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BIRKETT Modulating Pilot Operated Safety Relief Valve

This reduces mechanical and thermal stresses at the seat, reduces inlet pressure losses, increases the discharge co-efficient and allows for lower specification body materials on corrosive duties.

Pilot valves will maintain full lift against high levels of back pressure, unlike spring loaded valves, which would need either differential setting or the addition of balanced bellows. The system operating pressure can be much closer to the set pressure on a pilot operated valve than with a standard spring loaded safety relief valve. System pressures in the region of 95% to 98% of set pressure are often accommodated.

As modulating pilots are of the non-flowing design, the risk of freezing due to pressure drops in the flowing medium is removed. Additionally, dirt particles are not transported to the pilot as the medium is static. This improves life in service and ensures trouble free operation. The valves are fitted with integral filters, and all process wetted parts (pilots, domes, tubes and fittings, pistons and nozzles) are made from stainless steel as a minimum. This reduces the risk of oxides contaminating seals and prolongs their life in service.

Type 4 & 8 Birkett Pilots are fully modulating. They are intended for use with gas, liquid and mixed phase fluids. Both types are non-flowing designs.
Modulating pilots are essentially diaphragm or piston operated safety valves with a feedback piston for fine control of the pressure in the dome. The main valve is opened in a controlled manner: the over pressure is constantly monitored and the opening of the main valve is proportionate to the overpressure.

The pilot controls the dome pressure: when the set pressure is reached, the main valve opens in proportion to the system pressure rise. The main valve will maintain a lift necessary to discharge the system flow. As the system pressure increases, the main valve lift will change to accommodate the new flow condition. As the system pressure falls, the main valve will begin to close, finally closing at a pressure just below the set pressure.

This valve is suitable for extremely high capacity duties. It achieves maximum discharge capacities by having a full bore 8” inlet with an available discharge area of 44.178 in² and two opposing 10” outlets, which can assist with reaction force problems.

All modulating pilots (Types 4 + 8) should be fitted with a back flow preventer.
A selection of accessories is available to suit system requirements. These include:  

• External Supply Filter
• Remote Pressure Sensing
• Heating or Cooling Coils
• Field Test Connector
• Remote Uploader
• Dual Pilots