·C
Acceleration loss of the reciprocating pump suction pipe, m liquid column; straight length of the pump suction pipe, m;
Va-the design flow rate of the pump, m/h;
C-pump type coefficient (see Table 3.0.1-2)
Di-inner diameter of the pump suction pipe, mm;
-liquid correction coefficient (see Table 3.0.1-3): (3.0.1-6)
-number of reciprocating times of the reciprocating pump, min-1. When the pump reciprocating times are unknown, for reciprocating pumps driven directly by steam, R is 20min-1; for reciprocating pumps driven by electric motors or steam turbines, R is 350min-1 (b)
When no buffer tank is installed on the pump discharge pipeline, the acceleration loss is calculated according to formula (3.0.1-7): Ha - 36L·Va·RC
Acceleration loss of the reciprocating pump discharge pipeline, m liquid column; Lz - straight length of the pump discharge pipeline, m; Dz - inner diameter of the pump discharge pipeline, mm.
The meanings of other symbols are the same as those of formula (3.0.1--6). (3.0.1-7)
Reciprocating pump type coefficient (C)
Single-acting electric pump or
Turbine driven pump
Double-acting electric pump or
Turbine driven pump
Table 3.0.1-2
Steam directly driven
Reciprocating pump
If the steam driven pump is driven by crank and flywheel, the "C\ value of the electric pump or turbine driven pump can be used. Liquid correction factor (K)
Fluid name
Most hydrocarbons
Amines, water, ethylene glycol
Table 3.0.1-3
When a buffer tank is installed on the suction (discharge) pipeline, the acceleration loss between the pump and the buffer tank is calculated according to formula (c)
(3.0.1-6) and formula (3.0.1-7), The acceleration loss between the suction (discharge) container and the buffer tank is taken as 10% of the value calculated by formula (3.0.1-6) and formula (3.0.17), and then the acceleration losses of the two sections of the pipeline are added together to obtain the total acceleration loss of the suction (discharge) pipeline. (3) Notes on NPSHa calculation
a. When determining the suction loss, please note:
(a) The pipe diameter is the inner diameter:
(b) The flow rate is the design flow rate of the pump. If the normal flow rate is used for calculation, each loss must be multiplied by the square of the flow safety factor;
(c) For several key pumps running in parallel during normal operation, the effective net positive suction pressure head should be estimated when a pump is suddenly damaged. This value is usually reduced; 108
(d) When the suction side container elevation is determined by the required net positive suction pressure head, the total friction loss of the suction pipeline should not exceed 0.6m liquid column:
(e) When the suction side container elevation is not determined by the required net positive suction pressure head, the total friction loss of the suction pipe may exceed 0.6m liquid column. The recommended practice is to determine the diameter of the suction pipe and the pump inlet pipe according to the control unit pressure drop of 0.23~0.46kPa/m.
b. The working pressure of the suction side container is the lowest working pressure that normally occurs. .c. The liquid level elevation "L" of the suction side container should be the lowest normal situation. When the chemical process professional does not provide it, please refer to Figure 3.0.1-2. d. The saturated vapor pressure of the pump inlet liquid should be the value at the highest normal operating temperature. e. The acceleration loss calculation formula for reciprocating pumps is applicable to inelastic and shorter suction pipes. In short, to calculate the NPSHa of the pump, the data under the most unfavorable conditions that normally occur should be selected for calculation to ensure To ensure that the pump does not cavitate and can operate reliably. L
Bottom tangent
Vertical vessel bottom outlet pipe
Bottom tangent
Horizontal vessel outlet pipe
Top of vertical pipe
Horizontal vessel vertical pipe outlet
Vertical vessel lateral outlet pipe
Bottom tangent
Tower bottom outlet pipe or head discharge pipe
0.15m~0.3m above the pipe mouth
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the suction side of the pump (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to obtain the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not have safety margins, which are included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Pump NPSHa safety margin
Pump types and uses
Boiler feed water pumps and boiler feed water circulation pumps, horizontal condenser hot condensate pumps
Vacuum tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower check pumps and liquid delivery temperatures between 15.5~ Pumps for CO stripping towers and the like between 205℃ Pumps for other purposes, such as pumps for raising the NPSHa of vessels
Pumps for conveying balanced liquids and liquids at vapor partial pressure
Pumps for conveying non-equilibrium liquids
Note①:
Explanation (Note*)
Table 3.0.1-
Safety margin
In calculating NPSHa, the submerged liquid column head above the suction nozzle of the suction cooling water pump should not be included.1-6)
-Number of reciprocating pumps, min-1. When the number of reciprocating pumps is unknown, R is 20min-1 for reciprocating pumps driven directly by steam and 350min-1 for reciprocating pumps driven by electric motors or steam turbines (b)
When a buffer tank is not installed on the pump discharge pipeline, the acceleration loss is calculated according to formula (3.0.1-7): Ha-36L·Va·RC
Acceleration loss of the reciprocating pump discharge pipeline, m liquid column; Lz-straight length of the pump discharge pipeline, m; Dz-inner diameter of the pump discharge pipeline, mm.
