Sizing an orifice / nozzle for pressure drop
Sizing an orifice / nozzle for pressure drop
(OP)
OK guys and gals, I'm new here but I'm hoping that you guys may be able to help me out. I'm tasked with creating a fixed flow restriction to test our pumps against. I know the pressure required, the flow rate, the inlet pipe size, etc. Basically I know everything I just need to calculate what size orifice or nozzle that I need to put inline to maintain a constant pressure at a fixed flow rate. I have two different flow conditions. Both of which we are simply pumping water for a fixed amount of time to commission our pumps.
Condition #1 - 727.2 GPM at 3000 PSI
Condition #2 - 727.2 GPM at 4000 PSI
Basically I'm looking for a way to calculate the orifice size required to achieve the 3000 psi and 4000 psi pressure against our pumps while flowing the required 727.2 GPM. The liquid is water and we will be pumping through a 2" XXH wall pipe (1.5 inch I.D.).
I've been using the calculator and formulas from this website:
http://www.efunda.com/formulae/fluids/calc_orifice...
And specifically I've been starting with the equation P1-P2 = 1/2*rho*V2^2 - 1/2*rho*V1^2
I combine those results with a coefficient of discharge Cd based upon the type of orifice or nozzle that I use and theoretically that should give me the pressure difference across the orifice correct? Or am I off base here? Thanks for the help!
Condition #1 - 727.2 GPM at 3000 PSI
Condition #2 - 727.2 GPM at 4000 PSI
Basically I'm looking for a way to calculate the orifice size required to achieve the 3000 psi and 4000 psi pressure against our pumps while flowing the required 727.2 GPM. The liquid is water and we will be pumping through a 2" XXH wall pipe (1.5 inch I.D.).
I've been using the calculator and formulas from this website:
http://www.efunda.com/formulae/fluids/calc_orifice...
And specifically I've been starting with the equation P1-P2 = 1/2*rho*V2^2 - 1/2*rho*V1^2
I combine those results with a coefficient of discharge Cd based upon the type of orifice or nozzle that I use and theoretically that should give me the pressure difference across the orifice correct? Or am I off base here? Thanks for the help!





RE: Sizing an orifice / nozzle for pressure drop
RE: Sizing an orifice / nozzle for pressure drop
assume a c value and you can calculate the theoretical value very easily. you don't really need an online calculator to do this, it is a simple formula
Q = CdA(2gh)^2
problem is that you will never assume the correct orifice coefficient nor will you be able to verify exact pressure so you will never get an accurate flow rate, at least not to the accuracy implied in your post.
you would be better off installing a pressure gauge, flow meter and a throttling valve
RE: Sizing an orifice / nozzle for pressure drop
RE: Sizing an orifice / nozzle for pressure drop
The orifice plates are drilled out. You can adjust the size of the plate by removing more material. Alternatively, you can have several orifice plates fabricated and use the size that fits your needs.
RE: Sizing an orifice / nozzle for pressure drop
I would say that a series of orifices ( 4,5 or 6) to take out 75% of your pressure drop then regulate with a control valve to fine tune your rather precise flow rate.
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RE: Sizing an orifice / nozzle for pressure drop
Do you have any feeling on if a nozzle will last longer than an orifice in the application?
RE: Sizing an orifice / nozzle for pressure drop
At the velocities you must be having, an orifice would wear out faster than a valve.
I really don't understand why a correctly sized and built choke valve is wearing out as fast as you imply. Can you supply details?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Sizing an orifice / nozzle for pressure drop
It's not that the choke valve isn't working or wearing out too quickly. It's just that currently we rent the choke valve setup and it has a very expensive monthly cost associated with it. And for something that really isn't used very often (or for very long periods of time) we feel like we are spending too much money on renting the choke valve. We're just testing pumps a couple times per month. We were just thinking that a simple fixed flow restriction would allow us to accomplish the same thing for a lot less money.
Thanks!
RE: Sizing an orifice / nozzle for pressure drop
I still think you want a stage spool, maybe a many as 10.
Your small orifice might easily cavitate or vapourise the water, see, https://neutrium.net/fluid_flow/cavitation-in-rest... The noise may also be very loud
I got about 3mm orifice hole diameter as a single plate which is just crazy.
These guys make some and others will as well. They advise multi stages above 300psi drop.
www.tmtecnomatic.com/multi-stage-restriction-orifi...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Sizing an orifice / nozzle for pressure drop
I am curious as to how you got the 3mm orifice diameter. When I use the online calculators or the orifice equation listed about they all show orifice diameters of somewhere between .60 - .75 inches depending on what we assume the coefficient of discharge to be. I may be doing the calculations wrong though.
Considering the Orifice Equation Q=Cd*A*SqRoot(2*G*h) Where h=pressure head, G=Gravity, Q= Flow Rate and A=Orifice Area.
I'm assuming that I'm trying to achieve 3000psi of pressure on the pumps and that would equal 6930 feet of head.
A flow rate of 727.2 GPM equals 1.6202 ft^3/sec
Gravity at 32.2 ft/sec^2
If we just assume Cd is 0.8
That leaves us with the Area of the Orifice A = Q/Cd*SqRoot(2*G*h)
That gives us an orifice area of 0.00303 ft^2 or 0.43655 in^2, solving for the diameter of the orifice that gives us around a 0.745 inch orifice diameter. Am I doing something wrong in my calcs?
RE: Sizing an orifice / nozzle for pressure drop
However I think noise and cavitation make a single plate hole unsuitable so I think it's not the best way to go forward.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.