Of late, many of the questions I’m getting about troubleshooting a compressor have to do with compressors that run, but generate very little pressure in the tank (far below the norm) and just keep on running.

I had some ideas about what was causing the problem, but also went and talked to a compressor repair depot, one that specializes in all kinds of compressors (even small ones) and got some more advice for you.

If you have a problem like this with your compressor, you probably want to read: Why won’t my ^%#$^$ compressor generate pressure?

They write, “oversizing an actuator by one bore size can result in a 50% increase in the cost of compressed air required for the application. If care is taken in this initial step of the design process, every component upstream of the actuator will have a better chance of being correctly sized and applied”.

Sound advice, I’d say.

Here’s more information on air actuators.

This issue:

The compressor worked just fine until I shut it off for about 1 minute and tried to turn it back on. The pump motor makes a humming or buzzing sound, not the usual pump sound. If I leave it buzzing for too long (maybe 5 seconds) it trips the breaker, so I don’t do that for fear that I’m burning something up internally. I unplugged it, drained air pressure, and let it cool down overnight for 12 hours. The problem still exists. There were no sounds or physical indications that the pump or compressor had a problem before shutting it off when it reached 100psi.

It was plugged directly into an outlet without an extension cord. I’ve been using it in this manner for 3 years without problems. I’ve tried several outlets, (GFCI, non-GFCI, and unused circuits), but there is no change. It is a 25 gallon, Sears/Craftsman, 175psi air compressor. It has a red lever switch for OFF and AUTO positions. I haven’t located any reset switch.

Are there internal fuses? Is there a reset switch? Any other ideas or something I can check?

Thank you.

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Bill says…

First, thanks for writing in.

Second, thanks too for such a good description of the issue.

From the sounds of it, you either have a failed capcitor or a failed motor.

Since compressor motors (along with all AC electric motors) require an “inrush” of energy to start, a capacitor is used to “jump start” the motor, since there’s not enough amperage in the typical home circuit to start the motor.

If the capacitor fails, then the motors can’t start, and it sits and hums until it pulls too many amps and pops the breaker.

Could be the motor, but I’d bet on the capacitor. Since the capacitor is cheaper to replace than a motor, if you want to do it yourself, start there. If you are taking it to a shop, they can tell you pretty quickly which is causing your problem.

Cheers,

Bill

If you notice that your compressed air control valves are getting plugged up all the time, it may be that you are using spool type air valves.

These have a sliding spool inside the valve body that redirects the air stream as the spool moves along, opening some air passages and closing others.

In a spool valve the air flow passages are sometimes quite small. If your airstream is dirty, then particulates can build up in the valve, either blocking air flow or causing the spool to stick so that the valve doesn’t shift.

You really should clean up your air, but if that’s not to be, then consider using a poppet style air valve that has relatively larger flow paths and less of a tendency to plug up. Also, poppet style valves tend to shift better when contamination is present in the valve.

I’m thinking about buying a small, home use sand blast cabinet that says it requires 10 cfm at 100 psi.  I have a 26 gal compressor that is rated for 6.4 cfm at 90 psi.

Would I be correct in thinking that I could probably make this work but only for short periods of time; in other words, if I start blasting the compressor will put out 10 cfm at 100 psi but only for a limited time.

Then the compressor will turn on and try and bring the pressure back up.

Since it’s not quite big enough, it will never be able to continuously operated at the required pressure/flow, but could be operated for short periods of time then pause to let the pressure build up again.

We are only talking about sand blasting some rusty trailer wheel hubs after all.

Thanks, Charles
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Bill says yes…

Hey Charles. Thanks for writing in.

I have a little 1.5 HP air compressor, and I use it to sandblast all the time.

You are correct in that, with a small compressor,  you will only be able to blast for a few seconds before the compressor kicks in.

If your compressor is rated for 6.4  CFM at 90  PSI, then that’s what it will give you.

The issue is, a blast gun will use much more than 6.4 CFM, even at 70 or 80 PSI.  It will drain your tank so fast that the pressure will drop below the point where the sand blasting is doing anything.

That’s why you have to wait for it to catch up. To get the pressure back to the point where the sand will actually take off the rust or paint.

Cheers,

Bill

Whenever possible, use a clevis style mount when installing an air cylinder.

You can have a rear clevis, and / or a rod clevis.

The use of these devices will help compensate for an alignment issue between the air cylinder and the tooling when the air cylinder is cycling.

If the tooling is not aligned correctly with the axial motion of the cylinder, sideloading can result. Sideloading will result in premature cylinder wear and early air cylinder failure.

How do i connect the hose from my compressor to the plumbing line?

What type of fitting or connector do i need?

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You know, I’ve had that same question asked many times on the ASK page on my compressed air information website and on this blog, and each time before I’ve answered it for each visitor.

I thought maybe it would be time to put this information up on the website for all folks to find, and so I don’t have to keep repeating myself, so I did.

Here is complete information about connecting your air compressor to air-using applications, for you. I hope you find it useful.

Norgren, a major manufacturer of compressed air treatment products,  reminds us that  “coalescing filters do not remove oil that is in the vapor state in the supply air. Vapors are typically removed using an activated carbon filter. Always protect a vapor removal element by removing oil aerosols with a coalescing filter before the vapor removal filter.”

Sounds like good advice to protect the life of the activated carbon filter.

Ah…. what I perceive is a simple question isn’t so simple if a person hasn’t ever done it, is it?

Here’s what you need to do.

First off, don’t worry about the fact that your compressor can generate 300 PSI. That’s a good thing.

On the discharge line from the tank to the coupler where you would connect an air line is a regulator. Not sure what this or does? Here’s complete info on air regulators.

All you have to do is “dial down” the pressure reading on this regulator (watch the gauge) to whatever pressure level you want your downstream application to see.

In your case, if you want to inflate tires without bothering to check the resulting tire pressure, set the regulator to the recommended pressure of your tire. That’s usually in the area of 35 PSI for light truck and car tires, but you need to look on your tire or on your car’s door post for the specs for your vehicle.

You connect your air line to the compressor discharge  coupler. Here’s info on those.

At the other end of the air line you need to have a tire filler tool (tire chuck) installed. The photo above is one of those.

One end fits onto the valve in your tire to allow air to flow in, and the other, with a  connector installed,  connects to the coupler on the end of your air hose.

Once you’ve got it all installed and connected, push the tire chuck onto the fill valve of your tire and the air will flow from your compressor into the tire and fill it to the pressure on your regulator gauge setting.

Make sure you set the regulator to the right pressure, or add air to the tire and then use a tire pressure gauge to check the tire. Make sure you don’t overfill the tires.

Good luck.

There are many applications that demand more protection than the typical 30-40 micron compressed air filter can provide. At one time, when air logic was the norm, the compressed air used in the control circuit had to be very clean indeed, as much of the logic had to do with the speed that compressed air passed through small orifices, and air cleaned even at the 40 micron level wasn’t clean enough.

In these types of applications a 5 micron or even finer filter would be installed.

In the event that the compressed air stream to that 5 micron filter was dirty, which is often the case, the element would plug solid in a very short time, as it was stopping small debris, but also the “bricks and 2 x 4’s” that accompany the compressed air from most compressors, necessitating an element change.

The finer sized element may not cost any  more than the 40 micron element used in a general purpose compressed air filter. The real cost to the user is in the interruption of production due to air starvation, as the small holes in the micro filter quickly filled and blocked passage of the compressed air requiring a machine shut down to replace the plugged element.

To extend the life of the finer-element filter, consider adding a 30-40 micron pre-filter just upstream from the finer element filter. This “coarser” filter element will remove all the  “bricks and 2 x 4’s” (yes, this is exaggeration) before they can get to, and quickly plug up, the finer element holes, thus extending the mean-time-between failures of the finer filter element, and improving machine up-time.

There’s lots more info on compressed air filters here.