Compressor will not build pressure

Your air compressor will not build pressure.

It runs, and runs, and seems to be working fine. There may or may not be air in the compressor tank. Or, the air pressure in the tank will reach a plateau, say 40 PSI for example, and even though it runs continuously, the compressor will not build pressure past that point.

The creates another problem, aside from not getting enough air to your air tool. An air compressor that will not build pressure runs on long past the point where it normally would reach the cut out pressure level and stop. The result is the compressor motor will overheat. Even though the compressor motor might shut down due to it having a thermal cut off switch, overheating the motor is never good. It also has negative impact on the compressor start and run capacitors too. If your air compressor will not build pressure even though it is running, shut it down until you get it fixed.

Reasons Why an Air Compressor Will Not Build Pressure

Let’s start by the various issues that may cause this, and then address each of these issues.

  • compressor intake valve failing
  • compressor pressure valve failing
  • compressor gasket failure
  • compressor piston seal failure
  • tank check valve is compromised

 Compressor Intake Valve Failing

As the reciprocating air compressor – that’s an air compressor with at least one piston that moves up and down or side to side to pump air – cycles, on the intake cycle, the piston moves away from the intake valve which opens as the piston moves and pulls a bit of a vacuum. Air from outside the pump head rushes into the cylinder through the intake filter. Then the piston moves into the compression cycle, and the air pressure building up inside the cylinder forces the intake valve closed.

In the image below, on this air compressor pump, the intake filter is circled in red. On your air compressor, the intake filter may look different from this one, but it will be located at or near the top of the pump housing. On the smaller air compressors, the intake filter may be under the shroud, if that model of air compressor has one.


Air compressor intake filter

Intake filter circled in red.

If the intake valve has been compromised, the symptom typically is air blowing back out the intake port.

Remove the intake filter, start the compressor, and carefully feel around the intake port. If the intake valve is failing, odds are good you will feel air pumping out this port. That being the case, it’s time to replace the intake valve.

Depending on the model of air compressor, the intake valve may be part of a “valve plate” which will also contain the pressure valve. If that is the case replacing the plate will also replace both valves, and there is no down side to that.

Compressor Pressure Valve Failing

This is a bit harder to diagnose.

When the compressor piston is moving into the compression stroke, the intake valve gets closed by the increasing air pressure in the cylinder, and, almost simultaneously, the pressure valve is blown open.

The pressure valve allows the compressing air into the air line running from the pump head into the tank. If this valve has failed, air will flow into the line to the tank, but as soon as the piston moves into intake cycle, air will flow into the piston from the intake valve, but it will also back up the line from the tank into the piston. The air cycling back and forth will not allow pressure build in the tank past a certain point.

With the compressor off and the tank drained empty, pull the line from the piston head. Start the compressor. If you are able to prevent air from blowing out the pressure port using other than your finger or hand, then that is a good indication that the pressure valve has failed.

This method of diagnosis is not foolproof, however. You will need to check and eliminate other potential problem sources before deciding that it’s the pressure valve.

If you determine to your satisfaction that it is the pressure valve that has failed on your air compressor, once again, it’s a pump teardown to repair or replace it.

What else happens when a compressor will not build pressure?

Please see here for the ongoing list and solutions to this compressor problem.



  1. We have an air compressor on are picker truck.When first started it builds to over a 120 psi.As the job goes on it goes down to 70psi and stays there.The compressor gets hot but does not shut down.Why won’t it stay at the normal air pressure?

    • What HP is the compressor, what flow demand for whatever compressed air equipment you are using. It sounds like it gets to the normal cut out at 120 PSI and stops when air is not being used, but when air is being used, the compressor cannot keep up with the demand. If you stop using air, will the compressor get up to cut out pressure and stop?

