Calculator / Curve Generator Tutorial

This Calculator will work out the Total Dynamic Head & NPSH(a) of a system and assist in drawing system curves. View our Pump Training pages for help with terms used in this Tutorial.

Refer to the letters shown on the screenshot of the calculator at right:

A: Find Pipe Date - Inside Diameter & Hazen Williams Constant. Find information for various pipe types & sizes:
1) Select pipe material from top drop down menu
2) the other two menus will then give a choice of pipe ratings.
3) Enter the data into the calculator (see "C" for more info).
"Hazen-Williams Constant" (HWC) is a number which relates to surface roughness of the pipe internal bore.

B: If you are using Internet Explorer 4+, you can view context help in this area. As your mouse hovers over text in the calculator, the information in this area will change.

C: This is the area where data relating to your pump system is entered, view our Pump Training pages if you need further help with terms used in this Tutorial.
1) Enter Flowrate in Litres / second in the text box. By calculating head at 2-3 flowrates it is then possible to draw a system curve to assist in pump selection and troubleshooting, visit our Pump School for more info.

2) Using a Foot Valve? Enter "1" into text box if a foot valve will be used. Calculation is based on hinged disk type valve with strainer, If a poppet type valve is used the friction loss is much higher, enter a higher number for small sizes and a smaller number for larger sizes, ie: enter "7" if 15mm, "6" if 25mm, "5" if 50mm and "4" if 150mm etc. Note: Using larger valves will normally reduce friction loss but there is a critical velocity required to allow valve to open correctly, under which excessive friction losses or hammering may occur.

3) Enter Suction Static Head.This is the vertical difference between the water level and the centreline of the pump in metres. If the water level is above the pump (flooded suction), then enter as a negative number (ie: -5). This is the one time in pump selection when it is a good idea to add a little extra margin, as it is difficult to estimate exact entry losses into the pump, we should allow for turbulence, losses due to turbulence, etc. So add a metre for confidence with NPSH. Warning, this calculator does not allow for friction loss due to fittings etc on suction side. Calculate system & then add suction fitting info into text boxes, click Calculate, & add additional loss to SUCTION STATIC and remove suction fittings from calculation, re-calculate.

3) Enter Suction pipe inside diameter in millimetres. If you know it, great! if not, Find Pipe Data at top of page and enter Inside diameter (ID) into the text boxes. If the suction pipe rises and hoses, it is likely an air lock can occur, which will greatly increase friction loss and therefore reduce NPSH(a) which increases chance of cavitation.

4) Enter Suction pipe length in the text box in metres. If the suction pipe rises and hoses, it is likely an air lock can occur, which will greatly increase friction loss and therefore reduce NPSH(a) which increases chance of cavitation.

5) Enter Suction pipe "Hazen-Williams Constant" (HWC). This is a number usually between 115 to 155 which relates to surface roughness of the pipe internal bore. Select Pipe Data at top of page and enter HWC into the text boxes.Experiment with the HWC value to simulate old pipe (guess-work only, try 10 -50 less than value for new pipe).

6) Enter Discharge Static Head in metres. This is the vertical height between pump centre and the final discharge point. If the discharge point is below the pump, then enter as a negative number.
If pipe rises ie: to 40m then drops to 30m:- Then 30m is usually the static head, but it is also necessary to calculate with 40m static head to confirm there is enough flow to fill pipe and establish the syphon effect that reduces static head to 30m . ENTER "DEMAND" PRESSURE - AS HEAD, ie: pressure required by sprinkler etc, if there are multiple sprinklers, the pressure is only added once. To convert to head , DIVIDE by: psi = 1.42, kPa = 9.789 (water only)

7) Enter Inside Diameter of discharge pipe in millimetres. If you do not have actual inside diameter, Find Pipe Data at top of page and enter Inside diameter (ID) into the text boxes.

