Designing a Pressure Safety Valve

[Dineshkarthi]

Hello all,

I am under the process of designing the Pressure safety valve ,the core component of PRV is spring.just i want to know about the spring design .For eg my max allowable pressure is 5 bar, then i want to set the spring to stay uncompressed at 5 bar and the spring has to compress after 5 bar for this condition how to decide the coil diameter ,spring dia ,no.of turns ,height of the spring.MOC for spring is Stainless steel.Is there any formula to find this values or any standard to refer ...pls anyone help in this case to design a spring and the spring seating area may be flexible it may vary accordingly but the set pressure is fixed...

Regards
Dinesh

 

[DEvens]

Welcome to the forum.

Designing such things is pretty straightforward.

First you must know the area of the valve you want to open when the pressure is too high. That will tell you how much force you need to hold back with a spring. Also, that will tell you something about the space you have in which to house a spring. You get this area based on how much flow you want for pressure relief. The length of the spring will help you pick the design. Do you want a coil, a wave, a leaf, etc.

You find the catalogue of a manufacturer of springs. You find a range of springs for which the force you want is somewhere near the middle. You pick a spring from near the middle of that range. The reason for this is that you want to the spring to be well away from the extremes of what can be manufactured. Why? If the maker could produce larger or smaller springs, they would. But if they do, they find that the springs are too difficult to make without failures. So you want to stay well away from those failing conditions. So you want the middle of the range.

Here is one such manufacturer. But there are others.

http://www.smalley.com/

The other thing you need to decide is, will this valve close on its own when pressure falls below some limit? If that is the case then you need to work a little harder. You need something that will open on pressure over a limit, then be a little "sticky" and stay open until pressure falls below a limit. This usually means some kind of mechanism that changes the force required for the valve to operate based on whether it is open or closed. Probably some kind of lever that changes where the spring operates when it opens, then puts it back when it closes. You can probably Google up some images of this kind off design.

 

[Baluncore]

Machinery's Handbook has a section on spring design.
Google and you will find.