Orifice Plate - Flow reduction

[IGSAM]

Hi,
We want to fabricate an orifice plate to reduce a flow in a pipe.
To summarize, we have two pumps running at 1,100m³/hr discharging into a treatment system that cannot handle more than 1,800m m³/hr. The pumps do not have a VFD.
Our quick solution is to reduce the flow using an orifice plate. I have base my calculation, to find what size of orifice we should install, on Bernouilli’s derive equation as shown on Wikipedia :

https://en.wikipedia.org/wiki/Orifice_plate

My problem is the formula requires a differential pressure.
I don’t have this value, and I could only have it if the orificie plate was already made and installed with two points of pressure measurements.
Does anyone have a way to pass over this issue? Or use another formula?

Thank you,

 

[MikeHalloran]

You need to model the pipe system well enough to get a load curve to superimpose on the pump curve to find an operating point, then add an arbitrary orifice, and repeat until you get to the flow you want.


Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

Or install a control valve and then close it until you get the flow rate you want...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

Have you considered an impeller trim on the pumps to reduce flow rate, a more economical long term solution?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[georgeverghese]

Pressure upstream of the square edged restriction orifice would be what you get from the pump at 1100m3/hr at the location of the RO, while that downstream would be the backpressure seen at the RO due to 1100m3/hr flowing into the treatment system.

This diff pressure at the RO is the permanent pressure loss and not the vena contracta dp. Also take into account any vapor space pressure in the downstream treatment system. For this RO to work, both upstream and downstream pressures at the RO must be relatively invariant with all operating modes you'd expect to have, else you may have to resort to a much more expensive control valve option. And of course, the fluid must be relatively solids free. And also check that the vena contracta pressure at the RO is above the saturation vapor pressure of the fluid you're pumping at the max operating pumping temperature. Typically beta ratio for this RO would be between 0.2 and 0.8, and RO hole dia should be more than 3mm.