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Orifice plate sizing

Orifice plate sizing

Orifice plate sizing

(OP)
Are you able to advise the size of an orifice plate that will be fitted into a fire hydrant main to give a pressure drop, (when 1 hydrant is running at full bore) from 180 psi to 55psi.

The main is Thin Wall Stainless Steel line with an internal diameter of 150mm, and a fire hydrant connection is nominally 50mm dia.

RE: Orifice plate sizing

No.

More data is needed, You need to know the required flowrate. If you do not have the requreid flowrate, then you need to specify the additional restriction caused by the firehpse and spray nozzle.

RE: Orifice plate sizing

(OP)
Thanks davefitz; I am anticipating a target flow rate of 450 Litres per minute (about 100 gpm). Does this help?

RE: Orifice plate sizing

Can one of you guys tell where I can down load a trail version to caculate or sizing orifice plate?
If there is a suggestion to buy one , please tell me! I really need it!

RE: Orifice plate sizing

I get about 0.705 inches (don't know how precise you want it).

RE: Orifice plate sizing

Hosec,

Just curious, why would you want to restrict the flow to a fire hydrant?

RE: Orifice plate sizing

(OP)
Thanks all for your comments:

1 TD2K - How did you calculate that? what is the correct formula to use?

2 EGT01 - This is a client request. I'll try and find out, but I can suggest that the main pressure of 180 psi (12.4 bar) results in a too high a reaction force on the fire fighting hoses.

RE: Orifice plate sizing

It's based on the formulas in Crane's paper on fluid flow.  If you don't have one, get it, it's a wonderful reference.

RE: Orifice plate sizing

hosec

with the crane paper, the flow to regulate and the drop pressure, you can get the inside diameter of the orifice plat for these variables

RE: Orifice plate sizing

hosec,
please consult the NFPA on this. I recall something about orifice plates not being allowed at all in firewater distribution pipelines in some applications. I don't know in what NFPA standard I saw it because I was going through the standards looking for something else.

charrid,
I can send you a exel spread sheet I drawn up that calculate orifice sizing I made for gasses if your interested. Else you can get the info from the ISO spec on the matter of flow restricting massflow meters from which I made. Can't remember the number though. To buy one such software is not necessary, the calculation is straight forward.
Martindup

RE: Orifice plate sizing

Actually, all of you are going down the wrong rabbit trail.  Orifice measurement is typical in the oil and gas sector, in particular, pipeline measurement.

There are several good programs available on the market.  Before spending a lot of really good doe, I would suggest a book by Miller, Measurement Handbook.  This book is an industry reference. a benchmark as so to speak, to orifice plate measurement computations for pipeline, hydrocarbon and related industries.  My suspicion is that it will lend itself well to water applications.

In general, you are running an ANSI Class 150 application which suggests that a beta ratio of 0.65 would give you near a 100 inch of water differential pressure across the orifice plate. This would suggest 0.705 inches is erroneous under the American Gas Association Report Number 4, which is equivalent to API 14.3, as a throat diameter for the orifice plate.  On the other hand, buddy wants a dP equal to 180 psi to 55 psi when the fire hydrant is full bore.  This is yet a bigger issue.

I would suggest using a Venture Nozzle and not and Orifice Plate due to structural mechanical issues associated with energy transfer to the equipment.  In conventional Bernoulli Obstruction Theory, why would you want to restrict flow to dP= 180 psi in a throat design anyways?  Number one, you're going to bend the orifice plate, number two, coefficient losses exceed expected dP losses, number three you need bolts bigger than Anna Nicole Smith's legs to keep the flanging together!

And from where I sit, that's getting rather ulgy!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

RE: Orifice plate sizing


Cockroach,

With all due respect, dropping 125 psi across an orifice is not that big a deal; less than 3800 lbf across the entire flat plate

In fact, the actual drop across the orifice will be somewhat larger than 125 psi because downstream pressure recovery should also be accounted for.

When applying (or misapplying, as the case may be) an orifice as a restriction - as a throttling device - using a venturi or flow nozzle would be exactly NOT the point.

Keeping Beta ("Beta" is a ratio, "Beta Ratio" is redundant.) within certain ranges is important when using an orifice as a flow metering device.

RE: Orifice plate sizing

Hosec,

I agree with COCKROACH, your client is trying to get something it may not work. The pressure drop that has been calculated probably is not relevant to your application. The problem is (my understanding) that you have a high pressure on the FF-pipeline, if you put an orifice you will drop the pressure only with full flow .
 