  2. Hi I have a Black Bull 4 gallon oil cooled pancake air compressor, I bought new from tractor supply around 2004 or later roughly, the symptom was it would only build pressure to 35-40 psi. So I opened the head and found a broken I guess Intake valve? There’s only one valve/reed so I replaced it with a new one. The gaskets looked good and had great compression. I would of changed gaskets to but I can not find parts for it anywhere. My model looks exactly like pictures included. After assembly it still won’t build past 40 psi. What could be wrong and where can I find parts? Thanks

    • Jim, when you say “I would of changed gaskets to but I can not find parts for it anywhere. “, that’s too bad, as I suspect that they are leaking at the 40 PSI area, unless you have the new valve in upside down, or, the piston seals too are leaking. Can you feel air existing the oil fill cap while the compressor is running? If so, that points to leaking piston rings.

      • No I feel no air leaking when running. the gaskets looked good except for a small piece by a bolt hole the corner flaked up, but it’s on the outside of bolt hole not inside. I’m pretty sure I put the valve in correctly, Where can I find parts for this compressor? I know it was sold under many other names including jobsmart.

        • I do feel air coming out of the oil cap but it also has a hole for venting in top of oil cap. Is there not suppose to be air blowing out of this cap? On the oil cap there is a sponge inside looks to be some kind of air vent am I wrong?

          • The vent hole is allow small amounts of air wicking by the piston seal to vent, or, as oil is consumed from the sump air can get in, or it would pull a vacuum. If you can feel air blowing out, your piston rings are shot, and quite likely the cylinder wall is scored. Tear it down to see. If it’s just the rings, measure them carefully, and you “should” be able to find a supplier of a replacement ring, just not from any compressor outlet. Google replacement piston rings to find distributors, and make sure you have the right dimensions.

        • If the gaskets are good, the valve is good, the pump piston rings are good, and the compressor is still not building pressure past a certain point, then it may be an electrical issue, in that the capacitor may be failing, but I doubt it. It sounds like a mechanical leak somewhere to me. If you look closely at the compressor, and compare it to many on the market, you will find that the style and external components are common to many makes. I doubt very much if you will find internal pump parts. The Black Bull brand seems to be Home Depot’s too, and you indicated that it was TSC where you bought it originally, yet these sources are not renowned for having internal components for any of their compressors. If you cannot find a used one to cannibalize, then I suspect you’ll be in the market for a new compressor. Sorry.

    • My compressor is similar to the onenin the pic at the beginning of the topic and was only getting to 40 psi like yours. I felt air coming out of the intake port. When i took the four screws off there is a plate that sandwiches two reeds and an aluminum gasket. On top of that plate is another gasket (see pic) between the intake port housing and plate. Because the middle strip of the gasket was dried out air was escaping back into then intake area. I went to auto parts supply and bought 1/16 cork gasket roll and used the old gasket as a template. Scraped it off with Exacto blade and used same to cut the custom gasket. Worked like a charm-pressure built up to 110 or so. Hope it helps.

      • Thanks for taking the time to post. Yup replacing gaskets with high heat, home made, gaskets often resolve this type of compressor issue.

  3. I have a Ingersoll rand ss3f2 air compressor it will build up to 40 psi then the motor will shut down, Thermo protected, thought we got a bad motor so took it back now on my 4th motor, and have replaced everything but the drain valve at the bottom of tank. checked the compressor with another one that I have and worked fine. I am Stumped?

    • Tell me about how you are getting power to the compressor, how long the extension cord, if you use a power bar, what amperage the breaker / fuse that the circuit has in the power panel, what else is plugged into that same circuit, and how far the socket into which your compressor is plugged is from the power panel. Your compressor symptoms have all the earmarks of a power supply problem.

  4. Bill Martin says:

    We have a very old two stage compressor probably came off a ship WW2 era. Will build pressure to 80 psi and not switch to second stage (we assume). Make maybe Ingersoll Rand brand with a 75 hp Westinghouse motor. Big boy. We cleaned the unloader valve and found a broken spring in another part of the unloader system. No help. Also problem is intermittent.. Any ideas?

    • Nope. intermittent problems are a witch to resolve. A picture of the old beast might help. Anyone else offer suggestions?

  5. Steve Stent says:

    I nust have a tiny cambell hausfeld 100psi max compressor that wont build pressure will run forvever and nothing happens wtf?

