Cascading TRV

[HunterJ]

I'm looking for a document or book to purchase that would help me design a cascading thermal relief system for pipes that contain a fluid that is block in by valves.
Thanks for any help,

 

[MikeHalloran]

What do you mean by 'cascading'?

Like a series of plugs made of Cerrobend or other low-melting-point alloys with different melting temperatures?



Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

I don't think there is one. It's just a matter of piping system system design. All you need to do is ensure you use the correct type of TRV, which isn't affected by back pressure and you always relieve into the same or high rated systems.

It's not too common to have more than one cascade and most times now people don't like the cross connection. Far simpler to include a closed drain system.

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[georgeverghese]

Tricky topic

A few tips:
a) Actual set pressure on a conventional RVs' is affected by backpressure. For example, a 10% increase in backpressure increases the SP by 10%.

b) Actual set press on a balanced bellows RV is unaffected by backpressure for backpressures up to about 70-80% of set pressure.

You can find this this nugget in the API 521.

Good luck

 

[HunterJ]

Thanks for the replies.
I’m looking at using the C series fixed cracking pressure check valve [10 psi] Swagelok check valve that will vent/relieve pressure back into a vented above ground storage tank. Max pressure in the tank based off fluid height would be 11 psig.
So I guess in a perfect world if the tank were full this would start to relieve once the pressure in the closed pipe reached 21 psi.

 

[georgeverghese]

Doesnt look like these Swagelok C series press diff valves could be called "safety relief valves".

They are just plain pressure differential valves.

 

[LittleInch]

HunterJ,

I believe you are correct.

This is not really what most people think of as a "cascading relief, nor is a "fixed pressure check valve" seen as a safety valve. the margin on setting pressure is likely to be much higher than a proper spring relief, possibly -50%, + 25%

If the tank level is low, then any pressure >10 psi will flow fluid back to the tank.

Is this what you want?

10 psi is very low - why so low?

This system as described does not make any sense.

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Also: If you get a response it's polite to respond to it.