In article , Michael
Kilpatrick writes
Hello all,

I've just inserted a solenoid valve in a run of Hep 15mm pipe to the
water inlet of the toilet header tank - this is part of my home-made
control system for the feed from the rainwater harvester tank (under the
patio) to provide the toilet flush water.

Solenoid valve: http://uk.rs-online.com/web/p/products/342-017/

My question is this: given that the valve has 1/2in BSP threads in
plastic, and that the easiest way of fixing the valve appeared to be get
this metal BSP-to-15mm-compression adaptor:

http://uk.rs-online.com/web/p/products/342-039/

should I, by default, always use PTFE tape between the metal female BSP
thread and the male plastic BSP thread of the solenoid valve?

Excellent, the new RS site let's you link directly to a part!

Or are such things designed to seal properly without such assistance?
Yes, there's a rubber washer inside the adaptor.

Looks like both are intended to seal to the flange with the rubber
washer so I wouldn't use tape. Without instructions to the contrary in
the product data I would lightly smear both sides of the washer with
silicone grease (not sealant) before assembly.

Not a bad price for bits either, RS used to be a lot more expensive for
this sort of stuff.

I'm just suspicious of these horrible plastic body threads, like those
on dishwashers and washing machines, which I always seem to have
problems with!

The compression fittings I think are fine. Yes, before anyone asks, I
did use the pipe inserts to do it properly when compression-fitting to a
Hep2O pipe. Although I won't guarantee not having overtightened - I'll
tell you tomorrow if the hallway is flooded...
--
fred
it's a ba-na-na . . . .