Water pipe diameters

[oldgit72]

I am planning my pipe runs for a new installation. In the reference book I am using it is suggested that different diameters are used for different appliances ie 8mm (toilet), 10mm (wash basin), 12mm (shower) all fed from a 16mm pipe from the nourrice. This will obviousle result in several reducers being required along with purchasing small lengths of some diameter pipe. As I intend to use PER which seems to be available only in 15m+ lengths,my question is, is it absolutely neccessary to use different diameters for all appliances or can you, for example, in a bathroom use 12mm for all and if so, what would be the disadvantages?

[Chancer]

I think it is just another example of traditionalism and tradesman trying to make what they do seem complicated.

In copper you dont need reducers as one size fits into the next, there is a minor cost saving on the smaller pipe sizes but you then have to stock all of the elbows and fittings, some people say that 8mm is needed to reduce the noise of a WC cistern filling with the high water pressure, I use WC's suspendu where the cuvettes are insulated and behind plasterboard so that is not an issue, I prefer for the cistern to fill quicker

They even use 8mm in public toilets which is ridiculous; a plombier tried to tell me it is the law! More like forcing shops etc to have moe cisterns to plumb.

All of the plombiers that I have seen that use PER, and more and more are going over to it seem to use12mm exclusively within the bathroom.

[LesFlamands]

Strictly speaking smaller diameter pipe is used to feed the toilet cistern so that if the toilet is flushed whilst the shower is in use it causes less of a draw on the cold feed resulting in less of a temperature change.

For a PER installation I would use the 20mm to supply hot and cold to the room, 16mm for the bath and shower and 12mm for the basin and toilet. All the reducing Tees are readily available.

[Chancer]

Thanks for that Charles, it all adds to my knowledge.

I guess its not so much of a problem with the toilet and shower in the same bathroom.

[BIG MAC]

And as we all know that to reduce the pipe size makes the velocity of the water increase and along with it the noise the plombier is talking.........anyhoo. What happens when you stick your finger across a hosepipe whilst oit is running? you reduce the bore of the pipe and the water comes out faster.......venturi effect same amount trying to get through a smaller gap goes faster.

If you use 12mm right up to the fitting it looks ugly IMHO but simple enough top use a compression fitting to take you back onto copper for the 'Tails' to appliances. Dont forget to use the correct inserts inside the pipe before putting the fitting on. I always wrap the olive once slipped onto the pipe in a few tight winds of PTFE Tape.

 

[Gluestick]

Here is a useful set of calculators for Pipe Sizes and other variables.

http://www.pipeflowcalculations.com/flowrate/index.htm

Remember, the pressure in a fluid pipe is constant: since the first principle of Fluid Dynamics is that liquids are basically incompressable.

In a practical sense too small a pipe can actually limit volumetric flow: example; I have a big Pressure Washer. 2.5 Kw motor, 160 Bar.

On the existing hose tap in my barn, this was plumbed in using 10 m.m. copper pipe. (Since a loo sits behind the barn wall in the house and it was lazy simple for the plombiere, before we purchased the place).

Using this makes the pressure pump cavitate.

I installed a proper 16 m.m. dedicated Hose Tap outside the house, fed from the main water feed. Pump works perfectly happily.

Thus whilst the concept of constant "Head" (Pressure) will always apply (Since water is an incompressable fluid) and whilst the nominal velocity will increase somewhat as pipe sizes are reduced, internal friction and the change to the laminar flow will restrict volumetric flow: and if the pipe is long enough, pressure will drop too; marginally.

Not too sure about your Venturi Effect, Mac; most venturis employ identical size piping before and after the restriction: as in a Carburettor. The Venturi is employed where the main jet sits.

Fluid Dynamics is an interesting area of study in any case.

Look at the analogy to Ohms Law: the most useful in comprehension.

http://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation

http://www.engineeringtoolbox.com/pipes-fluid-flow-pressure-loss-t_18.html

Venturi Effect:

http://en.wikipedia.org/wiki/Venturi_effect

Bernoulli's Principle:

http://en.wikipedia.org/wiki/Bernoulli's_principle

 

[oldgit72]

Thanks all for the responses. I think i'll probably use 20mm/12mm for all. I take the point about 12mm pipe looking a bit ugly but as I intend to box as much in as possible then this shouldn't be an issue. Also, i am planning on putting isolating valves to each outlet and I've heard these are expensive in France. As I am in the UK until next week, should I buy these in the UK? would they be compatable with the PER pipes used in France and would I make much of a saving? I need 13 valves to isolate all hot/cold feeds.

