2 Stage Compressor Problem (too much pressure)

[perkinscl]

I have a smaller Speedaire 2 stage compressor I use for occasional car maintenance and air nailers. It always worked great until recently.

After building up pressure, the belt is very hard to turn and the motor ends up kicking the breaker in the main.

Here's my troubleshooting steps and info:

• Pulled the belt off and narrowed down the compressor pump. When under pressure, the pulley is hard to turn by hand.
• Pressurized/filled the tank, pulled the input pipe to the tank to check the unloader valve. No air coming out.
• Pulled the unloader valve and it seems to be free and working correctly.
• Noticed that when I pulled the pipe off of the pump (no presure in the pump), it became easy to turn again.
• The pressure builds fine and the compressor runs great otherwise.

?? I'm lost, not that I know really what I'm doing. I've read a lot trying to educate myself.

Could it have something to do with the flapper valve? I took off the air filter and they seem dirty.

Thanks!! Pic for click...

 

[Zrexxer]

OK, first things first... you've got your terminology all confused, and I think that might be one of the things keeping you from getting this diagnosed. To begin with, that's by no means a two stage compressor - so anything that you've read about diagnosing two-stage pumps, disregard. Second, the valve in the tank isn't the unloader, that's the check valve. The fact it's not leaking is good. You say you "pulled the unloader valve" - what are you talking about? If you're talking about one of the safety valves with a ring in it, that's not the unloader, either.

From the symptoms you describe, your head unloader is not functioning. On that model, the unloader is most likely incorporated into the pressure switch. When the compressor cycles off, the pressure switch activates a little lever that opens the head unloader, taking pressure off the head so that it can restart on the next cycle.

How about a picture of your pressure switch from the working side?

 

[jaker10]

On mine there is a line that runs from unloader valve to the pressure switch that releases pressure in the line between the compressor and the unloader. I've been calling it a unloader valve too. But come to think about how it works it is a check valve.

 

[The Cobbler]

sounds like it isn't unloading . previous poster nailed you on some terminology and explained very well.
when the compressor shuts down after building pressure, do you hear a pssst at the end ? that's the unloader doing its job. if you don't hear any air escaping, the unloader or some part of the unloader system is failed.

 

[Miss_Sissy]

Zrexxer is right; it's not a two stage compressor.

If the motor runs, reaches the target pressure, and then stops, the pressure switch is okay. If you do not hear a hissing sound after the pump stops, then the unloader is not functioning. That leaves the air in the pump under high pressure and the motor can't start it against that pressure. This is a typical unloader:

 

[LS6 Tommy]

I don't see a switch mounted unloader in the picture. My guess is the gauge was put in the unloader port on the check valve.

Tommy

 

[perkinscl]

Thank you for the response. Yes, I'm sure I have my terminology mixed up.

The check valve is what I pulled. You should be able to see it in this pic behind the pressure switch.

A little history on this compressor:
A couple years ago, the on/off switch (incorporated into the OEM pressure switch) stopped working. I replaced it with this model: http://www.amazon.com/dp/B008JVM456/ref=pe_385040_30332200_pe_309540_26725410_item

On the original Speedaire setup, there was an unloader line coming off of the check valve going to their pressure switch. The pressure switch I bought didn't have a connection, so I plugged the check valve port.

I don't understand why the pressure switch would make the pump have high pressure when off?

 

[perkinscl]

OK, this is starting to make sense now, thank you all for your replies.

The press switch I have does have a built in unloader valve. I also added a 150psi safety valve that you can probably see in the picture.

 

[Zrexxer]

If you plugged the pressure line port in your check valve, you disabled the unloader function. Remember when you said you pulled the copper line between the head and the tank, and the pump turned freely? That's because there was nothing relieving the pressure in that line until you took it off. The unloader would normally make sure that pressure in that line is bled off at the end of each compression run cycle, enabling an easy start the next time.

 

[perkinscl]

If you plugged the pressure line port in your check valve, you disabled the unloader function. Remember when you said you pulled the copper line between the head and the tank, and the pump turned freely? That's because there was nothing relieving the pressure in that line until you took it off. The unloader would normally make sure that pressure in that line is bled off at the end of each compression run cycle, enabling an easy start the next time.

