Why so many leaky service valve stems around?

[alan_man]

Hi fellas, just curious to know how many people often come across leaky valve stems on split systems (as in leaks past the seal out into atmosphere). There have been a number of times where I have investigated systems low on refigerant to find the leaks usually come from the service valves. Twice now I have removed/reinstalled two units where upon re commissioning you get the slight hissing sound while winding the valve out, one started oozing oil and bubbling up. A few jiggles can "re seat" the seal but it does not inspire any confidence at all. On a new unit I recently installed, was called back not even 2 weeks to find it was low on refrigerant. Low and behold upon removal of blank caps there was bubbly oil residue around the rim of valve stem. It was as if undoing them valves for the first time "broke the seal" or something. I am thinking to use some form of gas tape before replacing the blank caps or is there some other means to repair this issue? What type of valve stem seals are usually used and can seals be replaced or does the 2/3way valve have to be cut off and replaced? I must admit most systems I come across with this issue are genrally older but I still do not find that as an excuse for this to happen, thanks in advance

[Tradewinds]

Hi Alan,
They are one of the most common points to leak. I was actually taught back in the day to always undo the gland (slightly) before adjusting any service valve stems. The reason they leak so much is because engineers simply open/close the valve straight away. When that gland is tight, it seals against the valve stem. If you move the stem with it still tight then it wears out the seals.
I think you can replace just the seal in them but sometimes the wholesalers dont stock them and its easier and quicker to replace the whole thing. Rather than wait for the new gland to arrive.

[sinewave]

Fujitsu's are the worst culprit for this I've found!

[Tayters]

Hi Alan,

AC service valves are designed to be opened all the way so the back seating seals same as on a rotalok. I make a point of checking they are back seated if working on one. Many times they aren't and of those roughly a third make a hissing noise when the cap is loosened to get the Allen key in. Not noticed any hissing on valves that were backseated.

Cheers,
Andy.

PS: Haven't forgotten about the relay thing - still treading that fine line!!