8) Enter Discharge Pipe total length in Metres. If your system has multiple pipe sizes, it is necessary to calculate each section of common size pipe and then add the friction loss for the next size pipe until all sections are included (only enter static suction & discharge head once). Where multiple branch lines and multiple discharge points exist, it is necessary to draw a system curve for each separate "system" then draw a new system curve by adding together all the flowrates which occur at the same head (ie: find the flow at 10 metres on each system curve and add flows together. Then repeat for 20 metres etc).

9) Enter Discharge pipe "Hazen-Williams Constant" (HWC). This is a number usually between 115 to 155 which relates to surface roughness of the pipe internal bore. Find Pipe Data at top of page and enter HWC into the text boxes. Experiment with the HWC value to simulate old pipe (guess-work only, try 10 - 50 less than value for new pipe).

10) Enter 1 for each fully open gate valve, Enter 0.3 for fully open ball valves, Enter 2-6 for fully open butterfly valves (2=400mm, 6=50mm). Enter 43 for each fully open globe valve.

11) Enter Number of Non Return Valves. Sometimes called Reflux, Check, one way valves. Friction loss varies substantially between actual types of valves, but a value of 1 should be close enough for industrial valves around 50mm, smaller valves will require a value around 2 (small poly loaded poppet type valves may be similar to a value of 6?) For larger valves around 300 mm, a value of 0.7 per valve could be used. Add these together and enter in text box.

12) Enter Number of standard Elbows. Use 1 for each 90 degree elbow, Use 0.5 for each 45 degree elbow, Use 0.6 for each long radius bend. Add these together and enter in text box.

13) Enter number of standard tees in text box. If the flow passes through the branch and not the "straight through" section, you will need to enter a value of 3 for each tee. Add these together and enter in text box.

D: This is where the results of the calculation will be shown after clicking the "CALCULATE" button.
1) TOTAL DYNAMIC HEAD. This shows the head in metres that the pipe system will create at the flowrate entered (ie: Duty Point). By calculating 2 or 3 duty points a system curve can then be drawn (they are very useful in selection & troubleshooting of pump systems. See our pump school for more information.
2) NETT POSITIVE SUCTION HEAD (AVAILABLE). This should be a minimum of one metre above the NPSH(r) value read from the pump performance curve, or the pump will cavitate. See our pump school for more information. This result relates to locations at sea level, deduct approximately 1m NPSH(a) for every 900m elevation above sea level. Temperature also reduces NPSH(a) by approx: 39°C=0.5m, 50°C =1m, 62°C=2m, 71°C=3m, 76°C=4m, 81°C=5m, 86°C=6m, 90°C=7m, 93°C=8m, 96°C=9m, 99°C=10m.

E: The "CALCULATE" button is used once all the data boxes in C) are complete. After viewing results you can generate an online system curve by clicking the "DRAW SYSTEM CURVE" button and following the instructions (see sections F), G), H), & I) below for more information.)

Refer to the letters shown on the screenshot of the calculator at right:

F: These boxes show the results of the calculation. This data needs to be entered into the boxes in the System Curve Generator "G)". The 1st & 3rd boxes of Function must be copied to each side of *(x^2)+ in the top Function box ( *(x^2)+ doesn't change). The greyed out sections don't need to be transferred to the boxes in the generator.

G: This is the data entry section of the System Curve Generator Applet. Enter the data from "F" into these boxes, TO EDIT: USE BACKSPACE, NOT DELETE. Note that the second and third boxes are complete and do note need to be changed.

H: Click "Plot it!" NOTE: Will not work until all required data is entered.

I: Click the "VIEW CURVE" button and the curve will be displayed. The (bottom) "x" axis is flowrate. The (side) "y" axis is head. The head axis starts at the static head NOT ZERO! If the scale is hard to workout, try changing the Maximum x Value. High numbers will show a multiplier (ie: 3 x10³= 3000). TO PRINT: Press "print screen" key & paste into Paint or other graphics program, then print.

This Calculator & Curve are provided for guidance only!
© 2004 Doyle Pump, except Java applet covered by the GNU General Public Licence.