More compressor help needed

[fred d]

Ok posted a few days back about a compressor issue.
I removed the check valve in the top of the tank and it seemed to be clogged/stuck.
I cleaned it with brake cleaner and it seemed to move freely, so I reinstalled it and the compressor and it worked. with the tank empty it ran great and kicked off at 130lbs and on again at 100PSI. Opened a valve on the end of the hose, drained it down and it kicked on at 100 and off at 130psi
So today was working in the garage with air tools, it tried to kick on but oncenit got down low enough it just Bind/stallEd.
We kicked off the breaker and I pulled the bleed valve on the top. It made one revolution and bound up again.
so I held the bleed valve open and kicked the breaker on and once it was up to speed, I released the valve and it filled the tank.
So….thinking that replacing the valve is the next move

THOUGHTS?

 

[MacMcMacmac]

Your blow down valve has stopped working, or the air line going to it is plugged. The fact that your check valve was gummed up leads me to believe you have the same issue with the blow down valve. Sometimes you can buy just the needle valve and replace the one on the pressure switch, but usually you just replace the whole pressure switch since the diaphragm inside it is probably the next thing to go, so you might as well do the whole thing at the same time.

Sometimes the little metal tab that pushes on the needle valve bends away from the needle and doesn't depress it enough to blow down the discharge line. In that case you can sometimes bend the tab enough to lessen the clearance between the tab and the needle valve so it will move further to help it blow down properly. Yours looks like it's inside the case so it would be both harder to replace, and harder to repair. By the look of that switch it's time for a new one anyway. It's also a bad idea to have live wires hanging over a sharp edge like that. When you replace it, use some proper wire clamps.

Don't use motor oil in a compressor, if that's what you have in it. It gums up everything and cokes up the valves.

 

[fred d]

Mac
i used Quincy compressor oil.
the blowdown valve worked as it should when it hit 130psi
when it went to restart for the first time with use at 100psi the Comp would not go, but by pulling the relief valve just above the check valve it removed the pressure so the motor could get up to speed.
Help me to understand how the blowoff valve worked at 130psi last night(I watched it) but today on the first start it has pressure.
also wires are not on a sharp edge and are secured to mounting frame with Zip ties
thank you for your response

 

[MacMcMacmac]

Well, barring motor problems or rpm too high, these are classic signs the compressor is starting against pressure. So either the blow down valve is plugged or the line is plugged going to it and not releasing air. Maybe there is leak back through the check valve getting trapped in the line. Is this a new motor? You might have capacitor or centrifugal switch issues. If you are sure there is no air being trapped in there, then you have a mechanical problem.

 

[hot_air_al]

Just my two cents on this...

Your gummy check valve is an indicator that something is going on with the pump. The rationale for that is simple: a correctly functional pump will discharge only air and water.

Oil being mixed in with it will, over the course of time, create the gummy goo that turns sticky first, then turns to the hard crunchy that you have to scrape off.

As far as the unloader/blow down... When the compressor stops at it's cut-out pressure, you should hear a sharp hiss for a few seconds, then a gradual lessening of it when the pressure is almost gone. There are two main areas of interest in the unloading operation, the check valve itself and the schrader at the pressure switch.

Next issue, what causes oil in the discharge? Takes a little investigation, however at the end of the story, too much pressure in the case of the pump eventually pushes the runny hot oil past the rings into the cylinder. Look at your pump case. With a pump of any quality, there will be a vent of some kind. Find the vent, and clean it well. If it won't clean, install a compressed air muffler. Check for sure if you are getting oil in the discharge. Plug a blow-gun in as close to the tank as possible. Put a clean white rag over the blow gun and let-er-rip for several minutes. You want to do this long enough to dampen the rag from the moisture. Let the rag air dry. Look for oil stains.

If you are getting oil, you WILL need to replace the valves at some time or another. No matter what, if enough oil is passing through to stain the rag, then that oil is already building up on the valves.

Next, look for heat related issues. You'll very likely have a copper line on the discharge of the pump heading to the check valve on your tank/receiver. During normal operation, the copper will darken some, but not enough to see the blue or black colors a person sees when metal is too hot. If you do see the blue or black colors, you have a heat issue at the pump. Clean the fins. Maybe setup a fan to blow across them. You don't want the discharge line to be much over 200F.

