What is an air compressor unloader valve?
An air compressor unloader (bleeder) valve allows the pump to start up smoothly. This component is for reciprocating air compressors.
When you stop the pump, the gas air compressor unloader valve will release the pressure that remains within the compressor chamber through a pipe (line). The unloader valve basically unloads air, hence its name. This is important to prevent starting up the compression process in a high-pressure environment.
In this article, we will answer all the questions you might have about gas air compressor unloader valves, including how they function and the symptoms of dysfunction.
How does the air compressor unloader valve work?
An air compressor unloader valve works by releasing air from the head of the air compressor. Stopping the air compressor means the line that connects the compressor chamber and the tank is highly pressurized. Thanks to the unloader valve, the high-pressure air will be released, returning the pressure to 1 Bar (atmospheric pressure).
If you ever used an air compressor before, you may have heard a ‘shshsh’ sound when you turn it off. This sound means that the air compressor bleeder valve is reducing the pressure of the compressor’s head and the pipe to atmospheric pressure.
Without this process, the motor pump will have trouble starting against the high pressure inside the pipe. If the motor is not powerful enough, it may even fail to start.
The chart below demonstrates the components connected to the gas air compressor unloader valve:
Simultaneously, a one-way valve called the check valve ensures that the air compressor tank keeps the pressurized air stored without leakage (see figure above). If your air compressor check valve is faulty, you may deal with issues related to the rapid emptying of the tank or continuous operation of the motor pump.
Learn how you can identify a faulty air compressor check valve by clicking here.
Air compressor unloader valve diagram
An air compressor unloader valve diagram depicts the different parts of this crucial component. The most important parts to pay attention to are:
- Inlet
- Outlet
- Vent port
The inlet is connected to the compressor chamber via a line. This is where the pressure will be high after turning off the motor pump.
The outlet connects the line to the air compressor tank. The vent port is responsible for depressurizing the compressor chamber and the line to make it possible for the motor to start again.
On the right side of the unloader valve diagram, you can see several pieces that allow you to adjust the cut-on and cut-off pressure (more on that later).
Bad unloader valve symptoms in the air compressor
Some bad unloader valve symptoms in the air compressor include:
- Difficulty starting the air compressor
- No blow-down sound when you stop the air compressor
- A continuous leaking sound (the ‘shshsh’ sound)
If the air bleeder valve is stuck (not opening), the pressure will build up inside the line that connects it to the compression chamber. As we explained above, a pressurized line means the motor might not be able to start against all that force.
Conversely, a leaking unloader valve produces a continuous sound during operation. This means the air bleeder valve remains open at all times.
If you notice any of these bad unloader valve symptoms in your air compressor, it is time to replace this component.
Where to buy an air compressor unloader valve?
You can buy a gas air compressor unloader valve online. However, you should pay attention to the compatibility of the air bleeder valve with your compressor.
The best-seller unloader valve on Amazon is the 131B pilot valve which comes with a factory setting of 125 PSI to 150 PSI. However, you can adjust the pressure of this valve.
Check it out by clicking here.
Frequently Asked Questions (FAQs) about air compressor bleeder valves
1. Where is the unloader valve on an air compressor?
As a rule of thumb, you can find the unloader valve on the pressure switch in smaller units. Once the pressure reaches the cut-off level, the compressor stops, and the unloader valve opens.
Bigger compressors, on the other hand, have a separate unloading valve that’s controlled by a small pilot valve. To identify where is the unloader valve on a compressor, look at the figure below:
Newer compressors contain something called a solenoid valve, which is electrically operated to control air pressure.
2. Where is the unloader valve on a truck air compressor?
The truck air compressor unloader valve is typically found in the compressor head with the remaining unloader assembly. The truck air compressor unloader valve can be a spring-loaded or poppet-type control valve. A component called the governor is responsible for opening the unloader valve on a truck air compressor.
3. How to replace the unloader valve on the air compressor?
Before replacing the unloader valve in your air compressor, you need to depressurize the tank by opening the drain valve.
After that, unplug the compressor and remove the line that connects to the inlet portion of the valve. Next, remove the quick-connect fitting with a wrench and disconnect any lines connected to the pressure switch. Finally, detach the unloader valve.
Congratulations! You just removed the unloader valve on your own. This is the most challenging step. Now, you just need to install the replacement valve.
Here are the steps to install a new air compressor unloader valve:
- If the connection of the pipe is worn, use snipping pliers to create a clean end.
- Attach the pipe to the new unloader valve.
- Reinforce the connection by attaching the quick-connect fitting.
- Place the new valve in the tank.
- Using the factory’s preset pressure value, adjust the new air compressor bleeder valve.
4. How to adjust the air compressor unloader valve?
Air compressor unloader valve adjustment is necessary when your air compressor does not cut on or idle at the pressure set by the manufacturer. In other words, if the cut-on or cut-off pressure is too high or too low, you need to adjust the unloader valve.
The main reason this occurs is when debris inside the air bleeder valve condensates. As a result, the spring will lose tension.
The video below details the steps on how to adjust the air compressor unloader valve:
5. What to do if the air compressor unloader valve is stuck open?
A gas air compressor unloader valve stuck open leaves you with two choices:
- Repair the faulty part
- Replace the entire valve
If you have the necessary tools and patience, you can disassemble the air bleeder valve to see why it’s stuck open. However, the easy solution would be to buy a new valve since they don’t cost much.
Takeaway message
An air compressor unloader valve is an extremely important component of the compressor that depressurizes the compression chamber and connecting line. Without this valve, the motor will not be able to start smoothly.
We hope that this article managed to explain everything related to air bleeder valves and how you can replace faulty ones.
If you found anything unclear, feel free to share your questions in the comment section below.
