www.patchn.com has a hydraulic forum so I posted the problem there.

http://www.patchn.com/index.php?option=com_fireboard&am...w&catid=3&id=120#120

Is anybody here brave enough to compete against the maintenance guys and the PLC guys?

I can see that I have "blown it". I didn't provide all the required data.

The valve constant is 4.6
The supply pressure is 2000 psi
The volume of oil that is being compressed is fixed. It is 41.42 cubic inches

Solving this problem can be done in a couple of ways.
1. Iteratively using a spread sheet or a CAS ( computer algebra system) such as Mathcad, Scilab etc.

2. Use algebra and calculus. The first part would require calculating how many cubic inches of oil it takes to raise the pressure from 1000 psi to 2000 psi given the fixed volume of 31.42 cubic inches. That part should be easy. The second part is calculating the time it takes for the required oil to flow into the volume. That is the hard part in that is it requires calculus. I had to look up the form of the integration as http://www.sosmath.com.

3. One can make an estimate of time it takes the pressure to go from 1000 psi to 2000 psi by assuming an average rate of change. When thinking in the field this is the method I use most often.

I tried to post the same thing to all three forums but I was frustrated because not all forums would accept greek characters. I was also frustrated because my OpenOffice spreadsheet solution was extremely slow for reasons unknown.

I can give the "I'm-not-an-engineer" answer. I know compressibility increases with temperature, but I'll assume 0.5 % per 1000 psi. Because we're adding exactly 1000 psi, I'm going to go ahead and assume you'd have to shove .5% more fluid into the same 31.42 cubic inch vessel. How does 0.157 cubic inches sound?

quote:

Originally posted by Josh Cosford:
I know compressibility increases with temperature, but I'll assume 0.5 % per 1000 psi.

Yes, see this
http://www.hydraulicspneumatics.com/200/Issue/Article/False/70094/Issue
The 0.5% per 1000 psi comes from 1000 psi/BulkmodulsOf0il which is 200,000 in my problem. This simplifies down to 1/200 or 0.5%.

quote:

Because we're adding exactly 1000 psi, I'm going to go ahead and assume you'd have to shove .5% more fluid into the same 31.42 cubic inch vessel. How does 0.157 cubic inches sound?

Your answer is right because you assumed the same value for compressibility as I did. That 0.5% per 1000 psi is not always true. In actual operation it can be much higher as in 0.6% per 1000 psi. This happens on high velocity systems with entrained air.

How, the question was really how long will it take for the pressure to increase from 1000 psi to 2000 psi given the information about the valve. Flow=Kv*sqrt(Ps-p) where Kv=4.6. This is not so simple but someone has already figured out the exact number using calculus and a iterative method on www.plcs.net
http://www.plctalk.net/qanda/showpost.php?p=294759&postcount=11
I didn't expect anyone to get the exact calculus answer but Nathan did it.

Peter wrote:

quote:

This is not so simple but someone has already figured out the exact number using calculus and a iterative method on www.plcs.net
http://www.plctalk.net/qanda/showpost.php?p=294759&postcount=11
I didn't expect anyone to get the exact calculus answer but Nathan did it.

I would expect this from persons TRAINED in their DEDICATED field and who WORK in the field they are TRAINED in on a regular basis. Persons with TRAINING in higher levels of Math and Physics who can figure out the formula you presented.

You notice that the response on this Forum, from UNTRAINED, well, except for week long course at a Hydraulic Manufactuers TRAINING SCHOOL on how to spell Hydraulics and the Manufacturers name putting on the school, or the good old College of hard Knocks, are few and fewer to practically none.

Isn't that to be expected from persons who fell into Fluid Power by default and find knowing almost anything puts them head and shoulders above the people they are working with or SELLING to?

Persons who can write articles for the one of only two Fluid Power Magazines and have their Fluid Power Training Books on that magazines Web Site.