  6. Have a 5hp 80 gal compressor that stopped building pressure and will continue to run and for about 15 mins it will gain maybe 20psi motor obviously is very hot. Took the filter off and feel little air coming out but will suction my fingers to the hole when closer. So after reading everyone’s posts I’m guessing the valves are done? Seals need replaced? Help shine a little light on this problem for me please and thanks.

    • The compressor symptoms certainly suggest that a pump repair kit, with valve plate, gaskets and maybe even pump rings is in order. I don’t know how old the compressor is, or how much use it gets, but over time, all of these are maintenance items, for sure.

  7. Hi,I’m not sure if this is where post my problem but her I go. I have an old Brunner v30 compressor and lately having a problem. My compressor starts normal and reaches 60 psi and then the motor really struggles.

    If I try to turn compressor by hand I can’t, figured it was the check valve pumping back to compressor head.

    Disconnected the pressure line and no air leaking back. Reconnected line and started compressor again and again bogged down but what I noticed was air leaking from what looks like an oiler with a spring cap on the head.

    At this point on the pressure regulator I released the pressure with the button which I think is the over loader which is connected by a 1/4 line to check valve. Now I can turn compressor by hand and motor starts but bogs down after about 20 sec. Now I’m at a loss, hope you can steer me in right direction. Thanks, Don

    • The first thing I would do is check the compressor motor run capacitor, Don. Lots of sites offer the “how to” of checking a capacitor. Please do that, and advise your finding.

  8. Sorry guess I should of posted instead of replying to one so I’ll try again.


    I have a similar issue to Marc, I have a Iron Horse IHD6160V1 that only build pressure to 100psi. One of the cylinders draws air well, while placing my hand over the intake on the second cylinder I feel absolutely nothing. I took the ‘bad’ cylinder apart and saw a damaged aluminum and replaced it. Put it back together and still the same issue.

    Your help would be greatly appreciation

    • Matt, you replaced a damaged aluminum what? When you had the cylinder disassembled, did you check all parts? When you reassembled it, did you use new gaskets?

      • Sorry, A damaged aluminum gasket (seen below), and yes replaced it. All other parts looked in working order I think. I have been reading more of the posts here and am thinking maybe replace the air filter assembly.

        • OK, so the pump head is metal to metal, as are the valves, no gaskets, right? Sure, check the intake filter, though I suspect that’s not the issue. If you’ve replaced the valve strip properly, and the cylinder is not pulling air in the intake when it’s reciprocating, the next check I would do is the cylinder seal(s). Both these cylinders pump air directly into the tank, I believe. It’s interesting that with only one cylinder working your compressor only gets to 100 PSI. I would have thought that even with only one working, eventually, the pressure in the tank would get to cut out, just take a lot longer?

          • I have left it for a pretty long duration, it only hits 100psi and the head that is not working is very hot. Ok check the cylinder seal, how would I do that?

          • Matt, before completely disassembling the pump, which is what you would have to do to get at the piston, try removing the line to the tank from the suspect cylinder, and see, with the compressor running, if air is being discharged from that cylinder? Careful, wear a work glove. Use something to try and block the outflow. If you can, odds are pretty good that it is this cylinder that has a problem, and it’s time to take it apart.

  9. Hi,
    I have a Craftsman 12 gallon 1HP 125 PSI compressor that someone gave me because it will not build pressure. It builds to about 25-30 psi and that’s it. Compressor keeps running. The tank does hold the 30 psi and does not leak. I empty the tank, remove the air filter intake and turn the compressor on. There is good suction at the intake until the tank pressure gets to that 25-30 psi then I can feel blowback at the intake. Valves and gaskets look good (not broken or burnt). But they are so light of a material I cant tell if they are bad or not. Any ideas? Thanks.

    • Well, if you feel air blowing back out of the air intake when the pressure gets to 25-30 PSI, that’s a valve failure. Even if there are issues elsewhere in the pump, the intake valve should be one way – air in – and any other issue should not cause air to blow back out. I suspect a valve kit is in order, and if you do that, change any gaskets too as they are likely to fail after a compressor pump rebuild if old ones are used.

