A leaking air compressor, not building pressure can be frustrating and compromise the job at hand. Whether your air compressor is not building enough pressure or your air compressor is leaking pressure once built-up, you can be sure there is something wrong, somewhere.

Now to find it….

Before you begin tearing anything apart, it’s always a good idea to perform some basic checks.

You’ll want to inspect the regulator knob that sets the pressure to make sure it works correctly. Give it a turn in its farthest direction both ways and ensure it’s moving smoothly. Check all air fittings that are visible for a tight connection.

Spraying soapy water and turning the air compressor on while checking the fittings will help as the soap in the water will start to bubble if air is escaping. NOTE: Do not spray water on any electrical fittings.

Make sure all your settings are correct and that it’s plugged into a proper power source that supplies the recommended voltage. After performing some initial test, if you still don’t find the issue, it’s time to break out the tools and start taking things apart. An air compressor that is leaking pressure can be from multiple different problems but commonly is either from:

  • Worn or Damaged Reed Valve
  • Damaged Piston Rings
  • Leaking Drain Valve
  • Faulty Check Valve

All of these problems are fairly cheap to fix and only need an afternoon and some basic tools to perform the maintenance. It’s recommended to purchase replacement parts from the manufacturer. Companies such as  Campbell Hausfeld have a wide range of replacement parts available online.

Let’s begin!

4 Common Air Compressor Repairs

REPLACING AIR COMPRESSOR REED VALVE / GASKET

Unscrew the air filter and remove any shrouds that may be covering the motor, and place it to the side. Now that you can clearly see the components that are hidden under the shroud, it’s a good time to check for any loose connections in the wiring and air fittings.  If everything looks good, you can move to the next parts to disconnect.

removing-head-bolt

Removing the 4 Head Bolts

Unscrew the brass nut that holds the exhaust tube onto the cylinder head.

  • Remove the 4 long head bolts that are located on the top of the cylinder head.

Now that you have your headcover removed depending on the model and manufacturer you’ll see a valve retainer that sits on top of the reed valve.

  • Unscrew the two screws that hold down the valve retainer and place it to the side.
Removing-reed-valve

Removing Valve Retainer & Reed Valve

Inspect the “U” shaped reed valve that’s located under the valve retainer for any cracks or signs of wear.

You want the reed valve to be uniform in size without abnormal wear.

Any signs of wear or damage and the reed valve should be replaced.

  • Next, take off the aluminum valve plate the reed valve sits on and inspect as well.

It’s not as common for the aluminum valve plate to get damaged but nevertheless, you should always closely inspect for any wear. Underneath the valve plate is a gasket, more than not the gasket will be shredded and damaged and need to be replaced. The gasket is a common reason for air compressors to leak pressure.

Gasket-Exhaust-Reed-Valve

Gasket & Exhaust Reed Valve

When the gasket is not seated correctly or is damaged pressure will escape from the cylinder head.

Lastly, you’ll find the exhaust reed valve in the shape of a tongue. The exhaust reed valve sits across the cylinder. Check for any damage or worn out spots and replace if necessary.

If you find that the components of the reed valve or gasket were the culprit, replace with the parts needed and put it all back together, follow along with your user manual if needed.

NOTE: It’s important the 2 small reed valve pins do not get lost.


REPLACING AIR COMPRESSOR PISTON RINGS

If your air compressor is leaking pressure, another culprit could be your piston rings. Commonly the thin V-shaped ring that goes around them to produce a seal will wear down or become bent.

Now that everything is taken apart down to the cylinder head you can do a basic check to see if pressure is being built from the piston.

Firmly place your hand over the cylinder opening to block air from releasing and manually spin the crank to have the piston do a couple of revolutions. You’re determining if the piston is capable of producing pressure.

If you find that the palm of your hand is being slightly sucked in or pushed away the piston is making good pressure, if you don’t feel anything then more than likely your piston rings are shot.

Piston rings create a seal inside the cylinder and help create and hold pressure in the combustion area.

To replace the piston rings remove the top cylinder body that encases the piston head. The cylinder body may or may not be held on by bolts, most models will not be held on by anything as the 4 main head bolts go down and through the cylinder body to retain it.

damaged-piston-ring

Damaged Piston Ring

The piston, depending on the make, model and size of the compressor will either have one or multiple rings. Check and examine the rings for any damage or wear to one side.

The most common style ring is going to be a V-shaped copper ring that goes around the piston head. The V-shape will eventually wear down and become flat against the piston and not hold any air pressure.

For a free fix, you can take a pair of pliers and bend the ring back into its V-shape and reinsert the cylinder cover and test. We’ve found that this can produce a good fix, but it’s recommended to just replace the entire ring as cheap as they are.


AIR COMPRESSOR DRAIN VALVE LEAKING PRESSURE

Another common malfunction that can result in loss of pressure, specifically, loss of pressure that has been built in the tank can be the result of a faulty or damaged drain valve. The purpose of the drain valve is to release moisture that accumulates at the bottom of the air compressor while in use.

When the drain valve gets damaged it can then start to release pressure from the tank.

Luckily fixing a damaged drain valve is a quick and cheap procedure. The drain valve is commonly located on the underside of the air compressor or on the side near the bottom.

With the air compressor off and unplugged, remove the drain valve.

Inspect for any damage, specifically looking at the o-ring.

The O-ring is a gasket that holds pressure inside the tank. When the O-ring gets damaged from regular wear and tear it will fail to withhold pressure and the result is a leaking tank.

To fix the drain valve you can either order a new OEM part from your manufacturer or you can simply replace the o-ring with a new one. After you replaced your new o-ring or drain valve simply screw it back in and your set. Turn the unit back on and bring it up to it’s max operating pressure. Keep an eye on the gauge to see if the air compressor is leaking pressure.

Problem solved.

NOTE: When replacing the O-ring, ensure that you are replacing it with an identical new o-ring. An O-ring that’s not the proper size or thickness will not seat properly and will continue to leak. Refer back to your owner’s manual for size specifications.


REPLACING AIR COMPRESSOR CHECK VALVE 

Check valves are another culprit when an air compressor is leaking pressure or having difficulty reaching max pressure. A check valve stops the compressed air in the tank from returning back to the pump and escaping through the outlet line to the pressure switch.

The check valve is located on the top of the tank and has a brass fitting that screws directly into the tank with two external airlines that run into it. One line is your main pressure intake and the other is your line that goes to the unloader and pressure switch.

When a check valve malfunctions it will allow air to escape through the unloader that’s located under the pressure switch or it will allow air to return to the pump causing it to not start back up again.

Perform a quick diagnosis by spraying soapy water on the check valve and unloader, if bubbles start forming, you have a leak. You can also manually feel with your hand for any air being released.

If air is escaping, replace the check valve.

Replacing the check valve is a quick procedure. Start by unscrewing the pressure intake line and the line to the pressure switch, then unscrew the check valve from the tank. Replace with a new OEM check valve and screw back on the two lines that were disconnected.

Start the compressor after completed and perform a quick check to ensure no air is escaping from the check valve or from the unloader.