[gto4evr]

Hello,

I'm working on my 80 gallon two stage compressor. I just replaced the pump with an HF head (that I hate) and decided to fix the secondary issue with the auto shut off valve. compressor turns on and runs up to 180 psi shut off, then restarts at 145. that part of it works. but around 5ish years ago I noticed that when it shut off at 180, the safety valve would engage that bleeds off the pressure through that little schrader valve and would bleed off pressure til it hit 150 before shutting off. I always assumed something was just bad on the switch. I had a different control switch that I changed out on the compressor when I replaced the pump head. same deal. it engages the safety and bleeds to 150. this second switch I had is identical to the small 20 gallon roll around compressor I have that shuts off at 175 and restarts at 145. on that compressor it shuts off and you hear just a momentary air bleed like it's testing the safety and then stops. (this is exactly how the big 80 gallon worked for the past 25 years for me). So I thought it odd that two switches are doing the same thing but that second switch I had was second hand from a scrapped compressor that I grabbed for safe keeping. so I bought a brand new switch. installed it and whaddyaknow....same damn thing. it shuts off at 180 and then bleeds the pressure down to 150 before popping closed. what the heck? I find it hard to believe 3 valves are all bad and doing the same thing but I see no way the original 80 gallon tank can be causing this? it shuts off at the correct pressure, it's just engaging the safety valve and bleeding all the pressure back out. so it can't be seeing a reason for the safety that I can understand. there's a small adjustment screw on the side of the head that I'd guess could be for adjusting the safety pressure? doesn't seem to have any affect by turning it one way or the other. (red arrow in picture) I know the main adjustment screw would be to adjust the 180 shutoff up or down.

I'm at a loss here. anyone have an idea what could be going on?

[Lemans64]

Sounds kinda weird, But mine was doing a similar thing where it would bleed down thru the blow off valve but not shut off. I did some research and found that the main output from tank
has a one way valve that can stick and create issue's like mine was doing. It had a piece of crap stuck in the valve, cleaned it and now is good. Might not be your problem but worth a check and see.

[gto4evr]

there is no valve to the switch in mine. there's an aluminum bung screwed into the top of the tank that I took off to check/clean out mine. that bung is tapped with four holes, one for the main air output, one for the pressure gauge, one for a manual control safety valve that I'm guessing blows when it reaches a certain pressure, but has a ring on it that you can pull open manually; and the last is where the power control switch screws in. there's a brass fitting on the top of the tank that the inlet air from the pump goes in. on the side of that is the small 1/4" line that runs over to the pressure switch that the main switch can activate (which is the one sticking open til 150 in my issue here) are you saying that brass inlet/bleed off tap might have a one way valve? I guess I can't wrap my head around how the air side of the bypass switch could be the issue - it's the shutoff switch that's engaging the bypass air valve open.

[Lemans64]

Mine did sound like air leaking thru bypass valve as well, but ya the piece on top of tank that the 1/4 plastic lines goes to has a check valve in it
that can stick and allow tank pressure back to the pump and or the shut off valve. Not saying this is your issue, but something to check. Once the system makes top pressure
the shut off blows off and stops the motor, the check valve in top of tank should close and not allow air to go back to switch thru the 1/4 line. Google it. Hopefully
i'm not making it more confusing, LOL.

[dataway]

You may know this already but, generally the hissing you hear on when a compressor shuts down is the "unloader" valve. A check valve maintains pressure in the tank, the unloader valve bleeds off the pressure that is on the compressor head ... it does this so it doesn't restart under pressure and overload the motor.

The unloader valve bleeding off should not show up on any of the pressure gauges. If you have a large drier, or after cooler between the compressor head and the tank it will take longer to bleed off as it must also bleed down the cooler lines.

It's been my experience lately that it's very hard to get a quality pressure switch these days, and doubly difficult to get one that also meets your pressure cut in/out needs.

My IR compressor is great, but the pressure switch is garbage, but it's very difficult to find anything except OEM (over priced crap) that meets the requirements and also has all the appropriate in/out fittings etc.

[gto4evr]

Originally Posted by Lemans64

Mine did sound like air leaking thru bypass valve as well, but ya the piece on top of tank that the 1/4 plastic lines goes to has a check valve in it
that can stick and allow tank pressure back to the pump and or the shut off valve. Not saying this is your issue, but something to check. Once the system makes top pressure
the shut off blows off and stops the motor, the check valve in top of tank should close and not allow air to go back to switch thru the 1/4 line. Google it. Hopefully
i'm not making it more confusing, LOL.

okay...I see what your saying. so technically that shut off always engages the little valve on the 1/4" line when it shuts the compressor off, but there shouldn't be air in the 1/4" line itself. I'll check it out tonight, thanks.

