ES_Pump_SM User Manual

1. Introduction

2. Pump Calculation

 

2.1 Pump Capacity

 

2.2 Pump Total Head

 

2.3 Net Positive Suction Head Available, NPSHa

 

2.4 Net Positive Suction Head Required, NPSHr

 

2.5 Energy Grade Line, EGL

 

2.6 Pump Efficiency

 

2.7 Pump BHP (Brake Horse Power)

 

2.8 Motor Rating, Motor Efficiency, Motor Power Consumption

3. Friction Loss Calculation

4. System Curve

5. Major Screens

 

5.1 Input Screen

 

5.2 Calculation Options

 

5.3 Node Flow Edit

 

5.4 Test Output

 

5.5 Pump Iso Window

 

5.6 Conversion of dP to K

 

5.7 Other Menu


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1.  Introduction (TOC)

Calculation of pump capacity and pump head, i.e. pump sizing, is one of basic calculation in power plant engineering as well as other plant engineering.   The pump sizing does not require sophisticate knowledge, but it is complicate calculation that may cause human errors.   Therefore, pump sizing normally done using computer software, and ES_Pump_SM is the software.

ES_Pump_SM performs its calculation in those ways below.

1) Piping pressure drop calculation is performed using the same way with those of ES_dPCalc, one of ENGSoft softwares.   Please refer to the User Manual of ES_dPCalc for details of piping pressure drop calculation used in ES_Pump_SM.

2) Two fluids, water and liquid, are calculated.   For water, the properties such as specific volume, viscosity and vapor pressure may be input using built-in steam table.   For liquid, those properties should be input by user.

3) Pump capacity is selected as the operating flow plus surge and wear margins.   For example, if user input the surge and wear margins as 4% and 6% respectively, the pump capacity is [Operating Flow x (1 + 0.04 + 0.06].

4) When calculating the friction loss head, the flow for calculation of friction loss is selected as the operating flow plus surge margin.   For the example above, the flow for the friction loss calculation is [Operating Flow x (1 + 0.04)].

5) Friction loss margin may be set by user.   The friction loss margin is applied only to the friction loss calculated for pipe length and fitting/valve.   The friction loss margin is not applied to the head by pressure and elevation difference between suction pipe inlet and discharge pipe outlet and the head by control valve pressure drop.

Please note that the friction margin is also applied to the pressure difference of "User Defined Fitting by dP".     ES_Pump_SM has system curve data generation option.    The "User Defined Fitting by dP" causes wrong system curve data because the pressure drop, i.e. friction loss, of the fitting by dP is constant regardless of pump flow.    

In the system curve which shows the variation of fixed flow resistance versus pumping flow of pumping system, only control valve, which is the only variable flow resistance in pumping system, should be the component having pressure drop value at rated operating flow.   The pressure drop of control valve has a separate input box other than the "User Defined Fitting by dP".   Therefore, if user has dP values for fittings/valves or equipment, it is recommended to use "User Defined Fitting by K".   To help user to convert the dP value to K value, "dP to K Conversion" function has been provided in ES_Pump_SM.

6) As described above, ES_Pump_SM has a option to generate system curve data.   The system curve data can be generated for five(5) equally-spaced pumping flow up to thirty(30) pumping flow as a maximum.   In the system curve data, 100% flow is selected as the operating flow plus surge margin, which is the base flow for friction loss calculation.   

The system curve data can be saved as an Microsoft(R) Excel(R) file, too.  When saving as an Excel(R) file, it is required to close the Excel(R) program running on the computer in order to prevent from Excel(R) error.   By using the graphic function of Excel(R) data file, user may draw system curve.

7) In ES_Pump_SM node inflow and outflow can be simulated.  In previous piping simulation programs of ENGSoft Inc., only one flow through a piping system could be simulated.   However, in ES_Pump_SM, the flow entering through each node or the flow going out of each node can be simulated also.   By using this node flow option, the flow through each pipe in a piping system can be differed.