  10. Hello,

    I have a Crafstman 5 gallon 1 HP air compressor model E102365 bought in 2008. Pressure won’t build past 25 psi and once turned off, will slowly drain, although I cannot hear any air leaking. When I remove the filter, start the compressor, and put my fingers on the two intake holes, it depresses my skin and sucks them to the holes. However, if I hold my fingers slightly off the holes, I can feel air coming out. Does that mean my low pressure valve has failed?

    I removed the cylinder head and looked at the valves but they are not broken (see attached picture). Do I need to replace both of the valves and the gaskets? Or is it possibly a different issue? There is a little bit of debris (both gunk and a few small bits of the blue gasket) that I cleaned off. I am a novice at this; this is my first time troubleshooting a compressor.


  11. Ernest Sparks says:

    Problem: DeWalt D55146 won’t pump higher than 60psi. Placed hand over air filter, plenty of draw. Installed new check valve, same issue. Valved air into tank from shop compressor to 160psi with no leaks anywhere. Held same 160psi overnight, still will not raise tank pressure. Replaced cylinder sleeve and piston ring, still 60psi max. Although valve body looked fine, replace it, still 60psi max. Although no leaks detected replaced O-ring on metal cylinder-to-tank line, still 60psi max. Removed air filter, same. Place finger over cylinder head intake port and motor speeds up indicating good valving. Release finger and motor slows to operating speed. Lightly machined head to perfectly flat, new O-ring gaskets, same 60 max psi. Soapy water all around cylinder head/valve assy while running, no leaks. I’m really baffled.

    • My but you have checked a lot, Ernest. Unless I missed it, what I’m not seeing is a check of the outflow from the pump to the tank. What happens if you block that port when the compressor is running?

  12. I have a 90 gal craftsman air compressor, the guage will read 100psi on the tank but wont fill a car tire past 26psi, all new hoses and accessories, any ideas?

    • Hi Warren. I think if you check the pages “no air out of the air hose” and “only a short burst of air” on this site, you’ll find the reason.

  13. I have a brand new compressor pump and it will only suck air from the outlet line and push air out from the air filter inlet. What can cause this?

    • Mike, we would suggest that when the compressor pump was assembled, the valve plate was inserted in reverse. It is possible, as noted in another post of yours, that it could also be a damaged compressor valve plate.

  14. Hello,

    My name is Tom. I have a 2016 Central Pneumatic 29 gallon 2hp air compressor in my shop. I have about 20 feet of line running to a spool of about 75 feet. I have a little blower that is the only tool i have hook up and as soon as it is powered up, i give it a squeeze and within a second or two it is out of air. The PSI gauge doesnt seem to deminish by this. How can i get the air to travel through this so i can fill up tires and use tools?

    • Ernest Sparks says:

      This suggestion assumes the outlet port of your air tank is not at the bottom. If you are trying to draw air from the bottom of the tank you heed to move the exit port to another location that is not near the bottom of the tank where debris can accumulate. Assuming this is not the issue and you have a quick disconnect at the compressor tank remove the air hose and insert your air nozzle into the quick coupler at the tank. Check to see if you have sufficient air directly from the tank. If not you may have a serious restriction with the coupler. If so drain all air from your tank, remove any coupling you have and restart your compressor with an open exit port. If you have plenty of air your problem is with the coupler. If you still have no air then the problem is with the construction of the air tank itself. You might try running a clearance sized drill thru the open port to see if that clears any obstruction. Do this with no air in the tank and restart the compressor to see if air does flow freeely. If you have plenty of air pressure at the tank, and thru the quick coupler your problem is with either the air hose itself or the coupler at the end of the hose. Good luck.

  15. I have a Husky 4 gal. pancake compressor. It is an older model from 2004. It was working and then it stopped producing any air pressure in the tank. I pulled the casing apart, and notice that it has a two cylinder and two motor assembly. When I turn it on, only one motor runs. It sounds like it always has before, but no pressure is built up. Is the second motor supposed to be running also? I don’t know if the second motor ever ran.

