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Replacing a Compressor Unloader Valve

If your compressor unloader valve fails to work properly, then your compressor will most likely not work properly either. Find more below about how its importance and how to replace it.

Replacing a Compressor Unloader Valve - KB Delta

The compressor unloader valve is very much important because it provides a critical function in preparing your compressor to restart after it shuts down; which is its beauty.

A failed compressor unloader valve, however, is one of the most common reasons why your compressor cannot restart after you have exhausted the fluid from the compressor tank. If the compressor unloader valve is functioning properly and correctly, the pressure in the tank will drop to below the normal cut in pressure level of the switch.

The pressure switch slips to allow power to flow through it, and the motor starts. If the unloader valve fails when the motor tries to start, quite often, the motor will lug and struggle to start. Typically, there will be a short circuiting; a breaker will trip or a fuse will blow, which is very damaging.

The compressor unloader is a valve part of the reciprocating piston compressor, which is small but critical. When the compressor stops, it blows off the pressure inside the discharge pipe. There is another type of unloader valve that can be found at the inlet of rotary screw compressors. This is called inlet valve or load valve.


What the Compressor Unloader Valve Does

Compressor unloader valves are very common in pieces of mechanical devices; heavy duty equipment or light weight machines. There are many types of compressors, which includes reciprocating, rotary screw and even gasoline or other fossil fueled compressors.

A reciprocating compressor have at least one cylinder, and may often have two or even three cylinders at times. The reciprocating compressors always have an unloader valve.


How the Unloader Valve Works

The pressure switch usually have an external unloader valve, and most times, it might have an internal unloader valve which incorporates an on/off switch on top, though not all valve have the switch. Regardless of how the line from the pump head or compressor is connected to the unloader valve in the pressure switch; an internal, underneath connection-like, the unloader valves perform the same function.

When the pressure in the tank reaches the cut-out pressure of the pressure switch, the switch trips to turn off, cutting power from the compressor motor.


Unloader Valve Opening

The process of turning the power off to the compressor motor happens electromechanically. And that means that electricity drives it. But the end result is a mechanical movement, which makes a set of points to move inside the pressure switch housing. What moves, typically, are set of points which open and close depending on the pressure in the tank.

Once the pin on the unloader valve is compressed, the fluid path through the valve is exposed to the atmosphere. And any fluid trapped above the piston vents is out. This occurs when the compressor either stops or cuts.


Unloader Valve Closing

When the pressure in the compressor tank drops to the pressure setting on your pressure switch, the pressure switch triggers again, and this time the arm or finger typically releases the pin on the unloader valve, allowing it to shut down, and prevents the compressed fluid from escaping into the atmosphere.


Where to Find the Unloader Valve in a Device

This unloader valve is often mounted on, or in, the pressure sensor on smaller mechanical devices such as a compressor. The unloader valve is also actuated when the press switch turns off the compressor.

The check valve, which prevents draining of the entire tan, is also placed right at the point where the discharge pipe of the compressor is attached to the storage tank.

From this control valve, a tiny tube or pipe runs on the pressure switch to the unloader valve. A simple solenoid valve is occasionally used on newer compressors to blow down the pressure.

There is also a large unloading valve on bigger compressors, which is operated by pressure from a small pilot valve. The unloader valve lies beside the compressor in this situation.


Signs to Replace Unloader Valve

Due to critical impact on the performance of pressure pumps, a failed unloader valve is immediately noticeable. Unloader valves, which are not working properly can cause the following damaging problems:

1. Pump motor losing momentum

Whether a pump is operated by a gasoline or diesel engine, it is a clear indication of a failure of the unloader valve to stop when the user ceases to use it.

Pressure buildup locks the internal components of the pump, which in turn prevents the powered engine shaft from rotating. Such a problem indicates that the unloader valve does not recirculate water properly back into the pump.

2. Absent of pressurized fluid

Unloader valve that is caught in the bypass position prevents water from reaching the pressure hose and the nozzle. If the engine of your pump is working properly, there will be an adequate supply of water entering the system and there will be no leaks in the system. However, a failure of the unloader valve is a strong possibility if you do not have access to the pressurized water.


Steps to Replace Unloader Valve

Fortunately, the unloader valves are normally placed on pressurized water systems in a popular, accessible spot. They can typically be found near or integrated with the outlets for high pressure water. On top of that, the unloader valve is often connected to a hose that carries water flow back into the recirculation pump.

Additionally, unloader valves may have a protrusion that covers a spring used to control water flow; this protrusion can appear as a knob, or you can see the spring below it.

Although, the basic replacement process for faulty unloader valves is exceptional to system producing and design. Below are a few guidelines that will help you with most unloader valve installations:


  • Before installation, make sure all inlets and outlets on your new valve match the old part.
  • If they are not included with the new valve, remove any fittings from the old valve and mount them on the new valve.
  • Use a few pipe thread tape wrappings to create a water-resistant seal between the pump and the unloader valve.
  • From the ends of the hoses that fit directly into the unloader valve, cut two centimeters so that you will have fresh, unstretched hose material to attach to the valve. If the old ones are rusted or appear worn-out, use new hose clamps.
  • Adjust the tension on the unloader valve spring so that it operates at the pump manufacturer’s specified pressure; too high or too low pressure can cause damage or prevent the unit from reliably operating.


Replacing a Compressor Unloader Valve - KB Delta

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