Next, look for amperage issues. Disconnect power at the breaker. Then remove covers as necessary and inspect wiring. Nothing should be blackened or burned.

 

[fred d]

Mac and hot air al
ok been doing some troubleshootin, but since I’m no officianido, not sure what to make of it.
Compressor at zero psi pumps up go to 130 psi when cold. blow off valve then releases the air pressure.
Watching the switch at the blow off valve it stays engaged compressing the Schrader valve.
As the tank bleeds down from use, the compressor kicks back on at a 100 psi and Schrader valve is released. Compressor functions as normal
Everything works If I believe it down it pumps back up.

if it sits over night with breaker off.
Flip breaker on next day, Then it tries to kick on when bled down to 100.
it acts as if there is pressure and goes a couple of rounds and then stops with motor trying to go.
I flip the breaker back off to keep from doing damage (motor has a reset switch).

have new motor and new check valve in top of tank

this morning after have same issues we checked amp draw
80/90 on each leg when motor is in bind.

pull pressure valve in the tank check valve and flip breaker on.
As pressure bleeds off at the pressure valve compressor comes up to speed.

I release pressure valve and everything works. While running amp draw is 16-17.5 on each leg.
Pressure up to 130 then kicks off as it should with the bleed down valve releasing air.

The only seems to be a problem when I switch the breaker off for the night. Then the next day the compressor doesn’t want to start one below 100psi.

 

[MatBirch]

I don't suppose you're shutting the machine down with the breaker while it's running?? Even so, overnight, I'd think that it would lose enough head pressure to not be an issue tomorrow...

 

[fred d]

Mat
i have been Turning the breaker off overnight. Did not want it to come on in the middle of the night and cause a problem.
So today I was off of work and decided to just let it slowly bleed down.
If I leave the breaker on and bleed it down quickly(5 minutes) it fires right back up, but if I wait a few hours and let it bleed down (like a small leak would)it pops the reset switch when it tries to come on.

 

[MacMcMacmac]

is this compressor in a cold location?

 

[The Cobbler]

what kind of compressor do you have?
I had a craftsman compressor that was always a bear to start . I installed a cold start bleed valve like this in the compressor discharge line and I never had a problem with it starting after that. it allows the motor to get started while bleeding off some pressure . It does slow the pump up from an empty tank, but it might help you in this case https://www.ebay.com/itm/262845540083?hash=item3d32d0a6f3:g:8nEAAOSw~AVYnPno

 

[The Cobbler]

you can also add more volume to the discharge line from the compressor to the check valve to let the motor spin up more before it hits the pressure too

 

[fred d]

Mac
Houston Tx….not cold

 

[fred d]

Cobbler
it is a Quincy compressor that I have had for a long time
motor just replaced

 

[Citation]

My guess is your check valve is still leaking. I'm going to assume you have a combined pressure switch/unloader valve similar to what was shown in post 2. Sometimes those have a manual (auto-off) control but on larger installed compressors they often do not.

That type of pressure switch closes the unloader valve any time the internal pressure switch is "on". So even if the breaker to the compressor is off and the motor doesn't have power, the pressure switch is trying to power the motor and thus the unloader is closed.

So consider this case. At the end of the day your tank pressure is 110 psi. Perhaps because of a leaking check valve, the tank leaks down to under 100 psi over night. While it's leaking down it vents the air thought the open unloader valve. However, once the tank pressure drops to 100 psi the pressure switch clicks to "motor on". That closes the unloader valve. Since you threw the breaker the motor has no power. But with the unloader valve closed, that check valve leak pressurizes the line from the head. Now you can't start the compressor in the morning.

This above case would still play out even if you had say a leaking pressure hose plugged into the output side of the compressor that was your primary leak.

A way to check this is turn off the breaker for the night. The next morning check the tank pressure. Is it under 100 psi (or what ever the kick in pressure should be)? If yes, use a screwdriver to press the unloader valve on the side of the pressure switch. Was it under pressure? If yes, your check valve is still leaking resulting in the motor starting against pressure.

If your pressure switch does have an auto-off selector then switching it to off would also open the unloader valve. Thus if the switch was set to "auto" but the breaker was off, the next morning switching the pressure switch to "off" would open the unloader and result in that rush of air from the unloader.