    • The absence of a picture makes it hard to be specific, Nick. We doubt that Husky would add and extra motor if it were not necessary, ergo, that one is not working is likely part of or the problem. Follow the power using a multi-meter to try and determine if power is getting to the motor that is not running. If, as we suspect, the second pump and cylinder are in sequence with the first, that it is not working would effectively block the flow of air to the tank. Please add details of what you found.

  16. Justin England says:

    I have a craftsman professional grade air compressor. got it used wasn’t building air pressure past 60 psi.

    I took head off reed valve assembly was junk and piston kinda of bad also replaced piston and sleeve and reed assembly it is a 2 stage compressor but other cylinder looks good and valves good why is it not building pressure past 60psi still

    • Hey Justin, when you rebuilt the Craftsman compressor pump, did you replace all gaskets as well?

      • Justin England says:

        Yes replaced all gaskets of rings everything I’m confused

        • If the air pressure rises to 60 PSI in the tank, and then will rise no further, and if the pump is running normally, then something is interfering with the flow of air from the pump to the tank. If the valves were installed with the correct orientation, if the piston rings are seated properly, and if the tank check valve is operating as it should, then it is likely that a pump gasket is letting go at the 60 PSI level, allowing air to flow back and forth between high and low pressure, without being driven down into the tank. Make sure no air is coming from the oil fill vent because if you feel air flowing out while the compressor is running, that’s a sign that the piston rings are leaking badly, Justin.

          • Justin England says:

            It’s a junky oil less compressor I just went back thru re did all the gaskets again and orings I can get to bout 75 psi but takes for ever guess I’ll cut my losses and just buy another one

          • Lets examine this, Justin. The compressor motor is running. When the tank pressure now reaches the 75 PSI, the air pressure stops building, but the compressor motor is still running, yes? No sign of laboring from the motor? If not, then assuming the tank check valve is OK, and since you have no sump for air to bleed by the piston seal into, then it pretty much has to be the pump valves or gaskets, doesn’t it? We share your aggravation with a compressor that will not build pressure, and if your patience is all used up with it, the your noted course of action would be logical. Good luck.

  17. HELP. My air compressor doesn’t seem to build up as much pressure after sitting thru the winter in my garage. Is there something I need to do to it?

    • Probably, Fred. Please read the pages about compressor pressure building problems found on this site for the things to check, and if you have a specific question about what you found, please identify the make and model with your reply.

  18. hi i have a dewalt air compressor model d55146 i plug it in, it fills the tank at 200 psi , but it wont recycle to fill it up air tank again it goes to 0 psi and it wont start. it will start again when i unplugged and plugged after some time . if someone can help i will appreciate. my guess is the valve pressure ??

    • That suggests that the motor may be overheating, Matias, and though the pressure switch trips to start the motor again, the thermal cut out prevents that from happening until the compressor motor cools. Or, double check and make sure that the unloader valve works when the compressor cuts out at the high pressure, OK? If the unloader valve isn’t unloading, then the compressor may have a hard time starting until the trapped air voids over time.

  19. Hi
    My compressor is an older belt drive. It is having trouble getting to full pressure. It runs well generating low pressure but will run slower and even stall out before it is supposed to cut out (110psi). I drained the oil and there was metal filings in the old oil. I’m guessing that’s a little bad…

    • willyr says:

      Yes, metal filings in compressor oil is not good. Empty the tank and pull and check the tank check valve. Make sure it’s working. If it’s gummed up then the backpressure generated as the compressor is trying to fill the tank could stall the motor. If that doesn’t do it, check the motor capacitors. See how on the pages of this site. If they are good, you may have an issue with the motor itself failing, or, you could be having a valve problem – or maybe a piston seizing problem – but since both require a pump tear down, check the other things first. Have a look at this page for more info: //

  20. Not sure if this is the place to ask but it seems like the right subject.

    At my work I have a Super Silent 50TCA attached to a gravermach and it seems to be having issues keeping pressure. It’ll start up, build up air and stop as normal, but doesn’t seem to kick back on when it needs to. I’m only able to get two or three cuts in with the gravermach before its out of air and I have to wait 5 or so minutes before the compressor decides turns back on and builds up air again, and it doesn’t seem to keep that air even when I’m not using it.