 For node flow input and editing, a window called as Node Flow Edit window has been provided in ES_Pump_SM.    In the node edit window, the inflow to a node is set as flow with plus sign and the outflow from a node as flow with minus sign.     In order to make the sum of node flow as zero for satisfying with mass conservation law, an open node should be selected in the node editing window and the node flow of the open node is automatically calculated by the program.

8) NPSHr value is calculated from the suction specific speed the user inputs.   The suction specific speed should be input in rpm-US gpm/feet unit only and the default value is 8500 rpm-US gpm/feet which is common value of normal pumps.

The user can set the minimum NPSHa ratio to NPSHr in [Calculation Option] window.    The program warns the user if the NPSHa value calculated by pump suction condition is less than the NPSHa value calculated by the ratio the user inputs, and then the program recommends for the user to lower the pump speed(rpm) to lower NPSHr value with the maximum speed recommendation.    Another way to lower NPSHr in addition to lowering pump speed is to lower suction specific speed, but it is not recommended.

9) ES_Pump_SM provides the pump efficiency estimated from the built-in data base, but the efficiency is just reference.    Estimation of pump efficiency by ES_Pump_SM is meaningless because pump efficiency varies widely depending on manufacturers as well as the model selected even in the same manufacturer.   It is better for user to input the pump efficiency according to the purpose of pump use and his own experience.   The user can input the pump efficiency for himself in the menu [Option] -> [Calculation].

Motor rating is selected from the built-in motor rating data base automatically considering the pump BHP and motor rating minimum margin that user inputs in option menu.   When motor rating is above 1000 kW, the motor rating is selected as the pump BHP multiplied by the motor rating minimum margin is.   

Motor efficiency is also provided by the program from the built-in data base automatically.  Motor power(motor power consumption) is calculated from the pump BHP and motor efficiency.   The user can also input the motor efficiency for himself in the menu [Option] -> [Calculation].

10) Pump specific speed is calculated based on the suction type(single or double) and pump speed the user input in the menu [Option] -> [Calculation].   Based on the pump specific speed, the impeller type is provided.   The provision is based on that 4200 rpm-USgpm/feet and below as radial type, 9000 rpm-USgpm/feet and above as turbine type and in between as mixed flow type.

11) In our previous softwares, the default units were metric engineering units when the softwares start.   In ES_Pump_SM, the user can select the default units from the menu [Option] -> [Unit] -> {Set the current units as default].

 

2. Pump Calculation (TOC)

2.1 Pump Capacity

Pump capacity is selected by the pump operating flow plus surge margin and wear margin the user inputs.   Surge margin is for flow fluctuation in the pumping system and the wear margin is for the aging of the pump.   Generally each of surge and wear margin is selected as the value in between 4 to 6 percent.   The higher the pump capacity, the lower the margin.

ES_Pump_SM calcurates the pump capacity as below.

 PpCapa = VFlow * (1 + SurgeMargin / 100 + WearMargin / 100)

where,

PpCapa

: Pump capacity

 

VFlow

: Pump volume operating flow

 

SurgeMargin

: Surge margin, %

 

WearMargin

: Wear margin, %

 

2.2 Pump Total Head (TOC)

Pump suction pressure is calculated from the suction pipe inlet pressure the user inputs using in flow direction the same method with those of ES_dPCalc, another software of ENGSoft Inc.   Pump discharge pressure is calculated from the discharge pipe outlet pressure in reverse flow direction.

From the pressures and velocities of pump suction and discharge calculated, the total head of pump is calculated.   Please note that in ES_Pump_SM, pump is located at a pipe outlet node, the elevations of pump suction and discharge is always same.  

When simulating vertical wet sump pump, the first pipe which has the pump at the outlet node shall have zero length and the next pipe to be considered as the column of the vertical pump shall be a vertical pipe having the same length of the pump column.     The pump total head so calculated is bowl head.   If user want the pump head at pump discharge flange, the pump column length shall be deducted from the head calculated.   The pump head at pump discharge so calculated is over-designed as much as the friction loss of the column, but it is negligible.

