Safe practices when working around relief valves.
- Wearing safety glasses, full face shield or both when working with relief valves.
- Having breathing apparatus available in case of emergency when working with relief valves.
- Use valve handle “lock out-tag out” procedures, to safely service relief valves in system.
- Knowing the location of and having access to safety showers, bubbler fountains, water hoses, exits, and first-aid equipment when working with relief valves on ammonia systems.
- Relief valves must be replaced every 5 years whether they have blown or not.
- If a relief valve blows it must be replaced. It does not matter if the relief valve reseats. Once a relief blows the relief valve blow setpoint can change causing:
Unexpected loss of refrigerant due to:
Seeping through the relief valve because valve did not fully reseat
Relief setpoint typically shifts to a lower setting, therefore valve could release or simmer at a lower pressure.
Inadequate protection of pressure vessel due to setpoint change. Typically the setpoint shifts low but not always.
Reliability. In time of emergency, you need to be sure your relief valve will operate properly.
Proper sizing of relief valves:
The minimum required discharge capacity of the pressure relief device for each pressure vessel shall be determined by the following:
C = ƒDL Where
C = minimum required discharge capacity of the relief device in pounds of air per minute.
D = outside diameter of vessel in feet.
L = Length of vessel in feet.
ƒ = factor dependent upon type of refrigerant. (ammonia (R-717) = .5) and (freon 22 (R-22) = 1.6)
NOTE: When combustible materials are used within 20 ft. of a pressure vessel, multiply the value of ƒ by 2.5
A number of guidelines for pressure relief Valve service and maintenance exist to ensure that pressure relief valves work correctly. Some tips in brief include the following.
- Atmospheric discharge lines should have adequate rain and moisture protection, and be capable of draining condensate and rainwater.
- Check to make sure the relief valve exit stays unobstructed.
- Routine maintenance of pressure relief valves should include visual inspection of the relief valve and discharge piping every six months.
- Relief valves should be replaced at intervals of no longer than five years of service.
- Maintain pressure relief valve data in an inventory record, including location, size, set pressure, manufacturer, capacity, date installed, dates of inspections, and latest date for replacement.
- Pressure relief valves should not be discharged during installation or start-up.
- Replace pressure relief valves once they have discharged.
Hansen’s Technologies Additional Tips
- Never expose your face or body to a connected relief valve exit.
- Avoid trapped ice build up between valves and other equipment.
- Reduce inlet pressure to zero before attempting to install or replace any pressure relief valve. Preferably, and as required by most codes, use a three-way dual shut-oft valve to isolate relief valves for individual inspection or replacement.
- Check the nameplate or installation date tag to be sure the time-in-service does not exceed five years.
- Look for corrosion and leaks. If there is any doubt about the internal condition of a relief valve, remove and inspect it internally. If there is any question about a valve’s condition, replace it.