pressure & flow question

[pmx_super]

The mains supply to my cold water cistern is from 2x 15mm pipes which join at a T to feed a single 15mm pipe which then connects to the valve.

Am I right in thinking that having the 2 supplies to the T won't make any difference to flow because they end up going into a single length of 15mm piping, but if I replaced this section with a 22mm pipe it would make a difference?

 

[Agile]

No you are wrong.

The flow is subject to resistance in a thin pipe !

Tony

 

[rebuke]

It sounds very odd having two pipes feeding in to a single one - are you sure you're looking at it the right way round (i.e. it isn't that one is a supply, one goes to your cistern and another feeds something else entirely (e.g. F+E tank)?

 

[pmx_super]

No you are wrong.

The flow is subject to resistance in a thin pipe !

Tony

Hmm, ok.. point taken, how about if we assume frictionless pipes?

I guess what I'm really getting at is will adding a 22mm pipe after the junction actually double (22/15 squared) the flow in this situation?

 

[pmx_super]

It sounds very odd having two pipes feeding in to a single one - are you sure you're looking at it the right way round (i.e. it isn't that one is a supply, one goes to your cistern and another feeds something else entirely (e.g. F+E tank)?

Oh yeah, that makes more sense.

I was thrown by the fact that the join was about 6" from the tank, and after a clear 2m vertical run from 2 parallel pipes. Come to think of it I know exactly where the second supply goes.