ES_Pump_SM calcurates the pump total head as below.

 TotalHead = (DisPR - SucPR) * 10000 * SVOL + (DisVel^2 - SucVel^2) / 2 / 9.81 + (DisElev - SucElev)

where,

TotalHead

: Pump total head

 

DisPR/SucPR

: Pump discharge / suction pressure, kg/cm2 abs.

 

SVOL

: Specific volume of pumping fluid, m3/kg

 

DisVel/SucVel

: Pump discharge / suction velocity, m/sec

 

DisElev/SucElev

: Pump discharge / suction elevation (same), m

 

2.3 Net Positive Suction Head Available, NPSHa (TOC)

NPSH available is the pump suction head over the vapor pressure of pumping fluid, which is available by the pump suction condition.

ES_Pump_SM calcurates NPSHa as below.

 NPSHa = (SucPR - SucVaporPR) * 10000 * SVOL

where,

NPSHa

: NPSHa, m

 

SucPR

: Pump suction pressure, kg/cm2 a

 

SucVaporPR

: Vapor pressure of pumping fluid, kg/cm2 a

 

SVOL

: Specific volume of pumping fluid, m3/kg

 

2.4 Net Positive Suction Head Required, NPSHr (TOC)

NPSH required is the pump suction head over the vapor pressure of pumping fluid, which is required by the pump in order prevent cavitation in pump.   The NPSH required is provided by pump manufacturers.

In ES_Pump_SM the user can specify the minimum NPSHa over NPSHr ratio in the menu [Option]-[Calculation...].    When the NPSHa over NPSHr ratio calculated is over the minimum value specified, the program warns the user, writes the NPSHr value in red color and recommends the maximum pump speed.   Another way to release the warning is to increase the pump suction specific speed specified, but it is not recommended.

ES_Pump_SM calcurates NPSHr as below.

 NPSHr = (RPM * VFlow^0.5 / S_English)^(1 / 0.75)

where,

NPSHr

: NPSHr, feet

 

VFlow

: Pump suction volume flow, US gpm

 

RPM

: Pump speed, rpm

 

S_English

: Pump suction specific speed, rpm-US gpm/feet, normally 8500 rpm-US gpm/feet

Pump NPSHr is determined by test at shop.   The suction pressure of the pump at test stand is lowered till the pump head drops suddenly a certain amount.   It is judged that the sudden head drop stands for cavitation occurred.    However, it is difficult to recognize the incipient head drop point.   Therefore, a certain amount of head drop is used to define NPSHr.   1% head drop NPSHr is the NPSHr value calculated from the suction pressure showing the head drop of 1% to pump rated total head.   When stating NPSHr, it is very important to identify the head drop percent.

Normally 3% head drop NPSHr is used.   However, if the NPSHa of pumping system reaches the 3% head drop NPSHr, there must be cavitation even if it is not so severe.   Therefore, in case of high energy pump like boiler feed water pumps that has high possibility of cavitation, incipient or 1% head drop NPSHr is also used in order to prevent from cavitation as a maximum.

 

2.5 Energy Grade Line, EGL (TOC)

If friction does not exist, the total energy of flow through a pipe kept constant.   Only the energy type is altered among pressure energy, velocity energy or elevation energy.   The Bernoulli equation shows this relationship.    Please refer to the user manual of ES_dPCalc.

When friction of pipe is considered, the total energy of flow through a pipe decreases along the flow direction by the friction energy.    Energy Grade Line is the line showing the total energy variation along the pipe flow.

ES_Pump_SM calcurates EGL as below.

H_EGL = Elev - RefElev + PR * 10000 * SVOL + Vel^2 / 2 / g

where,

H_EGL

: Energy grade of a point in pipe, m

 

Elev

: Elevation of the point, m

 

RefElev

: Reference elevation, m (ES_Pump_SM uses the suction pipe inlet elevation as reference..)

