When I turn on the unit it builds pressure like it used to, then it stops when it reaches the top pressure. When the motor stops it hisses and within 30 to 45 seconds the unit has to go on again. Sometimes it works fine, like it suppose to. But lately it does the hissing and loss of air more frequently.
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Probably a faulty non return check valve, when the unit reaches pressure air in the delivery pipe is vented down at the pressure switch. If the check valve is passing back this will cause the unit to try to start against a pressure causing it to pull high amps and trip. If there is a constant hiss coming from the pressure switch when the unit stops it will be the non return valve. There should be a short hiss of air when units stops If there is no hiss at all when the unit stops it could be a faulty pressure switch. If it is a quick fix would be to create a small leak on the delivery pipe to vent the line down.
It is normal for there to be a hiss from the pressure switch for a
second when the unit stops, this allow any pressure in the line to be dissipated
so next time the unit starts it doesn't have a pressure to start
against. If it is constantly leaking it will be a problem with the non
return valve. It is normally a brass fitting on the tank that the
compressor pipe goes to. It may just have a bit of debris not allowing
it to close properly, You need to drain down all air and remove the cap
on the brass fitting, there should be a rubber shuttle with a spring
behind, if it is hard an cracked it will need replacing or it may just
need a clean.
first you have a reciprocating pump and the hissing you ear probably comes from the unloading valve on the pressure switch(it will look like a bike tire valve)if there is air coming out the valve when the compressor is off it probably means you have a bad check valve.This valve is use to unload the pressure inside the pump for an easy start .a motor always drive more amps on start up if you cant unload this pressure you will trip the overload(you probably have a reset button on your motor)check the specs on your pressure relief valve ,its a small pump maybe its just adjusted to high.in this case your pressure relief valve will open .If the pressure is fine and there is air coming out the relief valve then you have to replace it!to adjust your pressure turn the screw on your pressure switch clockwise to increase and counterclockwise to decrease .usually you have a 30 psi between cut-in and cut-off called the pressure differential.It can be adjusted on some pressure switch.be sure you put some teflon tape on the treads if you replace something to avoid air leaks.hopes this help!
If you hear a hissing sound from the gas cap then the o ring that seals the tank is either cracked or tore. the tank has to build up pressure. thats where u r hearing the hissing sound replace it, it should stop after.
Your problem falls into one of two categories the first is the tank is leaking the second is the compressor is leaking. Try this run the compressor for a minute or two and turn it off if to hear a hiss the tapers off slowly your tank is leaking some were check the drain on the bottom of the tank, the pressure relief valve on the top or side of the tank and all other connections between the compressor and tank.
In the event there is no hiss this means the problem is the compressor you may have a bad reed valve or a bad check valve depending on the type of compressor.
put a manual oil pressue gauge on the truck and make sure your not losing oil pressure, it would not be wise to assume the gauge is bad and turns out your wrong and need a new motor ;(. could be the sending unit but best to check for pressure before throwing any parts at it please rate -jeff
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