PRV spring range

[chloe1127]

Hi Valve expert,

I currently reviewing relief valve calculation from vendor. as per my understanding the spring range should be at least +/-5% of set pressure or at least the set pressure is within the spring range. what would be the effect if the minimum or maximum value of the spring is equal to the set pressure? is there any written guideline on what should be the minimum/maximum tolerance on the spring range?

thanks in advance.

 

[bljnv]

For a relief valve to be set at a pressure which is on the higher side for the given spring range, the spring is comparatively soft for the given set pressure load. This can cause the valve to achieve an early lift and longer blow down. Conversely if the spring is comparatively stiff, the valve might have shorter lift and short blow down. The tolerance of the spring is calculated accordingly. As long as the set pressure falls inside the spring tolerance this does not a matter.

 

[RVAmeche]

ASME relief valves come with a certified set pressure and flow capacity. As long as these values meet your needs, I wouldn't worry about the spring tolerances too much.