The meanings of the other symbols are the same as those in formula (3.0.1--6). (3.0.1-7)
Reciprocating pump type coefficient (C)
Single-acting electric pump or
Turbine driven pump
Double-acting electric pump or
Turbine driven pump
Table 3.0.1-2
Steam directly driven
Reciprocating pump
If the steam driven pump is driven by crank and flywheel, the "C\ value" of the electric pump or turbine driven pump can be used. Liquid correction factor (K)
Fluid name
Most hydrocarbons
Amines, water, ethylene glycol
Table 3.0.1-3
When a buffer tank is installed on the suction (discharge) pipeline, the acceleration loss between the pump and the buffer tank is calculated according to formula (c)
(3.0.1-6) and formula (3.0.1-7), The acceleration loss between the suction (discharge) container and the buffer tank is taken as 10% of the value calculated according to formula (3.0.1-6) and formula (3.0.17), and then the acceleration losses of the two sections of the pipeline are added together to obtain the total acceleration loss of the suction (discharge) pipeline. (3) Notes on NPSHa calculation
a. When determining the suction loss, please note:
(a) The pipe diameter is the inner diameter:
(b) The flow rate is the design flow rate of the pump. If the normal flow rate is used for calculation, each loss must be multiplied by the square of the flow safety factor;
(c) For several key pumps running in parallel during normal operation, the effective net positive suction pressure head should be estimated when a pump is suddenly damaged. This value is usually reduced; 108
(d) When the suction side container elevation is determined by the required net positive suction pressure head, the total friction loss of the suction pipeline should not exceed 0.6m liquid column:
(e) When the suction side container elevation is not determined by the required net positive suction pressure head, the total friction loss of the suction pipe may exceed 0.6m liquid column. The recommended practice is to determine the diameter of the suction pipe and the pump inlet pipe according to the control unit pressure drop of 0.23~0.46kPa/m.
b. The working pressure of the suction side container is the lowest working pressure that normally occurs. .c. The liquid level elevation "L" of the suction side container should be the lowest normal situation. When the chemical process professional does not provide it, please refer to Figure 3.0.1-2. d. The saturated vapor pressure of the pump inlet liquid should be the value at the highest normal operating temperature. e. The acceleration loss calculation formula for reciprocating pumps is applicable to inelastic and shorter suction pipes. In short, to calculate the NPSHa of the pump, the data under the most unfavorable conditions that normally occur should be selected for calculation to ensure To ensure that the pump does not cavitate and can operate reliably. L
Bottom tangent
Vertical container bottom outlet pipe
Bottom tangent
Horizontal container outlet pipe
Top of vertical pipe
Horizontal container vertical outlet pipe
Vertical container lateral outlet pipe
Bottom tangent
Tower bottom outlet pipe or head discharge pipe
0.15m~0.3m above the pipe mouth
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the suction side of the pump (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to obtain the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not have a safety margin, which is included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Pump NPSHa safety margin
Pump types and uses
Boiler feed water pumps and boiler feed water circulation pumps, horizontal condenser hot condensate pumps
Vacuum tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower check pumps and liquid delivery temperatures between 15.5~ Pumps for CO stripping towers and the like between 205℃ Pumps for other purposes, such as pumps for raising the NPSHa of vessels
Pumps for conveying balanced liquids and liquids at vapor partial pressure
Pumps for conveying non-equilibrium liquids
Note①:
Explanation (Note*)
Table 3.0.1-
Safety margin
In calculating NPSHa, the submerged liquid column head above the suction nozzle of the suction cooling water pump should not be included.1-6)
-Number of reciprocating pumps, min-1. When the number of reciprocating pumps is unknown, R is 20min-1 for reciprocating pumps driven directly by steam and 350min-1 for reciprocating pumps driven by electric motors or steam turbines (b)
When a buffer tank is not installed on the pump discharge pipeline, the acceleration loss is calculated according to formula (3.0.1-7): Ha-36L·Va·RC
Acceleration loss of the reciprocating pump discharge pipeline, m liquid column; Lz-straight length of the pump discharge pipeline, m; Dz-inner diameter of the pump discharge pipeline, mm.
