How to Replace Reed Valves in an Air Compressor? | Head Fix

Replace reed valves by disconnecting power, venting all pressure, removing the head, fitting new reeds and gaskets, and torquing bolts to spec.

For the full breakdown, see our best Air Compressor Valves guide.

It sits under the pump head and acts as a one-way flap, so when it stops seating, compression suffers. You’ll notice it as longer fill times, weak flow at the tool, or air pulsing back out of the intake filter.

The repair is eight steps: kill the power, vent every tank and line, pull the head, swap the reed plates and gaskets in the exact orientation they came out, then reassemble and torque the head bolts to the manufacturer’s number.

Before You Start: Power, Pressure, And The Right Parts

Begin with the pump disconnected from electrical power and every pressure vessel and air line vented to zero. Midmark’s documentation for its P52 and P72 compressor pumps covers both points: the P52/P72 reed valve replacement procedure says to disconnect the pump at the electrical power and vent the air lines to remove pressure before any disassembly starts.

Three things worth settling before you touch a bolt:

• Vent everything. Open the tank drain and any line valves, then wait for the gauges to read zero. Opening the head with stored pressure behind it can throw parts across the shop.
• Match the kit to the pump. Reed valves are not universal. Kits are listed for specific pumps — an OEM reed valve kit for DeVilbiss twin-cylinder oil-lubricated pump models, for instance, and a Central Pneumatic rebuild kit for specific Harbor Freight compressors. Order by the model number stamped on the pump’s nameplate.
• Plan on new gaskets and seals. Replacement procedures call for fresh gaskets during reassembly, and reusing old ones is a common leak source.

Replacing Reed Valves In A Compressor Pump: The Full Sequence

The job is head off, swap, head on — eight steps that cover most pumps, with bolt torque as the step that decides whether the head seals. Set the old bolts aside in order so each one goes back into the same hole.

1. Disconnect power and relieve pressure. Unplug the unit or flip the breaker at the panel, then drain the tank and open the lines until every gauge reads zero.
2. Remove the head or valve plate assembly. The reeds sit under the head, so the entire casting has to come off to reach them.
3. Note the orientation before lifting anything out. Record which valve plate is which, which way each reed faces, and where every gasket, seal, and O-ring sits. A phone photo works well for this.
4. Remove the old reeds and gaskets. Lift out the reed plates and reeds, then inspect them for warping, cracks, pitting, or broken tabs. Pitted, cracked, or broken valves go in the trash, not back in the pump.
5. Clean the mating surfaces. Scrape off old gasket material and wipe both faces down so no debris remains — a stray chunk is enough to hold a reed off its seat.
6. Install the new reeds and gaskets in the recorded order. Orientation is the step that fails most often. SENCO’s enhanced valve-plate instructions place the first reed valve in the thick lower plate and the second in the thinner upper plate, oriented toward the motor and cooling fan as shown in its drawings. SENCO also notes that no gasket goes between the valve plates; the seal belongs at the head/cylinder interface.
7. Reassemble the head. Seat the plates and head, then run the bolts down in a crossing pattern so the gaskets compress evenly.
8. Torque to spec and leak-test. Tighten the head bolts to the torque your manual lists, then bring the compressor up to pressure.

What Torque Do Compressor Head Bolts Need?

Torque is model-specific, so the value in your service manual beats any generic number. The spread between documented procedures shows why: