A safety relief device prevents the pressure of refrigerant from rising above a safe limit. They can be used with a storage vessel, or with a system component such as a receiver or water-cooled condenser. They function when operating or high-limit controls fail, and when the vessel is exposed to excessive heat.
The pressure relief valve is a pressure-actuated valve held closed by a spring or other means. It automatically relieves at a predetermined pressure. The pressure relief valve is adjustable- but, once set, the valve is sealed to prevent tampering. It is important that relief settings not be adjusted in the field. If the seal is broken, the valve should be replaced with a correctly adjusted and sealed valve. The setting should be 25% above maximum system operating pressure (MSOP). This safety factor gives enough spring force on the valve seat to keep a tight seal, yet allows for other factors that cause settings to vary.
An excerpt from Technical Institute Manual #2, as part of the Certificate Member Exam preparation, for the Refrigeration Service Engineers Society. Visit the online store for more information from the HVAC/R Training Authority.