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View Full Version : Why Vapour traps are neccessary on PRV's







Grizzly
14-07-2015, 07:41 PM
Hi Guys!
Just for Fun and Instruction.
The attached shows just how much water can accumulate in a s/steel Vent Line.
Making the pipework configuration critical. The standing water against the prv outlet has caused the seat to fail on 3 out of 4 prv's.
In fact the one you see is the remaining good one because the leaking by Ammonia in the others.
Resulted in no standing water left in them.
These pipes are led away from the Pac, up through the roof and along another adjoining roof for about 30 metres before they vent. (Less populated Area!)
Because of the poor (Site Fitted - Dairy!) pipe design and Install with huge amounts of s/steel pipe subjected to atmospheric conditions with no vapour trap. Huge amounts of Water have been produced within these pipes. All flowing backwards to the PRV's!!!

The Video only runs for 40 odd seconds, but I can assure you it was leaking and then shut off prior to taking the footage. It continued after stopping as well!

Something not seen to often but highly informative in my humble opinion.
Next time you see a red cross through a Danfoss diagram you will know why!
Grizzly

https://youtu.be/-0If3qLo1Ic

Thanks to my Colleague John for his input.

al
14-07-2015, 09:08 PM
An extra check for the maintenance sheet, not something that ever crossed my mind, nice one Grizz!

Grizzly
14-07-2015, 09:13 PM
An extra check for the maintenance sheet, not something that ever crossed my mind, nice one Grizz!

Nor have I Al!
Hence the post!
Grizzly

RANGER1
14-07-2015, 09:59 PM
Grizzly,
Good basic information that's worth knowing.
Our codes state to be checked annually, remove fitting, check inside for deterioration, can't say we really do it.
If it were like a steam relief, you could give it a manual blast every now & then, that would be fun.

Vent line s also meant to be checked for obstruction also , like some kind of nest etc
Outlet would have a "S" or "P" trap with a small hole drilled in bottom for any moisture build up etc.
On some we fill with oil on plate freezer to stop condensation inside -20 deg room

Superfridge
18-07-2015, 11:10 PM
I have struck this only once before. The location of the PRV did not favour water draining to it and when I cracked the union to drain the water it smelt of NH3 and it stained the area it drained too. My thoughts at the time was that the PRV was weeping undetected for some time and the NH3 absorbed water via the vent line which accumulated at the PRV. Possible?????

sterl
30-07-2015, 06:44 PM
We have encountered circuits where virtually all of the safeties had some water at or near the outlets....

What we believe is that one safety does lift or weep; and the refrigerant in the shared discharge pipe got absorbed by the water at the outlet of other safeties. We have found Aqua on the discharge of a safety that still had an intact rupture disk on the inlet side of the safety: conclusion being, the adjacent valve was not the source of the NH3.

Tycho
31-07-2015, 09:37 PM
I always put an oil trap on the discharge line for the safety valves.

I design it like this: (paint drawing, but you get my drift :))

13839


For an added bonus you can put a sightglass on the oil trap to see if there is water accumulating.

Føroyar
09-08-2015, 03:01 AM
Tycho, this is standard on ships, with a sightglass on both sides of the U to check for water.
This is a common problem where PRV are not maintained as the should be, is it not ?

Tycho
13-08-2015, 10:17 AM
Tycho, this is standard on ships, with a sightglass on both sides of the U to check for water.
This is a common problem where PRV are not maintained as the should be, is it not ?

It is a standard and a requirement by some class agencies, but it's not always checked and therefore not installed.