The way a fire hose works may be different; it has a variable nozzle (orifice) itself and this will reduce the flow, less flow, less pressure drop on the orifice, less pressure drop, higher reaction force
MARTINDUP is right you should review the applicable code too. In China they sell hydrants with a pressure reducer intergrated because they accept only 4 bar in hydrant located inside buildings.

RE: Orifice plate sizing

(OP)
Some good points here. - I will check up on the crane's paper on fluid flow (I presume that it is the  "Crane Technical Paper No. 410" - found following a web search), and Miller's Measurement Handbook.

martindup - I would be interested in seeing the spread sheet - I can be mailed at andrew_1_3@hotmail.com

 

RE: Orifice plate sizing

I think that Foxboro (Invensys) have free flow meter sizing software.

John

RE: Orifice plate sizing

I have a piece of Vba code for sizing orifice plates according to EN ISO 5167(1995-11).At the moment it is done for air flow but can be easily upgraded for different fluids.
m777182

RE: Orifice plate sizing

I concur with TD2K on .70 inches, by separate means of calculation for a permant head loss of 125 psi @100gpm in a 6 in nom size pipe.
Can't comment on whether it is allowed to have orifices in fire mains, leave that to a NFPA guy.
Orifices can be made thicker, but that isn't the question posted.

RE: Orifice plate sizing

Get a free orifice plate sizing program from a flow measurements representative such as Emerson / Daniels or such...make the sales reps work for you.

RE: Orifice plate sizing

Dear friend,
Please refer British Standard BS 1042, you can design on your own orifice plate.

regards,
KMP

RE: Orifice plate sizing

hosec
I agree with this opinion that orifice plate not use on hydrant pipes.
but  "ISO-5167 standard" and "shell flometer eng. handbook" are good reference to designing orifice plate for water and gas.

RE: Orifice plate sizing

May I know where can I get a flow coefficient,Cf versus beta (orifice outer diameter/orifice inner diameter) graph? How do I obtain flow coefficient without doing experiment? Thanks for answering.

RE: Orifice plate sizing

In the EN ISO 5167-1995/A1 you will find in TAB A1...TAB A11 (pages 4..14)values for coeff. C as a function of beta(for beta=0.1 to 0.5 by step 0.2 and 0.5 to 0.75 by step 0.1), Re-number (for Re=5E3 to 1E8) and type of deltaP joint ( 3 types of deltaP joint).
m777182

RE: Orifice plate sizing

Hello mech52
I wrote a Vba code for orifice sizing according to EN ISO 5167-1995 too; at the moment it works for air flow only because that was what I needed.
m777182

RE: Orifice plate sizing

The Chem. Eng. Plant Notebook of August 17, 1987 brings an article by Herman E. Waisvisz titled Quick sizing of restrictive orifices that may serve as a tutorial, with a worked out example.

RE: Orifice plate sizing

I agree with TD2K. The result is a 0.7 inch hole in the center of the plate. However you must chek that the plate is cavitation free. With 125 psi delta P and 55 psi downstream pressure the cavitation coefficient is less
than the plate cavitation index, so you will have cavitation and noise in the plate. To avoid this I suggest to use a multiple orifice plate. I have tested different plates of this type (3 to 30 inches size) and the first
results were piblished in POWER, September 1991.I n this paper you can find how to calculate multiple perforated plates.
Regards

RE: Orifice plate sizing

I am amazed, How many answers focus how to size a orifice plate (probably well intended) but

does a properly sized orifice plate solve the problem described originally?

Hosec, focus on your problem you will see that an orifice plate will only work at full flow as soon as you reduce the flow or use the nozzle at the  tip of the fire fighting hose the parameters are different.

Kind regards

RE: Orifice plate sizing

If NFPA allows, I don't see the orifice a problem. The pipe is for one hydrant only. If the discharge valve is an on-off valve, you always get full flowrate; if the valve is a throttling one, when the flowrate is smaller, the orifice does give a smaller pressure drop, but the throttling valve will do the rest.
But I have the same concern with aatara, cavitation can be a problem. Multiple orifices can be a good choice.
Regards

RE: Orifice plate sizing

Hallo,

I have searched the net for the article about quick sizing of restrictive orifices ( chem. eng. plant handbook, augustus 17 1987 ) as mentioned by member 25362. I did not find it. How can i obtain a copy of the article.

Kind regards

W. Kleppe

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