 |
Pressure Washer Pump Cavitation
The problem? A 3 inch diameter hole had been blown clear through the casing of the pump manifold. He informed me that the pressure washer pump was defective as he had done nothing wrong. Nothing wrong? This high quality pump was not eligible for warranteee as it had extreme cavitation damage. An expensive replacement pump had to be purchased which needless to say strained a friendship.
Cavitation means that air cavities are forming in the liquid that we are pumping. When these cavities form at the suction of a pressure washer pump several things happen all at once. We experience a loss in capacity. The efficiency drops. The thousands of cavities or bubbles will collapse (explode) when they pass into the higher regions of pressure causing noise, vibration, and damage to many of the components. In my case it produced an explosion within the pump strong enough to blow a hole through a metal manfold casing. These cavities form for four basic reasons and it is common practice to lump all of them into the general classification of cavitation. In no particular order these are: Vaporization No Inlet flow or interruption of flow
Air ingestion
Flow turbulence About Vaporization A fluid vaporizes when its temperature is too high. .In designing pumps the assumption that fresh water at 68 degrees Fahrenheit (20 degrees Centigrade) is the fluid being pumped. You can lower the fluid temperature caused from excessive time in bypass mode by squeezing the trigger gun which introduces new cool water into the pump. It is a good idea to insure that a thermal relief valve is a component of your pump. It is an even better idea not to leave a pump in bypass mode for more then 2-3 minutes without squeezing the trigger gun or shutting down the power source. Remember a pump can "heat up" faster than you would think when in bypass mode. Both vaporization and air ingestion have an effect on the pump. The air bubbles (cavities) collapse as they pass from the inlet of the pump to the higher pressure side . The main effect of air ingestion is loss of capacity.The ultimate effect is total pump failure.
Although air ingestion and vaporization can both occur they have separate causes and solutions In some types of pumps. air ingestion is not as severe as vaporization but both can and will cause serious damage. We would prefer to have the inlet liquid flowing at constant pressure and flow. Variations are referred to as turbulence which can cause the suction of the pump to introduce air into the system. Recognize Cavitation The most obvious sign of cavitation is a hammering noise. This noise can be either consistent or intermittent depending upon the degree of cavitation and damage to the pump. Vibration of the pump and system will also be noticeable as the pump is starved of fluid. Eventually flow and pressure will decrease. Check your system for these conditions which may contribute to, or directly cause, cavitation: Inadequate inlet line size Insufficient inlet flow or excessive suction Excessive inlet line length Rigid inlet plumbing Too many elbows and/or fittings Excessive temperature build-up of pumped fluid Air leak in inlet plumbing Agitation in supply reservoir(turbulence) Inadequate increase of inlet flow for fluids of greater specific gravity Inadequate increase of inlet flow for higher temperature fluids Clogged inlet filters. It is important to carefully check your system during assembly and operation to avoid the serious damage that can be caused by cavitation. Understand the causes and symptoms of cavitation. Top tier pump manufacturers offer generous 5 year warranties but ALL of these warranties are voided in cases of pump cavitation.
|
