Air Compressor Problem

[metalwarrior]

I have a Powerbase air compressor which is pretty similar to this one: http://www.autobarn.com.au/products/15/198/4112873

It should get the air inside the tank to about 120psi before it shuts itself off, but it stops increaseing pressure at 30psi and never shuts off.

It just started doing this recently, before now it has worked quite well. I don't use it that much and it is about 3 years old. Sometimes I leave it with air in the tank rather than emptying it out and opening the tank drain valve.

I have checked and there are no obvious leaks that I can hear. The filter looks like it is still in good shape, and it has enough oil in it still.

Does anyone have any idea what could be causing this to happen or what I might do to fix the problem?

[digi2t]

Sounds like the anti-return or unloader valve may be stuck or damaged. The anti-return valves function is to open during the compression stroke, allowing air to go to the tank, and close when the piston is in the intake stroke. This give the piston a chance to pull in atmoshpheric pressure and prevent the air in the tank from escaping through the cylinder. It's generally located on the head, right where the pipe that feeds the tank is located. The unloader opens only when the compressor come to a stop. It releases any compressed air in the cylinder to atmmospere, thus the piston is not in compression the next time it starts up. If it were, the motor would not be able to generate enough inertial force from a dead stop to turn the compressor. One way to check it is as follows;

WARNING: This test involves removing the belt guard. Please take adequate safety precautions. Also, compressed air can injure. Wear safety glasses and gloves.

-First, remove the belt guard.

-Run the compressor until it charges as much as it will (30 psi in your case).

-Stop the compressor, AND UNPLUG IT.

-Listen for any leaks and note where they are coming from.

-Ensure that you have some pressure in the tank. With a gloved hand, holding your hand open, and only with your palm gently and slowly try turning the large pulley of the compressor through 2 or 3 revolutions. As you do, listen for any escaping air from the intake. DO NOT AT ANYTIME CLOSE YOUR HAND ON THE PULLEY OR BELTS. If there is any compressed air trapped in the cylinder, the flywheel may jog under the power of the trapped air, taking your hand with.

If you hear air coming out the intake, it's the anti-return valve. If not, it's the unloader stuck open.

NOTE: The unloader is the valve that make a sudden hissing sound just after your compressor stops. If your not hearing the telltale blast of escaping air after the compressor stops, it's a good sign that the unloader is stuck open. Their location on compressors generally varies, but they are usually directly or indirectly connected to the crankshaft in some manner. When the compressor starts, the inertial force closes it, when it stops, it opens. If you have a manual, they sometimes provide a parts breakdown drawing. Should be on there. Let me know what you find.

Finally, if you don't feel comfortable in any way shape or form about the above test, take it to a shop. I'm an industrial mechanic by trade. I get paid to fix things like this, hence my livelyhood is insured. Yours isn't in this case. After 25 years in the business, I still have all my fingers and limbs. Unlike some poor fellows that have crossed my path during my career, I love to play guitar and that love is top of mind on every job I do. Get my drift.

Cheers

[anderekel]

Another thing is that it's really not a great idea to leave the tank full of air. The tank collects water when it fills up and draining the air out also gets rid of the water. If the water stays in the tank it can easily cause it rust. Not a good thing, now it likely won't make a difference for a while, but if you keep doin' it it'll only get worse. Don't know what your problem could be, but good luck with it.

[digi2t]

Anderekel is absolutely correct. Compressors naturally produce moisture due to the fact that the air, having been compressed, also rises in temperature. Once in the tank, it cools and the moisture condenses out. It's important to remember to drain the tank at regular interval. This won't stop the tank from corroding, but will go a long way in extenting it's life span. Due to the fact that compressors will naturally produce moist air, it's hyper important to have a good air drying system downstream of the tank if you ever decide to use paint spraying equipment. If you don't, the moisture in the tank will kill your paint job. A good water sepatator will also go a long way in extending the life of your air tools. But even then, respect the maintenance procedures of the particular tool i.e. 1 or 2 drops of air tool oil after use, etc.

Thanks again to anderekel for the note on the tank.

Cheers.

[metalwarrior]

I pulled it apart and couldn't see anything wrong with it - I'm no expert though.

It isn't a belt drive so I couldn't do the test you suggested digi2t.

After putting it back together again it is still suffering from the same problem.

