Orifice plate sizing 1

[hosec]

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.

 

[davefitz]

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.

 

[hosec]

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

 

[charrid]

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!

 

[TD2K]

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

 

[EGT01]

Hosec,

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

 

[hosec]

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.

 

[TD2K]

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.

 

[duika]

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

 

[martindup]

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

 

[Cockroach]

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

 

[poetix99]

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.

 

[abcmex]

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.

 

[hosec]

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

 

[jsummerfield]

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

John

 

[m777182]

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

 

[jimkden]

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.

 

[stewbaby]

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.

 

[kmpillai]

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

regards,
KMP

 

[stanier]

SIze your orifice plate on line

http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm