Talk:Orifice plate

message: I have just completed re-writing this article and I believe it now a better article.  I still intend to add a section on gas flows through orifices in the next few days. - mbeychok 22:53, 2 May 2006 (UTC)
replies: text: Looks very good, Mbeychok.  I just have one suggestion, to shorten the lead section per WP:LAYOUT#Lead_section.  The equations would probably work better in their own section. Coming into the article cold, I'm used to a general lead section with details in later sections. Spalding 03:20, 15 July 2006 (UTC)
replies: text: Done. Thanks for the suggestion. - mbeychok 04:25, 15 July 2006 (UTC)
thread_title: Complete re-write and expansion

message: Thank you for your useful article on the pressure drop across an orifice plate. It would be useful if you could add a section on the losses that occur across the orifice plate. It is frequently necessary to know the losses in a system and in some instances - such as in the outlet to a variable declining rate water filter - an orifice plate is used to increase the losses to prevent excessive flow.
217.15.119.158 13:40, 5 December 2006 (UTC)
replies: text: Perhaps I don't understand your question, but Equation 2 in the article relates the mass flow to the pressure drop (P1 - P2) across the orifice for a liquid. By a simple re-arrangement of that equation, you could easily solve for the pressure drop, which is the pressure loss across the orifice, is it not? - mbeychok 19:28, 5 December 2006 (UTC)
replies: text: Thank you for your response. The pressure change in Formula 2 is due to the change in velocity in the orifice arising from the the Bernouilli Equation. If you measure the pressure downstream of the vena contracta the pressure will recover but not to the same value as the upstream pressure because of energy losses in the device. It is these losses that I would like to be able to quantify. 217.15.119.158 11:26, 6 December 2006 (UTC)
replies: text: I apologise for mis-understanding your question. I don't have one at hand, but any good textbook on fluid dynamics or fluid flow should have that information for you. - mbeychok 16:57, 6 December 2006 (UTC)
thread_title:  Losses in orifice plate 

message: These are the reasons why I deleted the external link to a "Simple orifice flow calculation":
*The equation in that link is only good for air and only for one specific air density (which means only for one specific temperature and pressure). 
*It is only good for the use of USA customary units, and we are now pretty much the only nation still using those units. The Wikipedia has a very large non-USA readership.
Basically, the linked calculation method was too limited and too simple for an article that is intended to explain orifice flow equations for use with any gas or any liquid. - mbeychok 01:46, 23 January 2007 (UTC)
thread_title:  Reason for deleting external link added by Loughmsa 

message: Flow through a sharp-edged orifice external link is not working please remove the same if it does not work for more. 59.180.94.55 10:49, 23 January 2007 (UTC)
replies: text: I fixed that link and it now works. It requires that Shockwave be installed and it did that automatically ... for me at least. - mbeychok 17:05, 23 January 2007 (UTC)
thread_title:  external link not working 

message: The article says that the coefficient of discharge can be calculated from the Reynolds' number (source given is Perry).  If someone knows how to calculate it, or has a copy of Perry to hand, I would be very grateful if they would add this information to the article (I have googled extensively in vain).
Cheers, 84.12.252.210 15:49, 4 July 2007 (UTC)
thread_title:  Calculation of coefficient of discharge from Reynolds' number? 

message: If anyone would like to fill in orifice pressures for viscous fluids... after all, most of them are, and it becomes pretty important at small radii...  Would be really nice!!! Cheers Michi zh 17:49, 26 September 2007 (UTC)
thread_title:  Orifice pressure for viscous fluids 

message: What distinction was the object of the last edit (09:16, 8 October 2007)?
The previous version says that an orifice plate "measures the rate".  It was changed to say that it "allows the measurement of the rate".
It raises the question: If the orifice plate only _allows_ the measurement to be made, then what actually _does_ the measuring?
It also raises the question: _How_ does it _allow_ the measurement?
Perhaps the point is that only people can measure?  Or perhaps that a connected differential pressure meter does a measurement which is ultimately interpreted as a flow rate?
Maybe the point is that the orifice plate is but one component in a total system which reports a flow rate.
The revised form is wordier.  Maybe it is necessary to expand the reader's vision beyond this one component.
To be consistent, the next sentence would seem to need tweaking as well:
"It uses ... Bernoulli's principle".  Actually, the orifice plate itself doesn't do this -- a person interpreting a delta_P reading might Bernoulli's principle.  More likely, they would use a precalculated chart.
Perhaps too much precision in language ultimately obscures the message by building a haystack around the needle?
I'm not suggesting undoing the last edit.  I'm just trying to understand why the wording was changed and to explore how much anthropomorphizing is appropriate in technical writing.
-- Ac44ck 16:01, 8 October 2007 (UTC)
replies: text: I completely agree with you. So I changed the wording again to avoid the excessive precision in the language. - mbeychok 17:31, 8 October 2007 (UTC)
replies: text: Re: edit at 01:09, 19 June 2008 by Gastester — "a device that is used to measure" seemed clear enough to me.  One might say that a magnifying glass can be used to "facilitate measuring" of distances, but a yard stick still qualifies as a "a device that is used to measure" distances. -Ac44ck (talk) 07:37, 22 June 2008 (UTC)
thread_title:  Measures vs. allows measurement 