The meanings of the other symbols are the same as those in formula (3.0.1--6). (3.0.1-7)
Reciprocating pump type coefficient (C)
Single-acting electric pump or
Turbine driven pump
Double-acting electric pump or
Turbine driven pump
Table 3.0.1-2
Steam directly driven
Reciprocating pump
If the steam driven pump is driven by crank and flywheel, the "C\ value" of the electric pump or turbine driven pump can be used. Liquid correction factor (K)
Fluid name
Most hydrocarbons
Amines, water, ethylene glycol
Table 3.0.1-3
When a buffer tank is installed on the suction (discharge) pipeline, the acceleration loss between the pump and the buffer tank is calculated according to formula (c)
(3.0.1-6) and formula (3.0.1-7), The acceleration loss between the suction (discharge) container and the buffer tank is taken as 10% of the value calculated according to formula (3.0.1-6) and formula (3.0.17), and then the acceleration losses of the two sections of the pipeline are added together to obtain the total acceleration loss of the suction (discharge) pipeline. (3) Notes on NPSHa calculation
a. When determining the suction loss, please note:
(a) The pipe diameter is the inner diameter:
(b) The flow rate is the design flow rate of the pump. If the normal flow rate is used for calculation, each loss must be multiplied by the square of the flow safety factor;
(c) For several key pumps running in parallel during normal operation, the effective net positive suction pressure head should be estimated when a pump is suddenly damaged. This value is usually reduced; 108
(d) When the suction side container elevation is determined by the required net positive suction pressure head, the total friction loss of the suction pipeline should not exceed 0.6m liquid column:
(e) When the suction side container elevation is not determined by the required net positive suction pressure head, the total friction loss of the suction pipe may exceed 0.6m liquid column. The recommended practice is to determine the diameter of the suction pipe and the pump inlet pipe according to the control unit pressure drop of 0.23~0.46kPa/m.
b. The working pressure of the suction side container is the lowest working pressure that normally occurs. .c. The liquid level elevation "L" of the suction side container should be the lowest normal situation. When the chemical process professional does not provide it, please refer to Figure 3.0.1-2. d. The saturated vapor pressure of the pump inlet liquid should be the value at the highest normal operating temperature. e. The acceleration loss calculation formula for reciprocating pumps is applicable to inelastic and shorter suction pipes. In short, to calculate the NPSHa of the pump, the data under the most unfavorable conditions that normally occur should be selected for calculation to ensure To ensure that the pump does not cavitate and can operate reliably. L
Bottom tangent
Vertical container bottom outlet pipe
Bottom tangent
Horizontal container outlet pipe
Top of vertical pipe
Horizontal container vertical outlet pipe
Vertical container lateral outlet pipe
Bottom tangent
Tower bottom outlet pipe or head discharge pipe
0.15m~0.3m above the pipe mouth
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the suction side of the pump (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to obtain the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not have a safety margin, which is included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Pump NPSHa safety margin
Pump types and uses
Boiler feed water pumps and boiler feed water circulation pumps, horizontal condenser hot condensate pumps
Vacuum tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower check pumps and liquid delivery temperatures between 15.5~ Pumps for CO stripping towers and the like between 205℃ Pumps for other purposes, such as pumps for raising the NPSHa of vessels
Pumps for conveying balanced liquids and liquids at vapor partial pressure
Pumps for conveying non-equilibrium liquids
Note①:
Explanation (Note*)
Table 3.0.1-
Safety margin
In calculating NPSHa, the submerged liquid column head above the suction nozzle of the suction cooling water pump should not be included.3m
Underground horizontal container
Container straight
Full drainage reflux container
Figure 3.0.1-2 Reference elevation of liquid level in the container on the pump suction side (closed container) 3.0.1.4 Safety margin of NPSHa
Subtract the safety margin from the NPSHα calculation result in 3.0.1.3 to get the final effective net positive suction pressure head of the pump system.
Reciprocating pumps do not take into account the safety margin, which is included in the calculation of friction loss and acceleration loss. For general centrifugal pumps, the safety margin of NPSHa is 0.6~1.0m, but for centrifugal pumps of different types and uses, the safety margin of NPSHa is also different, see Table 3.0.1-4. Safety margin of pump NPSHa
Types and uses of pumps
Boiler feed pumps and boiler feed circulation pumps, horizontal condenser hot condensate pumps
Decompression tower kettle liquid pumps
Vertical and horizontal surface condenser hot condensate pumps Normal temperature and pressure cooling water pumps
Pumps with suction pressure <70kPa (gauge)
Multistage pumps and double-suction impeller pumps
Automatic starting pumps
Absorption tower liquid pumps and liquid delivery temperature between 15.5～ Pumps for CO stripping towers and the like between 205℃ and 300℃ Pumps for other
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