Differential Pressure and Flow

[aschelske]

We have a pipe with a butterfly valve, connected to a blower that blows only air. I'm seeing programming that takes the square root of the actual differential pressure reading, then multiplies that by (25775.2). Can anyone tell me what the (25775.2) is and how someone came up with it? This is an existing program and system. The person who set it up, passed away over a year ago.

25775.2 * SQR(DF PSI) = Air Flow

Thank you!

 

[Deleted member 4993]

We have a pipe with a butterfly valve, connected to a blower that blows only air. I'm seeing programming that takes the square root of the actual differential pressure reading, then multiplies that by (25775.2). Can anyone tell me what the (25775.2) is and how someone came up with it? This is an existing program and system. The person who set it up, passed away over a year ago.

25775.2 * SQR(DF PSI) = Air Flow

Thank you!

This is not a question of math!

In what "subject" this equation is coming up?

Is it in a hand-book?

Look for citations/references (in the book where you found this equation) and study those!

Sorry - no short-cuts available!!

 

[aschelske]

First off, your exclamation point usage was unnecessary.

Second, this IS math in the form of physics. Trying to calculate flow using differential pressure in a pipe.

Third, the subject is called the real world. I explained in my original post that it is an existing program and system. It's not from a book. It's not homework. It's a real life calculation in a programmable logic controller. A person who died, wrote this program. I'm trying to figure out how they came to have this equation. I've tried searching for a solution with no avail.

Fourth, I'm not asking for a short-cut. Just asking for help, because this is not my area of expertise. Stop bein a rude.

 

[tkhunny]

Did you read the rules for the use of this forum? Apparently, not.

Anyway, how would you calculate Air Flow? It is likely a simplifying approximation, but maybe not.

I've had the pleasure of turning old MatLab code into modern LabView code. Let's see your thoughts. Maybe can help, but not if you don't follow the rules. We're not a private consulting service.

 

[Deleted member 4993]

First off, your exclamation point usage was unnecessary.

Second, this IS math in the form of physics. Trying to calculate flow using differential pressure in a pipe.

Third, the subject is called the real world. I explained in my original post that it is an existing program and system. It's not from a book. It's not homework. It's a real life calculation in a programmable logic controller. A person who died, wrote this program. I'm trying to figure out how they came to have this equation. I've tried searching for a solution with no avail.

Fourth, I'm not asking for a short-cut. Just asking for help, because this is not my area of expertise. Stop bein a rude.

First off - your given equation is NOT math using any logical scientific discipline.

25775.2 * SQR(DF PSI) = Air Flow

is not dimensionally balanced.

Thus, the so called "constant" (25775.2) most probably has a dimension - depending on the dimension of "air flow" (which is also missing).

Second - I have spent 30 years doing engineering "in real world". And I am sure that incomplete equation CANNOT be from a real world (by the way I have worked with sub-sonic and super-sonic airflows - through rigid pipe, flexible pipe, over and under air-wing, you name it.....) situation.

Third - my suggestion would be that you go to the department of mechanical/chemical engineering (of your nearest university/college)- and "hire" a graduate student who can do some research for you to find the COMPLETE equation and TEACH you how to implement it in your LOST REAL world programme.

And talk about being rude......

 

[mmm4444bot]

Can anyone tell me what the (25775.2) is and how someone came up with it?

Based on the information that you've provided, I would say, "probably not".

It appears to be a conversion factor (that is, a parameter), and, individually, parameters often apply to only a subset of specific situations.

This is an existing program and system.

Do you have access to the program code? If the programmer were a professional, their annotated code would explain the parameters.

If you cannot access the code, then read the system's documentation.

If you find the documentation lacking, then you'll probably need to contact someone familiar with the physics specific to the given situation (i.e., provide ALL specifications), to ask whether they can determine the source of that parameter. (It may take quite some time, before an individual with the knowledge and interest required comes across your thread in this forum, but you're welcome to wait.)

Either way, we wish you good fortune. :cool:

 

[aschelske]

First off - your given equation is NOT math using any logical scientific discipline.

25775.2 * SQR(DF PSI) = Air Flow

is not dimensionally balanced.

Thus, the so called "constant" (25775.2) most probably has a dimension - depending on the dimension of "air flow" (which is also missing).

Second - I have spent 30 years doing engineering "in real world". And I am sure that incomplete equation CANNOT be from a real world (by the way I have worked with sub-sonic and super-sonic airflows - through rigid pipe, flexible pipe, over and under air-wing, you name it.....) situation.

Third - my suggestion would be that you go to the department of mechanical/chemical engineering (of your nearest university/college)- and "hire" a graduate student who can do some research for you to find the COMPLETE equation and TEACH you how to implement it in your LOST REAL world programme.

And talk about being rude......

It is from a real world situation, I can screenshot the running PLC program, if you'd like. The DP PSI is an actual analog input into the PLC, at which point gets put into the equation I provided. No one here knows what the constant value (25775.2) is or how it was calculated. The person who did this, was self-taught and didn't document anything he did. I guess you could say he was ensuring job security. Too bad he wasn't smart enough to not die in a car crash that was caused by him being drunk. You're not going to make me feel bad for returning your rudeness. It was uncalled for and unnecessary. I was just asking for help. I actually got a good response from someone and they are willing to work with me. Thank you for your time, regardless of it's waste.

 

[aschelske]

Did you read the rules for the use of this forum? Apparently, not.

Anyway, how would you calculate Air Flow? It is likely a simplifying approximation, but maybe not.

I've had the pleasure of turning old MatLab code into modern LabView code. Let's see your thoughts. Maybe can help, but not if you don't follow the rules. We're not a private consulting service.

Which of the 3 lines of rules are you referring to, in your question as to if I read them? I have not broken any of the rules on the Forum Rules page. The PLC program I have, that has been running for many years, simply has a DP PSI analog input into the PLC. It is then put into the equation that I provided in my original post. That is all I have to work with. I don't know how the constant (25755.2) was calculated, because the guy who created this program died in a car crash caused by him being drunk. The system works just fine, we're just trying to figure it out so we can know what is being done. Someone responded to my post with helpful information, so I'm going to work with him and hopefully get this figured out. Thank you for your time.

 

[mmm4444bot]

Which of the 3 lines of rules are you referring to…

I apologize for the confusion.

tkhunny was referring to the forum guidelines. Some of the old-timers here remember the forum's prior software (in which our read-before-posting guidelines were generally referred to as the "forum rules"). The new platform came with a global set of built-in rules (the ones you read), and the link for those was named "Forum Rules" by the developers. We cannot change the link's name, hence the ambiguity.

This site is run by volunteers. We mostly service students who get stuck with their homework. Many students come here and post something that amounts to academic dishonesty. Sometimes, it's difficult for us to sort out who's who.

Most of the volunteers here are happy to lend a hand to non-students (once the intent is understood), as their personal time permits. Speaking for myself, if answering a question were to first require a lot of research at my end, I would probably not get too involved.

Thank you for your understanding.

 

[tkhunny]

OP You did not address my second question.

 

[Deleted member 4993]

OP You did not address my second question.

Anyway, how would you calculate Air Flow?

I suspect s/he does not know the significance of your question. My concern about dimension of the constant remained unanswered.