Andy wrote:

Perhaps I'll step back a bit and ask if anyone can identify these valves
then ?

I'm assuming they're check valves, anyone confirm this ?

Here's a closeup :-

http://www.knownentity.com/pics/bath/valves_closeup.jpg

If you take one out and look in it, it should be obvious (typically a
small axial plunger on a stalk with a spring, flow in one direction
pushes the plunger away from the seat and allows water to flow, in the
other direction it pushes it into its seat and prevents flow, with no
flow the spring returns the plunger to its seat.

Either way, if its a gravited fed shower on both hot and cold then you
won't need a check valve.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/