On Mon, 13 May 2013 06:31:45 -0700, wrote:

The issue is that one half of a 10 year old union from manufacturer A
may not seal correctly with one half of a new union he buys today from
manufacturer B.

I understand.

If it leaks, I'll replace that part of the plumbing, since, with the
unions, everything should be easy.

If it's any consolation, that unused "yellowed" union is, in fact,
the same age and batch as the existing "blackened" union is.

http://www3.picturepush.com/photo/a/...g/12921651.jpg

To explain further, about a year or so ago, I had replaced a broken
Jandy valve after draining the pool, and at that time, I added the one
now-blackened union on the outlet of the pump. I knew that a union
only on the outlet pipe without a union on the inlet pipe was useless,
but I was adding it knowing that someday (like yesterday) I would
be adding a union to the inlet side of the pump.

I had bought two unions at the time, so I left the unused union
outside in a plastic bucket. Over time, that unused union yellowed.

So, the good news is that the unions are 'matched' in time and batch;
the bad news is that one sat outside in the hot sun for a year.

I'll let you know if it leaks; but if it does, it will be easy to
replace, since the hard part was always the inlet side, and not
the outlet side.
http://www4.picturepush.com/photo/a/...g/12921662.jpg

Note: If it wasn't easy to replace, you can rest assured I would
have used all new equipment!