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Sonny's-Carwash College™ Tip of the Month

Inspecting Prep Gun Wand Nozzles for Excessive Wear

CarWash College™ Preventive Maintenance Tip of the Month

December 20, 2007
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At CarWash College™ we teach preventive maintenance. This month we are going to talk about a piece of equipment that has more than one function, the prep gun. The prep gun is used to keep a car wash tunnel clean and is often used for prepping the vehicle before the wash. If this piece of equipment fails, it could lead to dirty tunnels and dirty cars, and who wants to replace equipment prematurely?

Prep Guns have an electric motor that is coupled to a high pressure pump and uses a regulator/unloader to set and adjust the pressure. The flow of water is sent through a high pressure hose out to the gun and wand, yet the system will not achieve high pressure without the addition of a simple nozzle. The nozzle is, in fact, a precision component and is responsible for the overall pressure and performance in the prep gun system. In most cases, wear in the nozzle will not be visible to the naked eye. In order to check wear on the nozzle it will be necessary to monitor the pressure gauge on the prep gun unit.

The prep gun unit pressure is usually set between 900-1000 PSI. Once the desired pressure is set, use a permanent marker to mark the setting on the gauge. When the pressure starts to drop below the mark, it is time to replace the nozzles. An important step before replacing the nozzle is to back the regulator/unloader all the way out so there is no pressure on the unit. Someone might have increased the pressure because of the worn nozzles and, when the new nozzles are installed, it could over-pressurize and blow the pump.

One common mistake made when the pressure from a prep gun drops is to adjust the pressure on the regulator/unloader. This puts unnecessary stress on the pump and can lead to premature failure. So, when the pressure drops, you can spend roughly $2.00 per nozzle to solve the drop in pressure or adjust the pump unnecessarily and potentially spend $380.00 to replace the unit.

Robert Andre is the Manager of On-campus Training for CarWash College™. Robert can be reached at For more information about CarWash College™ certification programs, visit or call the registrar's office at 1-866-492-7422.