Will changing 15mm to 22mm increase flow rate?

[eveares]

Hi all, got a quick question regarding pipe size and flow rate.

From where my new 28mm mains comes in blue plastic pipe and then gets reduced to 15mm at the internal stop cock and is all 15mm onwards inside, if i replaced this with a 28mm to 22mm internal stop cock and then run 22mm pipe to a 22mm to 15mm T junction where the water splits for cold supply upstairs and combi boiler supply, would this improve flow rate over the all existing 15mm? Especially when using cold and hot upstairs at the same time?

Regards: Elliott.

 

[Johntheo5]

What, roughly, is the total length of 15MM pipe to the T that you are proposing to change to 22mm and what are the 15mm lengths of the cold water supply and the combi supply, after the split?

 

[dilalio]

Check flow and pressure at the mdpe.
Get water supplier to check pressure and flow rate at their stop tap.

 

[Alec_t]

For a given pressure differential between the two ends of a tube the flow rate is theoretically proportional to the fourth power of the radius, and flow resistance is the inverse of that. So for the same lengths of tube with the same pressure differential, going from 15mm to 22mm reduces flow resistance by a factor of nearly 5 (allowing for wall thickness). The overall flow rate will be governed mainly by the 15mm tube if it is the major type in the system.

 

[eveares]

What, roughly, is the total length of 15MM pipe to the T that you are proposing to change to 22mm and what are the 15mm lengths of the cold water supply and the combi supply, after the split?

About 3.5 meters from the main 28mm to 15mm stop cock to where it splits at the T to feed the cold upstairs and the combi's supply. The lenth between the T and the combi boiler is about 1.5 meters and the lenth between the T and the furthest cold tap upstaits is about 3 meters.

 

[dal5band]

If there is a problem i.e. combi boiler shower output is effected by a cold tap being opened elsewhere then it may be worth it.

 

[Johntheo5]

Those lengths are relativel short.
If you assume 15mm pipe has a ID of 12mm and assuming no change and using 3.5+1.5, 5M then the pressure loss at 25LPM is 0.69bar.
If the 3.5M is changed from 15mm to 22mm and assuming the 22mm has a ID of 19mm then the pressure loss (at 25LPM) is 0.259bar.
Based on the above, a flowrate of 42LPM will result in a pressure loss of 0.67bar (almost the same as making no pipe changs) so well worth it if you have low static mains pressure.
Measuring the flowrate from any cold water tap on the end of this 1.5M pipe will point to some idea of the mains pressure.

 

[Madrab]

In most domestic settings 15mm pipe can flow more than enough if the mains dynamic flow and pressure is available to maintain it, that's the key driver for flow.

The only real drawback can be velocity and therefore noise if 15mm pipe needs to supply numerous outlets - water velocity above say 2ms and you will start to hear the flow through the pipework, noise can mean wear and tear.

Good design standards recommends 22mm from the stop tap out to each branch point for a given outlet for most domestic situations

 

[dilalio]

In most domestic settings 15mm pipe can flow more than enough if the mains dynamic flow and pressure is available to maintain it, that's the key driver for flow.

Mate, why bother with the things that you and I suggest when there's so many physics boffins on ere!

Occam's razor anyone?

 

[JohnD]

From where my new 28mm mains comes in blue plastic pipe

Blue plastic pipe is probably not 28mm

What size is it really?

Because metric pipe is described by external diameter, and plastic pipe has thicker walls than copper, 25mm plastic is equivalent to 22mm copper, and 20mm plastic, to 15mm copper.

AFAIK, the stopcock needs to be of the larger size, or it will obstruct flow.

Some people fit smaller stopcocks because they are cheaper.

 

[Madrab]

If it's relatively modern Blue MDPE, it will be 20mm, 25mm or 32mm.

Unfortunately they don't offer a full bore lever type valve for 25mm to 22mm, it would have to be a traditional turn down compression stop tap. Alternatively reduce the 25mm to 22mm just prior to the valve and then use a full bore 22mm lever valve.

 

[eveares]

I stand corrected, it was 25mm MDPE in, not 28mm. I realised that once I looked at the original stopcock had 25 and 15 written on each side of it, referring to the pipe sizes. Don't know where I got the 28mm number from, before I actually checked.

Anyway I decided to proceed ahead and replace the 15mm copper pipe with 22mm copper pipe. Soldering was not to hard once I got the knack of it.

Now as below.

Regards: Elliott.

 

[Dereekoo]

And has it made a discernible difference?

 

[Madrab]

That would be more the preferred solution as far as the internal distribution pipework sizes and setting out would be concerned.

I have to ask though - what was the problem with the flow before all of this? Were there pressure and flow tests performed to allow a before and after comparison?

 

[dilalio]

I'd hazard a guess that this was to improve the hot supply from the boiler as not first draw off and being robbed of flow by kitchen tap and appliances.