Many leaks on hot gas defrost line

[Frigoriste]

Hello!

I have a problem on a hot gas defrost line. Almost once a week, my new client has a leak happening on hot gas line and we lose 300 pounds of ***** every time. With current ***** price, we must found the source of this very quickly.

Here's a summary of the system:
- 1 liquid line
- 1 suction line
- 1 hot gas defrost line
- 1 unit Cancoil RCU1A060
- 10 evaporators
- Controlled by Delta

The design of the hot gas defrost line:
- Main line is 150 ft long (1 3/8")
- Branch to coils are max 20ft long (5/8")
- Lines isolated with armaflex
- There is a loop (U) in the middle of the main hot gas line to absorb line expansion (because of heat)
- Solenoide valve at each coils to control defrost. No solenoide at the beginning of the main line.

Can it be "water hammer" on this kind of design? With hot gas defrost, velocity is high and gas may condensate in the line. If so, how can I avoid it?

It there any other reason that may cause this problem.

In RE we trust!

[Mark]

Frigoriste,

Welcome to the forum.

Where on the Hot Gas Line are the leaks?

Mark

[chillerman2006]

Hello!

I have a problem on a hot gas defrost line. Almost once a week, my new client has a leak happening on hot gas line and we lose 300 pounds of ***** every time. With current ***** price, we must found the source of this very quickly.


Hi Frigoriste

where exactly is the leak ? What leaks ? fitting ? solder joint? solenoid?

I must say if I was your client, by the second failure in two weeks I would have refused to pay you for the return visit, give you the chance to rectify for free and if not employed a company that can resolve leaks. Needless to say any outstanding invoices would also not be paid.

chillerman

[r.bartlett]

are the pipes clamped too rigidly

[Grizzly]

Hi Frigoriste.
Are you sitting comfortably, I am going to tell you a story!
Many years ago whilst the site Engineer of a large cold store, my colleagues and I had a slow leak on the main R22 (800kg plus) plant.
Despite numerous many handed leak checks over the pipework and valve stations. Even whilst initiating a defrost cycle (Hot Gas) on each of the valve stations. We never could find the leak which over a long length of time resulted in large gas losses.

Having had a automated leak detection system fitted the offending leak was identified on a particular hot gas valve station.
Which was occurring approximately 40 Min's into a 1hour defrost cycle.

To explain, each valve station feeding it's own evaporator was a 3 pipe system.

1) Liquid line.

2) hot gas line.

3) Suction line on a common header with the wet return controlled by a pm valve.


What was happening was as the hot gas solenoid valve opened initiating defrost, all was gas tight.

However once the system had been at defrost temperature and pressure for sufficient time.
(The little rubber O ring under the bonnet of the solenoid shuttle ( Danfoss ). Which is more like a cylindrical square shaped rubber than an o ring.)
This O ring which had perished from the continual hot, cold, hot, cold, operations. Started to leak and leak big time!

Maybe you have a perished o ring or similar there are similar on the pm valves.

Try leak checking after the defrost has been on for a good way into its defrost duration.

Don't forget if someone has stood on a pipe flange and stressed it, then you could develop a leak as the heat expands it's joints.

The fact that the leak happens on defrost is a bonus in some ways.

I would be checking joints and seals first.
Good luck Grizzly.

[Emmett]

are the pipes clamped too rigidly
Or too loosely? I have seen leaks occur on line with solenoid valves when they are supported rather than strapped! In my case it was the result of "water hammer" if the pipes jump/move when the solenoid cycles I would bet on that. Please respond to the other requests for more information, knowing where the leak is developing may be the clue we need to help you resolve the issue.

[chillerman2006]

Hi Grizzly

one to watch for mate
friends or not you would have got the boot too after second visit :D haha

If I can not find a leak, time to book it for a helium leak check

then if not found with leak detection fluid

time for a mass spectrometer, just set it high at first as this coupled

with helium will find leaks that do not exist with the molecular size of hcfc's

R's chillerman

[shooter]

give us a drawing of the system, makes dicussion easier.
is there a pressure control valve to put the hot gas higher in pressure, if so is it on correct pressure as when defrost starts the pressure of the hot gas can go above blow pressure of safety, The good value for this one is max 1 bar difference, I have seen several systems with wrong settings.
You will see hammer as the hot gas enters a very cold evaporator, if you want to avoid put a slow opening valve in the main hot gas and open it when defrost is asked for.
danfoss valve is a PM3 +CPV +solenoid

[Grizzly]

Hey my man!
They would have had to sack people a lot higher up the food chain than me.
Just how I am meant to use helium etc.
When plant is operational?
As I say this one only became apparent after fitting permanent leak monitoring equipment.
Which is mandatory nowadays on a plant larger than 300kg.

Back in those days we only used helium in balloons, besides which I don't think it would of liked my trusty halide torch. :D
What colour would the blue flame of changed to?

Frigoriste is lucky he has if I read his post correctly an empty system to leak test.
What he does not say is what refrigerant he is running on.
Grizzly

[chillerman2006]

Hi Grizzly

I know mate, Just kidding :)

If I can stay one or two yards behind you on knowledge, I am doing well

..........................................................................

For those not familiar with ''mass spectrometers'' see attached

they can be hired out these days, as the cost new is +£15k for half decent one

So dont drop it :eek:

R's chillerman

[kaelte_technik]

Dear Frigoriste,

There must be some sort of a liquid header around 200 mm long at the end of the liquid line in multiple cases connected in one position, this is to absorved the expansion and contraction that will happen and will not affect your fittings like elbows and tee's. I supposed the leakage you encounter is mostly in the liquid line bends.

Best regards,

Kaelte

[texas64]

With that large of a leak, one could probably see evidence and probably hear refrigerant escaping!