Bring Fluid Power Training to the level of the TRAINED and DEDICATED IN THEIR FIELD persons on the PLCS Web Forum and you would not see such a discrepancy in the amount of intelligent feedback.

Should not be that way Peter but that's the real world of Fluid Power. Fluid Power is and will remain on the Fringes until it is recognized as a field of endeavor that needs TRAINED/DEDICATED persons designing circuits and maintaining them.

You cerainly have done a service by showing the discrepancy so VIVIDLY.

Bud, I am glad you are beginning to understand that this isn't just a hydraulic problem. It is a general education problem. There are plenty of people out there that know little about hydraulics that can do the math like Nathan. I doubt Nathan, the person the got the exact solution, knows much about hydraulics. To him it is just a math problem. Nathan works for a company that sells HMI software. I doubt he has even worked on a hydraulic system. The point is that understanding math and physics is MUCH MORE IMPORTANT than knowing hydraulics. If one knows math and physics then solving the hydraulic problems is easy. This is why there is no hydraulic degree. It isn't necessary but the math and physics is.

Now don't get me wrong. There are plenty of maintenance items that are very important. Welding, designing manifolds, joining pipes so they don't leak. There are plenty of tricks in you books. Most of us geeks would look at a bunch of hydraulic parts and the tools and not know what to do with them. I have only changed a hydraulic valve once. I don't like to get my hands oily or dirty.

I was in the field last week. My customer had to synchronize 3 axes to a fourth. The RMS error was .055 mm between the actuators or 55 microns. I only tuned one actuator. I let the other 2 people that worked for our hydraulic distributor tune the other actuators with the same results. Hydraulic can control every bit as well as servo motors but it doesn't happen by accident. Some one, I/we, must know the math and physics to make this possible. Can you do this with a flow divider? No.

quote:

Originally posted by Bud T:
Peter wrote:

quote:

This is not so simple but someone has already figured out the exact number using calculus and a iterative method on www.plcs.net
http://www.plctalk.net/qanda/showpost.php?p=294759&postcount=11
I didn't expect anyone to get the exact calculus answer but Nathan did it.

I would expect this from persons TRAINED in their DEDICATED field and who WORK in the field they are TRAINED in on a regular basis. Persons with TRAINING in higher levels of Math and Physics who can figure out the formula you presented.

You notice that the response on this Forum, from UNTRAINED, well, except for week long course at a Hydraulic Manufactuers TRAINING SCHOOL on how to spell Hydraulics and the Manufacturers name putting on the school, or the good old College of hard Knocks, are few and fewer to practically none.

Isn't that to be expected from persons who fell into Fluid Power by default and find knowing almost anything puts them head and shoulders above the people they are working with or SELLING to?

Persons who can write articles for the one of only two Fluid Power Magazines and have their Fluid Power Training Books on that magazines Web Site.

Bring Fluid Power Training to the level of the TRAINED and DEDICATED IN THEIR FIELD persons on the PLCS Web Forum and you would not see such a discrepancy in the amount of intelligent feedback.

Should not be that way Peter but that's the real world of Fluid Power. Fluid Power is and will remain on the Fringes until it is recognized as a field of endeavor that needs TRAINED/DEDICATED persons designing circuits and maintaining them.

You cerainly have done a service by showing the discrepancy so VIVIDLY.

Let me see if I get what you're saying, Bud. You think the hydraulics field needs trained and dedicated people?

Peter, I'll try the equation later in the week. Mondays and Tuesday I have school right after work, until 9 PM.

The company I work for now, spends more time designing and assembling working circuits for engineering companies. A customer will send us a circuit for a mine elevator brake, for example, and we compile and assemble components. Very little math and physics involved.

As an aside, Peter, can you explain to me what Root Mean Square means? It's used in rating amplifier output, but I remember back in the day, that my math teacher couldn't explain what it meant...