message: The formulae, stated for the expansion factor is used with nozzles and venturis, according to perry's handbook.
The formulae for Y for orifices is different :
Y = 1 - [(1-r)/k](0.41+0.35Beta^4)
Comment plz.  —Preceding unsigned comment added by 195.73.116.62 (talk) 10:08, 5 March 2008 (UTC)
thread_title:  formulae expansion factor 

message: Is the applicability of the non-choked flow equation to real gases overstated somewhat?
Equation 2 seems to be exact for real gases.
The text beneath the "Flow of gases through an orifice" heading mentions that the first equation for Y is for ideal gases. Equation 3 is an approximation of Y for usual values of \beta.
As equation 4 seems to rely on equation 3, wouldn't equation 4 be for an ideal gas?
Equation 5 restores some reality to the situation by introducing the compressibility factor, but I'm not sure that it eradicates the approximation of ideal gas behavior in equation 3. -Ac44ck (talk) 22:52, 7 November 2008 (UTC)
thread_title:  Non-choked flow equation 

message: I find that the removal of middle dots to satisfy an unreferenced "SI convention" creates ambiguity in the text.
Removal of the middle dots is contrary to MOS:NUM#Conventions:
:When units are combined by multiplication, use a middle dot (·) to separate the symbols. For example ms is the symbol for a millisecond, while m·s is a metre-second.
The change from "kg/(m ·s²)" to "kg/(ms²)" raises the question: "Is that kilograms per millisecond squared?" Perhaps it should be "obvious", but it may not be.
The discussion here http://www.unc.edu/~rowlett/units/symbol.html also suggests using a dot and says "symbols should not be placed next to one another with nothing between them." -Ac44ck (talk) 19:28, 26 December 2008 (UTC)
thread_title:  Middle dots to separate units 

message: The calculated massflow for a given orifice and given pressure drop is about a factor 4 too small. This statement is based on :
- reality check with real orifices in real applications where the flow is measured by calibrated flow transmitters (error approx 1%).
- comparison with the results by CONVAL ver 8.0 (engineering software package).
168.88.70.34 (talk) 12:17, 1 February 2011 (UTC)
thread_title:  Gas massflow calculation in error 

message: This is a useful derivation to have in the Wiki, and it is mathematically correct.  However, I find it conceptually unclear where Cd is introduced without explanation.  It simply adjusts the flow term.  This is done after the continuity equation is utilized, so a reader might conclude that the mass balance has to be adjusted using Cd.  
in fact, the mass balance cannot be violated.  Cd accounts for frictional losses in the original energy balance.  It would be better, therefore, to introduce it in the energy balance.  I would suggest that, after the first equation is presented with "negligible friction losses" that it then be presented with the final term multiplied by 1/Cd^2 to include the friction loss.  Carrying this term through will then give the 7th current equation where Cd is introduced in the present version.
I am new to this and do not know how to edit the entry itself, so I'm only participating with a talk entry.
Skdentel (talk) 14:23, 22 September 2011 (UTC)
thread_title:  Where should Cd be introduced 

message: Here is an equation for volumetric flow calculation for an orifice plate flow meter found in an app note of an instrumentation manufacturer emerson. I think it is intended for use with various grades of natural gas.
Qv = 218.527*Cd*Ev*Y1*(d^2)*[Tb/Pb]*[(Pf1*Zb*hw)/(Gr*Zf1*Tf)]^0.5 
Where
Cd = Orifice plate coefficient of discharge
d = Orifice plate bore diameter calculated at flowing temperature (Tf) - in.
Gr = Real gas relative density (specify gravity)
hw = Orifice differential pressure in inches of water at 60 degF
Ev = Velocity of approach factor
Pb = Base pressure - psia
Pf1 = Flowing pressure (upstream tap - psia
Qv = Standard volume flow rate - SCF/hr.
Tb = Base temperature - degR
Tf = Flowing temperature - degR
Y1 = Expansion factor (downstream tap)
Zb = Compressibility at base conditions (Pb,Tb)
Zf1 = Compressibility (upstream flowing conditions - Pf1, Tf)
It seems to be saying that the volumetric flow rate Qv is proportion to the square root of the differential pressure (hw) multiplied by some other factors. It does not seem to be evenly remotely equivalent to the equation given in the article. (Why don't they ennumerate the equations in Wikipedia articles?)  Why is there so much discrepancy? (Entropy7 (talk) 23:32, 17 January 2012 (UTC)
thread_title:   Is practice different from theory? 

