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In the old days the unloader system was used extensively - the compressor was kept running but prevented from pumping by an air regulator opening and lifting a compressor valve.
When the electrical air pressure switches were expensive and more suited to 3-phase industrial equipment the above system allowed small, light and inexpensive "domestic" compressors to become available.
Since that time production in developing countries have made the electrical pressure cutout switch virtually universal, though unfortunately the quality is poor by comparison and often have a limited life.
I suggest you investigate the electrical pressure switch of your compressor. Often a hefty whack with a screwdriver handle when the compressor is reaching the cutoff pressure will persuade it to work again for a while, otherwise replacement will be needed.
The air is coming out of the pressure switch but the problem is the tank check valve. The tank check valve is on the tank where the large line from the pump feeds into the tank. There is also a smaller line, either plastic or copper, from the check valve to the pressure switch. When the pump shuts off the check valve is supposed to close and the pressure switch opens a valve that lets the head pressure bleed off through the small line. This lets the motor start the next time without any pressure in the head. If the check valve isn't closing properly the air will leak out as you describe.
The pressure regulator on an air compressor is designed to let the pump motor run until the pressure in the tanks reaches their safe level. While you are using the air the pressure drops in the tanks until it reaches the level where the pressure switch turns the motor on again and refills the tanks to their rated level. The pressure where these two things happen is usually with in ten psi above or below the rated levels because few regulators are so precise and are affected by temperature that they turn and off exactly at the rated pressures. If a pressure regulator is damaged or broken it is possible for the tank to either reach unsafe high levels or not turn on when the pressure drops to where it should restart the motor. If you are in doubt, have the regulator checked or replaced as overpressured tanks are very dangerous.
You will need to replace the switch, as it contains a pressure switch as well. This is what actually shuts the unit off when it has built to the regulated pressure desired. You will be able to find a new pressure switch from any Ace Hardware.
If it doesn't try to start, then it could be the pressure switch. Another suspect could be the thermal overload on the motor. The motor (or just the overload) might be overheating and shutting the unit off, then allowing it to restart when it cools.
Is there any humming, or does it blow the breaker? When ot shuts off, do you hear a brief hiss of air?
If there is humming or breaker blowing on restart, or no hiss of air at shutoff, the pressure switch unloader valve is probably bad. If the air blows off, and there is no humming, and the compressor doesn't reliably start, it is probably the pressure switch. If pressure drops too low, give the pressure switch a tap with a screwdriver. If it starts then, the pressure switch is your problem.
Hi, my name is John. Welcome to FixYa. Look on the pressure switch and see what the max. is. I have some notes here I will have to locate them and I will post them here if you still having problems, but it sounds like you need to replace the pressure switch. Thanks for choosing FixYa...John
Emglo airmate compressors are set from the factory to shut off at around 125psi. There is an adjustment (remove cover to pressure switch) that will controll the cut-off pressure but it is not recommended changing the factory setting. There is also a safety valve installed that will open at about 160psi. It is a small brass device with a pull ring. When things go wrong with the pressure switch (rectangular box with power cord coming out of one side) the safety will pop open. There is a pressure regulator with round knob on panel that will lower the pressure to the tool, however this regulator does not control the pressure switch. Let you compressor run untill it shuts off and verify pressure to be about 125, if it is then all as well. Good Luck
Most single stage compressors come with a pressure switch set to shut off at 125 - 145 psi. These switches become less efficient over time and will Begin to fail but remain useful. A safety valve (brass plut with pull ring) is installed somewhere on your compressor set to open at aprox. 160psi. If the pressure switch shuts off before the safety valve activates you could probably continue to use the unit. If however you would like to have the unit shut off at 125psi replace the switch any switch that can be installed in the space allowed. The black tubing that you see is the unloader. When the unit reaches set pressure and shuts off, the small valve under the pressure switch will open and release the pressure in the tubing. This allowes the compressor to start with no back-pressure. For max. life of compressor make sure that there are no leaks in system and upplug when not in use.
Pressure switches are sold in pressure ranges from 45psi to 160psi. Some brands are better constructed than others. A squareD switch will give long life being used w/o extension cord. Good Luck