Pilot Operated Pressure Relief Valve - Axelson

An Axelson pilot operated pressure safety relief valve is designed to be used on oil and gas production systems, compressor stations, gas transmission (pipeline) facilities, storage systems and in all gas processing plants; whenever there is a need to exhaust the overpressure volume of gas, vapor and/or liquid.

What's the big difference?  The pilot operated valve has unique design features that make this pressure relief valve better than the spring loaded valve.

pilot operated relief valve by axelson




Axelson Pilot Operated  Relief Valves include the following models -

  • Type HF - a full lift, pop-action valve with a fixed (5% to 7%) blowdown using a single non-flowing pilot. Applications for this design include gas and/or vapor service. It is available in sizes ranging from 1" to 8" with pressures from 25 psig up to 6000 psig.

  • Type HD - a full lift, pop-action valve with an adjustable blowdown pilot. Applications include gas and/or vapor service. It is available in sizes1" through 8" with pressures ranging from 200 psig up to 6000 psig.

  • Type GD - This valve has the same operational characteristics of the Type HD, however the body of the valve is designed to provide a vertical straight through discharge. The GD valve is available in 6" and 8" sizes only with operating pressures ranging from 200 psig to 1480 psig.

  • Type HL - a modulating opening valve with a fixed (2% - 7%) blowdown using a single non-flowing pilot. The valve is designed for gas, vapor and/or liquid service. Size offerings are 1" through 8" with operating pressures from 25 psig to 1480 psig.


FULL FLOW CAPACITY - In addition to the various API orifice sizes, Axelson pilot operated pressure relief valves offer FULL inlet size flow capacity through the valve. Many times this allows us to recommend smaller size valves at a cost savings to the customer.

BACK-FLOW PROTECTION -  The unique Axelson split piston (optional) is designed to eliminate the effect of pressure in the discharge system back-flowing into a relief valve on installations where several valves discharge into a common manifold.

SIMPLE MAINTENANCE - All maintenance, including changing the valve seat, can be performed using ordinary hand tools without removing the valve from the installation.

NON-FLOWING PILOTS - Axelson non-flowing pilots reduce the problems of "freeze-up" caused by the pressure drop through the flowing type pilots.

PRECISION OPERATION - The pilots of Axelson relief valves can be set externally with exactness and will maintain accuracy of set pressure and reset pressure over an unlimited number of cycles.





Contact our parts department with the manufacturer's name, model number and serial number of your relief valves. This information can be found on the nameplate. We will see if parts are available or if the valve is obsolete and quote the proper replacement. or Send Email

TOLL FREE 1-877-244-4883


  1. Type of Valve

  2. Inlet pipe size of valve

  3. Rating of inlet and outlet flanges:  RF, RTJ or Other

  4. Type of seal (hard or soft)

  5. Set Pressure (pressure at which the valve will open).

  6. Blowdown Pressure (pressure at which the valve will open). If not specified, valve will be set with minimum blowdown).

  7. Manual Blowdown valve (optional)

  8. In-service test unit (optional).

  9. Construction and trim (unless otherwise specified, standard construction and trim will be furnished).

  10. Characteristics of gas being controlled.

  11. Specific gravity or molecular weight of gas.

  12. Temperature of gas

  13. Back pressure (pressure on outlet).

  14. Specify any special markings or identification




Axelson pilot operated relief valves operate on the principal of unequal areas exposed to the same pressure. When the relief valve is closed, system pressure is pushing upwards against the piston seat seal on an area equal to the inside diameter of the seat. Simultaneously, the same system pressure, passing through the pilot, is exerting a downward force on the piston acting on an area approximately 50% greater than the inside diameter of the seat. The resulting differential force holds the valve tightly closed. As the system reaches the discharge set pressure of the valve, the tighter the piston seal becomes until the time the system pressure reaches the relief valve discharge set pressure. At that moment, and not before, the pilot cuts off the supply of system pressure to the top of the piston and vents that system pressure which is located in the chamber above the piston of the relief valve. At the same instant, the relief valve pops open. When the predetermined blowdown pressure is reached (either fixed or adjustable), the pilot shuts-off the exhaust and re-opens flow of system pressure to the top of the piston effectively closing the relief valve. 


Over the years, P. C. McKenzie Company has literally sold thousands of Axelson Pilot Operated Relief Valves. We receive calls daily requesting replacement parts to keep these valves in operation. Normally, replacement parts are not a problem and we can respond quickly to our customers. However, many of the older valve models, the D-3 and F that carry the Garrett or USI name, have become increasingly difficult to source parts for. 

Most of these valves date prior to 1960, when three USI manufacturing concerns merged under the name of Axelson, Inc.

We will try to supply parts for the older valves but suggest the implementation of a valve replacement program that focuses on these obsolete valves. This would allow customers upgrade to current technology in the form of the Axelson HF, HD and HL valves. It also eliminates the problems and frustrations of trying to locate parts that are no longer obtainable.

P.C. McKenzie Company
P.O. Box 112638
Pittsburgh, PA 15241
Fax: 412-257-8890
Phone: 412-257-8866
P.C. McKenzie Company
1365 McLaughlin Run Road
Pittsburgh, PA 15241


 Pilot Operated Pressure Relief Valve - Axelson Safety Relief Valve