message: Equation 8, and the previous equations from which it was derived, do not seem correct. Looking at the expression within the square brackets inside the square root, as P1 becomes larger, the value of the square bracket decreases. This gives a lower volume flow rate. It is self evident that increasing upstream pressure must also increase volume flow rate through the oriface plate. In some of the related equations it will be an increase in mass flow rate.
Another problem with Equation 8: In the nomenclature M is described as Molecular Mass (also known as molecular weight). However, the units shown are for Molar Mass, not Molecular Mass and I suspect that Molar Mass is correct.
Bicyclehub (talk) 22:02, 30 July 2012 (UTC)
thread_title:  Closed: Equation 8 not correct? 

message: Having checked Equation 8 by using another method, it seems that it is in fact correct. The volume flow rate does increase at first, but then starts to reduce when p1 is approx. 100000Pa greater than p2 (in my equipment at least). This is counter intuitive. If you pull a tack out of a bicycle tyre you would expect more air to issue when the tyre is harder. The velocity at exit, on the other hand, does continue to increase as p1 increases. This is (I guess)why blowing harder on a trumpet makes a louder sound. And why a bicycle tyre hisses more noisily in the early stages of deflating.
Bicyclehub (talk) 08:25, 2 August 2012 (UTC)
thread_title:  Closed: Equation 8: Correct! 

message: What's going on here in the compressible flow section? It isn't clear at all. How has equation 4 been substituted into equation 3 to get the next line? The result looks OK, but it appears like the last equation has actually been derived by another route to that claimed in the surrounding text(in the bottom line, where has the Karman constant and beta gone from equation 4?)
(3)\qquad \dot{m} = \rho_1\;Q = C\;Y\;A_2\;\sqrt{2\;\rho_1\;(P_1-P_2)}
(4)\qquad Y =\;1-\bigg(\frac{1-r}{k}\bigg)\bigg(0.41+0.35\beta^4\bigg)
\dot{m} = C\;A_2\;\sqrt{2\;\rho_1\;\bigg (\frac{k}{k-1}\bigg)\bigg[\frac{(P_2/P_1)^{2/k}-(P_2/P_1)^{(k+1)/k}}{1-P_2/P_1}\bigg](P_1-P_2)}
JBel (talk) 07:29, 18 October 2013 (UTC)
replies: text: Quite right. (4) is the empirical formula for Y, also found in ISO standards as ϵ (epsilon), for thin-edge orifice plates used for flow measurements with β in the range 0.2 to 0.75. The following formulae are for flow through orifices with smaller β and are not generally used for flow measurement. I'll try to make it less misleading but I may not succeed in making it clear. NebY (talk) 11:43, 18 October 2013 (UTC)
thread_title:  Hard to fathom step in compressible flow derivation 

message: The article says the discharge coefficient Cd should be modified by the "velocity approach factor sqrt(1-beta^4), producing the "flow coefficient" C.  The reference for this (1)no longer leads anywhere, and should be removed.  Someone's lecture notes may be a dubious reference anyway!
In section 6.2 of this fluid mechanics tutorial:
http://www.freestudy.co.uk/fluid%20mechanics/t9203.pdf
it shows an equation to account for the same inlet velocity phenomena, however if you dissect it a small bit you find that the above correction factor is actually sqrt[1-beta^4*(p2/p1)^2/k].    This is not insignificant in the result.  If this is true, the page should be corrected, and and new reference added.
Ad000000 (talk) 17:28, 14 November 2013 (UTC)
replies: text: I agree that theoretical section seems to have been corrupted and could benefit from close analysis and rewriting. For various reasons, I'm more keen to bring the practical section up to scratch, leading up to the handful of equations normally featured in standards and practical handbooks. So if someone else would like to tackle the theory section.... NebY (talk) 18:41, 24 February 2014 (UTC)
thread_title:  Flow coefficient error? 

