Triplex plunger pumps

Triplex plunger pumps are the most common types of pumps used in the pressure washer industry.  The majority of these pumps have solid ceramic plungers or pistons that move the water through the pump and hold pressure created by the nozzle restriction at the end of the spray wand.  These ceramic plungers are very hard and make an excellent seal for high pressures but are not indestructible.  Ceramic plungers can become brittle when the pump is run without water, causing thermal shock.  Thermal Shock occurs when the ceramic plungers are heated due to the friction of the dry plunger moving against the pump seals from lack of water to the pump. The introduction of cool water to the heated plunger will cause a crack or cracks usually ruining the length of the plunger.  The cracked plunger then allows water to leak past the seals and can be visible by a water leak between the manifold and crankcase of the pump or by turning the oil in the crankcase a milky color due to the emulsification of the oil and water mixture.  This will cause a lack of lubrication then overheating, then, catastrophic failure such as thrown connecting rods etc. 

The typical scenario might be as follows:  One attaches the garden hose to the pressure washer, then the high pressure hose to the machine; one starts the machine expecting water to come spraying out,  then one realizes after a minute or two, that the water is not turned on.  One then turns on the water to the running pump with heated plungers causing the plungers to break and leak.  Always have water flowing to your pump before start up.