Why is it a compressor will not build pressure? Does the following describe what’s happening, or rather, what’s not happening, on your compressor?
The motor runs and runs. The pump sounds like it’s operating, but the air pressure in the tank is not rising in pressure at all. Or, the pressure in the tank rises to a certain pressure level and then the pressure stops rising, even though the compressor continues to run and run.
Here’s why a compressor will not build pressure.
The air compressor is really a pump driven by an electric motor, or perhaps with a motor driven by other fuel types like gasoline or diesel.
The part that actually compressors the air is often referred to as the pump, or compressor pump.
This is an air compressor pump, though it’s missing the pump head cover in this photo.
In the photo above, part of what’s missing is the pump head, which will contain an intake port. This pump is also missing the valves or valve plates which open and close depending on whether the pump is in the intake or compression cycle.
On all compressors the pump pulls in free air from the atmosphere through an intake. That intake port on the pump typically has a filter on it to keep dust out of the pump. The pump is then supposed to drive the air it takes in into the tank, and in so doing increases air pressure in the compressor tank.
Different styles of air compressors, reciprocating versus rotary screw for example, accomplish this with different methods, yet they pretty much all do the same thing, suck in air from around the room or through an outside air intake and drive that air into a tank to build up pressure.
When a compressor pump is driven by an properly working motor, and the pump is cycling, why won’t the pressure in the tank build? Next comes things to check.
What to check on an air compressor when the compressor will not build pressure?
The air compressor reed or flapper valves (also known as the intake and pressure valves, or suction & discharge valves) are a common cause of why an air compressor will not build pressure.
The image below shows the valve plates (top of the photo) and reed valves (bottom left of photo) from one smaller air compressor. It also shows the gasket (bottom right in the photo).
Compressor Valve Plate Kit
If the compressor valves or gaskets are what the pump problem is, then it will be necessary to disassemble the pump to repair that problem. The issue is in determining whether it is the valves that is the problem.
One clue to a prospective valve problem is if air is exiting the intake port when the compressor is cycling. Removing the intake filter briefly will help determining this. If air is escaping there it’s a pretty good bet that the intake filter flapper is damaged in some manner.
If it’s the pressure side reed valve, or if the pump head gasket that is creating the problem, that’s harder to diagnose, yet the symptoms are the same. Either no pressure builds in the tank or the tank pressure increases to a certain point and then stays there, regardless of how long the compressor runs. That might even result in the compressor shutting itself down if the motor overheats.
The only real check here is to pull the pump head off and examine what’s what. If a reed valve is damaged, that’s usually pretty obvious. If the gasket its weakened and blowing open at a certain pressure, that’s harder to see.
The solution to the latter is to replace the gasket regardless of whether the reeds are damaged or not.
That’s not all. What else to check when an air compressor will not build pressure?
So, start pulling the pump apart, but wait, before you do that, there are other reasons why an air compressor will not build pressure. Pretty much all of them are found here on this liked page.
Get some help with a compressor that will not build pressure!
You can certainly use the form to ask a question about what to do when your compressor will not build pressure.
Please provide as much information about what your compressor as possible. The make, the model, the age of the compressor, how much it is used, the type of power supply… anything that you can think of that will help us (myself and the many visitors) help you with this air compressor problem.
If you’ve got a suggestion about solving the compressor problem that someone else has posted on this page, please add a comment if you would.
My thanks…
Bill
I have a (Campbell Hausfeld) wl6500 compressor which has served me well. Recently, the pressure wont go above 60psi. It starts no problem the first time in the day, it pumps till 60psi then stops. The pump no longer kicks in when the pressure drops. I have to put the switch in the off position for about a minute and then the motor will start and I again can build up pressure. Thanks for your time. I will need to make a decision as to whether to try and repair or replace. This is a vertical / horizontal model which… Read more »
Had a power outage while it was running. Motor sound changed. When I got power back it runs but won’t build pressure.
I have a craftsman 5 hp 22gal. Model # 919.165220 always has made a lot of noise, but now it only gets up to 40 psi an stops building pressure, motor stays running, air intake is not blowing air out, it has a o-ring gasket that looked to be okay, any suggestions ???
My Campbell Hausfeld compresses will not give any pressure . The gauge only goes 20 than stops . Can you help me please
Senco PC0970 probably 10 years old. Will only blow air out of the cold start valve which is on top of the pump head. Tank check valve is operating properly . I have replaced the cold start valve, no help. It does not blow air out of the air filter.
I have a 6 gallon pancake ridges compressor that runs but won’t build pressure. It’s model # OF60150HB. 150 psi and has a remove tank from service date set for 12/2028. Anyone had this problem with this specific air compressor and if so boy I’d sure like to know what the problem is because I need it for work and it’s not that old. 120v. Please let me know if y’all have any ideas as things are slow right now and would rather salvage this one until things pick up. That’s so much for your time!!
I have a Kobalt 8 gal oil free air compressor model #0300841. fills to 150 PSI. I have had this for just over 5 years purchased new. It started to not fill the tank all the way. It will run normally on start at 0 pressure, fill the tank to less than 100 psi and the motor stalls and then hums until I turn it off. The run capacitor has tested good. The check valve has a plug in the valve at the tank. I pulled that plug with no air leak. I pulled the start capacitor and am going… Read more »
I have a Goodwrench GM 5005 5 HP 25 gal tank air compressor that only builds to 75 psi and does not stop running. I only feel suction through the intake. I am thinking it might be the check valve going into the tank. What do you think? All suggestions appreciated.
1991 VT5588704 hausfeld 230v 5hp 60 gal dead reliable all these years. One day the motor spun but no pressure -found broken belt-purchased new ebay belt claimed for the VT was 49″(returning for correct 50″) but was barely able get it on motor pulley with 1/2″ play. Fired it up with pressure building to 30lbs only then belt started coming off big pulley, ran straight edge small pulley out 1/4″ (I’ve never touched anything less oil change on it since purchase). Tapped/set pulley in towards motor 1/4″, fired it up, belt started coming off again. Removed air filter cap for… Read more »
my hitachi 8gal gass compressor. today a hose blew off this fitting for like 10 seconds before I got it back on and then now I only get 50lbs of pressure. do I start taking the motor appart? or do I just buy a new unloader valve cause is that whats breaks when something like that happens?
Sad to say, I know what you mean.
Happy to say glad you got it sorted.
You’re welcome. And thanks for the update.