Help!!! Shell and Tube Evap Leak

[tommy Gun]

hi all this is my first ever post so here goes....

i was currently doing a service on a York chiller set and found a gas leak comming from the shell and tube evaporater from the end plate. :eek:

i pulled the cover and the insulation of the end plate to see where the leak was comming from.



i reclaimed the reamining gas which was left after all four systems had been pumped down (closing the liquid line and suciton service valves on all systems to minimize possible leak spots) and started to check the nuts on both end plates where at the right torque setting (5o pound) I found some where a little lose and had traces of oil comming from the after niping the lose ones up i pressure tested (with nitrogen) on system 1 over night to see if i had fixed the problem.

However when i returned the next morning i had found that the gas had equalized between all four systems therefore indicating a leak in the gasket behind the end plate. I then pressuried the midle system (system 3) and found that the nitrogen that i was pumping in was imediatley escapeing in to the near by system (system 4)

As takeing off the end plate is a pritty major job in attempt to prevent me haveing to do this i tried lossening all the nuts one by one on both end plates (but not all the way as to make sure the gasket dose not fall)and then re- torque them to the correct amount this but this was to no avail as the system still leaks.

This system is about five years old and about a year ago the same problem occured and another tradie had replaced the gaskets on both ends (but had trouble finding the factory replacements so had to get some made) they were made out of 3mm thick rubber. the new gaskets seemed to be doing the trick until now.

- Just wondering on any info that anyone has about this problem or perviouse ones they have done, beacuse obviously something is happening for this problem to occur and i dont wont to go to all the effort to replace the gaskets to have it leak a year later. ?

-Maybe could the baffel be warped form factory?

-What is the usual material used for gaskets on these vesels is rubber right? (have been told the they use lead because rubber can shrink and perish to easily??

-the chiller

MOD: YCAS 1063 EC50

SERRIAL: RHTM 9620 AA

VESSEL Number: 375 31526-002

the style of chiller set is a

YORK Style F 50Hz four screw compresers

Any infomation that any one could give me would be much appreciated!!! any question if i have missed something or if you need photos just email me on harri6@bigpond.net.au cheers tom

[Argus]

Welcome to the forum and I note you’re in at the deep end.

Twin evaporators sharing the same shell and tube evaporator can be a pain to fix if you have a leak on the tube sheet area, but in my experience there’s only one thing to do. If you have a leak between circuits at either end plate, take the end plates off and do it properly, otherwise, you will be chasing the same leak around for years. Once it leaks through it will always leak through – all the retightening in the world won’t put it right.

I don’t know about York evaporators, but I spent some years working on big Carriers and there isn’t much difference between them and any other big evaporator in the shell and tube department as far as I can tell.

I will be certain that the manufacturers will specify the tube sheet gaskets and the material for very good reasons. If it’s a flat plate end sheet with bolts, you will have a distance plate with the passes outlined so you will need two gaskets at each end. Most manufacturers will also specify a jointing fluid on the gasket (then again, some may not). So I urge you to get the proper stuff and do it right the first time, by the book – no short cuts.

Next, the vexed question why it’s leaking. Did you mention that the leaks are repetitive? Had it before?
It’s unlikely to be old age or metal fatigue after 5 years, so there must be a cause.
If so, I’d take the opportunity to examine the tubes closely when you get the end plates off.
Look for distortion in the shape, flattening or puckering at the ends. If you find anything other than a nicely round tube all the way down, suspect freezing and look for a cause. When big chillers begin to freeze they start by telling you about it. You will hear creaks and cracking sounds from the tubes. Perhaps it’s an unmanned chiller an all this will go unnoticed.
Next the tubes begin to distort with ice forming in the shell. This is why you are seeing if there is any shape distortion because it exerts pressure that flattens the tubes. Sometimes the ice forms at the location of the expansion valve and this will be where there may be distortion in the tube sheet that may result in a leak through the web separating the circuits. You can plug off anything up to about 10% of the tubes if they are randomly spaced, but not in a cluster.
If there is more than that in a cluster, consider replacing the tubes or the whole evaporator.

If there has been distortion, make sure that the tube plates in contact with the gaskets are dead flat, not distorted, otherwise you will not get a good contact when you reassemble and it will leak again.




Good luck

.

[tommy Gun]

hey mate thanks for your quick respose just wondering i rember last time when the other tradie took it off i saw some photos of the tubes and they looked like some one had crimped the ends of all the pipes like they where still fully open but they had all little marks in the ends of them could this be a sign of freezing.

Also i have checked the heater on the vesel that keeps the vesel at a constant temp this seems to be in good working order??

Am i right in saying that if the vesel has had a freeze it would be looseing some efficiency depending on the how bad it is like a cold room or split system????

cheers mate am really keen to get this right love learning about this stuff is really interesting

[Argus]

.

That’s OK. Keep posting if you have questions.

Tubes are usually expanded into the end sheet with a coat of sealant using an expanding mandrel or something similar. They may protrude a couple of millimetres beyond the sheet and may have a mark or two on the ends outside. Don’t worry about this. What you are looking for is any tubes that show flattening inside their length from one end to the other. In extreme cases they will be completely closed off. This is a sure sign of freezing.

Depending on how many tubes are affected, loss of performance can result from tubes restricted in this way. The clue will be in their distribution – if they are in a cluster there will probably be a loss of performance and probable impaired evaporation.

The nature of slow partial freezing is that it can happen without you knowing it. It’s not what everyone thinks of as a major freeze-up, which is death-by-iceberg for a tube bundle.

It may be that this is not happening at all, but there’s only one way to find out.

If this is an outdoor package unit, the shell heater is there only for frost protection in cold weather – not a freeze protector.
Freeze protection on the chiller should be covered by a leaving water temperature sensor and a flow switch.

.

[absrbrtek]

The rubber factory gaskets tend to leak out and between circuits. I replace them with Garlock type gaskets and use a gasket sealant such as Permatex. Works every time. Also check to see if the head is warped, I have seen some .060 out of flat, had to have them milled flat again. JMHO

[tommy Gun]

hey mate are you talking about your experience with a similar york machine as i am talking about. if so where about do you get garlock gaskets and the permatex from cheers mate


The rubber factory gaskets tend to leak out and between circuits. I replace them with Garlock type gaskets and use a gasket sealant such as Permatex. Works every time. Also check to see if the head is warped, I have seen some .060 out of flat, had to have them milled flat again. JMHO

[absrbrtek]

Not sure where you buy this in the UK. We just buy the materials at the supply house and cut our own gaskets. Real PITA due to the gaskets intricate design. It pays off in the long run as this will be the last time you will be doing it.
hey mate are you talking about your experience with a similar york machine as i am talking about. if so where about do you get garlock gaskets and the permatex from cheers mate

[tommy Gun]

hi all just letting you no we havesince pulled the ends of and after checking them for square we found the the baffel plates where really badly warped have since got them mecheined and are in the processof putting them backon and getting the system back to good working order thanks to al that helped cheers tom ;)