Pump head & What It means To You

Every pond pump driven by electricity is fitted with a motor. The motor is normally rated in watts or kilowatts. This is a measure of the amount of energy the motor can generate at absolute maximum and at 100% efficiency. Make sure the delivery pipe from the pump is not kinked or is being restricted by a build up of algae inside the pipe.

A simple way to look at how a pump works

Have you ever tried carrying a bucket of water up a flight of stairs? It can be a bit tiring. Now try carrying 2 buckets of water up the same stairs and you will feel extra tired ... in this second instance you have used twice as much energy because you had to lift twice as much water to the SAME height. Another way of looking at this is to carry one bucket up twice as many steps ... once more you will be more tired because you had to use more about twice as much energy than was required to move the single bucket of water up half the number of steps.

Exactly these principles are at work in any pond pump.

Let's go back to any pump in a pond environment. Normally you want to pump water up to a waterfall and when you do this you may have noticed the water flow is less than what was coming out of the pump at ground or at a lower level. This is because the pump has a motor that is always operating at its maximum operating point in terms of energy being supplied to the pump through the electric cord. In practical terms this means if you want to lift the water higher than the pond surface then with a fixed amount of energy the pump compensates by reducing the amount of water it can lift. Just like the stairs example.

You can thus see that any pump will share its energy ... some to flow and some to lift. The more the lift the less the flow and vice versa.
Every pump box states MAXIMUM HEAD and MAXIMUM FLOW. What do these bits of information means and why are they pretty useless bits of information?

Pump head is ALWAYS measured from pond surface to inlet to waterfall. It does not make any difference if the pipe does not go straight up. The vertical distance is what matters as in the diagram above.

MAXIMUM HEAD

The height at which flow STOPS ... eg if this figure is 6 feet then at a height anywhere between 0 and 5.9 feet there will be some, but different amounts of, water flow. However at 6 ft there will be NONE.

MAXIMUM FLOW

This happen at the level of the pond surface and is the flow with no pipe attached to the pump.

As you now understand the energy from a pump's motor is shared between flow (actually mass) of water and the height (head) to which it must be pumped. In a real pond situation it becomes a bit more complicated because when water flows through a pipe, or via a "T" piece, bend, fountain nozzle, or through a valve etc some energy is required to overcome friction losses in these different parts of the system. Once more because the pump's motor (energy output) is fixed it means that the water flow is reduced for any specific height pumped. We refer to these "things" as flow restrictions.

In practice you need to remove or lower the impact of any restrictions to flow. You therefore will get better pump performance if you do the following ...

• Use widest diameter pipe you can

• Use shortest possible pipe length

• Do not kink the pipe (a big problem with thin-walled plastic pipe)

• Do not use valves, T pieces, Y pieces, sharp bends etc in your pipe-work if you can avoid it.

• Prevent build-up of algae inside the pipe by using NON-transparent piping.

• When you use stepped connectors cut off the smaller diameter steps.

• To totally and accurately specify a pump you need to know 3 things

• Volume of water flow required

• Height to which this flow must be pumped

• Head (or friction loss) loss due to restrictions in pipe and fittings.

This last component is complex to calculate and this is where you should use my calculator (set of 12 calculators are free when you buy my book.

In a normal situation if you add 20% to the height you want to pump to this will normally be safe. You would use this new number .... Actual Height + 20% .... to specify the right pond pump.

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