Splitting flow in a pipe system 3

[ThinkQuick]

Hi guys,

I need to spec a pump to provide the correct pressures / flow rates for multiple fire hoses and sprays. The sprays need 500kPa and 23 m3/hr of flow constantly. However if a valve was opened upstream of the sprays to operate a hose (through a reducing tee piece) how would I work out the resulting pressure drop at the sprays.

Cheers.

 

[racookpe1978]

1. Provide more information.

Draw your entire network of pipes and hoses and tees.
Provide desired flow rates at each outlet.
Provide pipe lengths (approximate at least) and ALL pipe diameters.
(If unknown, make a guess, and label that guess)
Provide available pump pressure and available flow rate.

Provide that drawing to those from whom you wish help.
Otherwise, we waste time speculating.

 

[LittleInch]

You either need a network model - many people here recommend EPANET for water systems - or you need to run some variations on flow using multiple sections between junctions and start iterating.

If the system is a relatively simple header and branch system, the key knowns are your end point pressures required and flows. Then you need to start summing up the flow in the branches and header as you go backwards towards your pressure source. The other key known is that the pressure at the branch point is the same for all the branches at that point.

Probably best to assume a fixed pressure for your pump to start with (although this will vary with flow in real life).

work out your worst case combination of flows and then that probably becomes your pump duty point. If you can manage that flow and pressure then all the rest will work, perhaps a little better than anticipated if only one hose or spray is working. In other words find your max flow and min flow and work out the pressure needed at the total flow for your pump. you might need some pressure regualtors in some locations for low flow cases.

Anything more than 5 or 6 branches and manual iteration takes a long time....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[bimr]

One would suspect that the fire code requires the pressure at the farthest hose connection be maintained while operating the sprays. So the sprays should not see a reduced pressure.

 

[ThinkQuick]

Thanks for the responses.

Thank you LittleInch I used a method similar to the one you suggested. For the purposes of the project they only required an approximation so modelling was not required.