    I thought that draining it might help, but even after that it does the same thing. I’m not hearing or feeling any obvious leaks, so I’m wondering what else I need to check to fix the problem, because otherwise my engraving has been taking three times longer than it should since I have to wait on the compressor to turn back on again.

    Any help would be appreciated! Thanks!

    • willyr says:

      When you say “I have to wait 5 or so minutes before the compressor decides turns back on and builds up air again, and it doesn’t seem to keep that air even when I’m not using it.”, that’s suggesting to us that it’s too hot to restart right away, and it needs to cool down to allow the thermal cut out to reset. As long as the power supply is good, no extension cord for example, the that problem points to a run capacitor on the motor or perhaps a compressor motor issue itself.

  21. Peter Timpson says:

    I have a HU5000 that will not build pressure. A friend told me that if the unloader and exhaust tubes get hot, it more than likely is a problem with the pressure switch. I swapped that out with a new one ($16) but still have no pressure. I’m thinking that I need to go into the head cover and check the valve. Any advice is certainly welcome.

  22. Just to say thank you for this page, instantly able to diagnose intake valve failing, turned out to be a gasket blown through, 10min job that saved me a whole heap of pain and expense.

  23. I just pickup an older 60 gal unit Campbell Hausfeld VT558/705AJ it was set at 120psi max i turned it up to 140psi seems to be working with no problems will i run to any problems with that or can i go higher i was running 150psi with my old craftsman compressor but i can’t buy parts for it anymore i did combine both tanks to make 120 gal

    • Hello Vern. It’s our opinion that the maximum pressure setting for any compressor that is established by the factory is the right setting for that air compressor. While we don’t believe that it’s a safety issue by over-pressurizing the compressor as the PRV should let go before that pressure level, if the components in the compressor are designed to run up to 120 PSI, will they perform properly and for as long at a higher pressure? We suspect not. We think by running this compressor at a higher cut out than it was designed for, you will shorten the time until something breaks. On the other hand, and if you can live with that, set the pressure where you want. Just make sure your PRV is working.

      • Ok It has a 150psi PRV

        • Which means that the “emergency” pressure release is set for 150 PSI to protect you. That cracking pressure is the pressure level beyond which the manufacturer has determined that it is unsafe for your compressor to go. If this was our compressor we wouldn’t make the change.

  24. manas panda says:

    i working in ingersoll 2nd stage compressor,but it not develop pressure,what can i do? i change inlet outlet valve with gasket ,plz help me

  25. My air compressor shows 120 psi in the tank but I’m barely getting any pressure at the tool. Any ideas?

  26. Eddie Standridge says:

    I have an Ingersoll rand 7100 compressor 2stage 175 psi 120 gal tank
    It does eventually build all the way up but it takes a longtime doing it. What should I check?? Valves or rings??


    • All of the above. The pages on this site about compressor problems address your compressor symptoms in great detail. Have a look at those pages, and start troubleshooting with the easiest, least invasive, checks. Then, you work your way towards tearing down the pump as a last resort. Typically though, once a compressor starts taking longer and longer to fill, odds are pretty good that a pump rebuild (valves, rings and gaskets) are part of the solution.

  27. Ok I have this compressor I built.

    The motor is a 2.5hp 3450 rpms with a 4 inch pulley. The pump is a 2 stage 1050 max rpm with a 12.5 inch pulley. The tank is a 15 gallon tank. Everything is new except the motor and tank, the motor was on my old powermate 2 gallon compressor.

    The problem i’m having is it will not build up pressure past 35psi then the motor bogs down and trips the breaker. all the test I run for trouble shooting tell me the check valve is bad. I have replaced it twice so far The belt is a little loose. I shortened the power cord on it to 3 ft when it was about 5. I’m retired Army so I been wanting to build my own compressor for awhile What i’m I doing wrong?

