Pump Fundamentals
Pipe Friction and Total System Head
The head a pump must produce is set by your piping, not by the pump. Estimating total system head correctly is what lets a supplier pick the right pump the first time, so it is the single most useful thing to work out before requesting a selection.
What Makes Up System Head
Static head
The vertical lift between source and destination levels, plus any difference in tank or vessel pressure. It does not change with flow.
Friction head
The loss from pushing liquid through pipe, valves and fittings. It rises steeply with flow, roughly with its square, and it falls quickly as pipe diameter increases.
Total system head is the sum of static head, friction head and any pressure difference between the suction and discharge ends. That total, at your required flow, is the duty point a pump is selected against.
Where Friction Comes From
- Straight pipe — loss grows with length and flow, and with rougher or smaller-bore pipe
- Valves and fittings — bends, tees, reducers and especially throttling valves each add loss, often expressed as equivalent length of pipe
- Velocity — undersized pipe raises velocity and friction sharply, so a slightly larger line can noticeably cut the head the pump must produce
Estimating a Duty Point to Send
You do not need a full hydraulic study to request a pump. A workable duty point comes from the required flow, the static lift, the pressure at each end and a reasonable allowance for pipe and fitting friction at that flow. Send those figures with the pipe size and rough run length, and the selection is reviewed against a real pump curve. If the estimate is uncertain, say so, and a suitable margin is applied rather than guessed.
System Head FAQ
What is the minimum information for a pump selection?
Required flow, static lift, end pressures, liquid and temperature, and the pipe size and approximate length. From that we build the duty point and select against a reviewed curve.
Should I size the pipe or the pump first?
They interact. Undersized pipe forces a higher-head pump and higher running cost. Send the intended pipe size and we flag if a larger line would give a better overall selection.
What if I only know the flow?
Send what you have. Flow alone lets us start, and we ask targeted questions about lift and piping to complete the duty point.
Build Your Duty Point
Send flow, lift, end pressures and pipe details and we translate them into a pump selection.
This is general engineering guidance for buyers of ANSI/ASME B73.1 process pumps. Final selection always depends on your verified duty point, liquid data and installation conditions. Send your data for a reviewed proposal.