Which is better Ball valve or Diaphram plate

[packstove]

We are modifying an existing refrigeration lines to add a temporary parallel evaporator coil loop. The idea is to isolate the coil, pump down the loop, and then remove the setup till it's needed again. once the coil is removed the system will return to normal single loop operation, but the existing connections that fed the temorary loop would still be present with only the two shut off valves from the liquid and suction lines, and possible threaded caps, from venting refrigerant into the environment. My question is, which Shutoff valve offers the best seal, ball valves or diaphram plate valves?

[dirk]

I would use ball valves as they have less pressure drop for suction line, but as a precaution install a short section of pipe that is welded closed after the valve. It is then easy to cut this pipe and extend if you ever need to re establish the loop.

[packstove]

Thank-you. A ball valve on the suction line does make sense, given the need to avoid pressure drop. We were hoping to not have to seal off the temporary loop with a brazed cap, but if that is th only sure way to avoid a sytem leak, then that may be the best solution. Thany you for your help.

[dirk]

A good quality ball valve will not leak, brazing pipes closed is only a precautionary and saftey measure.

[nike123]

A good quality ball valve will not leak, brazing pipes closed is only a precautionary and saftey measure.
Everything leaks. Only question is at what rate.

[dirk]

We obviosly still need to review our understanding of physics.
PLEASE ENLIGHTEN US !!!!

[nike123]

Does this brings some light?

http://i50.tinypic.com/5njdkl.jpg

[dirk]

Dont believe presumptions that are not based on scientific evidence.
It is impossible to put a ball with a two inch diameter through a hole of one inch.
It may be more accurate to say materials, welds or mechanical seals may deteriorate over time.
The author in his opening statement contradicts himself.
Put a drop of oil on a sheet of glass FOLLOWING YOUR ARGUMENT THE OIL IS LEAKING THROUGH THE GLASS. THIS IS IMPOSSIBLE THE MOLECULAR STRUCTURE OF THE TWO MATERIALS DOES NOT ALLOW IT .

[nike123]

Yo didn't got the picture. Glass bottle will leak at cork-glass junction, not thru glass material itself.