I took some pics but I'll have to download a program to resize them before uploading them.

[Acousticraft]

Ive worked on both industrial and truck compressors over the years. A very common problem is the springs that hold the valves closed break so the air just bypasses. If its done a lot of work the seat the disk seals on gets worn or a carbon buildup stops it sealing properly as well.

If you havent used it much an inlet valve may be stuck shut. Without seeing the compressor I would envisage the cylinder head would need removing to get acess to the valves for inspection.

Edited January 27, 2008 by Acousticraft

[metalwarrior]

This is what it looked like when I took it apart:

I also unscrewed and pulled off the black square thing in the bottom right and ripped the gasket in half

The only valve with a spring I could find looked like it was in good shape:

http://img521.imageshack.us/img521/2391/compressor03bt0.jpg

This is where it came from:

http://img521.imageshack.us/img521/5840/compressor02fb0.jpg

[digi2t]

OK, didn't realize it was direct drive. No biggy for the gasket, get a roll of gasket material at the local auto parts shop (same thicknes), and just cut a new one. Put a TINY BEAD of sealant such as LocTite 515 on both sides around the edge inside the bolt circle, and down the middle between the 2 openings before reassembly. You don't want any sealant to squeeze into the head valves when you retorque the head, so keep the bead as small as possible. The small spring valve that you disassembled is the anti-return valve. Allows the air to go to tank, but not escape back to the cylinder. The small tube leading away from the valve I believe goes to your pressure switch. There should be another piece to this valve that fits on the end of the spring, somewhat like a disc or a fawcet washer minus the hole. Make sure this is all very clean, put a few drops of air tool oil on the parts and reassemble. The "black square thing" is the cylinder head. The 2 rectangular pieces are the intake and exhaust valves. Before you throw the head back on, inspect the inside of the cylinder. Use a flash light if required. The bore should be fairly shiney and smooth. If it's badly scratched or scored, it's toast. Inspect the intake/exhaust valves as well. They should be clean, flat and smooth. If they are "embossed" with the pattern of the port which they cover, highly likely that they don't seal properly anymore and are leaking by. If everything seems OK, put the head back together (don't forget the gasket), and ensure that you evenly tighten the bolts which secure the head. Work in an "X" pattern, and go in stages. A little tighter each time around until all of them are tight. Use your experience removing them to judge how tight to torque them. Now do the following test.

-Leave the air filter off and prepare a small squirt bottle with about 2 oz. of air tool oil handy

-Empty the tank of air

-Run the compressor. Place your palm over the intake while it's running.

If you feel a constant suction while the comperssor is running, this is good. Let it run until it gets to the pressure where it stops charging but keeps running (30 psi in your case) and place your palm over the intake again. If you feel your palm popping off the intake in sync with the compressor, or it doesn't seem to be sucking as hard as when you first started it, then one or both of those rectangular valves is at fault. If your palm is being pushed and pulled on the intake, it means that the compressed air which should be going to the tank is blowing by the valves and back out the intake. You can take it a step further, and while it's running, squirt some oil into the intake and watch your pressure guage. If the pressure begins to rise and then fall again, it may mean that the piston rings are stuck, dirty, or toast. The oil artificially serves to seal the blowby. Let me know what comes up.

Cheers

[Acousticraft]

There should be two valves with springs. One for the inlet and one for the outlet. That looks like the valve housing that is sandwhiched between the cylinder and cylinder head. You would need to remove that to get at both valves.

Heres a link showing how a compressor works.

http://www.popularmechanics.com/home_journ...131.html?page=2

[digi2t]

There should be two valves with springs. One for the inlet and one for the outlet. That looks like the valve housing that is sandwhiched between the cylinder and cylinder head.

If you look carefully at the picture, the valves are visible. Darker rectangular objects, one on top of the cylinder and the other on the head. These "valves" in some cases don't have springs, but rather use the air pressure to flop back and forth between intake and exhaust cycles to open and close the ports. Like reed intakes in 2 stroke motors.

Cheers

[Acousticraft]

You may well be right about having no springs as I havent had one of these modern (Chinese built)? compressors apart.

The symtoms point to faulty valves or shot piston rings. As the compressor is not that old then the issue of one or other valve not sealing properly is most likely the cause, maybe because of moisture if you havent drained the tank each time its shutdown.

