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Freezing of pilot sensing lines

Freezing of pilot sensing lines

Freezing of pilot sensing lines

(OP)
Hello I have a quick question. What effect does freezing of pilot sensing lines have on its operation? Pre mature lifting? or potential for overpressure? Any insight will be appreciated. Thanks

RE: Freezing of pilot sensing lines

Either one.  When water freezes it increases in volume by approximately 4%.  If there is a couple of feet of tubing between the freeze point an the pilot, it would be just like shutting a valve and trapped pressure will only increase slightly.  If the freeze is very close to the pilot, it can simulate a very high pressure (especially if there is liquid water between the freeze and the pilot.

Heat tracing and insulating pilot lines is a very good practice.

David  

RE: Freezing of pilot sensing lines

Pilots freezing, plugging, or contamination in general is potentially dangerous. if freezing is a concern, heat trace and insulate is a good idea as zdas04 mentioned.

I am presuming the source of freezing is due to ambient conditions. If the freezing is due to process conditions, heat trace/insulate may not work and you will need to find alternatives.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
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RE: Freezing of pilot sensing lines

(OP)
Thanks all. I understand theoriticaly why a pilot valve will open prematurely before reaching its set point if the sensing line freezes.

However, I still dont understand why it will NOT open when it reaches set point due to sensing line freezing up. The operators i spoke to said they haven't seen this before. Can some one explain if this is indeed a likelihoo?

Thanks.

RE: Freezing of pilot sensing lines

Did you read my post?  The freeze can act like a shut block valve which makes it really hard for the control valve to close.

David

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