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Contactor
17-03-2011, 10:12 PM
Hi Everyone,

Called to a system today which is showing all the signs of pumping down on the TEV.

Its a Danfoss on R404, multideck 4-5c set point.

I've checked the strainer and it's fine.

Does anyone know if these fail in such a way that this is possible, if the phial loses its charge or some kind of mechanical defect?

Thanks.

monkey spanners
17-03-2011, 10:27 PM
Yes they do fail like that sometimes. I have one that has just done that on a milk tank that i have to go back to and change. The older chrome plated ones seem to lose the spring pressure so that when you undid the flare the orifice no longer popped out 2mm or so but the stainless/brass ones seem to fail and also still have a bit of spring tension sometimes.

Heres a short vid of the cr@p i found in one of the 'good' valve on the same system :eek:

http://www.youtube.com/watch?v=Lo3YD0Fy5yM

mikeref
17-03-2011, 10:36 PM
Hey Jon, that "STUFF" in the strainer is garbage getting past your drier:eek:. You know that some has now gone through the valve and sandpapered its inner-workings don't yar?.. Another call coming up;)... Mike.

monkey spanners
17-03-2011, 10:51 PM
Hey Jon, that "STUFF" in the strainer is garbage getting past your drier:eek:. You know that some has now gone through the valve and sandpapered its inner-workings don't yar?.. Another call coming up;)... Mike.

Yeah, its not good is it! When i go back with the new tev i'm going to see it the 'stuff' is magnetic, i'm wondering if its wear metal from the comp which dates from the 1970's, Good old Prestcold L375!
The other thing i wondered about is the customers relative does vehicle air con so who knows what in if he's been topping it up...
Am thinking of fitting a burn out drier and changing the compressor oil at the same time as i fit the valve. The comp runs with a very high head pressure because its in a loft pulling air from the cow yard so the condenser soon gets blocked with cow hair, poo dust and staw so i'm sure this doesn't help much either.

Tayters
18-03-2011, 09:36 PM
Yes. I have worked on systems that have failed this way.

I find a good way to check the valve when it is apart is to push the orifice up in to the TEV body. It should go up against a bit of pressure. If the orifice slides straight in and the flange bit goes up against the body with no resistance then time for a new valve.

Hope that makes sense. If not I'll elaborate further.

Cheers,
Andy.

mbc
19-03-2011, 03:31 AM
Chinese danfoss TEV valve is not good, %20 has same problem.
go to Denmark or Mexican type or ALCO TEV .

Contactor
19-03-2011, 07:55 AM
Thanks everyone. Its as you describe with no resistance on the orifice, it just slides straight in and stays there. Is this because the phial has lost its charge or has the spring or something broken? Maybe both could be responsible?

Thanks.

monkey spanners
19-03-2011, 02:17 PM
I'd say its because the phial has lost its charge. If you ever have a valve shut down completely but need to pump the system down to change it, cut the phial pipe off right close to the bellows on the valve, then hold the end of a gauge line over the connection so the rubber gasket seals and pressurize it with some ofn, it'll be the same as if the phial was still ok and make the valve open, i'd also adjust the superheat screw before to fully open just to help out. Easier that getting the recovery machine out!

Tayters
19-03-2011, 10:17 PM
I'd agree it's because the phial has lost its charge. I've only changed a few and all but one had no obvious signs of damaged phial/capillary so I'd imagine the bellows had gone. The other was actually a Sporlan TEV type with changable power head. Looked like 20 years in a damp environment caused pitting which made its way to the bellows area.

The only other thing you can try before breaking into the system is to hold a warm rag around the TEV to melt any ice which may have formed due to moisture in the system.

Cheers,
Andy.

Contactor
20-03-2011, 08:57 PM
Oops, looks like some idiot put the covers on the wrong way and the vibrations damaged the phial capillary, wonder who that was...

Thanks for the tips, I will try forcing with OFN next time!

lowcool
22-03-2011, 01:39 AM
cut the phial pipe off right close to the bellows on the valve, then hold the end of a gauge line over the connection so the rubber gasket seals and pressurize it with some ofn

best idea since sliced bread MS.if there was a top ten for em you would surely be up their
maybe webram might give us electronic scales

mikeref
22-03-2011, 07:32 AM
Hi lowcool, Monkeys suggestion was something i never considered either:o!! What crossed my mind in thoes situations was,.. is the valve buggered or is it just full of restrictive contaminants? (to put it nicely:rolleyes:).. Mike.

night_marios
22-03-2011, 08:28 AM
hi,i agree with the other,guys !You better inspect the capillary of the valve if there is an obvius leakage,it happens very often!

lowcool
23-03-2011, 01:49 AM
agreed mike,if its not moisture it is more likely to be valve failure then maybe an orifice problem or strainer

young gun
01-06-2011, 08:51 AM
the few times ive had a tx valve pump the system down, ive had moisture in the system, i poured HOT water over the valve, and watched the suction pressure go back to normal, then evacuated the system.

and the other time was i had a blocked externally equilizing line