The valve youve pulled apart on the side of the tank is a non return valve so once the air enters the pressure tank it cant backflow to the compressor.

[metalwarrior]

I just tried taking the air filter off and testing the suction. To me it seemed pretty similar at start up and when full.

I didn't have a squirt bottle to try the oil test though.

I'm thinking of just giving up on it and upgrading to a better model. I am about to start spraying some guitars soon so I will need something more reliable.

[Acousticraft]

Can you hear air leaking back thru the inlet when its up to its max pressure and turned off?

[metalwarrior]

No, there are no audible leaks when it's off and up to pressure.

[digi2t]

Well, if your going to be painting keep this in mind- CFM. Cubic Feet per Minute. Make sure your next compressor will produce about 50% more CFM than what your highest consuming tool uses. All air tools have their CFM ratings on the packaging. If your not sure, Google it and you'll find out quick enough. A larger resevoir helps tremendously as well. No use having a big compressor on a tiny tank. What you want to avoid is the compressor constantly running. It should cycle to recharge the tank while your consuming air. If your on par or exceeding the capacity, the compressor will run continuously. Faster wear, and more moisture in your tank since the compressor will be running hot. For painting, invest in a good water separater and air dryer. For a small shop, a dessicant type dryer is relatively inexpensive and effective. There are types that you simply change the dessicant when it becomes too saturated, and others that are in cartridge form. You dry out the cartridge in the oven. Both type are colored, the color changes to inform you of their condition. These two items should be top of mind when shopping for your next compressor.

Cheers

[metalwarrior]

The water separator you are talking about is the thing you put just below the handle of the spray gun right?

And by air dryer you mean some thing totally seperate thats not connected to anything? The only dessicant I know of are those little packets (that look like sugar sachets) that get shipped with some products.

[Acousticraft]

I just had another thought.

Can you hear air leaking into the crankcase by removing the oil filler cap. This would indicate air is leaking past the outlet valve and escaping past the piston rings down the bore.

Im sure it is a moisture related problem and there is corrosion that causing vital parts not to seal.

[digi2t]

If your just a weekend warrior I guess that would work, but if I was painting my (or someone elses) prized guitar, I wouldn't trust those things as far I could throw a city bus. Here is a link to what a real water seperator looks like;

Water seperator

and a dessicant dryer;

Dessicant dryer

the dessicant dryer has a sight glass through which you may observe the color of the media. When a certain color, you change it. I mounted mine on the wall of my shop beside my compressor. The seperator has a drain on the bottom of the bowl. You just drain it occasionally. My setup is; compressor - seperator - dryer - tool.

Also, when considering this equipment, ensure to size it to the capacity of your compressor. If your compressor puts out 10 CFM at 90 PSI make sure that the seperator a dryer meets or exceeds that rating. If they don't, then they won't work to their maximum effectiveness i.e. moisture will still make it to the end of your line. Again, use the 50% rule. 10 CFM @ 90 PSI compressor, go for a seperator and dryer that can handle 15 CFM.

My compressor puts out 15.8 CFM at 90 PSI, mounted on an 80 gallon upright tank (5 HP @ 230 volts). Cost me 900$, but it was one of those things that I only wanted to buy ONCE in my lifetime. Plus the upright tank takes up less space in my shop. I actually went the extra mile and installed an automatic tank drain. Everytime the compressor comes on, it momentarily activates my drain as well so my tank stays nice and dry.

Figure that a conventional paint gun can use anywhere from 5.5 to 9.9 CFM at 40 PSI depending on what your spraying. I hedge my bet with the lower pressure requirement of the gun, so I exceed my 50% advantage. The biggest air hog in my arsenal is my orbital sander at 17 CFM at 90 CFM. I bought it when I was working in a body shop, so air supply there wasn't a concern. With my compressor, for the few times that I've used it, I have to work in spurts. If I go hog wild on it, I know my rig won't be able to keep up. I've only used it 2 or 3 times in the last 5 years at home, so no big deal. Ideally you want the compressor to be able to work up a charge and take a break while you work. The LAST thing you need while painting is for your compressor pressure to drop below your required operating pressure during a shoot. I garantee you will throw the gun further than a city bus.

Cheers

[metalwarrior]

I just had another thought.

Can you hear air leaking into the crankcase by removing the oil filler cap. This would indicate air is leaking past the outlet valve and escaping past the piston rings down the bore.

