Simple manifold with spaced outlets - how to get equal pressure?

[doyle]

My problem is this:

10 meter long pvc pipe, 5 cm diameter (water @ 20 deg c)
10 holes, one every 91 cm.
One end is capped and a pump is on the other end(75kPa gage)

How do i calculate varying hole sizes to obtain equal flows at each hole and equal water heights?

Thank you very much!!!
doyle

 

[butelja]

There are 2 basic options:
1.) Make the manifold pipe large enough in diameter that the velocity head in it is negligible (<10%) compared to the pressure drop across the orifices. You can then use equal sized holes and achieve nearly equal flow rate.

2.) If a smaller diameter manifold is used so that the velocity head is no longer negligible then it is more complicated. Some form of a &quot;static regain&quot; method must be used, similar to how it is done duct sizing in HVAC. This involves looking at the manifold velocity decrease (and static head increase) downstream of each takeoff. The next hole is sized based upon the slightly higher pressure. The efficiency of the static regain based upon velocity change can range from 50% to 95%. For accurate results, model testing will probably be required.

 

[jhelm]

One other simple option that should closely approximate the desired result is to design the manifold so that the flow is split and enters from each end, if this is practical. The loop will minimize the velocity head and balance the flows to each side, provided that the piping is identical on each leg.