pressure for a combi

[easyecho]

I wish remove the airing cupboard and have a better shower so a high flow combi ( 2 bathrooms and 5 adults). Taking advice from the forum I had 3 plumbers including the gas board for a quote. No used a pressure gauge and visually checked the flow from the kitchen tap and said not enough pressure.

I have a new 25mm mpde supply to the house with 2m of 15mm before the 15mm stop valve. The stop tap in the pavement and inlet the the house are fully open. At the kitchen tap I have 12 l/m. With a gauge on the garden tap, 2 m from the house stop valve I get 20m+. With the kitchen tap fully on I still get 6m at the gauge..

The gives some questions.
As the kitchen tap is a mono bloc mixer is the flow restricted (.6 bar back pressure )so gives a bad indication of flow avaiable?

Does the 15mm stop tap limit the supply to the house?

If I reduce down from the 25mm MDPE to 22mm with a 22mm stop valve and 22mm to the boiler what flow can I expect .
Thanks for reading the message

 

[gas4you]

The larger pipe will give a slightly better flow but the pressure will remain the same.

I cannot see that going to 22mm will increase your flow by 50% though, which by your figures at the kitchen tap, is what you should look for to get the most out of a storage combi.

 

[Agile]

I have a new 25mm mpde supply to the house with 2m of 15mm before the 15mm stop valve. The stop tap in the pavement and inlet the the house are fully open. At the kitchen tap I have 12 l/m. With a gauge on the garden tap, 2 m from the house stop valve I get 20m+. With the kitchen tap fully on I still get 6m at the gauge..

20 m and 6m are lengths of meters!

Do you mean litres per minute?

What kind of gauge were you using?

Its quite possible that pipework and fittings are restricting the flow rate.

Tony

 

[easyecho]

sorry I meant 20m head and 6m head. The gauge had a full scall deflection of 2 bar (20m head).

The greenstar high flow 440 (DWH 20 l/m) tech data says 1.5 bar inlet pressure for max DHW rate. so why am I getting only 12 l/m at the tap with 2 bar?

 

[kevplumb]

cos your installer either has not taken the flow restrictor out or you might have the pressure but not the flow rate

 

[Gasguru]

First get a gauge that can read a higher pressure - perhaps the needle is hitting the end stop.

Measure the static pressure ie the maximum pressure with no water flow. This the pressure in the water main in the road.

You need to tee the gauge into a pipe off the outside cold tap. You could use a washing machine hose and some cheap iron fittings to form the tee. Then connect on a 22 stopcock to adjust the flow. Now you can measure the flowrate (time the flow onto a bucket) against dynamic or working pressure.

Since you have at least 20m (2 bar) static you should be able to achieve more than 12 l/min. Perhaps the kitchen tap is very restrictive or you stopcocks etc are blocked. Connecting onto the outside tap should verify this. Be aware that stopcocks often contain check valves or there may be checkvalves fitted upstream of the stopcock so rear flowrates will be a tad higher straight off the main.

With 1 Bar on the gauge you should achieve at least 9 litre/min (the legal minimum) but the water companies make the law up as thy see fit.

 

[easyecho]

Hi have taken some further readings.

Static 2.2bar.
flow 4 l/m @ 2 bar
flow 8 l/m @ 1.5 bar
flow 12 l/m @ 1 bar
flow 15 l/m @ 0.5 bar
flow flow 18 l/m @ valve fully open.
When the Combi data gives the required inlet pressure for max DHW flow I assume it is flow pressure so I recon I can forget about a combi as most require 1bar + so max DHW for me will be arround 12 l/s.

I get 30 l/m from bath tap with 0.3bar (22mm from header tank)
I have new 25mm x 30m MDPE from main to house so I must have huge flow restriction in the 4-5m of 15mm fittings to where I took the readings.

Any comments please.