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Safety Valve vs. Relief Valve
4

Safety Valve vs. Relief Valve

Safety Valve vs. Relief Valve

(OP)
I vaguely recall reading that there was a difference (by definition) between a "safety valve" and a "relief valve".  I think most people use these terms interchangeably, but is there a difference?

Is one used for liquid service and the other for gas/vapor service?

RE: Safety Valve vs. Relief Valve

Relief valve:  That part of your body that keeps the feces inside.

Safety valve:  That part of the toilet that gets the feces out of the house before it runs out over the floor.

RE: Safety Valve vs. Relief Valve

My guess is that a relief valve would be any valve that opens in response to a specific differential pressure and that a safety valve is a special case of a relief valve that must meet the requirements of a code or regulation.

RE: Safety Valve vs. Relief Valve

Similar idea to MintJulep, a Relief valve is an operational valve that is designed to open/close at lower pressure/vaccume, a Safety valve is to protect the equipment in exceptional circumstance.

Mark Hutton


RE: Safety Valve vs. Relief Valve

3
hmmm... there are also expressions like Safety Relief Valves and Safety and Relief Valves.

Definitions extracted from the Pressure Relief Valve Handbook available from the link below are,

Safety Valve

A safety valve is a pressure relief vavle actuated by inlet static pressure and characterized by rapid opening or pop action. (It is normally used for steam and air services)

Relief Valve

A relief valve is a pressure relief device actuated by inlet static pressure having a gradual lift generally proportional to the increase in pressure over opening pressure. It may be provided with an enclosure spring housing suitable for closed discharge system application and is primarily used for liquid service.

Safety Relief Valve (Interesting!)

A safety relief valve is a pressure relief valve characterized by rapid opening or pop action, or by opening in proportion to the increase in pressure over the opening pressure, depending on the application and may be used either for liquid or compressible fluid.

http://www.tycovalves-na.com/ld/CROMC-0296-US.pdf

Moral of the story(IMHO): Confuse others when you are confused.

Regards,


RE: Safety Valve vs. Relief Valve

I feel soo relieved - and safe - after having read quark's definitions. Star for you!

Now for a similar question: What is the difference between an Emergency Stop and a Rapid Stop? (Hint: there are several different Emergency Stops, but I have a problem deciding which is what).

Gunnar Englund
www.gke.org

RE: Safety Valve vs. Relief Valve

The actual devices are (or can be) identical.

It's a question of application. A relief valve will, in many circuits, open occasionally, continually, or possibly continuously. It's a working part of the circuit.

The safety valve application should never open in normal use (apart from test). It's the final safeguard that stops things blowing apart and hurting people. If a safety valve keeps opening, something's wrong.

Maybe this should be in the 'Piping & Fluid Mechanics' forum - it's a valid technical thread.

Cheers - John

RE: Safety Valve vs. Relief Valve

Skogs,

In the world of rail airbrakes, where I actually have some standing, the emergency brake system bypasses most of the control features and devices from the brake system and uses only highly reliable, and mostly fail-safe components.  The intent is to have a system with a high probability of applying the brakes when requested.  While the brake force may be higher than a normal brake application that is secondary to the reliability need.

RE: Safety Valve vs. Relief Valve

skogsgurra,

   A rapid stop is what happens if you did not notice you should have done an emergency stop.  :)

                      JHG

RE: Safety Valve vs. Relief Valve

In machine tools, the E-stop may go around the NC control, and directly de-energise the motors and engage some form of braking. That may be electric-release/spring-apply brakes, a shunt across the motor, or whatever.
The idea is: halt all moving parts, regardless of what the control system may think it is doing.

Jay Maechtlen
http://home.covad.net/~jmaechtlen/

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