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Although safety valves are by far the most common devices used for plant protection in steam systems, there are several other devices available to protect plant from overpressure conditions.
Whilst some of them can be used in place of a safety valve, most have their own unique applications and indeed some devices, such as the bursting disc, may be used to complement the safety valve.
• Weighted pallet - This is the simplest type of overpressure protection device, and it is on lowpressure tanks and condensers, for pressure relief, vacuum relief or both.
A weight is applied to the top of a disc, keeping it closed until the pressure acting on the underside of the pallet equals the weight. Due to the large weights required to keep a pallet closed, this type of valve is designed for low pressure applications below 0.1 bar. For higher set pressures,
the weight required would be prohibitive and dangerous if oscillation of the pallet occurred at valve opening.
• Counterweight safety valve - Although these have been largely superseded by spring-loaded safety valves, they are still sometimes used for low-pressure applications. The closing force of the safety valve is provided by a weight rather than a spring. As the closing force is provided by a weight, it will remain constant and once the set pressure is reached, the safety valve will open fully.
Spirax Sarco Limited
Tel: +44 (0) 1242 521361
Fax: +44 (0) 1242 573342