Mains pressure v's flow in West Sussex

[Brooksie]

I have been measuring domestic mains pressure in the Horsham area using a Monument guage screwed onto standard 3/4 inch garden taps.

I've found that in the country the pressure can be higher than expexted eg 5.4 bar, 7.3 bar but the flow into the cold water storage tanks in the loft is low if not a bit pathetic.

On the Horsham estates the pressure seems to average around 3.5 bar but the flow into the tanks is noticably greater. Have not measured the flow though to quantify.

Can enyone explain this please? What is the fundmental relationship between pressure and flow?

Thanks in advance for you help
Martin

PS : Almost all the rising mains above ground I've come across so far are 15mm pipe.

 

[Mike Jackson]

Pressure in any given area will be a constant. The flow is dependant on the bore of the pipe so if it is restricted the flow is less.

 

[Puddle]

your tanks filling slowly could be a faulty ball valve restricting flow to tank or a isolation valve not opened fully

 

[justlead1]

Hi. If the problem is cistern not filling quick enough? try fitting an equilibrium ball valve. This will give you a much greater flow rate. Good luck

 

[Alanka]

It would be really useful and informative if you measured the flow rate as well as the pressure at the garden taps! You can do this by simply timing how many seconds it takes to fill a bucket (typically 2 gallons, 10 litres) or a measuring jug at full bore. Then calculate the flow rate in litres per minute.

 

[Bernie2]

Try OFWAT site, its got a lot to say about low pressure and flow. Its in the FAQ's section under the heading of "What levels of service should a water company provide" click on the title then go to the bottom of the page and click on the report itself. Low pressure comes under DG2. Its a good read.

Apparently water companies are allowed to keep pressures low in their distribution system to help avoid leaks, but not lower than the stated minimum of 10 metres head with a flow rate of nine litres per minute .

Incidentally pressure will fluctuate depending on how you measure it. One measure is static with no water running and the other is dynamic with the water running. If your fitting an appliance then its the dynamic pressure you usually want to know.

Also you will probably find pressure is greater at the bottom of a hill than it is at the top. Get a contour map and have a look at your readings.

So if its only a 10 metres head or about 14.2 p.s.i or 98.0665 kPa, that is just less than 1 bar, how you get it up to the top flat in a block of flats 10 stories high is a job for pumps, pneumatic tanks and water store tanks?

Hope this helps