R.F. MacDonald Co. services and sells boilers, pumps, composites and accessories for commercial and industrial applications.


At Fulflo, each relief valve must have flow capacity equal to the pipe lines which it is connected. The sliding piston concept and internal design contours of Fulflo valves provide unique flow and stability characteristics for reliable performance.
Fulflo valves are designed to operate reliably at pressures from 2psi to 1,000psi. The Fulflo valve reduces velocities and minimizes system power loss.

• V-Series
• FV-Series
• OV-Series
• A-Series
• SVB-Series


Pressure Safety Valve (PSV)
  A pressure safety valve actuated by inlet static pressure and characterized by rapid opening or rapid popping   action. This safety valve is tight shut-off and is for safety only. Meets ASME SEC. VIII (Not a Fulflo valve)

Pressure Relief Valve (PRV)
  A pressure relief device designed to re-close and prevent further flow after normal conditions have been   restored. (Fulflo)

Relief Valve (RV)
  A spring loaded pressure relief valve, actuated by the static pressure upstream of the valve. The valve opens   normally in proportion to the increase in pressure over the set pressure. (Fulflo)

Safety Relief Valve (SRV)
  A pressure relief valve characterized by rapid opening or pop-action in direct proportion to the pressure   increase, depending on the application. (Fulflo)

Conventional Safety Relief Valve (CSRV)
  A spring-loaded pressure relief valve whose performance characteristics are directly affected by change in the   backpressure of the valve. (Fulflo)

  The pressure existing at the outlet of a pressure relief valve, due to the pressure in the discharge system. The   pressure can be constant or variable. It is the sum of the superimposed and build-up pressure.

Cracking Pressure
  The pressure which the valve starts to leak flow through the valve, but before the set pressure.

Set Pressure
  The inlet pressure the valve is adjusted to open, maintain or control under service conditions.

Differential Set Pressure
  The pressure differential between the set pressure and constant superimposed backpressure.

Superimposed Backpressure
  The pressure existing at the outlet of the relief device at the time the device is required to operate. It is a result   of pressure in the discharge system coming from another source. This pressure may be constant or variable.

  The pressure increase or accumulation above the set pressure when the valve is discharging flow.

About Fulflo

Fulflo was established in 1912 and is celebrating its 100th anniversary. Located in Blanchester, OH, Fulflo was incorporated in 1933 under its present name and trademark. Patents for the original guided piston, direct acting relief valve were obtained in 1935, coinciding with the onset of fluid power systems. The need for providing large flows without excessive bulk was met by the pilot-valve-control relief valve which was patented in 1943.
Fulflo parts and valves are used in oil and gas refineries, are essential to the military, including ships and aircraft carriers, and amusement roller coaster rides.