3/4" bath taps & 15m pipe

[Egremont]

Can anyone put a figure to how much running a 22mm supply through a short lenth of 15mm pipe will reduce the flow?.

My bath has 3/4" taps but 15mm pipe up to the taps immediately behind the bath (0.2m hot, 0.5m cold). I'm trying to understand if it's worth upgrading (in spite of very difficult access) to 22mm to improve bath-fill times [when I put in a 2.0 bar booster pump with 22mm pipes to the bathroom]. The cross-sectional area of 15mm is about 2.1 times less than 22mm, but I'm thinking that the water in 15mm will run faster so the flow won't be reduced/increased 2.1 times?.

A related thing, the hot tap supply is hidden behind the bath overflow. Does anyone know how to disconnect the overflow for access - it's black concertina plastic with a black plastic round piece backing the overflow - can't seen any nuts or screws to undo.

Thanks - Egremont

[Set Square]

The flow will depend on the *overall* resistance of the flow pipe - including all the elbows and tees and the restriction of the tap itself. A short length of 15mm pipe probably isn't going to make much difference.

There is probably a screw which can be undone from *inside* the bath - maybe the bit which also holds the fixed end of the plug chain. Failing that, the whole of the bit inside the bath may unscrew from the bit outside the bath. [Have a look at a bath waste and overflow in a plumber's merchants - and you'll see how it all fits together].

[OldBill]

On the cheapo types often all of the inside-the-bath round metal bit screws onto the outside plastic overflow adapter. Very easy to cross-thread. Its standard practice to have to remove the overflow to work on the hot tap feed. But don't bother, as SS says replacing the

15mm will make sod all difference.

[john.stumbles]

Not at all that you'd notice.

[Egremont]

OK I'll leave well alone - thanks for saving me an awkward job!.

There's just the one elbow in the existing 15mm cold supply, none in the hot. As I usually use more hot than cold to fill the bath, I'd thought of upgrading the existing cold (more accessible), then switching tap heads and re-plumbing that as hot. But I probably won't even bother with that.

Thanks, Egremont.

[Christian McArdle]

Very little at 2 bar. Perhaps more at low pressure.

Christian.