Last week Hawk Pumps, manufacturers and distributors of a range of quality high-pressure pumps, shared a few tips about cavitation in piston pumps. This week Hawk share a detailed case study on cavitation in piston pumps.
The pump in this case study is a standard Hawk, Italian-manufactured high pressure pump with an output of 15l/min at a pressure of 200bar. The maximum recommended temperature for this pump is 60°C.
This pump was being utilised on a farm using borehole water, which is known to have high levels of calcium. Furthermore, water of 80°C was being pumped.
This resulted in the following damage:
The manifold valve outlets and inlets were encrusted with calcium deposits. The valve cages were stuck inside the manifold and extremely difficult to remove:
Signs of leakage and corrosion to the brass head were visible on the underside of the pump. The seals had failed due to the high temperature of the water and the lime deposits, causing leakage.
The valves, after removal, showing damage and residue from calcium deposits:
The connecting rods have shattered and have knocked holes through the crank case. All of this is the result of a number of factors:
- Calcium build-up due to high-temperature water
- Cavitation caused initially by hot water going through the pump, resulting in water vapour being created in the head.
- Further cavitation caused by calcium build-up, restricting water supply and causing the pump to destruct.
The pump casing showed extensive damage. And while the oil was leaking, the alloy conrods were overheating and were melting to the crankshaft:
Ideally, the water should be heated after the pump and not before. Furthermore, even though the water is being heated after the pump, a water softening system should be installed because of the high calcium content of the water. This will protect the boiler as well as the pump, particularly if the bypass is being fed back to the pump.
Should the customer insist on pumping hot water through the pump, they could use a High-Temperature Pump, which is available from Hawk Pumps and can handle up to 80°C water. This is a more complicated solution as, not only would a water softener need to be installed, but the water would need to be pressure fed at more than one bar, but no more than two bar, to prevent cavitation from water vapour.
To find out more about Hawk Pumps, visit: hawkpumps.co.za.