Compressor acting up.

[Willy]

Normally when the unloader packs up they hiss air continually

When this happens it means that the one-way check valve is leaking. This should not be confused with a failure mode to the unloader valve. This check valve is a separate valve whose only function is to isolate the compressor from the tank in order to prevent back-flow from the air receiver tank into the compressor when it is not running. The line between the compressor and this check valve would have full system pressure on it if it were not for the unloader valve which is usually incorporated into the pressure switch. When the pressure switch reaches it's preset cut out pressure it also activates the unloader valve thus bleeding the high pressure air in the line between the compressor head and the check valve thus allowing an easier startup of the compressor without needing to start under a load.

It will usually be attached to to the pressure switch, and it will also be connected to the check valve via a small diameter cooper tube. Sometimes they can be replaced separately, sometimes not. The pressure switch will have a small metal tab which pushes down onto the little plunger in the unloader valve in order to bleed the air from the line between compressor and check valve.

Remember the OP's complaint was that he could not hear air leaking out when the compressor shut off. So my guess is that the check valve is functioning and the unloader is not.

Below a representative example of one type of replaceable unloader valve.

[metalmagpie]

My compressor is kind of loud. I think I'll start looking for a Hushy! :-)

[garyhlucas]

I would check the check valve at the tank which you’ll find on most of those compressors. They get rusty and leak by keeping the unloader from working. Got a nice compressor in great shape for $10 because that valve kept it from starting a second time.

[A.K. Boomer]

Keep in mind it could be just fine and it's just a matter of adjustment,

if it's actually sealing then that's most likely the case, the compressor switch "trips" the air release upon shut off, should be a small metal plate just above the release valves stem... make sure this mechanism is aligned and coming into contact and actually depressing said valve upon shut off...

[fastfire]

When I replace this I will do just that to see what can or can't be done to repair it.

[plunger]

It is simply a non return valve. The problem is if you can get spares for the washer that does the seating. There is serious heat here. I made a washer of delrin and it worked well.

Untill it melted.

[RMinMN]

Has anyone taken an unloader valve apart to see how it is made and if it is repairable? Some things can be repaired easily, some are made to only be replaced.

[plunger]

Normally when the unloader packs up they hiss air continually

[JRouche]

It sounds like you need to replace the pressure switch/unloader valve.
When the compressor kicks out due to having reached the required pressure the unloader valve portion of the pressure switch releases air pressure from the compressor head allowing it to restart without being under load thus making it much easier to start.

Yes, what he said. Umm to add. It wont hurt the compressor if you dont change it out.

They do it so a small motor could start a high compression pump on standard 220vac without snapping breakers all the time.

Its common with all large piston compressors also. Even rotary compressors. JR

[Willy]

It sounds like you need to replace the pressure switch/unloader valve.
When the compressor kicks out due to having reached the required pressure the unloader valve portion of the pressure switch releases air pressure from the compressor head allowing it to restart without being under load thus making it much easier to start.

[fastfire]

Used to be when my compressor shut off it would release the air, I think between the compressor head and the shutoff valve?
Recently I've noticed it doesn't do that anymore. Anyone know if something needs to be done?
IT IS A HUSHY 7HP 60 GALLON TANK.