    Update: I tighten the belt replaced check valve again. I tested the capacitor in the motor all good. Now the compressor will reach 60 psi before cutting out. It doesn’t trip the breaker but it does trip something in the motor.

    • Seth. We put your two posts together. That you’ve checked the check valve is good. Sorry that you replaced it an it didn’t make any difference. We wonder what the amperage of the breaker in the circuit into which you plug your compressor is? It should be a 20 amp in our opinion. You say something in the motor trips. What we suspect is that this is the thermal cut out, cutting power to the motor as it is overheating. Yup, could be mechanical load overloading the motor, but it may also be that the motor is just under powered – by that, we mean, not getting enough juice from the circuit. Want to check that and advise? Is the motor really hot when it trips off?

      • The motor is cool to the touch when it cuts out In the morning im running a new line with a dedicated 20 amp breaker. The motor came off my old coleman powermate. before using it I cleaned it up check what I know to check and all was good. It very well could be just worn out.

        • Cool to the touch when it cuts out could indicate a centrifugal switch problem on the motor. Or, as you say, it could be worn out. It may be less expensive to have it rebuilt and rewound than buying new. If it’s an oldie, it may be of better quality than motors today. You might check around to see if you’ve got electric motor rebuild shops close by, and if so, ask for a bid on a rebuild? Good luck.

  28. Herman Vanden Broek says:

    I have an Eagle C5160V1 5hp single stage compressor. It is listed as 18.5 CFM at 90 lbs pressure. It shuts off at about 125 lbs. I use a small die grinder for sanding wood and can go easily 15 not 30 minutes at a stretch. When I’m using it the unit can keep up but never shuts off. would a small die grinder use that quantity of air? Also it has 3 cylinders and the intakes vary widly in the amt of vacuum that builds up if put your finge on the openings. I bought the unit recently 2nd hand so no returns. :))) Any help or insight is appreciated.

    • A die grinder uses quite a lot of air. Since there are so many brands and sizes, we cannot be sure if the grinder is using more than the 18.5 CFM your compressor is reputed to supply, or if there is a problem with the compressor itself. Turn off the compressor, drain the tank down to below the cut in pressure setting, and without using any air, time how long it takes for the compressor to reach cut out pressure. With a 5 HP and that capacity, it shouldn’t take too long, even on the 60 gallon tank. If the recharge time seems inordinately long, then yes, you may have a valve issue, particularly as you note, “the intakes vary widly in the amt of vacuum that builds up”.

      • Herman Vanden Broek says:

        Thanks Willyr,
        I appreciate the help. It loads up fairly quick but not sure how quick it should be. I should have timed it I guess. Have a call in to an Eagle dealer in Calgary and waiting to hear back. Long weekend etc. :)) I’m sure I can do a re and re on the cylinder heads if necessary. Might be a fun project and get me away from my lathe for a time.

  29. Chris M says:

    Hi, My compressor is not replacing the air fast enough in the tank to be able to use any of the tools, even the inflator. I have done a few checks and it appears that there is a small amount of air coming back out of the intake once i removed the filter. I have noticed that on the pump head there are 2 big nuts which i assume are the intake and out let valves?? The one over the intake does not have a spring in it but i can see the plate and if i gently push it with my finger it flexes up and down freely but the other one has a spring in it so should both have springs in the valves??
    Regards Chris

    • If air is coming out of the intake port, then your compressor certainly has a valve problem. As to the two big nuts on the pump head, since we have no idea what make or model of air compressor we are talking about, we have no idea if they are the valves, nor can we advise about springs. Some air compressors use the air itself to open or close valves. You may want to have a look on line to see if you can find a valve kit for your compressor.

  30. I have been pulling my hair out w my Craftsman 7hp 175psi 60 gallon tank model #919165610 oil less compressor. It won’t build pressure past 35 psi, was working fine late fall, then it seemed to take longer to build pressure up to 175, and then finally it would not build pressure past 50. Tore down and the cylinder rings were shot and there was scoring on the cylinder and the reeds looks ok.

