Easy Unloading

Unloader operation is simple. When the trigger is depressed a valve in the spray gun opens, and water moves from the outlet side of the pump through the hose to the spray gun. When the trigger is released the valve closes and the unloader is activated, either by an increase in pressure (a pressure-actuated unloader) or a reduction in flow (a flow-actuated unloader).

The unloader diverts the flow of water from the outlet side of the pump back to the inlet side, causing water to flow in a loop back to the pump under virtually no pressure, rather than to the nozzle under operating pressure. Flow may be directed back to the pump inlet or to a float tank.

An unloader is a valve that shunts flow to another path when certain conditions occur (when the spray gun is closed). When the flow stops initially, there is an immediate increase in pressure or "pressure spike" at the spray gun, because it takes a moment for the unloader to be actuated into bypass. The severity of this pressure increase at the spray gun depends on a number of variables: the length of hose between the spray gun and pump, the pump type and speed of operation, and the unloader valve adjustment.

Easy Start Valve

Easy start valves make starting gas engines easier. The easy start valve allows relief of system pressure at the pump head when starting a gasoline engine and then seals when full system flow or pressure is reached, thereby eliminating trapped pressure in the pump and hoses. The easy start valve is a low-pressure bypass or relief valve, which directs water into bypass until a certain pressure is reached. Since water is directed to bypass in 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 insystems with larger gasoline engines, such as 8 HP or larger.

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

Controlling Pressure Spike Severity

Avoid Overheating in Bypass

A machine should not be run in bypass mode continuously. When a machine is in bypass mode the temperature of the water in a closed loop system increases rapidly due to friction. It is undesirable for most pumps to handle water temperature in excess of 140 degrees Fahrenheit.
Occasional discharge at the spray gun replaces water in the loop and prevents pump damage from high temperatures.

A temperature-sensitive valve or pump protector on the bypass line can provide
pump protection.

Use the Unloader to Regulate Pressure

Pressure and flow actuated unloaders can both control pressure to a certain extent by adjusting the tension on the spring holding the piston in the valve in place. (Remember, this is called a pressure regulating unloader.) The difference is that tightening the spring on a flow unloader under pressure can move and damage the seals while the same action only compresses the spring on a pressure-actuated unloader.

An unloader is not an absolute ON-or-OFF device. Rather, it can allow a certain amount of flow to bypass the hose to the spray gun and return to the inlet side of the pump. Tightening or loosening spring tension with a nut or handgrip on the end of the unloader opposite the outlet port sets the amount of bypass.

Remember: An unloader does not necessarily divert all of the water flow into bypass. Some water may flow through the system and some may be diverted into bypass.

This means that the flow of water to the nozzle, and, consequently, the amount of pressure produced at the nozzle, can be regulated to some extent by adjusting a pressure-actuated unloader.

Change The Nozzle

Changing the nozzle to either a larger or smaller orifice sizes will control the pressure, a larger orifice size will give less pressure and a smaller orifice will give you more pressure. However, using a smaller nozzle than rated for the equipment can overstress the system or increase the amount of amperage demanded by the motor to the point that the circuit breaker is tripped.

Periodic Unloader Adjustments

What generally happens is that the operator notices a decrease in pressure at the nozzle. Under normal circumstances this is a sign of nozzle wear and means the nozzle should be replaced. However, a quick fix can be to simply tighten the adjusting nut on the unloader to decrease the amount of water in bypass. But if no water is being diverted from the nozzle, then there is no way for pressure to increase. All that happens in this instance is that the pressure spike increases. Never adjust the unloader past the point where nozzle pressure no longer increases.

Some unloaders manufactured today have a small handgrip for unloader adjustments instead of the nut. In the case of at least one manufacturer this hand grip not only makes adjustment easy but hides two set screws that limit the high and low pressure adjustments which can be made on the unloader.

Remember: The unloader is generally intended as a pressure-regulating valve. When it is, setscrews usually limit the range of adjustment. Improper unloader adjustment can cause system damage.

Other Uses of the Unloader

Some component manufacturers recommend always having a little water in bypass if only to cushion the valve seat. Without some circulation the check ball is slammed into the valve seat causing scoring of the ball. Additionally, bypass flow can compensate for nozzle wear. As the nozzle orifice erodes, water is diverted from bypass to the spray gun, and operating pressure is maintained.

Benefits of Pressure Unloaders

• Allows for easy pressure adjustment.
• Less susceptible to clogging with debris.
• Allows volume of water to be reduced for operation of unit in steam mode.
• Compensates for a two spray gun system.

Benefits of Flow Unloaders

• Reduced pressure spike.
• Harder to make unnecessary adjustments, which can damage the system.
• Reduces pressure in discharge hose and pump to near zero.
• Reduces thermal expansion damage to heating coil.

PRESSURE RELIEF VALVE

This is a simple pressure relieving safety device. Aside from the unloader, a second line of defense is the pressure-relief or pop-off valve, which is set to release water to the atmosphere when a set pressure is exceeded. However, this valve can be adjusted as well to suit a variety of equipment output pressures.

The pop-off or pressure relief valve prevents over pressurization of the cleaner’s system by allowing water to escape and reducing the system pressure. If pressure were not relieved, another component such as a spray gun, hose, or pump might fail instead.

The valves are built for a certain range of pressure, say from 1000, 2000 or 3000 psi. The valves are adjustable within these ranges but over adjustment can present a safety problem. A safety valve can be adjusted to the point where it no longer functions as a safety device. Instead of the safety valve functioning as an artificial weak point in the fluid system, over pressurization may cause a rupture at a real weak point, perhaps with disastrous results.

When properly adjusted, the valve should be set at just over the normal spike pressure so the valve will not be actuated every time the unloader sends water into bypass.

• Pressure-Relief or Pop-Off Valves
• Prevent over-pressurization.
• Can be adjusted to suit system needs.
• Can be reset.

RUPTURE DISK

Burst Disk

This safety device is an artificial weak point in the pressure-handling portion of the cleaning system. When pressure reaches the critical point the disk bursts and system pressure is relieved. The disk is engineered to burst at a certain pressure; usually a bit above the machine’s rated operating pressure. This allows for normal pressure spikes. In other words, the disk, which can be screwed into a port on the high-pressure side, is a nonadjustable artificial weak point in the fluid system.

The burst disk performs roughly the same function as the pop-off valve except that it must be replaced instead of reset. This presents a safety hazard if the operator replaces the burst disk with a solid plug.

Burst or Rupture Disks

• Nonadjustable pressure release.
• Can only be defeated by removing the disk and plugging the port.
• No moving parts to require service or to fail.

Thermal Burst Disk

This burst or rupture disk is made of a lead alloy that melts when high temperatures reach a critical point. The thermal burst disk must also be replaced and cannot be reset.

• Nonadjustable over-temperature protection.
• Can only be defeated by removing the disk and plugging the port.
• No moving parts to require service or fail.
• Protects against steam explosion.

Steam Release Valve

A pop-off valve for steam. The valve is reset by a thermal spring inside. Generally these valves are found only on steam cleaners. This valve opens when steam pressure builds to a critical point in the system and allows excess steam pressure to escape.

• Provides protection against steam vapor buildup.
• Protects against steam explosions.