How To Choose Pipes, Fittings & Tubing For Ponds & waterfalls.
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.
In every practical situation however it is impossible to get this amount of energy out of the motor and to transfer it directly to the water that is being circulated. In fact the amount of energy or power that's lost between switching the pump on and finally getting water to flow over the waterfall is enormous.
In some cases you have a degree of control over how well you sue the power generated and in others no control at all. For example the heat lost by the motor getting hot is totally beyond your control. What you can control and in fact must do so to get the best from your garden pond and waterfall pump is as follows ...
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Length of pipe from pump to waterfall inlet
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Diameter of pipe from pump all the way through the pumping system
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The number and type of fittings in the pipe-work
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Bends and other restrictions in the tubing and pipe-work runs.
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The type of pipe or tubing used in the system
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Then use of valves to regulate flow rate
I've seen many installations where the size of pipe from a pump is far too small in terms of pipe diameter. I've also seen many cases where pipes are kinked because a rock has fallen onto the pipe or the pipe has been bent to go around a corner.
Bends, sudden direction changes (eg T pieces), small diameter pipe all restrict water flow through pipes and as such try to avoid anything that interrupts smooth water flow through the pipe from the pump to the waterfall. Think about this for a moment and find let me describe an analogy ...
Let's say you're running down the street to catch a bus which you just saw cross the intersection ahead of you and disappear into the street at right angles to the one you're running down. To be able to turn the corner you have to slow down and then speed up again if you going to catch the bus and this takes energy. This is the same in a water system. If you make the water go round a bend energy is lost. You can think of the water as slowing down and then having to speed up again. This is a waste. The sharper the bend the more energy or power is lost.
The correct term is that the pressure drop through the pipe is increased and in any system increase in pressure drop translates into reduced pump flow.
Algae inside the pipe also creates restrictions so try to avoid using transparent piping (sunlight allows algae to grow so transparent pipe helps this process. Black piping is best.
Inevitably in almost all situations there is a need for fittings and bent pipes. Just make sure you don't overdo it.
To make allowance for this loss of energy add 20% to the head or height you want to pump. For example let's say yoru waterfall inlet is 2 metres and you want to pump 1000 litres per hour over it (about 450 gallons per hour) then choose a pond pump that will deliver 1000 litres per hour NOT at 2 metres (6.5 feet) head but at 2.4 metres head (8 feet) ... in this way we've allowed for 0.4 metres ( 1.5 feet) of head to be wasted in piping or tubing systems.
Remember ...
Make sure you get the widest diameter pipe that will fit your pump and that it's length is as short as possible. For most pond pump situations do not use pipe less than 1 inch (25mm) in diameter unless you can't avoid it (for example in very small fountain pumps)
Paying attention to these 2 factors will save you electricity costs (and with oil at present prices we need to save as much energy as we can)
MAXIMUM HEAD
The height at which flow from any pump STOPS ... eg if this figure is 4 feet then at a height anywhere between 0 and 3.99 feet there will be some water flow although it will get significantly less as the height increases and approaches 4ft. However at 4 ft there will be NO water flow at all. Many people believe wrongly believe they will get 1000 gallons max flow from a pump at its maximum head of say 4ft
MAXIMUM FLOW
This happen at the level of the pond surface and is the flow with no pipe attached to the pump. The fact that the pump is sitting at bottom of the pond does not make any difference.
The electrical energy from a pump's motor is shared between flow (actually mass) of water and the height (head) to which it must be pumped. What this means in simple terms is that you cannot have both more flow AND more pressure form the same pump. You must choose ... do you want more flow or more head (pressure). And you can choose somewhere between zero and maximum flow and zero and maximum head.
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 ...
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Use widest diameter pipe for your waterfall pump
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Use shortest possible pipe length to go from the pump exit to the inlet of your waterfall.
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Do not kink the pipe.
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Do not squash the pipe under rocks
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Do not use more valves than necessary. Reduce T pieces and/or Y pieces and/or sharp bends to a minimum.
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Prevent build-up of algae inside the pipe by using NON-transparent piping. Black ribbed pipe is best in fish pond environments
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When you use stepped connectors cut off the smaller diameter steps. Use the maximum step diameter you can.
To totally and accurately specify a pump you need to know 3 things
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1. Volume of water flow required
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2. Height to which this flow must be pumped
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3. 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. In a normal situation if you add 20% to the height you want to pump this will normally be safe. You would use this new number .... Actual Height + 20% .... to specify the pump.