In the schluter thread, I mentioned a leaking shower valve. There were in fact two leaks; one from a fault in the valve itself, and a larger one where the connection to the valve had failed. I have a new valve on the way to remedy the first problem, but when I install it I want to make damn sure that the connections aren't going to fail again.
All four connections to the valve are 3/4" parallel BSP. There's no appreciable inner face to seal against. None of the outer faces are machined smooth, although the two outlets are in fact relatively flat. The inlet ports are decidedly not flat, with a roughly shaped groove around them that's broken by a slot and ridge - not really a good sealing surface.
When I put it in the first time, I tried various kinds of seals. I ended up with polythene washers on three of the ports, and an O ring (which I'd tried earlier, based on the groove) on the hot inlet (it seemed to be working, so I didn't replace it with another polythene washer). However, I don't really want to fit the new valve like this, as I have very little confidence in it.
I used 3/4" parallel male fittings before. Would I be better off this time using taper fittings with PTFE?
Pete