Comment on this..

[AB6005]

Say i have a PSV provided for a system in which the rated flowrate of the PSV is 10 times bigger than the required sizing flow rate.Ultimately my inlet and outlet pressure drop are not within the code limits.In this case is there any possible solution available other than going for a smaller size PSV or modification of PSV including Bellows,pilot,remote pilot.can i comply for codes with the available system ???

Remember my pressure drops are very high of order say 70-80% of the set pressure.So changing pipe size is not helping me that much and my valve is full lift type.

please help me out..................

 

[lizking]

liquid or vapor service?

 

[dcasto]

Just put in a smaller one or a modulating pilot operated.

 

[insult2injury]

The relieving capacity with backpressure below typical limits may be 10 times bigger than required; however, the relieving capacity with 80% backpressure will be much less.

I2I

 

[JoeWong88]

Agree with dcasto...

I still don't understand why you have large PSV with small relief load... there are so many practical problems associate with this arrangement... Code compliance is just on paper...

JoeWong
Chemical & Process Technology

 

[maddocks]

Rig the PSV with a custom orifice or install one upstream to split the load.

 

[AB6005]

@ Lizking.Its a vapour service device...........

 

[AB6005]

@ insult to injury - no i face inlet pressure drop problem here..............

 

[AB6005]

@ maddocks

on 1st option - is it possible to fix a custom made orifice in a existing device(PSV)???

2nd option - what do you mean by split load ???the problem i am facing here is the sizing flowrate is very less when compared to device rated flow.

 

[insult2injury]

Has the vendor been consulted regarding the application?

I2I

 

[lizking]

You may have been able to work something out if it was liquid service. But if this is truly an ASME Code application & vapor service, you are what is commonly known as "screwed."

 

[Homayun]

If your inlet line losses are so high then the PSV is probably not even gonna open (fully) meaning that your equipment won't be prtected.

 

[AB6005]

@ Lizking

great reply..........Yeah i know i am screwed and if it is a liquid service we can apply square law.i escpaed by this on couple of devices.

cheers...........

 

[AB6005]

@ Homayun...

yes i agree with you.....My system is not safe.

 

[JoeWong88]

Guys...
Is partial modification of exisiting PSV acceptable from code and authority viewpoints ?

Who dare to certify correct Kd factor for a modified PSV ?
If answer is vendor, check with vendor if they are willing to...also check the cost...

After modification, is the PSV API or ASME compliance ?

Is the modification cost is lower than replace a small PSV ?

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JoeWong
Chemical & Process Technology