Thank for your insight Zrexx. The pressure switch I replaced it with has an unloader valve, but not a port to screw the air line to unless I misunderstand how to install it (very possible).

I thought the unloader in this switch would get the pressure from thank via it's (the pressure switch diaphragm). Does it need to be connected to the check valve?

It's worked fine for about a year, since I replaced the switch until now though.

 

[Zrexxer]

Thank for your insight Zrexx. The pressure switch I replaced it with has an unloader valve, but not a port to screw the air line to unless I misunderstand how to install it (very possible).

I thought the unloader in this switch would get the pressure from thank via it's (the pressure switch diaphragm). Does it need to be connected to the check valve?

It's worked fine for about a year, since I replaced the switch until now though.

I can't say why it's worked up until now, unless your motor has just been powering through the hard startups before and now it's starting to get tired.

Yes, the pressure switch gets the air to operate directly from the tank. However, if it's going to relieve the pressure in the line from the pump, there has to be a connection to that line. Remember that check valve in the tank? It isolates the tank so that air can't just bleed all back out.

The feed line to the unloader on the pressure switch ties into the check valve, but on the line side, not the tank side. That allows it to just relieve pressure on the line and the pump head. This is critical when starting up, because an electric motor draws the greatest amount of current at "locked rotor" conditions - basically when it's trying to start a load that just won't rotate. The amp draw at startup like this can be 3 or 4 times the running amperage of the motor. This is why you're popping the breaker. If that line has no pressure when the motor starts though, it can get up to speed and start rotating the pump.

That's probably more confusing than anything, but I think you're on the right track now to getting it operating correctly.

 

[perkinscl]

Yes, I feel like we're getting somewhere.

So now I know I need to get the the check valve connected to the unloader valve.

Can I put a new unloader valve in on the port that I plugged on the check valve?

Or is there a way to connect the check to my pressure switch? I don't see how /where it would connect.

Here's a picture of the bottom of the pressure switch next to the check valve.

 

[JeepinMike]

I could be wrong, but I believe your unloader port on that pressure switch is the black push fitting with the blue collar...

 

[Zrexxer]

Can't say for sure but that looks like a push-lock fitting for tubing...

 

[perkinscl]

Does this pic help? The blue piece pushes in and pops out on its own.

 

[perkinscl]

I just pushed some rubber tubing in and it fits and locks in.

So I connect tubing from this to the check valve?

 

[Ducs]

Yes, to the port on the check valve where you have the gauge screwed in. That gauge is of no use for you there.

 

[jim keris]

in your picture the valve on the left is the check valve. where the guage is screwed in is where you plumb to the pressure switch unloader valve Buy a square- d pressure switch with unloader port and built in switch $40.00 at northern tools plumb relief valve and guage at tank outlet.

 

[perkinscl]

Thanks for the help everyone. Got it running correctly last night.

 

[Zrexxer]

Good deal! I don't know what kind of tubing you used, but just keep an eye on it because that discharge line will get hot as a firecracker. Don't want it to melt.

 

[nehog]

Can't say for sure but that looks like a push-lock fitting for tubing...

First that valve to the left is the unloader.

Second, the place where someone screwed a gauge is where the unloader line connects.

Third, that port where the red arrow points is the unloader port. Remove the gauge, plumb that line to the valve. Insert the unloader valve between the tank and the compressor output.

 

[redmondjp]

Good deal! I don't know what kind of tubing you used, but just keep an eye on it because that discharge line will get hot as a firecracker. Don't want it to melt.

+1

I'd source a 1 foot long piece of 1/4" copper line at the hardware store and replace that plastic tube, for this very reason.

 

[Zrexxer]

First that valve to the left is the unloader.

Second, the place where someone screwed a gauge is where the unloader line connects.

Third, that port where the red arrow points is the unloader port. Remove the gauge, plumb that line to the valve. Insert the unloader valve between the tank and the compressor output.

First, that's not right. The valve on the left is either the check valve, or the safety relief valve, depending on what you're referring to, not the unloader. Second, Im guessing you didn't read the thread where he's fixed it already...

 

[perkinscl]

Yes, it's working great, but I didn't know that hose would get hot. I'll replace it ASAP with copper. Funny, I threw the original hose away. I remember it being black and flexible. I might check the auto parts store for an industrial hose. It's small though.