 

PR

: Gauge pressure of the point, kg/cm2 g

 

SVOL

: Specific volume of pumping fluid, m3/kg (constant because of incompressible fluid)

 

Vel

: Velocity of the point, m/sec

 

g

: Gravity acceleration, 9.81 m/sec2

The difference of EGL between pump discharge and suction is pump total head.

 

2.6 Pump Efficiency (TOC)

Pump efficiency differs depending on pump manufacturers as well as pump models even in same manufacturer.    Therefore, the estimation of pump efficiency is meaningless.   The best way is to estimate by the user based on his own experience.

ES_Pump_SM provide with estimated pump efficiency, but the efficiency provided is just reference.   The user can input his own efficiency in the menu [Option]-[Calculation...].

 

2.7 Pump BHP (Brake Horse Power) (TOC)

ES_Pump_SM calcurates pump BHP as below.

PumpBHP = MFlow * TH / Eff_Percent * 100

where,

PumpBHP

: Pump BHP, kgf-m/sec

 

MFlow

: Pump mass flow rate, kg/sec

 

TH

: Pump total head, m

 

Eff_Percent

: Pump efficiency, %

 

2.8 Motor Rating, Motor Efficiency, Motor Power Consumption (TOC)

Unlike pump efficiency, motor rating and motor efficiency have been well defined by industry.   ES_Pump_SM provides motor rating, motor efficiency and motor power consumption estimated from the built-in data.   Motor rating minimum margin can be input by the user in the menu [Option]-[Calculation...] and motor rating is selected to have the minimum margin over the pump BHP calculated.     Motor efficiency can also be input by the user in the menu [Option] - [Calculation...].

Motor power consumption is calculated by the equation of "Pump BHP / Motor Efficiency(%) * 100".

 

3. Friction Loss Calculation (TOC)

The friction loss calculation of pump suction and discharge pipe is just same with those of ES_dPCalc software.   Please refer to the user manual of ES_dPCalc for details of friction loss calculation.

 

4. System Curve (TOC)

The system curve of pumping system shows the pumping head variation versus pumping flow, except the head loss of the flow control valve which makes up the head difference between pump H-Q curve and system curve.

There are two kinds of pumping head.   One is the head which does not vary with pumping flow, and the other varies with pumping flow.   The head by the pressure difference between pump suction pipe inlet and pump discharge pipe outlet(pressure head) does not vary with pumping flow.  The head by the elevation difference between pump suction pipe inlet and pump discharge pipe outlet(elevation head) does not vary with pumping flow, too.    Whereas, the friction loss head by pipe length, fittings and valves varies with the square of pumping flow.

Therefore, the system curve of a pumping system has the head value of pressure head plus elevation head at zero pumping flow, as shown the figure below, and then, as the pumping flow increases, the system curve rises in square curve reflecting the friction loss head variation.

In the system curve figure below, the New System Curve shows the system curve without consideration of friction margin, and the Aged System Curve is with consideration of friction margin.

In ES_Pump_SM, the pump head is selected as the head crossing the Aged System Curve plus the head loss of the flow control valve at the flow with surge margin(Q'), and the pump capacity is selected as the flow with surge and wear margin(Qr).

The H-Q curve of the pump selected such is the New Pump H-Q Curve and the H-Q curve moved horizontally leftward by wear margin is the Aged Pump H-Q Curve.

 

 

In ES_Pump_SM, the system curve data is provided as a part of text output and the system curve data can be exported as Microsoft(R) Excel(R) file.   When exporting as Microsoft(R) Excel(R), all Microsoft(R) Excel(R) files opened should be closed in advance in order to prevent from Excel(R) error.

