What is the difference between a safety valve and a relief valve?
Short answer
| Aspect | Safety Valve | Relief Valve |
|---|---|---|
| Fluid | Compressible (steam, air, gas) | Incompressible (liquids) |
| Opening | Full-lift (pop action) | Proportional |
| Use | Boilers, air receivers, steam systems | Fuel oil, lube oil, hydraulic systems |
- Purpose: Both prevent overpressure in shipboard systems
- Fluid type: Safety valve for compressible fluids (steam, air, gas); relief valve for incompressible fluids (liquids)
- Opening action: Safety valve full-lift (pop action); relief valve proportional opening
- Typical use: Safety valve on boilers, air receivers; relief valve on fuel oil, lube oil, hydraulic systems
- Governing instruments: SOLAS (pressure relief obligations), IACS UR Z25 (pressure relief valves)
Full answer
The full answer explains each point step by step, with the regulations and figures behind it and the discussion from other candidates. It is in the MEO Class II section of the Marine One forum, open to members enrolled for the MEO Class II exam.