5 Reasons Why Your Air Compressor Is Slow to Build Pressure (And How to Fix it)

Compressors are incredibly useful for a wide range of tasks around the house and the shop. But, like any other system, there are certain things that can happen to your compressor that can cause it to malfunction. A common issue is that the compressor is slow to build pressure. In some cases, the compressor keeps running but never gets up to adequate pressure for your needs. Other times, the compressor is just slow to build. Luckily, I’ve got you covered with 5 reasons why your air compressor is slow to build pressure — and how to fix them. 

A slow-building air compressor can be frustrating, to say the least. But more than this, it can actually damage the compressor if you continue to run it without addressing the issue. Most commonly, this issue causes the motor to overheat, which is never a good thing, even with the thermal cutoff that helps protect the motor when it gets too hot. 

With that in mind, let’s look at the five reasons this could be happening to your compressor. 

1. Compressor Pressure Valve Failing

If a compressor’s pressure valves (sometimes called flappers or reeds on reciprocating air compressors) are failing, the pressure won’t build up in the tank, even though the motor continues to run. 

Or, sometimes, this problem only becomes apparent when the tank builds up a certain amount of pressure, then the motor continues to run without additional pressure buildup. 

If the problem is the pressure valve or switch, then air will be pulled in on the compression movement, but the failing valve or switch will allow that air to escape when the compressor goes to pull additional air in. Essentially, this back-and-forth movement of air will prevent pressure buildup. 

To diagnose this issue, turn the compressor off and drain the tank. Pull the line out of the piston head. Start the compressor and see if you can block the airflow from the pressure port using an object (do not use a hand or finger or any other body part). If you can easily block the flow, it’s likely the pump pressure valve that’s at fault. 

How to Fix a Compressor Pressure Valve

Fixing this issue generally means rebuilding or replacing the pump, which requires some expertise. It may not be the most cost-effective option, depending on how much you paid for your compressor and how long it has been running. 

2. Compressor Intake Valve Failure

A failure of the intake valve causes a similar problem to that of a failing flapper or pump pressure valve. When an intake valve is going bad, the compressor will take air in, but the air will escape via the bad valve before it has a chance to be compressed. 

Some air may make it into the tank while the rest escapes through the intake valve. This is why you may see some pressure buildup, which may stop at a certain point. 

You can diagnose this problem by removing the air filter to check the intake port. Once you’ve removed the filter housing and the compressor is running, you can very carefully place a hand near the intake. If you feel that the intake is sucking air in, it’s not likely the valves that are causing your issue. However, if you feel air coming out of the port, it most likely is the pump pressure valves that are at fault. 

How to Fix a Compressor Intake Valve

Fixing this problem generally requires replacement of the valve plate on smaller air compressors. Some compressors allow you to replace only the valves, but this will depend on your compressor. The problem here is that it’s often hard to find new valve plates for smaller compressors. But it’s worth checking with an online search using your compressor’s make and model. 

3. Piston Seal Failure

An air compressor operates with a pump, which pulls air into the compressor. These pumps have piston rings that act as seals and prevent oil from too much oil getting into the compressor’s cylinders. 

When one or more of these piston seals fail, it becomes harder for the pump to maintain pressure, which is essential for optimal compression. This loss, in turn, makes it harder for the compressor to compress air efficiently, which can prevent the buildup of air pressure. 

To troubleshoot this issue, find the oil intake tube (if your compressor has one) and see if there’s any oil or air coming out of it. A steady flow of air coming out the oil fill tube usually means a failing piston ring. 

How to Fix a Piston Seal Failure

The best thing to do if the piston seals are failing is to rebuild or replace the pump. One option is to take apart the pump and replace the rings. If this is the way you go, it’s a good idea to replace other components while you’re at it, like the valve plate and the gasket kit. 

4. Gasket Failure

Air compressors have valve plates that contain the intake and pressure valves. These valves are separated by a gasket. If this gasket fails, everything else on the compressor will work as it’s supposed to, but the air will flow through the failed gasket, which will prevent the pressure from building up. 

This can be hard to identify because it often happens only when the pressure reaches a certain point. That pressure can then be too much for the faulty gasket, which then begins to leak. 

Unfortunately, taking the pump apart is likely to damage the gasket anyway, so a visual inspection won’t tell you much. So if you do take the pump apart, replace the gasket, even if you aren’t sure that’s the problem. 

How to Fix a Gasket Failure

As mentioned above, gasket failure can be hard to diagnose. Your best bet is to replace the gasket, and any other pump components that may be at fault while you’re at it. However, depending on the cost of your compressor, this repair may be prohibitively expensive. You may just want to purchase a new compressor. 

5. Broken Tank Check Valve

An air compressor’s check valve is usually a simple component that works to prevent air backflow from the tank to the line. As the air compressor works, the air travels through the pump head and the line and into the tank. The check valve is located between the line and the tank. While the air is traveling through, a simple flap in the check valve stays open, and when the compressor turns off, the flap should close to prevent air from flowing out. 

So if the check valve is broken, it can allow air to flow out of the tank. Or it can prevent the flow of air into the tank in the first place. 

The best way to diagnose this issue is by checking the unloader valve when the compressor is not running. If there’s constant air leaking out of the unloader valve, it usually means that the check valve is faulty. 

How to Fix a Broken Tank Check Valve

A broken tank check valve should be replaced to remedy the issue. This is generally pretty easy to do and only includes the cost of the replacement check valve. 

How Long Does it Take for an Air Compressor to Fill Up?

It can be hard to know whether your compressor is taking too long to fill up, especially if the compressor is new to you. There are many factors that determine how fast your compressor should fill, but here are some common fill times for compressors of different sizes. These are all approximate, so keep that in mind as you read. 

  • Compressors 10 Gallons and Under – Shouldn’t take more than 5-10 minutes to fill from zero to 125 – 150 psi. 
  • Compressors over 10 gallons – No longer than 20 minutes.

These numbers are at the outside and indicative of the lowest common denominator. Many air compressors will fill much faster than this. Consult your owner’s manual for information on the correct fill time for your compressor. 

Conclusion

It’s frustrating to have a malfunctioning air compressor. If it can’t build pressure, you won’t be able to use it for much. And most of the issues that cause this can be found in the pump area, which houses the valves, seals, and gaskets that are most likely to cause the compressor to have trouble building pressure. 

Depending on the compressor, it may not be worth it to try and repair the issue yourself, unless you know a little bit about how the compressor works or you want to learn. Taking the compressor to a repair shop can often cost as much as a new compressor, depending on the issue. Still, it’s helpful to be able to diagnose the issue to give you an idea of how to go about fixing it.

Justin

Justin is a full-time blogger with a passion for anything DIY. When he's not hanging out with his wife and son, you can find him putting the finishing touches on yet another home project he's taken on. He's also the creator of AllAboutAirCompressors.com.