 

5. Major Screens (TOC)

5.1 Input Screen

Upper left side frame is for showing pump iso-metric drawing, and, by double clicking the frame, pump iso-metric edit window can be activated.    Upper right side frame is for calculation input frame.   Lower left side frame is for showing the calculation results of piping system.   Lower right side frame is for showing pump calculation results.

ES_Pump_SM calculates two liquid, i.e. water and liquid.   The picture shown above is for water calculation.   For water calculation, only pressure and temperature are required for suction pipe inlet condition and other properties such as specific volume, viscosity, etc. are input by the software automatically..   When the condition represented by the pressure and temperature the user inputs is steam, then the software warns the user and proceeds the calculation with saturated water automatically.     For water, the user can input the suction pipe inlet condition by using the steam table by clicking the steam table command button below the frame.

In case of liquid, the user has to input the pressure, temperature, specific volume, viscosity and vapor pressure at (pumping) temperature of suction pipe inlet.

For both water and liquid, the user has to input the volume flow or mass flow of suction pipe inlet and the pressure of discharge pipe outlet.   The texts the user has to input have green back ground color.

The vapor pressure at (pumping) temperature is used for checking the vapor formation in pipe and calculation of NPSH available.

The specific volume of suction pipe inlet is used for entire pipes of pumping system constantly.

More detailed calculation results are shown in the text output window to be described below.

 

5.2 Calculation Options (TOC)

By clicking the menu [Option]-[Calculation...], the Calculation Option window is shown.   The options are self-explanatory.

 

5.3 Node Flow Edit (TOC)

By clicking the menu [Option]-[Node flow...], the Node Flow Edit window is shown.   In the Node Flow Edit window, the user can input or edit the node flow.

The open node to be selected in drop-down list is the node the user can not input or edit.   The open node is the node to be used by the software in order to make the sum of node flow zero in accordance with mass conservation law.

Inflow to a node is set as flow with plus sign and outflow from a node as flow with minus sign.

 

5.4 Text Output (TOC)

By clicking the menu [Window]-[Text output window], the Text Output window is shown.

In text output window, the detailed calculation results are shown.

 

5.5 Pump Iso Window (TOC)

The Pump Iso window is shown by double-clicking the iso-metric drawing or clicking the menu [Window]-[Iso window].   The Pump Iso window is just same with the Pipe Iso window of ES_dPCalc except the following.   For use of Pump Iso window, please refer to the user manual of ES_PipeIso.

The difference of Pump Iso window from Pipe Iso window is the pump location frame and control valve frame.   

In Pump Location frame the user can select the location of the pump from drop-down list.   The pump always located the Out Node of a pipe.

In Control Valve frame, the user can select the location of discharge control valve from a drop-down list, and input the pressure loss of the control valve.   The reason why the control valve has a separate input frame is for system curve generation.   When the pumping system is simulated without discharge control valve, the pressure loss of the control valve must be input as zero.   For the pressure loss of control valve, no friction margin is applied.

 

5.6 Conversion of dP to K (TOC)

As described in Introduction clause above, the use of "User Defined Fitting by dP" is not recommended for system curve data generation.   ES_Pump_SM has the function of "Conversion of dP to K" in order to assist the user.    The function can be activated by clicking the menu [Auxiliary Calculation] - [Conversion of dP to K...] in Iso Window.

In the "Conversion of dP to K" window, the surge margin and friction loss margin input boxes are provided and the margin values of the current calculation are automatically input to the boxes.   The K value so calculated results in the dP value the user wants, considering the surge and friction loss margin.

 

5.7 Other Menu (TOC)

1) [Option] -> [Unit] -> [Set calculation units...]

Set the units for current calculation.

2) [Option] -> [Unit] -> [Set the current units as default]

Set the current units as default units which the software starts always with.

3) [Option] -> [Calculation title]

Set the calculation title.

4) [Option] -> [Text Ouput] -> [Show calculation details] check

Set whether to show the pipe calculation details in the text output window.

(TOC)


Copyright (c) 2003 ENGSoft Inc., Seoul, Korea, All right reserved.