Difference Between Safety Valve and Relief Valve

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In This Article,You Will learn Difference Between Safety Valve and Relief Valve in Details.

Whenever we talk about the pressure in the process industries we come across two types of safety equipments and that is the safety v/v and the relief v/v.

Most of us think that both are same thing but that’s not the case. Though their functions are same yet there are certain differences among them. Both of them are used in the industry to prevent the accumulation of excess pressure, but there are operational differences between them.

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Let us first know about relief v/v and safety v/v then we will understand difference between safety valve and relief valve in details.

What is Relief Valve ?

Relief valves which are also known as Pressure relief valves are one of the protective devices which are used to protect a pressurize working system and equipments from getting damaged due to an over-pressure or excessive pressure conditions.

Difference between safety valve and relief valve

An important factor of consideration in the relief valve is the effects of back pressure in the system.

Relief valves are one of the important safety device fitted to protect the equipment from overpressure.

It opens at a pre set pressure to prevent the system failure.

In every pressurized working system there is a set pressure under which the system works properly and efficiently, this set pressure is known as set point and when the pressure is above set point the relief valve opens and the excess pressure is released.

What is Safety valve ?

A safety valve is a type of Fail safe device which is used on a system to prevent its failure and malfunctioning.

Difference between safety valve and relief valve

It works by releasing the pressure when the pressure inside the system exceed a preset pressure, thus preventing the system failure.

The safety valve is so constructed that when the pressure gets above the preset limits it automatically lifts and release the pressure .

So the basic function of the safety valve is to remove the excess pressure in order to prevent any damage to the vessel.

In addition to this, it also ensures that the pressure should remain within limits in the near future.

It is made very sensitive such that even for a slight increment in the pressure lifts the safety valve and gets closed quickly as soon as the pressure is released to maintain the desired pressure in the vessel.

Difference Between safety valve and relief valve

Safety Valve

  1. Directly open the design lift at set pressure.
  2. Can Open Manually by Easing Gear.
  3. Setting pressure is just above the working and not more than 3 percent above the approved the working pressure.

2. Relief Valve

  1. Setting pressure is 10 percent above working pressure.
  2. Opening is proportion to the increase in pressure.
  3. Can not open manually.

Difference between relief valve and safety valve figure

Difference Between the Safety valve and Relief Valve ?

1.Definition of relief valve vs safety valve

From the definition of both the valves we can conclude that the relief v/v which is also known as the pressure relief v/v is a safety device which is used to maintain a proper preset pressure in the vessel or the system within a prescribed limit condition to prevent a situation of over pressure.

Or we can say that the relief valve releases the excessive pressure from a system to control the pressure level in the system.

On the other hand, the safety valve is a protective device which is used in a system to control the pressure inside the system under a predetermined limit.

It works by releasing out the excess liquid or gases when the pressure becomes too high which can damage the vessel.

2.Function


The pressure relief valves are generally used in the hydraulic systems to control the pressure within specified limit and when the pressure increases than the preset value.

It lifts up and provide an escape of the excess pressure through an alternate channel or bypass provided in the system back to the source from where the input is coming or may be a different chamber provided to accept the excess of the liquid.

On contrary in case of safety valve, the main function of the safety valve is to provide safety to the property, life, and the environment which can get damaged due to failure of the system because of the excess pressure.

So we can say that the safety valve opens when the pressure inside the system increases beyond the designed and set pressure limit.

3.Operations of Safety valve And Relief Valve

On basis of operations , Difference between safety valve and relief valve are:-

The pressure relief valves are generally used in the hydraulic systems to control the pressure within specified limit and when the pressure increases than the preset value, it lifts up and provide an escape of the excess pressure through an alternate channel or bypass provided in the system back to the source from where the input is coming or may be a different chamber provided to accept the excess of the liquid.

On contrary in case of safety valve, the main function of the safety valve is to provide safety to the property, life, and the environment which can get damaged due to failure of the system because of the excess pressure.

So we can say that the safety valve opens when the pressure inside the system increases beyond the designed and set pressure limit.

4.Set point

Difference between Relief valve and safety valve on basis of Opening of valve on set pressure.


Now that we have discussed a lot about the “Set Point” & “set Pressure” in the above points.

They may sound similar but are different.

We used the set point in case of the relief valve, the “Set Point” basically refers to a point set to the lowest maximum pressure rating which means that the pressure is set below the maximum operative pressure which is allowed for a system to operate without being get into the state of overpressure.

The relief valve starts to open when the pressure goes beyond the set point.

The set point is measured in pounds per square inch (PSIG) and is not allowed to exceed the maximum allowable working pressure (MAWP).

But in case of safety valve the pressure is pre determined according to the materials used in the system and the type of work it performs.

Summary of Relief valve vs. Safety Valve

In Simple words we can say that the relief valve pressure is set to maintain and control the pressure inside the system, the set pressure is dependent on the working pressure of the system.

On the other hand , the pressure of safety valve is set on the basis of various factors of consideration like the material used, the environment in which it has to be used, the type of work it has to perform.

Basically the pressure for safety valve is so set to prevent the device itself from getting damaged.

Let us take an example for better understanding :

we know a boiler has both relief valve as well as safety valve.

Suppose we have a boiler whose working pressure is 6 Bar.

Now the set point for pressure relief valve is 6 Bar so that it whenever the pressure inside boiler increases beyond 6 Bar the relief valve opens.

But at the same time the boiler is made of some material which is set to work on certain fixed pressure above which it may explode or develop crack.

So here the safety valve comes into action.

The boilers material used for 6 Bar will have the materials which can withstand upto 12 Bar (it depends on the manufacturer) So the Safety valve will be set to 7-8 bar so as to prevent the boiler failure.

So, from the above example I hope I have been able to clear the concept of Difference between Relief valve and safety valve.

Relief valve wikipedia

Safety valve wikipedia