How it Works: Pilot Unloader Valve

Instead of one component doing all these things, the piloted unloader valve is a multifunctional part. It can activate an engine idle control and reduce oil consumption by equalizing pressure between your pump’s tanks with checked valves for each cylinder as well! In this article we’ll go over what it does in detail, so you know when yours needs servicing or adjusting on gas engines too!

The maintenance schedule will also include discussion about how to adjust them properly including pictures.


The diagram below shows the components of our most common piloted unloader valve, part number 131B.


pilot air compressor valves


Piloted unloader valves are most commonly used in gas-powered air compressors but can also be found in electric. They work by combining a pilot valve with an additional component, called “unloading.” When running on compressed gasses or electricity for example during operation of your engine at high speeds (such as when starting), this special type will remain closed until pressure reaches its set level where it then opens up and releases excess ventilation needed while pressurized inside cylinder head(s). This keeps any possible escaping fluids from reaching sensitive parts within the machine that could cause damage if spilled onto them; thus preventing accidents!


  1. Make sure the top toggle lever is in the down (horizontal) position.
  2. Loosen locknut (1) by turning counterclockwise several full turns.
  3. Gently turn differential setting (2) clockwise only until the internal rod makes contact with the steel ball inside.
  4. After making contact, turn differential (2) counterclockwise exactly 1/4 turn.
  5. Secure position by tightening lock nut (1) and proceed to top end setting.
pilot valve


  1. For the standard top-end setting of 135 PSI, adjust differential (4) so that 3 threads show above locknut (3).
  2. Loosen locknut (3) by turning counterclockwise several turns.
  3. Turning (4) clockwise to increase the top end pressure setting or counterclockwise to decrease.
  4. Begin at a low setting by turning counterclockwise one full turn. Proceed to fine tuning instructions.


  1. Start the engine/motor and observe the tank pressure gauge. As tank pressure approaches 135 PSI, the unloader valve should begin unloading at the felt muffler and cause the gas engine to slow down to idle speed.
  2. If the pilot valve does not unload as tank pressure approaches 135 PSI, slowly turn top end setting (4) counterclockwise until the pilot starts to unload prematurely (at 105 PSI).
  3. Turn top end setting (4) clockwise in 1/4 turn increments, tap down on the internal rod at toggle and repeat until desired top end setting is reached.
  4. If the pilot valve begins to rifle (sputter), fine tune differential setting (2) 1/16 turn in either direction until rifling stops.
  5. After fine tuning, secure setting by tightening locknuts (1 & 3) while holding settings (2 & 4).

For air compressor maintenance, contact Pacific Air Compressors in Portland, Oregon. We are a full-service air system installation and maintenance shop. Contact us today at (503)674-2744 or online to schedule a service appointment.


Dear valued customers,

We normally keep all our inventory in stock. However, due to backorders from many of our vendors and parts shortages, some items that we have listed may not be in stock or could have a long lead time although they show as available on our store. If you need your items right away, please call or e-mail to ensure availability.