Orfice design, pressure vs flow, water

[ttdmt]

How do you do a simple approximation of the back pressure vs flow characteristics for a certain dia hole for an incompressable fluid? I need to get 1 gallon of water per min thru a series of holes (a sprinkler head basicly). I have the number of holes, how do I calculate the proper dia. I have a range of pressure available up to 70 psi. I don't know for sure till I see the water hit the target, but I think the 15 to 25 psi range will be best for this application.

 

[RWF7437]

A submerged circular sharp edged orifice flow may be calculated using:

Q = C*A*(2gH)^1/2

Where A = area in sq ft
g = accel. of gravity = 32.2 ft/sec/sec
C 0.6
H = pressure head in feet of water

 

[ttdmt]

Thanks, I think I will do an try a couple experiments. This should be invaluable to imform those efforts.

All The Best,

TTDMT

 

[SooCS]

Unless you are designing a sprinkler nozzle, use this standardized formula,

Q = K (P)^0.5

Q flow in gpm
P pressure in psi
K factor (refer to the manufacturer's catalog)

 

[ttdmt]

Thanks for the equation. Can you give me a couple of manufacturers, preferably ones with the K factor data on line.

I am trying to design a sprinkler. I have to do a rain test and the spec calls for .8gpm to fall on the specimen at a 45 degree angle. The test specimen is good sized. So the sprinkler head is going to sit at a 45 to gravity and measure 32" x 45" long. I was going to put holes in the sprinkler at 3 x 3" ctr's. From the equ RWF7437 gave me I am afraid this concept for the sprinkler is going to require rediculusly small holes. I don't want the pressure so low the water dribles out (cause it will arc instead of hitting at 45 degrees)of the sprinkler. I also don't want to pump much more water than required, cause it makes the test unrealisticly difficult. Do you have ideas on how I can do this without drilling ridiculously small holes?

Regards,
TTDMT

 

[SooCS]

I dont design sprinkler head. I design fire protection systems.

Well your can try "bete", "Argus", "Wormuld".

But NFPA 13 do give some example sprinklers discharge characteristics.

e.g. Nominal Orifice size (in) / K factor:
1/4" / 1.3 to 1.5
5/16" / 1.8 to 2.0
3/8" / 2.6 to 2.9
7/16" / 4.0 to 4.4
1/2" / 5.3 to 5.8
17/32" / 7.4 to 8.2
5/8" / 11.0 to 11.5
3/4" / 13.5 to 14.5

Best of luck