Controlling Flow from the Cleaning System

The trigger gun and unloader valve are the two main components of the most common control and safety system for high pressure cleaning equipment. Depressing the trigger allows water to flow out of the system through the spray nozzle under pressure while releasing the trigger stops water flow. The unloader valve, sensing water flow stoppage, diverts water flow back to the pump inlet. The pump, however, continues to run and pump water.

A Valve System
The trigger gun, with the unloader valve, forms a valve system which gives the operator immediate control of water flow from the gun. Water flow can be turned on or off by depressing or releasing the trigger, or in "dump gun" systems, output pressure can be drastically reduced to safe levels without stopping flow. An unloader valve is not needed on a system with a dump gun.

Using the Trigger Gun Avoids a Walk to the Switch
In most pressure cleaning equipment, the pump motor or engine is turned on and off at the machine. The operator, however, may be cleaning as far as 100 feet away. When he wants to stop the motor or engine. The trigger gun and unloader provide the desired control literally at the operator’s fingertips. The valves in the trigger gun and unloader can be thought of as a pair of traffic cops, directing the "traffic flow" of water in the cleaning system.

Diverting the Flow
The gun and unloader make up a two-part valve system that directs water flow back to the pump inlet or the float tank. The gun shuts off the flow of water, causing the unloader to re-circulate the water back into the inlet side of the pump. This is called sending the water into bypass. Pressure-actuated unloaders are opened by the increase in pressure occurring when the valve in the gun closes. Flow-actuated unloader valves send water into bypass when there is a sudden change in flow.

Total Shut-Off Options

There are a number of ways to shut off output besides the gun and unloader combination. Today, a number of automatic systems have been developed which allow for complete pump and power shut-off when the trigger gun is released. However, none of these systems is used as widely as the unloader valve. A pressure switch is commonly used on Karcher cleaners, and some manufacturers have designed or used specialized devices including radio remote controls. Consolidated Chemex two-step cleaners use a gun with electrical switches mounted in the handle. These manually operated switches are wired to the machine through an insulated tube that is part of a pressure hose assembly, which may be 80 to 100 feet long. The Chemex gun switches control the pump motor and solenoid valves, which govern the flow of the two cleaning chemicals, used in the two-step cleaning process.

Some steam or combination cleaners may not use a trigger gun but may have a similar device to divert water flow away from the nozzle. Walters Manufacturing uses a lever-type assembly to actuate a valve, which diverts water flow at the inlet end of the spray lance.

Open Guns

Some cleaners, especially older or less expensive ones, may not have a trigger gun at all. These cleaners may present a safety hazard, especially if the output is hot water or at higher pressures. With an open gun machine, it is important that an operator maintain control of the lance at all times during operation and especially when the equipment is started.

An open gun machine’s lance may be fitted with a pistol grip to allow better control of the lance. This may be a specially designed gun or simply a trigger gun without the valve and trigger assembly. Some open lances are designed with a handle of bent pipe with a rubber grip. This handle is simply welded to the lance.

Trigger Control is a Safety Must

Today, the conventional wisdom is that a cleaner with an open gun is unsafe. However, a number of United States manufacturers still produce equipment without trigger control, especially less expensive and lower pressure hot water, combination or steam cleaners. It is a good rule of thumb that when a cleaner has an open gun, a dump gun should be suggested.

NOTE: Using a dump gun with some types of chemical injection systems may result in a cleaner configuration that will apply chemical whenever water flow is dumped away from the pressure nozzle or in the low-pressure mode.

Acting in Combination
The use of the unloader in combination with the gun is a prime example of how safety and control functions can be combined in a single subsystem of a high pressure cleaning system. The unloader and trigger gun, in combination, act as both a safety device and as a control and convenience feature. Should the operator lose control of the gun, it automatically shuts off the flow of the water to and through the nozzle.

A "Deadman" Control
The standard trigger gun is a "deadman" type safety device for the spraying nozzle. The valve requires positive operator action (pulling the trigger) to allow water flow through the spray nozzle. When the trigger is released a valve closes in the gun and water flow stops. The trigger also gives the operator positive on/off control over cleaning operations. The trigger gun works with another device in the system to divert or stop pump output when the trigger gun valve is closed. This companion control device may be an unloader or a pressure switch.

Real Danger
If there is no trigger gun control, especially on a cleaner producing higher pressures and flows, loss of control of the lance can cause serious damage to the equipment, the object or objects being washed, and other objects or structures nearby. The operator or other persons in the cleaning area may be injured.