Hawk Pumps, manufacturers and distributors of a range of quality high-pressure pumps, share a few technical tips and tricks on managing a pump’s inlet supply.
The right supply for the job
An unsuitable inlet supply can cause even the best-designed pump to malfunction and surprisingly serious problems can result from even the simplest of issues – or can go unnoticed by inexperienced machine operators. The most notable and common issue is pump cavitation. Remember, there is no standard set-up for a pump system, because no two systems are the same. But understanding cavitation and following a few simple rules can prevent cavitation.
What is cavitation and how does it relate to inlet supply?
Water is supplied to the pump through the inlet valves. The feed should be double that of the pumps requirement.
When a high pressure pump is starved of water, the vacuum will result in water vaporising and cause cavitation. Also, any leaks in the inlet plumbing will allow air to be sucked into the pump. You will know your pump is cavitating when it starts to vibrate and make a very loud knocking noise. As the air or vapour bubbles are compressed, they implode and the shock damages the pressure seals and the valves.
If the pump is run dry for a period, heat caused by friction on the plungers through lack of water, followed by bursts of cold water, cause the ceramic pistons to shatter.
The back end of the pump can then be destroyed as a result of the cavitation. Damage is done to 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.
Simply ensure that the water supply is sufficient for the pump and that no air is able to enter the water feed.
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, as 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.
In one case study, a client who operated a car wash at a garage asked us to investigate why the pump was damaged due to cavitation shortly after he installed his high pressure washer. The investigation yielded that the tap feeding his pressure washer came from a pipe that also fed the wash-room (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. This caused insufficient inlet supply to the high pressure pump.
A header tank is an inexpensive yet effective way to protect your system from cavitation and a valuable tool when in doubt about the standard of the water supply.
- Pumps with a flow rate of 15L/min or more
Hawk installs 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 placed higher than the pump system to enable it to be gravity fed.
It is preferred that the water supply is fed through the 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 is not 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 plumbing in a water supply to your high pressure pump system:
Rule No. 1: Avoid friction loss
The pump system should be as close to the water supply as possible, using minimal possible piping. This reduces friction losses. Pipe friction is also reduced by using a larger diameter pipe that limits 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 elbows, tees, reducers, etc. These restrictions cause an uneven flow, which can introduce turbulence and air entrainment. That 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 a 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.
To find out more about Hawk Pumps, visit: hawkpumps.co.za.