9
Thermal Bypass System
When the trigger on the gun is not squeezed, the water in
the pump is recirculating and under pressure. This condition
causes the water in the pump to become hot. Excessively
hot water may cause damage to the pressure washer pump
elements. To resolve this problem, some
Generac Portable Products®
pressure washers
are equipped with a thermal bypass system. Figure 2.5
depicts components of such a system.
At a water temperature of approximately 140°F, the thermal
actuator stem will push the thermal piston off its seat.
Heated water will then bleed out of the pump to the
ground. As cool water enters the pump, the thermal
actuator stem retracts and the thermal piston closes against
its seat, halting the water bleed-off.
Chemical Injection
Generac Portable Products®
pressure washers
commonly incorporate a means of adding wax or
cleaning/sanitizing chemicals into the low-pressure water
stream. As depicted in Figure 2.6, the chemical injection
assembly includes a venturi, a spring-loaded ball and seat, a
chemical siphon tube, and a strainer.
As low-pressure water flows through the injector venturi
throat, its velocity increases and its pressure decreases. The
suction created by the low pressure at the venturi throat
draws the liquid chemical through a strainer into the siphon
tube, around and past the spring-loaded ball, through small
orifices in the venturi, and into the water stream.
Chemical injection only operates at the low pressure setting
because detergents and chemicals require some soak or
residence time on the surface to be cleaned. Low pressure
also avoids splashing, over-spraying, and waste.
Section 2 • Pressure Washer Components
Portable Pressure Washer Familiarization and Troubleshooting Guide
Figure 2.5 — Thermal Bypass System
Item
Name
1
Thermal bypass actuator
2
Thermal bypass actuator stem
3
O-ring
4
Thermal bypass piston
5
Thermal bypass spring
Item
Name
1
Venturi o-ring
2
Spring
3
Check ball moved OFF valve seat
4
Chemical injection fitting
5
Chemical injection venturi
6
Discharge port
7
Chemical solution reservoir
8
Siphon tube strainer
9
Chemical siphon tube
Figure 2.6 — Low Pressure Suctionof Chemical Injection
System
