restricting and flow orifice plate design

[PMCap]

I need to design restricting orifice plates and flow orifice plates. Medium in both cases is water at 175 F.

There are many calculators on line for orifice plate design. Are these calculators equally applicable to both restricting orifice plate and a flow orifice plate design?
Are there any differences in there design and configuration requirements and do different standards for design apply such as square edge - rounded edge - plate thickness,discharge side bevels?

For restricting orifice plate designs the Client provides me pipe ID and orifice plate hole size, flow, upstream pressure and temperature and is requesting permanent pressure loss at max flow. The restricting orifices have no downstream pipe with discharge below the water surface of a lake.

For flow orifice plate designs the Client provides me pipe ID and orifice plate hole size, flow, upstream pressure and temperature and is requesting permanent pressure loss at max flow and delta P at full scale flow.


Thanks

 

[chemebabak]

PMCap,

Your first question is the most important: " Are these calculators equally applicable to both restricting orifice plate and a flow orifice plate design?"

As you may know, a restricting orifice (RO) is a plate with a hole in it. The purpose of ROs is to limit flow. An FO is an RO that has been sized to limit flow to a specified amount. You may say that all FOs are ROs but not all ROs are FOs just like all squares are rectangles but not all rectangles are squares, except that both ROs and FOs are plates with holes in them. The only difference is the calculations.

It seems that the client considers the only distinction between an RO and an FO is the DP at "full scale flow". How is your client defining max flow vs full scale flow?

 

[25362]

Suggest you use the search fixture on top of this page just by writing restriction orifice. You"ll find hundreds of entries. Some will satisfy your query. The same concerning measuring orifice.

 

[davefitz]

A flow measuring orifice has a lot more fabrications details associated with it than does a RO. Sharp edged, exact locations of upstream and downstream taps, and need for straight pipe lengths upstream and downstream are design requirements not imposed on RO's.

The software used for design could be the same, but the RO design is only focused on permanent frictional pressure drop and perhaps checking for cavitation. The FO output of primary concern is the temporary , dynamic pressure loss measured by the DP Xmittter- don't confuse those 2 different pressure losses.

 

[zdas04]

The permanent pressure drop vs. dynamic pressure drop distinction is far more important in gas flows than water flows, but it still should not be ignored. A key element in forcing a flow to shed pressure permanently is length of the hole. In gas measurement the plate thickness is limited to a tiny range because of this (that is also one of the reasons for the bevel on the backside of the plate, to minimize the length of the restriction to the minimum value reasonable without deflection).

For a restriction orifice I want length. In both gas and water I in sizes 3-inch and smaller I use "choke nipples" which are generally a 6-inch billet of metal with threads on both ends and a hole in the middle. I've found that all of the pressure drop in one of them is permanent. I've also found them to minimize cavitation by developing a flatter dP vs. distance curve than you can get with a plate. Since water is basically incompressible, you can use a RO for measurement (in gas they would violate the "incompressible" assumption in Bernoulli's Equation).

David Simpson, PE
MuleShoe Engineering

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