What is the difference between safety valve and relief valve

Safety Valve - generally it is used for gas or steam applications, and it is characterize by rapid, full opening action.
Relief Valve - liquid applications, opens in proportion to the increase of system pressure over the opening pressure

I hope you can understand now.

I agreee with tmech03's assessment. Also:

Safety valves are often rated by a standards agency. They are designed to open even after long periods of inactivity. They often will not reseat once opened.

Relief valves will typically operate many thousands of times without failure. However, they are not designed for long periods of inactivity.

I agree with the above answers.There is a little to add to it. Safety valves are always mounted on vessels to protect them against pressure build up (even if discharge valves are closed accidently) whereas relief valves are installed on pipe lines to relieve excess pressure and are normally installed across pumps. A good example can be seen in pressure cookers, the center valve is a relief valve whereas it has a safety valve in case relief valve fails.

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Originally Posted by meherbabu

What is the difference between safety valve and relief valve

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There is no difference they are one in the same. If pressure gets to high relief valve/safety valve opens, which prevents an explosion. So it is a safety device. That's how they became to be known as one.

I agree with them , safety vavles in normal operation is closed
But u can find some relief is open in normal operation specially which are in discharge of pumps it works as minimumflow & make stability for pressure

There IS a difference between safety valve and a Relief valve!! A safety valve is supposed to relief pressures from unsafe to safe ranges. Whereas Relief valves are supposed to MAINTAIN the pressure... Consequently the requirement is addressed by the design which enables a SAFETY valve to POP OPEN at a certain pressure, but sit back closed on a pressure significantly lower... For instance, a Safety valve may pop open at 13.3 bars and sit down on a pressure of 12.7 bars. This difference is called Blow down and it ensures that the valve is not kept open...

Safety valve is for safety. Relief valve is for relief.

Superb...

Safety valve allows for pressure accumilation even while dumping excessive pressure. It can be simply described from an example. As in a container which is filled at a constant rate of water and a valve at a level which open at when the water amount reaches its level. The amount of valve open can be adjusted (like in a safety valve). Now when the water reaches the valve level valve opens and dumps the excess but at the same time water fills and safety valve regarding to the example do the same, when a pressure reaches valve opening pressure it opens and dumps the excessive pressure allowing for a pressure accumilation. And safety valve is designed to allow to pressure drop of 3% of the pressure of the containing pressure before closing. So it opens when the pressure reaches its limit, allows for pressure build up, and dumps excessive pressure and closes when pressure drops below designed opening pressure.

Relief valve is designed to open and dump pressure without letting to exceed (or reduce like in a safety valve) its designed pressure.

The difference depends on the standards which you are working with. For example, when working with industrial applications the term relief valve and safety valve may indeed mean the same thing. In either instance a block valve will be installed on the inlet to the safety of relief valve. This is typically tightenged with a valve wrench.

Safety valve releases excessive pressures directly to the atmosphere while relief valves recirculates the excess pressure backto the suction line.

Difference in the operating range only

Safety valve the pressure go to the atmosphere and the relief valve it will back to the system

In Pressure Relief Valves, Popping Pressure and Seating Pressure will be same.
In Pressure Safety Valves, Popping Pressure will be more than Seating Pressure.

Please go through this link for further clarifications. .

http://wiki.answers.com/Q/What_is_Difference_between_relief_valve_and_safety _valve

Que: Turbine oil temperature is increasing after circulation through its bearings. So, which of the two valves, the inlet & the outlet, of the oil cooler should be throttled to maintain its temperature to normal..?

Que: A boiler with no stamp. How would u size the safety valve..?

Safety valve is opened spring use in steam and gas only not in liquid..
Releif valve coverd spring use in all places .

Dear msk, I disagree with your saying that relief valves are mounted on pipings, rather than mounting them on the vessels directly. If this is so, where are the pipings seen in pressure cookers. How could say that " relief valves are installed on pipe lines to relieve excess pressure and are normally installed across pumps. A good example can be seen in pressure cookers, the center valve is a relief valve whereas it has a safety valve in case relief valve fails.". Do explain me the same.

This example is good to understand the difference, and to add safety valves are used for plant safety and relief valves basically for the process safety and off-course plant safety by default but not up to the full extent.

Safety valves are used in gas applications and mounted on the vessels, drums and tanks, and relief valves are used on pipe lines where liquids are flowing, (Thermal relief valves & pressure relief valves).

Thermal relief valves are due to the temp increased - related pressure buildup and Pressure relief are due to the system related - pressure buildup on the out let of the pumps etc. and we have to engineer the type of the valve acc to the requirement and feasibility.

There is another term Pressure safety relief valve, which takes the pressure to more safe level after the popup.


M.V.Ramesh

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Q: there is a safety relief valve with orifice diameter of 1.35 inch and area of 1.43 square inches ,if I want to select a
Replacement valve that is according API standard ,which kind of orifice designation
Is the perfect choice?(J orifice)?

Q: I have a safety valve with orifice diameter of 1.35 inches and orifice area of 1.43 square inches and I want to replace it with a valve according API standared ,please help me which kind of orifice designation should I choose? J type?