Im sure it is a moisture related problem and there is corrosion that causing vital parts not to seal.

There is a little hole in the oil cap, and there is a leak coming from there only when the compressor is turned on, but doesn't let air out when switched off.

Is there a way to fix it or is it totally screwed?

[digi2t]

I just had another thought.

Can you hear air leaking into the crankcase by removing the oil filler cap. This would indicate air is leaking past the outlet valve and escaping past the piston rings down the bore.

Im sure it is a moisture related problem and there is corrosion that causing vital parts not to seal.

There is a little hole in the oil cap, and there is a leak coming from there only when the compressor is turned on, but doesn't let air out when switched off.

Is there a way to fix it or is it totally screwed?

The hole is there as a breather. As the piston goes up and down, a certain pressure/vacuum cycle is created in the crankcase. If the breather hole wasn't there the oil in the crankcase would foam up and not provide efficient lubrication and would also end up blowing the oil into your air system. When you say air "leaks" from the hole, a small amount of air coming from the hole is quite possibly normal. Excessive air would probably blow some oil out of the crank as well. If this is the case, then I would be tempted to say that your piston ring(s) are at fault. Refer to my oil in the intake test in my previous reply to determine if it really is the rings that are at fault. Just out of curiousity, how old is this compressor, and how much action has it seen. Also, do you live in a humid climate? Albeit long-distance, I'm brainstorming your problem. It's getting personal now .

Cheers

[metalwarrior]

The hole is there as a breather. As the piston goes up and down, a certain pressure/vacuum cycle is created in the crankcase. If the breather hole wasn't there the oil in the crankcase would foam up and not provide efficient lubrication and would also end up blowing the oil into your air system. When you say air "leaks" from the hole, a small amount of air coming from the hole is quite possibly normal. Excessive air would probably blow some oil out of the crank as well. If this is the case, then I would be tempted to say that your piston ring(s) are at fault. Refer to my oil in the intake test in my previous reply to determine if it really is the rings that are at fault. Just out of curiousity, how old is this compressor, and how much action has it seen. Also, do you live in a humid climate? Albeit long-distance, I'm brainstorming your problem. It's getting personal now .

Cheers

The compressor is about 3 or 4 years old I think. It has not seen much use at all, mostly just used to blow dust off stuff. Sometimes it would go for months without being used. In the beginning I used to drain it every time I would use it, but lately when I use it more often I haven't bothered.

The climate here in Adelaide, Australia is fairly dry most of the time.

I will try the oil test next time I am in the shed.

I had a look at some new air compressors today and it looks like I will be limited by my power supply which is 240v / 10amps.

The biggest one I can get is 250 litres per minute, 174 litres free air. I think that's 8.8cfm / 6.1cfm.

It has a 58L (15 gallon) tank.

The gun I just bought off ebay consumes 130lpm (4.6cfm), so that compressor should get the job done, but it's gonna cost me $600

Edited January 31, 2008 by metalwarrior

[stringkilla]

May I suggest that you check the adjustment on the pressure gages. I had a direct drive many years hence and it was preset at 30 lbs psi. There are two. The one on the left is for the tank. Try to open it as far as 90 lbs psi then adjust the out going pressure gage to your desired pressure. If you are painting with a gun a water trap is mandatory. By the looks of the picture it has a preset valve on it, the thing with the yellow or red castellated cap on it before the outgoing valve. Also if it has an line oiler take that off. It oils the air to lube the tools. Sometimes that preset valve serves as a line oiler also.Try to maintain dry, oilless air. Good luck. Killa

[metalwarrior]

while it's running, squirt some oil into the intake and watch your pressure guage. If the pressure begins to rise and then fall again, it may mean that the piston rings are stuck, dirty, or toast. The oil artificially serves to seal the blowby. Let me know what comes up.

I tried squirting some oil into the intake when it was running and most of it got blown back out the intake and also some smoke was created.

I tried turning it off and then squirting some more oil in there before turning it back on and once again it got blown back out the intake, this time all over the shed. There was smoke too. The pressure change was minimal if any - less than 5 psi.

There was also some oil sprayed out on the other side of the compressor, where the little copper tube connects to the pressure gauges. I didn't get a chance to look into it though because the whole thing was pretty hot by that stage.