Spring pressure control pilots work by sensing and balancing the downstream pressure against a pilot control spring that has been adjusted to a set point. Variations in load or pressure are immediately sensed on the spring pressure pilot diaphragm, which acts to control the position of the main valve, ensuring a constant downstream pressure.

Operation of Spring Pressure Control Pilots:

An external pressure-sensing line is attached to the downstream pressure piping. The downstream pressure is fed back to the underside of the pilot diaphragm, balancing against the spring force in the pilot, causing the pilot valve to move. This movement opens or closes the pilot valve. An open pilot valve allows a flow of steam through the pilot seat and signal line, and on to the underside of the main valve diaphragm. The force from the steam pressure pushes against the main valve spring to control the main valve position. The main valve opens or closes in response to its diaphragm movement.

When downstream pressure rises to the set point of the pressure pilot valve spring, the pilot valve closes, shutting off steam flow to the main valve diaphragm. The steam trapped under the main valve diaphragm bleeds off through an orifice, allowing the main valve to close.

• Accurate control of downstream pressure even with varying upstream pressure or load conditions.
• Spring pressure control pilots may be combined with temperature or solenoid pilots to provide multiple functions.
• Modulates to handle wide range of system loads.
• Used on steam service only.
• Normal failure mode of pilot is open, while failure mode of main valve is closed.

Features of Hoffman Specialty Series SPS Spring Pressure Control Pilots:

• Lightweight, compact size prevents strain on mounting pipes.
• Packless construction eliminates seals that wear out and leak.
• Tight shut-off provided by hardened stainless steel pin and seat.
• Travel stop and cover on diaphragm helps prevent over-pressurization damage.
• Removable strainer helps prevent debris from entering pilot.
• Maximum temperature 450° F (232° C)
• Maximum operating pressure 250 psig (17.3 bar)

Primary Applications of Spring Pressure Control Pilots: