This type of unloader may be referred to as a “Trapped Pressure” type or just
"Pressure" type. This type of valve opens to bypass when it senses the pressure
build up of the pump output having nowhere to go. The main characteristic of this
most commonly used valve is how it traps the pressure in the hose when the
trigger of the pressure gun is released and unloading excess pressure between
the pump & unloader.
The disadvantage of this type of valve is the spike of pressure felt by the
operator and sprayer/pressure washer components when the trigger is again
squeezed. This creates a "kickback" effect on the gun/wand so be careful when
using ladders or other types of access equipment. The “kickback” effect is most
noticeable when working with pressures above 1000 PSI. The “Fox” sprayer line
is factory set at 800 PSI for customer comfort and safety.
Pressure Sensitive Regulating Unloader
When your system uses a trigger gun that stops the water flow from the pressure
pump the unloader valve must be employed. Understand that when the trigger of
the gun is released the water flow to the nozzle is interrupted. The power source
and the pressure pump are still running, without some pressure system safety
device the water would have nowhere to go, building pressure until pump
damage occurs.
Enter the Unloader Valve. The most basic function of the unloader is to act as a
"traffic cop" to the water flow in your system as soon as it senses "pressure
build". When the “Pressure Build” condition is met the unloader will then actuate
the piston assembly to divert the water flow toward the bypass port. When this
is occurring the pump is said to be in "bypass mode" and the unloader valve is
said to be "cycling". This scenario ends when the trigger is squeezed alerting
the unloader valve to redirect the flow to the gun and high pressure nozzle once
again.
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The Siebring sprayers have a ball-valve installed down stream from the pump
and just before the unloader. In the open position, the majority of the by-pass
fluid is directed back to the pump. In the closed position, the majority of the by-
pass fluid is directed to the tank, the remainder circulates through the manifold.
This design constantly supplies cool fluid to the pump & manifold, eliminating
concerns regarding manifold temperatures.
