Pressure Switch Unloading Valve

[Stan]

Every so often when my mac700 is building up pressure and reaches the cut-out point, the valve on the side of the pressure switch (I think it is called the pressure switch unloading valve) seems to stick open and lets air pour out. Therefore the motor runs continuously and never shuts off. Is this a common problem and do I need a new pressure switch or should I adjust something on the valve?

[joe]

It does not sound like a problem with the unloader valve, but rather the check valve. If the check valve on the tank is not functioning, it will allow air to keep flowing out through the unloader. The unloader is supposed to only dump air off the top of the piston head to allow for easier starting. After the compressor has stopped running, the only way for air to get to the unloader valve is through the check valve.