PORV are also called POSV (Pilot Operated Safety Valve), POPRV (Pilot Operated Pressure Relief Valve), or POSRV (Pilot Operated Safety Relief Valve), depending on the manufacturer and the application. Technically POPRV is the most generic term, but PORV is often used generically (as in this article) even though it should refer to valves in liquid service.

The Motherwell Tank Protection range are pressure only valves. All combinations are available in a range of sizes from 50mm (2″) to 300mm (12″) and with flanged outlets or vented to atmosphere.

• provide accurate pressure relief when operating near to the design pressure of the tank
• overcome the problems of back pressure generated at the discharge of the valve due to pipework, scrubbers etc.

The valves are available in a range of sizes and flange configurations and are certified compliant with European ATEX and PED directives where applicable

The Pilot-operated Relief Valves features can be summarised below:

Advantages:

• Smaller package on the larger pipe sizes.
• More options for control.
• Seals more tightly as the system pressure approaches but does not reach set pressure.
• Control pilot can be mounted remotely.
• Some designs allow for changes in orifice size within the main valve.

Disadvantages:

• More complex.
• More expensive at smaller sizes (starts to even out as pipe size increases).
• Small parts in pilot valve are sensitive to contaminant particles