Not All The Controls In The Fluid System Are Fluid System Controls

Fluid system controls allow the operator to stop or start the flow of water through the nozzle and may allow for varying pressure and volume of flow as well. Fluid system controls may also be used to prevent excess pressure or bypass temperature buildup in the fluid system.

For the most part, fluid system controls are valves or valve systems. Some of the control devices plumbed into the fluid system may not, however, be fluid system controls, but may be boiler system controls instead. Such devices include flow switches, vacuum switches and pressure switches. However, some of these devices, particularly pressure switches, may be used as fluid system or burner controls. It is not the type of device but how it is used that is important in this instance. Vacuum switches may also be used as fluid system controls.

Some fluid system controls not dealt with in separate sections are discussed here. Many of the devices or components in the fluid system can be classified as controls. Controls make cleaning equipment easier and safer to use. Controls allow versatility: the adaptation of pressure, flow, temperature and chemical dilution to suit a specific cleaning situation.

Controls can prevent catastrophic equipment failures, which could cause serious property damage, personal injury or even death. Many of the components on a pressure cleaner are controls. The better the design and engineering of the control system, the safer the cleaner is likely to be.

There is a good deal of crossing over between control types. Boiler controls, for example, are generally electrical switching devices, which control current flow to the burner system. Some of these switches are activated by the fluid system’s action. We will now look at the various control devices which can be installed in and function as a part of a high pressure cleaner’s fluid system.

The Easy Start Valve
The easy start valve and the throttle-back valve are controls installed to reduce wear on the system.

The easy start valve allows relief of system pressure when a gasoline engine is starting. Essentially the easy start valve is a low-pressure bypass or relief valve. That is, the easy start valve directs water into bypass until a certain pressure is reached. Since water is directed to bypass at low pressure, the load on the pump and, consequently, the engine is less than the normal operating load and engine starting is eased. This valve can be especially useful in systems with larger, 8 hp and up, gasoline engines.

The valve consists of an inlet fitting, a valve ball and spring, a valve seat and an outlet fitting equipped with a low-pressure hose barb. The inlet fitting has a hole drilled through it with a substantially smaller diameter than the inlet line.

Easy Start Valve Action

Water flows through the valve inlet and pressures against the valve ball. The ball, in turn, presses against the valve spring, which passes through the valve seat. When the engine first starts, water pressure against the ball is insufficient to overcome the spring tension and water flows around the ball into bypass.

As the engine speed increases, so does the pump speed. As the pump nears normal operating speed, the spring tension is overcome and the ball is pressed into its seat, stopping flow to bypass.

NOTE: Starting load on the engine may also be reduced by starting the system with the gun open and the system either adjusted to produce low-pressure or the high-pressure nozzle removed.

The Throttle-Back Valve:

This valve design reduces gas engine rpm when the system is in bypass and there is little load on the engine and increases engine rpm when the demand for system pressure resumes with the opening of the trigger gun valve. Most engine manufacturers equipment their general purpose engine designs with governors to keep the engine from over-revving when load is suddenly lost as normally occurs in a cleaning system when water flow is diverted to bypass.

Back To Idle
The throttle control valve goes one step further by throttling the engine back to an idle when system pressure drops. A cable connects the valves plunger to the engine throttle and a spring returns the throttle control arm to idle position when tension on the cable is released.

Throttle Control Valve Action
When the trigger is depressed water pressure increases in the system, forcing the plunger in the throttle control valve against a spring in the valve housing. The action is much like the action of a pop off or safety relief valve. However, when the plunger moves, the cable is pulled and the engine rpm is increased. As rpm increases, so does pressure and the plunger moves further and the increase in engine speed continues until the correct running speed is reached. The governor on the motor prevents the engine from achieving an undesirably high speed.

When the trigger is released, water is diverted to bypass and system pressure drops. The spring in the valve pushes the plunger back and tension on the throttle cable is released. The spring on the throttle control arm mounted on the engine then returns the engine throttle to idle.

Check Valves

Check valves are like one-way doors. They allow water to flow in only one direction. They are used in many applications in cleaning equipment control systems. Check valves keep water flowing through the pump in one direction, help control chemical flow, and are important in many other components. Check valve uses include the use of the valves as back flow preventers and as inline check valves. They may be included at a number of points in the system. There is likely to be a check valve in the chemical line foot, and pressure-actuated unloaders incorporate a check valve.

Pressure Regulator Valves
The pressure regulator valve is an alternative to the float tank for inlet line pressure control. Either the float tank or the regulator may be used to reduce inlet line pressure to allow for upstream chemical injection. This may also be called a zero-pressure regulator.

Thermal Relief Valves

The thermal relief valve protects the pump from excessively high temperatures generated in bypass. When water is in bypass back to the pump it gains temperature from crankcase friction. Under normal operation the heat generated by crankcase friction is passed on through the system with the water flow essentially acting as a coolant for the pump. When the pump is operating in bypass, the water keeps gathering heat from the crankcase and returning this heat to the pump. If bypass is to the pump inlet, temperature increase will be more rapid than if bypass flow is returned to a float tank. This valve works like a safety relief on an automobile radiator cap.

The thermal relief valve consists of a bronze body with an inlet fitting into which is set a metal sensor extending outward into the path of bypass water flow. A spring holds tension on the valve to prevent leaking. A threaded plastic cap secures the spring in the body. There is a discharge port on the side of the relief valve. The valve is preset to open at a certain temperature, usually around 145 degrees Fahrenheit.

When the valve opens, water is released through the discharge port and fresh, cooler water is drawn into the bypass loop. When the bypass temperature drops sufficiently, the valve closes and the process of heating and discharge begins again.

NOTE: Equipment with a thermal relief valve should not be connected to a hot water supply.

Thermal Relief Valve Service
To service the thermal relief valve, remove the entire valve body from the machine. Visually inspect the sensing probe. The probe should be tight enough in the valve body that it cannot be turned by hand. If the probe is loose, unscrew it and clean the threads. Apply Lock-Tite to the threads before reinstalling the probe. The plastic spring retaining cap unscrews to allow access to the spring and seal assembly. When the thermal relief valve is mounted directly in the pump inlet, be certain the probe is tight in the valve body. If a gas engine powers the unit, vibration may loosen the probe. If the probe comes loose, it will be sucked into the pump inlet, blocking inlet water flow and reducing discharge water volume.