Oversize Pressure Relief Valve 1

[nyinyi68]

How to determine valve is oversize? What is the percentage consider more than the required capacity of Liquid service valve? Does the liquid service Pressure Relief Valve chatter?

 

[LittleInch]

You might have had more response in the Safety relief valve forum, but to start the ball rolling, my repsionse is;

You determine what your maximum relief flow is - either the maximum inlet in the event of a blocked outlet, maximum flow in the vent of fire or some combination of events - only you know your system. Then compare it ot the max flow formt he valve data sheet or vendor data.

Percent more than required - Up to you, but normally this is just a commercial decision that you don't wna tto have valve and attachments any bigger than they need to be. As a guess i would say no more than 200% of max rated flow.

All spring relief valvess can "chatter" f the actual pressure approaches the set presusre by less than 10%, or maybe 3-4 % for a pilot operated system. If flow in is low compare dto relief valve rating then chattering is quite posisble as the valve lift, volume escapes and presusre drops, the valve re-seats, then pressure rises again etc etc. if you're operating this close to the valve limit then you should either,
increase the set point,
lower the operating pressure,
replace witha pilot operated releif valve -
install a much smaller one set below the main valve which can then releive at a constant rate.

Hope this helps.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[nyinyi68]

Thanks LittleInch .
My question might be weird.
My customer want a thermal relief valve to replace. The existing valve capacity is very low and model is obsolete.
I try to replace new valve and minimum capacity is still higher about 150% than the existing valve's capacity.
So, customer concern that valve could be chattering due to over size valve. That's why I came to this question.

 

[LittleInch]

150% over current rating for a Thermal relief valve should be Ok. TRVs can " simmer" on a hot day, but at this sort of flow you should be Ok. I long remember walking around an aviation fuel manifold on a hot day wondering what all the hissing noises where when I then noticed all the locked in sections were at 100 barg and the TRVs were gently hissing. You really need a bit more flow than a TRV is aimed at to make a relief valve "chatter".

you'll only be able to confirm by testing or fitting one or two.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[nyinyi68]

Thank you very much for your answer.