message: Pertaining to Equations 6 asnd 8, should the value and units for R be 8314.5 J/kmol-K?184.71.62.254 (talk) 14:52, 17 December 2013 (UTC)
replies: text: It could be. But why prefer a bigger number with a bigger unit? - Ac44ck (talk) 04:41, 18 December 2013 (UTC)

text: No, that would not be compatible with the other SI units. If your density calculations are out by a factor of a thousand, then I suggest checking that you are using the molar mass in kg/mol. Many handbooks provide the molecular weight instead, which must be multiplied by the appropriate molar mass constant of 0.001 kg/mol to give the molar mass in kg/mol. NebY (talk) 09:40, 18 December 2013 (UTC)

text: OK now I see the units of M are in kg/mol. I am so used to seeing them in g/mol or kg/kmol that I overlooked that.  My error.  Apologies.184.71.62.254 (talk) 14:46, 18 December 2013 (UTC)
thread_title:  Closed: Value and units for Universal Gas Constant R 

message: There is no explanation nor any links to other articles on what this is, nor how to calculate it, or even what it means. The equations and most of the article are very dependent on this variable but there is absolutely no explanation of where b4 comes from except "set it to a value between .2 and .6". That's not very helpful or explanatory.  — Preceding unsigned comment added by 98.172.66.86 (talk) 14:48, 2 May 2014 (UTC)
thread_title:  Closed: Beta /B4 Factor 

message: oops sorry my mistake I posted to the working page  — Preceding unsigned comment added by 203.97.93.222 (talk) 21:38, 5 August 2015 (UTC)
replies: text: The second equation concerns mass flow, which is higher - in a given orifice at a given differential pressure and so forth - for denser fluids. You may be thinking of volume flow; apply the preceding equation and you'll see that the volume is indeed lower with denser fluids, as you'd expect. NebY (talk) 21:41, 9 August 2015 (UTC)
thread_title:  Closed: Equation 2 seems incorrect density should be on denominator? 

message: Reference 13 and 17 not working. Please check.  — Preceding unsigned comment added by 59.99.242.131 (talk) 01:35, 19 December 2015 (UTC)
thread_title:  References not working 

message: I came here trying to figure out about how much pressure drop I'd get across a small orifice at a given flow rate. The formula, to a precision of 1% is way shorter than one line.
What's currently on here is really not very useful to me, and I think I'm not alone by far.
I'll be adding a more simple formula for the special case of non-turbulent flow though an orifice which is smaller than 1/10th of the pipe, to a precision of about a few percent.
Now my question is: Where should it go to? My suggestion is after the "pipe" section, and adding an "exact" to the title of the Computation section. Michi zh (talk) 14:56, 4 February 2017 (UTC)
thread_title:  Shouldnt a much more simple formula be added? 

message: Doing the math for a restrictor plate (30 micron hole in a 6mm tube), pulling 100mbars vacuum against atmospheric, the two formulas for compressible flow give different results by a factor of 3. If someone would pinpoint me to why this is (I'm guessing that its due to the limits of applicability for the ISO method, which is used to calculate epsilon and that the version without epsilon is correct for my case), I'd gladly do the research and detail it in the article. Michi zh (talk) 09:50, 8 February 2017 (UTC)
thread_title:  Apliccability of compressible flow formulas. 

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thread_title:  External links modified (January 2018) 

message: It starts from:
p_1 - p_2 = \frac{1}{2}\cdot\rho\cdot V_2^2 - \frac{1}{2}\cdot\rho\cdot V_1^2 
and
q_v = A_1\cdot V_1 = A_2\cdot V_2  
but p_1 and p_2 stand for the pressure at a distance from the orifice. 
And so should V_1, V_2, A_1and A_2.
Subscript 1 and 2 should each stand for a specific location.
Yet A_2 is the section of the opening.
BartYgor (talk) 08:14, 21 February 2018 (UTC)
thread_title:  Mistake in Theory - Incompressible flow 

message: The following sentence can not be correct. Neither the absolute pressure nor temperature have any relevance regarding flow. There might be no flow at all but still a high absolute pressure and/or temperature.
It has to be a pressure differential across the orifice. Hence I remove this:
:"Even compressible flows of gases that vary in pressure and temperature may be measured with acceptable uncertainty by merely taking the square roots of the absolute pressure and/or temperature, depending on the purpose of the measurement and the costs of ancillary instrumentation." --Eheran (talk) 06:52, 16 July 2019 (UTC)
replies: text: Yes, measuring temperature and pressure's often a good substitute for measuring density, but you still need the pressure differential. 92.19.24.47 (talk) 13:00, 12 October 2019 (UTC)
thread_title:  False statement about absolute pressure ~ flow 

message: Noticed there's a swedish language article about the same thing which isn't linked in the "lanugages" part. I don't know how to link the different lanugage articles together so thought someone else on here might help.
The swedish article can be found here https://sv.wikipedia.org/wiki/Strypfl%C3%A4ns
Not sure why they aren't connected already
Dux Ducis Hodiernus (talk) 13:40, 15 January 2020 (UTC)
thread_title:  Swedish version of the article