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China air compressor unloader valve just for you

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BISON is a leading manufacturer of air compressor unloading valves, offering a range of high quality and reliable products for a variety of applications. An unloading valve is an integral combination valve designed to facilitate continuous operation of air compressors, whether they are powered by gas engines or electric motors.

With a state-of-the-art production facility and commitment to quality, BISON is able to produce a large number of air compressor unloading valves while ensuring that each valve is manufactured to the highest standards of quality and reliability.

Whether you are in manufacturing, construction, automotive or aerospace, BISON air compressor unloading valves are sure to meet your needs and exceed your expectations.

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Types of air compressor unloader valves

Although air compressor unloading valve types vary by compressor manufacturer and type, there are two main types, mechanical and electrical:

Mechanical air compressor unloader valves

Mechanical air compressor unloading valves are the most common type of air compressor unloading valves. They work by using differential pressure to control the flow of air through the compressor. Normally, when the pressure within the compressor reaches a certain level, the unloading valve opens to allow air to escape. This reduces the load on the compressor and helps extend its life.

One of the advantages of mechanical unloading valves is their relative simplicity and reliability. They don’t require electricity to operate, which means they can be used in environments without electricity. Additionally, they are generally less expensive than electric unloading valves, making them a cost-effective choice in many applications.

However, mechanical unloading valves do have some limitations. For example, they are not as accurate as electric unloading valves, and they may not respond quickly to pressure changes. Additionally, they may require more maintenance than electric unloading valves because they rely on mechanical parts that will wear out over time.

Electric air compressor unloader valve

Solenoid valve is an electric device that controls the amount of air passing through a line. It closes, releases or flows according to system requirements. During start-up, compressor air is unloaded to a free outlet for the first few cycles to reduce the torque required by the motor.

Solenoid valves are divided into three types: direct-acting, semi-direct-acting and indirect acting.

The electromagnetic field produced in the solenoid coil is the only factor influencing how the direct acting valve operates to close or open the valve. Semi-direct acting valves combine the functions of direct and indirect valves. Additionally, the circuit function of the solenoid valve determines the port and the position of the valve (open or closed) when de-energized.

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BISON air compressor unloader valve


air compressor unloader valve

BISON air compressor unloading valves offer high-performance and efficient operation, are durable and reliable, and are easy to install and maintain. As a leading manufacturer, BISON has a large production capacity, advanced production techniques, and stringent quality control measures.

A detailed guide for beginners to advanced customers

What is an air compressor unloader valve?

The air compressor unloading valve is a device used by the air compressor to release the trapped air in the compression chamber and tank discharge line when the motor stops.

Drawing air through the unloading valve is critical for the compressor motor to start up again effortlessly. If not, the motor can have trouble overcoming the large initial torque produced by the load produced by the air in the compression chamber and tank drain line.

What is the function of the air compressor unloader valve?

The function of the air compressor unloading valve is to release the remaining air in the compression chamber and related pipelines when the motor is turned off.

A pressure switch is what the compressed air flows through before it enters the tank, which evaluates the pressure between maximum and minimum established limits. When the compressor is working, the air receiver will accumulate compressed air until the pressure reaches the preset maximum value. When the maximum preset value is reached, the pressure forces the internal piston of the pressure switch, causing it to move upward, opening the contacts, and shutting off the motor. Air in the compressor chamber and tank discharge line is immediately released into the atmosphere through the unloading valve. This action closes the check valve and prevents the air in the tank from escaping. Once the tank pressure reaches the minimum, the pressure switch contacts snap back together, and the motor starts up again.

Drawing air through the unloading valve is critical for the compressor motor to start up again effortlessly. Otherwise, the load created by the air in the compression chamber and tank drain line produces a high initial torque that the motor may struggle to overcome.

Selection criteria for air compressor unloader valve

When selecting a unloader valve for use as an air compressor unloading valve, in addition to the suitability of the valve to work with air, the following factors should also be considered:

Capacity (Kv value)

The Kv value determines the airflow through the unloader valve. Knowing the required Kv value will ensure you select the correct valve with the required capacity. 

Maximum operating pressure

The unloader valve must be able to handle the maximum operating pressure of the compressor. Choosing a valve with a maximum operating pressure that exceeds the compressor’s pressure is important to prevent valve failure and ensure safe and efficient operation.

Connection type and size

Make sure the pipe thread matches the unloader inlet thread type and size. Adapters can be used if the required unloader  valve connection size is not available.

Unloader valve material

The material of an air compressor unloader valve can affect its performance and durability. It’s important to select a valve with materials that are compatible with the application and can withstand the temperature, pressure, and chemical conditions of the system. For valve bodies in compressed air systems, a good choice is to use brass for the housing material, and FKM (Viton) seals due to their good thermal and chemical resistance.

Solving common problems related to air compressor unloader valve

air compressor unloader valve repair kits

If the unloading valve of the air compressor is faulty, it will cause leakage. If the valve is not opened properly, it may even cause the compressor motor to fail to start. The causes and solutions for these common problems are as follows:

Dirty valve

Sometimes external elements (dust, teflon, etc.) can contaminate the inside of the solenoid valve and cause the device to malfunction. To confirm that this is the cause of the problem, disassemble the valve, inspect the internal condition, perform an appropriate cleaning, reinstall the solenoid valve, and test it to check its performance. It is also recommended to check the piping upstream of the air compressor unloader valve. The dirt could come from another point in the system, and cleaning the inside of the valve might be a temporary solution, but the problem will recur.

Damaged internal components

During an internal inspection of the solenoid valve, any parts found to be damaged (diaphragms, seals or O-rings) must be replaced.

Electrical problem

Verify correct voltage and frequency. Check the condition of the coil and measure its resistance; if it tends to zero, the coil is burned and needs to be replaced. 

Contact BISON to learn more about compressor unloader valves

As a leading supplier of quality compressed air equipment to companies in a wide variety of industries, BISON can answer all of your questions about unloading valves, their purpose and how they work. Please feel free to contact us for more information.

frequently asked questions about air compressor unloader valve

The unloading valve may be installed on or placed inside the pressure switch if you possess a smaller reciprocating air compressor. When the switch turns off the compressor, it activates the valve. A small tube or pipe runs from the check valve (a device that prevents the entire tank from draining) to the unloading valve.

Larger air compressors typically have larger unloading valves that are controlled by air pressure from a smaller pilot valve. In this arrangement, the valve is usually located next to the compressor.

When the air pressure in the compressor tank reaches the cut-off pressure of the pressure switch (the point at which air is no longer delivered), the switch automatically opens and interrupts the power supply to the motor. This process causes the unloading valve to open and vent the accumulated air.

When the tank pressure drops back to the predetermined setting on the pressure switch, it causes the switch to trip again. This action causes the unloading valve pin to loosen, preventing compressed air from escaping into the atmosphere.

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