 

[Zrexxer]

Yes, it's working great, but I didn't know that hose would get hot. I'll replace it ASAP with copper. Funny, I threw the original hose away. I remember it being black and flexible. I might check the auto parts store for an industrial hose. It's small though.

Just run a compression cycle and then put your hand on that copper discharge line... Ask me how I know this... lol

Seriously though, my Campbell Hausfeld (and that's what you've got - even though it's branded Speedaire, it was manf'd by CH) had a black plastic line for the unloader, too. I don't know what the material was, but it held up fine. What you used may work fine, you'll just have to try it an see.

 

[perkinscl]

Just run a compression cycle and then put your hand on that copper discharge line... Ask me how I know this... lol

Seriously though, my Campbell Hausfeld (and that's what you've got - even though it's branded Speedaire, it was manf'd by CH) had a black plastic line for the unloader, too. I don't know what the material was, but it held up fine. What you used may work fine, you'll just have to try it an see.

Wow! You know this compressor! I bought this used about 3 years ago for $75 from an auto trim shop. Minus the on/off switch not working when I bought it, it's been great. I think I put about $75 in parts (fittings, pressure switch, new drain valve, etc).

Do you have any idea how old it is? Value? Reason why I ask is I seriously debated getting a new similar replacement when it had issues. It looked like the similar CH at Tractor Supply was about $400. Moot point now, it seems to be working great. I resealed all of the connections with teflon and changed the oil. I just have to remember to drain the tank after use.

 

[LS6 Tommy]

The valve on the left is either the check valve, or the safety relief valve, depending on what you're referring to, not the unloader

That is a combo unloader/check valve. I mentioned it in my first post, but not too well. I edited my original post to state it more clearly.

Tommy

 

[Zrexxer]

That is a combo unloader/check valve. I mentioned it in my first post, but not too well. I edited my original post to state it more clearly.

Tommy

Nope. The unloader valve is on the pressure switch. The check valve is a just a check valve. It does have a port for the unloader line, but it's nothing but a check valve.

 

[Ducs]

You won't be able to use a copper tube from your check valve to the unloader valve. The unloader valve you have has a push-on style fitting designed to accept only plastic tubing. Even if copper tube fits in there, it will leak. You would want to source nylon pneumatic tubing. Nylon is rated for up to 200 degrees F.

 

[LS6 Tommy]

Nope. The unloader valve is on the pressure switch. The check valve is a just a check valve. It does have a port for the unloader line, but it's nothing but a check valve.

I know the unloader is on the operator. I didnt mean to infer the combo valve worked alone as an unloader. Again, I should have spent a little more time on the first post. The port is what makes it a combo valve. There's no reason to have a guage on the discharge of the compressor. Without the port it's just a check valve...

Tommy

 

[redmondjp]

You won't be able to use a copper tube from your check valve to the unloader valve. The unloader valve you have has a push-on style fitting designed to accept only plastic tubing. Even if copper tube fits in there, it will leak. You would want to source nylon pneumatic tubing. Nylon is rated for up to 200 degrees F.

Yes, I was going to post that the black tubing can be rated for that temp - it is used on heavy-duty truck air systems.

However, having used those push-to-connect air tubing fittings at a previous job, there is no reason why a copper pipe won't work in one - it's nothing more than an O-ring that seals on the OD of the pipe, and a spring-steel retainer ring (that will probably still bite into the much softer copper). Just make sure that the copper tube is cut clean, square, and that the tube is perfectly round for the first 1/4" on the end.

To the OP - to remove the plastic tube from the quick-connect fitting on the unloader valve, you have to press in on the blue ring at the end of the fitting, while also slightly pushing in on the tube first and then pulling it back out while holding the blue ring in.

 

[perkinscl]

Thanks guys. It's all working correctly (gauge removed from check valve and replaced with unloader tubing). I do need to replace the clear tubing I have with high temp black tubing.

Where can I get this? I think it's 1/4" OD, 3/16" ID. It's pretty small. Harbor Freight didn't have it, I may try Tractor Supply next.

 

[rburke65]

I don't know where you can get it. What if you just Google it and maybe find a local supplier?