[Bob Wilson]

Have extended central heating pipes to fit new rad. in different position using 15mm comp. fittings with directional arrows. May have mistakenly fitted them the wrong way round. When valve opened will it make a difference ?? Looking at the type of valve fitted and opening one with a screwdriver it appears to still open.

[Proff]

In all my years I have never seen a compression coupler with an arrow on it (not even when it belonged to the MOD). The only thing I can think of is that you have fitted a Non-Return-Valve and if it is it will definitely make a difference if it is the wrong way round, the rad won't work. If it does work then all you have done is put a little restriction in the way, but if it works that is no prob.

[Bob Wilson]

Only mentioned the directional arrow as I was curious how it works? When you look down the bore of the valve the ball valve opens and closes OK, but one side has a metal insert with 4 holes on its periphery ?? Must do something?

[Proff]

It sounds very much like you have fitted Non Return Valves. If it was a compression coupler there would be nothing inside it. You can get compression fittings about the same length as the NRV and they are marketed as repair fittings if you would like to replace them with as little hassle as possible. As I said, if it works no probs.

[Bob Wilson]

Looked at a spare coupler with same directional arrow and 'the penny dropped'. The design is that the pressure side has a round metal disc inside to secure an 'o' ring. When the valve is closed it appears the pressure exherted on the disc/ 'o'ring will assist in sealing the valve, hence the directional arrow. Probably down to which manufacturers coupler/design you happen to have available.
Purley academic really, but the mystery is now clear. Yes, when its closed or open the arrow doesn't really make much of a difference to the functionality.