Two pumps can look similar on paper and behave completely differently in use, because they are built to do opposite things. One is designed to move a large volume of water against very little resistance. The other is designed to push water high or far against a lot of resistance. These are the high flow and high head ends of the pump world, and understanding the difference is the single most useful thing you can know before choosing a pump, because no pump gives you the maximum of both at once.
Flow and head, defined simply
Flow is the volume of water a pump moves in a given time, measured in litres per minute or cubic metres per hour. It is the answer to "how much water".
Head is the height and resistance the pump can push against, measured in metres. It is the answer to "how high or how far". Head is not just vertical lift: it includes the friction the water meets travelling through pipe and hose, so a long horizontal run adds head just as a vertical climb does. Our guide to how to read a pump curve shows how the two are plotted together.
Why you cannot have both at once
Every pump trades flow against head along a curve. At zero head, with nothing to push against, a pump delivers its maximum flow. As the head rises, the flow falls, until at the pump's maximum head the flow drops to nothing. This is true of every pump ever made, which is why a headline maximum flow figure is never the flow you get in a real installation. We explain that trap in detail in our guide to why max flow is not your real flow.
What changes from pump to pump is the shape of that curve, and that is what makes a pump high flow or high head. A high flow pump holds a large flow but only at low head. A high head pump holds its pressure up to a great height but moves less water while doing it.
What makes a high flow pump
A high flow pump uses a large impeller and a wide internal passage to move a big volume of water, but at relatively low head. These are the pumps for moving a lot of water a short distance with little lift: clearing a flooded field or car park, emptying a large sump, dewatering a shallow excavation or shifting surface water fast. A contractor pump like the APP HD-15, which moves around 830 litres a minute, is a high flow pump. You will find the range in our high flow pumps collection, and they overlap heavily with flood and drainage work.
What makes a high head pump
A high head pump is built to push water up or far, against significant resistance. It does this either with a peripheral design or, more often, by stacking several impellers in series so each one adds pressure, which is why borehole and high-pressure pumps are long and narrow. These are the pumps for lifting water from a deep sump up several floors, pushing it a long distance across a site, feeding a sprinkler system that needs pressure, or drawing from a borehole. A pump like the Tsurumi HS or the APP KHL-20 sits at this end, and the full range is in our high head pumps collection.
Frequently asked questions
What is the difference between flow and head on a pump?
Flow is how much water a pump moves in a given time, in litres per minute or cubic metres per hour. Head is how high and how far it can push that water against resistance, in metres, including both vertical lift and pipe friction. Flow answers how much, head answers how high or how far.
Can a pump be both high flow and high head?
Not at the same time. Every pump trades flow against head along a curve: maximum flow comes at zero head, and flow falls to nothing at maximum head. A pump can be designed to favour one end or the other, but it cannot deliver its maximum flow and its maximum head together.
Do I need a high flow or high head pump for flooding?
Usually high flow, because most flooding is about moving a large volume of water a short distance with little lift. The exception is where the water has to be lifted a long way up or pushed a long distance to a discharge point, which adds head and may call for a higher head pump. Work out your total head to decide.
Why are high head pumps long and narrow?
Because they build pressure by stacking several impellers in series, each adding a step of head, and a slim body lets them fit down a borehole. This multistage design is what allows them to push water high or far, at the cost of moving less volume than a wide, large-impeller high flow pump.
