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Glossary of Terms

Disch. HWC:
Enter Discharge pipe “Hazen-Williams Constant” (HWC). This is a number usually between 115 to 155 which relates to the surface roughness of the pipe internal bore. Find Pipe Data at top of the 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).
Disch. ID (mm):
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.
Disch. Length (m):
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).
Disch. Static (m):
Enter Discharge Static Head in metres. This is the vertical height between the 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 syphoning 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)
elbow:
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 the text box.
Flow (L/sec):
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.
Foot Valve:
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.
Friction Loss
The amount of pressure/head required to ‘force’ liquid through pipe and fittings.
Gate Valves:
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.
N.R. Valves:
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 the text box.
Nett Positive Suction Head
Nett positive suction head (NPSH) – related to how much suction lift a pump can achieve by creating a partial vacuum. Atmospheric pressure then pushes liquid into pump. A method of calculating if the pump will work or not.
NPSH (m):
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.
Pipe data:
Find Pipe Data – Inside Diameter & Hazen Williams Constant. Find information for various pipe types & sizes: 1) Select pipe material from the drop-down menu 2) the other two menus will then give a choice of pipe ratings. 3) Enter the data into the calculator “Hazen-Williams Constant” (HWC) is a number which relates to the surface roughness of the pipe internal bore.
Pump Head
Centrifugal pump curves show ‘pressure’ as head, which is the equivalent height of water with S.G. = 1. This makes allowance for specific gravity variations in the pressure to head conversion to cater for higher power requirements. Positive Displacement pumps use pressure (ie; psi or kPa) and then multiply power requirements by the S.G.
S.G.
Specific gravity. weight of liquid in comparison to water at approx 20 deg c (SG = 1).
Specific Speed
A number which is the function of pump flow, head, efficiency etc. Not used in day to day pump selection, but very useful as pumps with similar specific speed will have similar shaped curves, similar efficiency / NPSH / solids handling characteristics.
Static Head
The vertical height difference from surface of water source to centreline of impeller is termed as static suction head or suction lift (‘suction lift’ can also mean total suction head). The vertical height difference from centreline of impeller to discharge point is termed as discharge static head. The vertical height difference from surface of water source to discharge point is termed as total static head.
Suction HWC:
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).
Suction ID (mm):
Enter Suction pipe inside diameter in millimetres. If you know it, great! if not, Find Pipe Data at top of the page and enter Inside diameter (ID) into the text boxes. If  suction pipe rises and falls, it is likely an airlock can occur, which will greatly increase friction loss and therefore reduce NPSH(a) which increases the chance of cavitation.
Suction Length (m):
Enter Suction pipe length in metres. If suction pipe rises and falls, it is likely an airlock can occur, which will greatly increase friction loss and therefore reduce NPSH(a) which increases the chance of cavitation.
Suction Static (m):
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.
Tee:
Enter the number of standard tees in the 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 the text box.
Total Dynamic Head
Total height difference (total static head) plus friction losses & ‘demand’ pressure from nozzles etc. ie: Total Suction Head plus Total Discharge Head = Total Dynamic Head.
Total Dynamic Head (m):
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.
Total Head
Total height difference (total static head) plus friction losses & ‘demand’ pressure from nozzles etc. ie: Total Suction Head plus Total Discharge Head = Total Dynamic Head.
Vapour Pressure
If the vapour pressure of a liquid is greater than the surrounding air pressure, the liquid will boil.
Viscosity
A measure of a liquid’s resistance to flow. ie: how thick it is. The viscosity determines the type of pump used, the speed it can run at, and with gear pumps, the internal clearances required.