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B.B.
29-10-2005, 03:52 PM
Hi,
Whilst attending a site the other day regarding a seperate issue, i had a visual inspection in the plant room. The plant comprises of 4 scerw compressors on Nh3 with thermosyphon oil coolers.Each oil cooler is fed liquid from a liquid header fed from a small liquid receiver. The oil cooler liquid receiver has a outlet valve, the oil coolers have inlet stop valves and outlet stop valves which are located at the inlet of the evap condenser.I noticed a small Nh3 leak on the flange of a safety relief valve which i was able to secure, but what cocerned me was the location of the valve. It is installed in to either side of the inlet stop valve on the oil cooler. This would mean isolating the small receiver valve, therefore liquid feed to all oil coolers, should the safety valve require to be removed. I think the valve should be on installed between the outlet stop valve as this would make it serviceable. Is there any reason that it has to be on the inlet side?:

US Iceman
29-10-2005, 06:21 PM
The oil cooler liquid receiver has a outlet valve...the oil coolers have inlet stop valves...This would mean isolating the small receiver valve, therefore liquid feed to all oil coolers, should the safety valve require to be removed.


Is there any reason that it has to be on the inlet side?

The short answer is yes. From the description you provided, the relief valve was installed in the liquid feed lines because the liquid line could be isolated by the valves.

If the liquid line was valved off, the line of course would be trapped full of liquid. Liquid which is isolated in piping can generate extremely high pressures due to hydrostatic expansion. A slight increase in liquid temperature can cause the pipe to rupture.

This is the reason the relief valve was installed in the liquid lines between the services valves.

This is a recommended procedure anytime liquid can be isolated between stop valves. Cold liquid is much worse, but this happens with any liquid temperature.

B.B.
30-10-2005, 03:44 PM
Thanks for your reply, but i cannot see how any valves etc are serviceable after the oil cooler liquid receiver valve without having to shutdown all compressors and transfer liquid in to surge drum and then vent down complete liquid header feed to oil coolers, which would be a lengthy process whilst not providing any cooling. If the liquid header had its own relief back to the receiver and oil coolers safety relief piped back in to the vapour/liquid return the safety relief valve and oil cooler would be serviceable on each circuit without shutdown of the plant. Any thoughts?

many thanks

US Iceman
30-10-2005, 05:44 PM
Can you provide a drawing of the piping layout? This would help to review your questions.

PobodysNerfect
30-10-2005, 06:48 PM
B.B.,

Your explication is not clear enough for me. What do you mean by "It is installed in to either side of the inlet stop valve on the oil cooler".

Anyway, pressure relief valves many times do not make maintenance work any easier.

I have attached some pages concerning pressure relief protection from "User Manual for ANSI/ ashrae Standard 15-2001"

Saludos,

Jan

B.B.
31-10-2005, 02:25 PM
Thanks for the info Jan, much appreciated. I will be returning to site tommorow, i will try and post a couple of pictures of the piping in the next couple of days.
Thanks for reply Iceman, i will try to attach some piping diagrams with the pics.

Thanks, B.B.