[gto4evr]

Originally Posted by dataway

You may know this already but, generally the hissing you hear on when a compressor shuts down is the "unloader" valve. A check valve maintains pressure in the tank, the unloader valve bleeds off the pressure that is on the compressor head ... it does this so it doesn't restart under pressure and overload the motor.

The unloader valve bleeding off should not show up on any of the pressure gauges. If you have a large drier, or after cooler between the compressor head and the tank it will take longer to bleed off as it must also bleed down the cooler lines.

It's been my experience lately that it's very hard to get a quality pressure switch these days, and doubly difficult to get one that also meets your pressure cut in/out needs.

My IR compressor is great, but the pressure switch is garbage, but it's very difficult to find anything except OEM (over priced crap) that meets the requirements and also has all the appropriate in/out fittings etc.

Hmmm this is making more sense too. I've noticed the motor struggles pretty hard trying to restart with the pressure in the tank already up at 150. I was attributing it to the crap HF compressor head. it makes a weird noise while filling, like water squirting through the lines. I hate everything about this head but the original style head (that I already replaced once about 15 years ago) was up to $1000 nowadays. thanks again for the info!

[gto4evr]

just a follow up, I took that inlet brass out and saw a little brass button rattling around with the remnants of a spring jamming it sideways. Thanks for the schooling on the "unloader" which I thought was just a safety bypass that engaged if it overpressured.

I've got a new valve on order. waiting curiously to see if it has any affect on the weird swishing noises that come and go as this new HF pump fills the tank. I'm hoping that noise was the shifting button moving around during the airflow going in.

thanks again guys!

[Lemans64]

Good to hear you found something, Hopefully all works out for ya. Ya there should be any air in plastic line when comp shut off.

[SRR]

Originally Posted by dataway

You may know this already but, generally the hissing you hear on when a compressor shuts down is the "unloader" valve. A check valve maintains pressure in the tank, the unloader valve bleeds off the pressure that is on the compressor head ... it does this so it doesn't restart under pressure and overload the motor.

The unloader valve bleeding off should not show up on any of the pressure gauges. If you have a large drier, or after cooler between the compressor head and the tank it will take longer to bleed off as it must also bleed down the cooler lines.

It's been my experience lately that it's very hard to get a quality pressure switch these days, and doubly difficult to get one that also meets your pressure cut in/out needs.

My IR compressor is great, but the pressure switch is garbage, but it's very difficult to find anything except OEM (over priced crap) that meets the requirements and also has all the appropriate in/out fittings etc.

I put this on my 80 gallon compressor and it works great. I adjusted it down to 150 PSI.

[beemergary]

Wow thats some high pressure but if the motor starts it ok. Mine has a one way valve which has a spring and rubber plug in the line to the pressure switch. If that rubber gets bad the pressure switch won't work right. I just make new ones outta 1/4" rubber. Those' s pressure switches are the same as a well switch as far as adjustments.

[dataway]

SRR ... that is exactly the unit I have saved in my Amazon list to try out when the OEM unit fails. Already the OEM unit unloader is getting lazy and I have to tap on it to get it to bleed properly.

No piston pump compressor is supposed to start with the head under tank pressure, so a higher tank pressure shouldn't be more load on the motor to start ... it will be more load to bring it up to 175 as opposed to 150 while pumping, but not on start up.

I run a big fan cooled after cooler and separators between the high pressure head and the tank so a lot of air to bleed off on shut down, but also a good low pressure volume to let the motor get up to speed on start up. Also makes the compressor considerably quieter as the high pressure isn't dumping straight into the tank on each stroke, it's going the through the cooler which acts as kind of a muffler, doesn't have that "ringing" of the tank as it gets close to shut off pressure.

[dataway]

A pic of the cooler setup.

[SRR]

Originally Posted by dataway

A pic of the cooler setup.

I have those exact filters on mine. Mine is also piped to the front of the garage with 30' of 1" copper pipe and another dryer/filter.

[dataway]

Since mine is portable I have most of the drying/cooling done prior to the air entering the tank. One last separator and the regulator after the tank, and a canister filter for the painting outlet. Rarely get more than a few drops out of the tank drain, but a ton out of the separators between the compressor head and the tank.

In the new shop I'll probably be plumbing it into a whole shop system like yours.

[gto4evr]

dang, haven't been online in a long time, i didn't expect this thread to continue! - dataway, I like the idea of the hour meter. wondering how hot your inlet pipe off that head gets. my original pipe was aluminum but was too short to fit the new HF head, and I replaced it with a longer copper line that gets so freaking hot it turns brassy yellow from the copper color.

that new valve did the trick on the bypass thing, but the weird water swishy noises that head makes is still there and is very loud and annoying. i don't like being near it when running because I feel like it's going to blow up or something!