I am designing an orifice plate to reduce the pressure in a system.  I know how to use orifice plates to measure flow via differential pressure, but I do not know how to calculate the losses in head pressure in a system due to this constriction.  Anybody know of some resources?

Here are my givens.

Fluid- Water
Pressure- High side 2800 psi
Pipe diameter- 3.438 in
Desired pressure downstream- 950 psi
Find Orifice diameter.

About 10 years ago a sub-committee of the API 14.3 Gas Measurement Committee developed a correlation for permanant pressure drop that was published in the April, 2000 version of API 14.3 Part 2 (section 2.4.5.1).  This is presented as a table where permanant pressure drop varies with beta ratio (for a 0.2 beta you lose 95% of the dP, for 0.75 beta it drops to 45%).

These numbers are for an API 14.3 plate.  If you increase the thickness of the restriction, the permanant pressure drop increases until it approaches 100% for all choke sizes at about 3 pipe diameters.

I concur about damage.  Since we don't know all the facts, I just led him to a water trough.

I've seen similar problems, the up and downstream pressures are fixed by other control systems.  If you needed to maintain a minimum flow on a pump with the given conditions, you size the orifice to do maintain the m inimum flow.  Yes it appears to be a waste of energy, but, it depends.  Small injection systems where min flow is 5 gpm, that wouldn't be much of a loss and the capital for an RO is almost zero compared to an elaborate valve.

Another place is where you have a blow down systen durin an upset. Example: There is a 2" ball valve that vents to VRU to get the material out of the system.  We didn't want to flow more than 15,000 lbs/hr.  Plug in the up/down stream pressures, max flow, bingo a .375 plate.  Its only used in an emergency, so worrying about errosion isn't a concern. we had this type arrangement all over the plant.

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