What you need to know about the Inlet Supply of your High Pressure Pump
Unsuitable inlet supply can cause even the best designed pump to malfunction. As a result surprisingly serious problems can be caused by the simplest issues or go unnoticed by inexperienced machine operators. The most notable of which is pump cavitation.
Remember, there is no standard way to set-up a system because no two systems are the same. However by understanding cavitation and following some simple rules, you can prevent it.
What is Cavitation and how does it relate to Inlet Supply?
Water is supplied to the pump through the inlet valves. When a high pressure pump is starved of water, it will suck in air and cause cavitation in the pump. You will know your pump is cavitating when it starts to vibrate and make a very loud knocking noise.
Bubbles of water that gets sucked into the system implode in the pump causing the vibration. In addition the alternating of heat caused by friction and lack of water, followed by bursts of cold water cause the ceramic pistons to shatter.
The back end of the pump is destroyed by cavitation. This includes the conrods, the plungers and the crankshaft. Cavitation also causes seals to wear and the valve plugs to burst.
When the crankshaft seizes it causes the motor or engine to seize, destroying more than just the pump.
Cavitation destroys the pump and possibly even the motor or engine it is coupled to. Thereby making it an expensive and inconvenient experience which should be avoided at all costs.
This is done by ensuring that the water supply to the pump is enough for the needs of the pump. Furthermore no air must be able to enter the water feed.
Cavitation causes the ceramic pistons to shatter.
The back-end of the pump is completely destroyed by cavitation.
Broken pieces of metal from the back-end will burst through the housing.
How to ensure the Inlet Supply is sufficient
Pumps with a flow rate of less than 15L/min
A connection to a domestic tap may be used for pumps that have an output of less than 15L/min so long as the water supply is not shared. The water pressure must also be fairly consistent. The water supply can be provided through one inlet.
We had a client who operated a car wash at a garage. Shortly after he installed his high pressure washer, the pump got damaged due to cavitation. He asked us to investigate why.
It turned out that the tap that fed his pressure washer came off a pipe that also fed the washroom (i.e. the toilets and basins). When too many people flushed the toilets and/or used the basins simultaneously, the water supply to the high pressure washer was compromised causing insufficient inlet supply to the high pressure pump.
A header tank is an inexpensive yet effective way to protect your system from cavitation. When in doubt as to the standard of the water supply, use a header tank.
Pumps with a flow rate of 15L/min or more
We at Hawk, install header tanks onto high pressure systems that have a flow of 15L/min or more as a standard feature to protect the system. Header tanks must always be situation higher than the pump system to enable it to be gravity fed.
Water supply will be fed through inlets on both sides of the pump.
Pumps with large flow outputs
Pump systems with an output of about 150L/min or more must have a booster pump to facilitate the supply of water to the pump. Gravity will not be sufficient. When a booster pump is used, it is not necessary to feed the water through both inlet valves.
Plumbing of water to the system and effect on Inlet Supply
Follow these simple rules when pluming in water supply to your high pressure pump system:
Rule No. 1: Avoid friction loss
The pump system should be situated as close to the water supply as possible, using the least length of piping. This reduces friction losses. Pipe friction is also reduced by using a larger diameter pipe thereby limiting linear velocity.
Rule No. 2: Use the correct size piping
The inlet piping to your pump must be sized to the pump volume. The plumbing diameter should be greater than the size of the port of the pump.
Rule No. 3: Avoid restrictions
Use as few restrictions as possible. This includes elbow, tees, reducers, etc. These restrictions cause an uneven flow which can introduce turbulence and air entrainment, which may result in vibration.
Rule No. 4: Ensure no air enters the suction line
Any joint in the inlet plumbing must be tightly sealed with Teflon tape or similar product to avoid air leaks and cavitation. There should be no kinks in the inlet hose or signs of damage.
To recap: If air is allowed to enter the pump, or the inlet feed water is restricted, the pump will cavitate. Most of the problems associated with positive displacement pumps are caused by water starvation or entrained air.