PSV (Pressure Safety Valve) and PRV (Pressure Relief Valve) are valve types used for process safety. The two terms are often used interchangeably and different opinions among engineers. However, more important is the engineer has to know exactly what he want.
Difference between PSV and PRV is as follows. A PSV serves to safety, namely the immediate need for securing the process. If seen from the way it works, PSV will immediately secure the process of excess pressure in a way erupted/ suddenly open while PRV serve to “loosen” the pressure and vacuum so that the condition does not become a hazard.
Pressure Safety Valve
PSV is a valve used to secure the pressure on compressible fluid or gas in pipeline or vessel. The PSV will fully open suddenly / “pop” when the pressure achieves set point.
Pressure Relief Valve
PRV is a valve used to secure the pressure on vessel, commonly, uncompressible fluid, and it should be open in proportional with the pressure condition and therefore the opening of valve is not sudden.
At above, we have explained the difference between PSV and PRV. However, in field condition is different. You will not be required to use the two terms above accurately. Instead you will find that in the field will depend up to you to call. It was due to manufactures’ mistaken in making brand marketing for their products. However, you must know what you need without having to fear any mention.
In the experience, if you need a valve for a pressure safety in a separator, heater vessels, scrubber and filter vessel then you can call it pressure safety valve (PSV) and when you need a valve for a pressure safety in the storage tank, then you need a relief valve PRV (breather valve), Thus the explanation of the difference between PSV and PRV.
There are more important things than you know the difference between PSV and PRV, that when you are dealing with the process conditions. When you are planning to procure a PSV or PRV, the thing you have to understand is the material of the PSV or PRV. Some things you should consider include the corrosive level of the fluid, temperature and pressure rating, which is also very important is the environmental conditions.
A PSV or PRV which will be installed on offshore field will be different from the onshore field or even in the room of a factory. The environmental conditions offshore will be in conditions with the salt level is quite high and affect the level of corrosive. Likewise, the fluid to be protected, whether or not containing H2S. Fluid containing H2S will require special material, usually materials with low sulfur content or even no sulfur content.
PSV and PRV material selection is very important. This is because it is a security device. When the security device fails to perform its function, the process conditions will always be overshadowed by events that are not safe. Above is difference between PSV and PRV and you may gain some insight how to pick up the righ ones for your process conditions.