Pilot Operated Safety Relief Valve background
Axelson was the first company to design and manufacture a relief valve operated by a pilot rather than a spring. A pilot operated relief valve, according to the 1992 ASME Code Section VIII, Division 1, Section UG-126, is a pressure relief valve in which the major relieving device is combined with, and is controlled by, a self-actuated auxiliary pressure relief valve.
According to ASME Section VIII, Division 1, Section UG-126, a pilot operated pressure relief valve is one in which the major relieving device is combined with, and is controlled by, a self-actuated auxiliary pressure relief valve. Axelson offers a number of valve configurations to accommodate a number of customer requirements.
The Axelson Design
Axelson pilot operated relief valves are engineered to relieve, blowdown and reset within extremely close limits. The controls can be set externally with great accuracy and will maintain that precision of set pressure and reset pressure over an unlimited number of cycles. The Axelson split piston design eliminates the effect of backpressure. The safety valves require no “per cent accumulation” or overpressure eliminating “simmer” at the seat, thus reducing maintenance.
Safety Valve Definitions
- Safety Valve – gas or steam applications, characterized by rapid, full opening or snap (pop) action.
- Relief Valve – liquid applications, opens in proportion to the increase of system pressure over the opening pressure.
- Safety relief valve – pressure relieving device suitable for use as a safety valve or relief valve depending on its application.
- Conventional Valve – spring loaded valve directly affected by back pressure.
- Pilot operated valve – Pilot controls the opening and closing of the valve.
- Overpressure – increase over set pressure of a relief device.
- Blowdown – difference between set pressure and re-seating pressure of a relief valve.
- Back pressure – the pressure exising at the outlet of the valve.