    The parts I have replaced so far – both piston and cylinders, new gaskets/ orings of course, the head plates (w/ the intake and exhaust reeds) , tank check valve and pressure gauge. I pulled the unloader out and blew through that … there is no leaks past the unloader valve or any other connection, the tank will hold what little pressure for a couple days …. there is a slight leak at the drain valve over time.

    Just runs and runs and runs, not building pressure past 35psi ….grrrrrrrr!

    What the halibut? I have posted on other sites and I get the same ol try this and this …. that has been done. For my sake, tell me something I missed that is simple, it’s only a pump/motor and tank!


    • willyr says:

      So Michael, just a bit frustrated, hmmmm? We share that. Sometimes air compressor problems drive us crazy too! The thing is, since people that try to help don’t have your air compressor in their shop, all they can do is offer suggestions as to things for you to try. So it runs and runs and only gets to 35 PSI? We could question the accuracy of the tank air gauge, yet even if it were faulty and the needle didn’t go past 35 PSI, the compressor should stop at the normal cut out pressure, regardless of the tank gauge display. So we assume that’s out. Are you getting any huffing out of the intake port? Pull the filter and check that, ’cause if you are, you’ve got a valve issue still, and it could be as simple as the plate installed reverse. The thing is, your compressor is not loading up and adding load to the compressor motor causing a thermal shut down. That suggests that you have functioning pump components but at 35 PSI the pump is no longer driving air into the tank, so where is that air going? If you have done as good a job on the rebuild as it sounds, the logical conclusion is that you have a gasket letting go between the high and low pressure sides at 35 PSI, at which point the pump simply pushes air back and forth and not into the tank.

      • Michael says:

        thank’s for the reply …. I did replace the tack pressure gauge, still 35psi. I replaced the gaskets twice now, once with the piston cylinder rebuild kit, and then when I replaced the heads…. which didn’t change a thing, grrrrr.

        I did take off the line before the check valve and there is enough air coming into the tank that it’ll depress you skin on your finger considerably. As far as the intake valve …. put your finger over the hole and it’ll suck your finger into the hole. lol.
        Can I replace the tank check valve, that is just have the intake line plumbed into the tank w/o the check valve? I know I need the unloader valve and the switch inline in order for the compressor to sense 175 psi and stop ….. I just want to try and get it past 35 psi for now!!!

        There has to be a mechanical fault somewhere …. any other suggestions?


        • Michael says:

          Oh,yeah, isn’t the low pressure side the first piston w the intake filter and then it pumps to the high pressure side, second piston, and then feeds the tank … yes? How can there be a leak when its plumbed with an air line and there is no leaks?



          • You are correct. A two stage compressor pre-compresses air in the first stage, sends it on to the second piston which then further compresses the air into the tank. Are you sure you don’t have a PRV letting go as there will be one somewhere in the line between the first stage piston and the second, and then one more PRV to protect the tank from overpressure. Is it possible with the compressor running you aren’t hearing air blowing out of one of the PRV’s and it were my compressor, I’d be thinking it’s the PRV between 1st and 2nd stage?

        • Sure, to test, plumb the line from the pump head right into the tank without a check valve. If the tank pressure bypasses the 35 PSI, then you’ve isolated the likely cause as the check valve. Of course, when the air compressor shuts off on high pressure cut out, all the air will bleed right back out of the tank and out of the unloader valve.

          • Michael says:

            There are no PRV between the first stage and the second stage, just a 3/8 ? line. I’m going to substitute the tank check valve w a pipe and see if it can’t build pressure.

            Think I’ll buy some gasket material and pull those heads off and cut out new gaskets, thou I don’t think there is anything wrong with them.

            I’ll take some pics today and post them.


  31. hi
    have cp road compressor made in the 70,s
    wont build up air
    any ideas whats wrong

    • Hi Martin… yes, a few ideas. Check out the navigation menu on the left, and follow the link to the page about air compressors that don’t build pressure for some ideas. After you have checked those out, feel free to leave another comment with any specific questions.

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