How does a restriction orifice reduce flowrate?

[Nichyin]

Good morning all,

I have a question with regards to sizing an orifice line.

I have a situation whereby the flow in the pipeline is 500kg/hr downstream of a valve =, of a certain gas, and my customer would like to restrict the flow to 200kg/hr.

The question is, when I input the data into my company's orifice sizing program, for the flow rates, what values do I put? I want to use 200kg/hr for the both the maximum and normal flow as we are sizing for a 200kg/hr line based on a given pressure drop, and I've done the necessary workings but I am still unsure about my method.

I appreciate all the help in advance!

 

[hacksaw]

Orifice sizing codes are generally for flow measurement only.

Restriction orifices are sized for thick plates and commonly with multiple orifices where noise is expected to be significant.

If you do use your sizing code, size the plate for pipe taps they most nearly represent the permanent loss. You can set the normal and maximum flow to the same number.

 

[bimr]

The restriction orifice causes an increase in pressure drop in the pipeline. The increased pressure drop reduces the pumping output.

There is an FAQ for orifices:

http://www.eng-tips.com/faqs.cfm?fid=841

 

[davefitz]

For the max flow case , first determine the valve's outlet pressure at max flow with the valve wide open and max valve inlet pressure , using the ISA valve equations.

If you know the RO restriction orifice's downstream pressure, then size the RO such that the pressure drop across the RO provides the required pressure at the valve outlet , previously calculated above. For a rough guess of a thick RO, there will be about 1.5 velocity head loss across an RO ( based on upstream conditions).

If the RO is being used to limit the "casualty flow" through the control valve to a value lower than the downstream system's relief valve capacity, then the removal of the RO in the future would be a safety issue- it is not clear if most plants would allow this use of the RO due to its safety implications.

"Whom the gods would destroy, they first make mad "