Thanks

[BIG MAC]

[quote user="Gluestick"]

Here is a useful set of calculators for Pipe Sizes and other variables.

http://www.pipeflowcalculations.com/flowrate/index.htm

Remember, the pressure in a fluid pipe is constant: since the first principle of Fluid Dynamics is that liquids are basically incompressable.

In a practical sense too small a pipe can actually limit volumetric flow: example; I have a big Pressure Washer. 2.5 Kw motor, 160 Bar.

On the existing hose tap in my barn, this was plumbed in using 10 m.m. copper pipe. (Since a loo sits behind the barn wall in the house and it was lazy simple for the plombiere, before we purchased the place).

Using this makes the pressure pump cavitate.

I installed a proper 16 m.m. dedicated Hose Tap outside the house, fed from the main water feed. Pump works perfectly happily.

Thus whilst the concept of constant "Head" (Pressure) will always apply (Since water is an incompressable fluid) and whilst the nominal velocity will increase somewhat as pipe sizes are reduced, internal friction and the change to the laminar flow will restrict volumetric flow: and if the pipe is long enough, pressure will drop too; marginally.

Not too sure about your Venturi Effect, Mac; most venturis employ identical size piping before and after the restriction: as in a Carburettor. The Venturi is employed where the main jet sits.

Fluid Dynamics is an interesting area of study in any case.

Look at the analogy to Ohms Law: the most useful in comprehension.

http://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation

http://www.engineeringtoolbox.com/pipes-fluid-flow-pressure-loss-t_18.html

Venturi Effect:

http://en.wikipedia.org/wiki/Venturi_effect

Bernoulli's Principle:

http://en.wikipedia.org/wiki/Bernoulli's_principle

 

[/quote]

 

So much for keeping it simple. so we have say 16mm pipe going to 12mm pipe going through a half inch fitting.....Pedants of the World unite!

[Gluestick]

Well; keeping it simple then, Big M, why do you think fire hydrants are so big?

And why are fire hoses so large in diameter?

'Cos they need the volumetric capacity!

Or the appliance pump cavitates.

[:-))]

[Chancer]

[quote user="oldgit72"]Thanks all for the responses. I think i'll probably use 20mm/12mm for all. I take the point about 12mm pipe looking a bit ugly but as I intend to box as much in as possible then this shouldn't be an issue. Also, i am planning on putting isolating valves to each outlet and I've heard these are expensive in France. As I am in the UK until next week, should I buy these in the UK? would they be compatable with the PER pipes used in France and would I make much of a saving? I need 13 valves to isolate all hot/cold feeds. Thanks[/quote]

I bought mine inthe UK and paid 73p each for them, I have yet to find them in France but my pal has seen them for sale for use with manifolds or nourrices, he reckons that they were more than €10 each.

As for compatibility I used mine on 15mm UK spec pipe and took off the other compression nut to fit the 1/2 bsp (or 3/8 with an adaptor)flexibles to the taps.

[oldgit72]

Can you buy 15mm pipe in France?

[RicandJo]

[quote user="oldgit72"]Can you buy 15mm pipe in France?[/quote]

....Nope.....

[Chancer]

Only from me and I aint selling!

15mm by 0.7mm wall thickness is a preferred size in the European norme EN1058 but France is too traditional to try anything else.

[BIG MAC]

[quote user="Gluestick"]

Well; keeping it simple then, Big M, why do you think fire hydrants are so big?

And why are fire hoses so large in diameter?

'Cos they need the volumetric capacity!

Or the appliance pump cavitates.

[:-))]

[/quote]

I dont think Fire Hydrants are 'So big'  and fire hoses are so large in diameter principally because they are a series of thin hoses drawn over each other, need to be handled by humans are heavy  so are optimised in size, weight and performance. A fire tender will be able to pay out many lines so in theory the hoses could be the same size as the main and if they were there would be little noise generated by restrictive fittings or smaller interim sections of pipe........or cut'n'paste merchants. [:-))]