A plumbing query

[zippy]

Been racking my brains on this one:

My kitchen hot tap has very low flow, as the header tank is only 2 metres higher than the tap.
Currently the pipe from header to the hot water tank is 22mm, and that from the hot water tank to the tap is 15mm and approximately 8 metres long.
I cannot easily change the last metre of 15mm pipe at the tap end, but if I were to change the rest of the pipe to 22 mm would it make any improvement at all to the flow rate ?

I'm sure I could get an answer by joining a plumbing forum, but thought I'd ask here first to save the hassle !

 

[garyi]

Well I think that the bottle neck would appear in the smallest part of the travel, i.e. at the tap end.

I don't think you will run 22mm pipe right out of the tap therefore your sink won't fill any quicker. A pump would help.

I might be wrong.

 

[steveledzep]

Problem may be with the tap. 2 metres head of water is about 0.2 bar. What is the required pressure for your kitchen tap ?

 

[steve watkins]

If it is a new tap you might also find a flow restrictor somewhere in the tap itself. Sometimes just screwed into the outlet. Once removed it should be a little better.

 

[mudlark]

Full pipe have a know flowrate for any head. I would guess the 1 m of 15 mm will have similar flow rate to the original pipe. (I'm only guessing from a recollection of the fluid dynamics I did at college 25 years ago)

 

[simeon]

Full pipe have a know flowrate for any head. I would guess the 1 m of 15 mm will have similar flow rate to the original pipe. (I'm only guessing from a recollection of the fluid dynamics I did at college 25 years ago)

Indeed. A narrower pipe will increase the velocity of the stream but not the amount of water coming out per unit of time (the flow rate).

Fluid dynamics from 40 years ago

 

[zippy]

thanks for the replies - I guessed it wouldn't make a difference.

re: other comments-

The tap was sold to me as 'low pressure' but in truth I don't believe it is. Trouble is you only find out these things after its fitted so cannot now take it back.

I did improve the tap a little by removing a mesh filter from the outlet.

I think I'll just live with it - can't be bothered to buy and install yet another tap and don't use the hot water that much anyway.

 

[Wilky]

Hi Chris.

Also check that the restriction is not caused by any isolating valves on the pipe run to the hot supply.

Best to use a full bore type valve (15mm gate valve or full bore lever).
Standard 'ballofix' type valves can have a very restricted bore often < 8mm and will definitely add to the problem.

Dave.