Josh wrote:

quote:

Let me see if I get what you're saying, Bud. You think the hydraulics field needs trained and dedicated people?

Was it really that OBVIOUS??????

I was just Happy that Peter pointed out the lack of Formal Training discrepancy so VIVIDLY.

I REALLY DO BELIEVE that Fluid Power would be way ahead of where it is now if Fluid Power TRAINING was equal to that given Mechanical and Electrical types. And, also, if TRAINED/DEDICATED Fluid Power persons were responsible for all the design and mainteneance functions there would be a lot more innovations in the Fluid Power field than we see at present.

However, after 25 years on the same Soap Box I'm beginning to get a slight feeling there may be something wrong with my position. Just a slight one though!

Peter, my little book worm,

I leave you alone for a little while and you go and make a stupid statement like this, what is the matter with you? For someone that knows NOTHING about hydraulics to assume that it is un-important and therefore dismisses hydraulic knowledge entirely is beyond being arrogant, they are dangerously uninformed.

Just when you gain some respect of what little knowledge you do have, you go and make a statement like this, which just undermines your position.

Math and Physics has not trained you when to speak and when to be quite, therefore math and physics has FAILED YOU?

Do not dismiss anyone’s hydraulic knowledge just because you cannot learn it or think it is unimportant, now my little bookworm you get the award for being the most arrogant and insulting person on the forum.


Peters quote:
“The point is that understanding math and physics is MUCH MORE IMPORTANT than knowing hydraulics. If one knows math and physics, then solving the hydraulic problems is easy. This is why there is no hydraulic degree. It isn't necessary but the math and physics is.”

Gary;

In case you have not followed the same thread on the PLCS Forum here is a link to it.

http://www.plctalk.net/qanda/showthread.php?t=42533&pag...ght=hydraulic%2A+oil

Peter is correct in saying the Electrical guys figured out the answer to his question a lot easier but they had more than a 2 week Eaton-Vickers school to fall back on.

GLK, where was your answer?

Peter, Bud,
I have listen for years of Bud tearing down fluid power, i.e. unless you can read and write, and have no degree, you are stupid, and hydraulics is so difficult to learn. Bud likes the electrical people; much better educated, smarter and he is very impressed that they can read and write.

Then stay on that forum and out of hydraulics, period.

Basically, Bud you were a door-to-door fluid power parts salesperson and stumbled across a little knowledge along the way. Not near enough to preach to others regarding anything other than BASIC hydraulics. I have read the posts on the PLC forum, and like this forum, it is dominated by just a few people who are experts on any and everything, much like Peter and you on this forum.

I am working on two jobs now that require a mechanical engineer, and PLC person, and let me tell you, I find a good person in these fields as often as I find a good knowledgeable hydraulic person, NOT OFTEN. As for Peter, take your quiz, rub two wires together and create a spark and stick it up you know where, then Bud will be in shock and awe wishing he was an electrical person.

Both of you guys have spent a good portion of your posts degrading the Fluid Power Industry and people that work in this field with servo formulas and dazzle, the other telling people without a degree you are stupid and need a license to work. I take offense to you two clowns that have the least amount of hydraulic knowledge, insulting and judging people that in fact, do have the knowledge, schooling and experience.

There are plenty of knowledgeable people in Fluid Power, and even more that are training and learning and will become the next generation of knowledgeable people in Fluid Power. The Fluid Power Industry is doing just fine, and will be even better when you two are gone.

Both of you need to move over to the PLC forum and remind those people how ignorant they are for not having a Mechanical/ Electrical degree, license or a PhD in Math and Physics.

Do not ever imply or state that because I did not par-take in some Friday Night Quiz or sell Miller Fluid Power cylinders door-to-door, I do not know what I am doing in Fluid Power.

By the way, pulling your pants down and holding an O-ring between your knees is not a static hydraulic seal. Neither of you two could work in the Fluid Power Industry I know today other than push the tool cart around. Stop insulting the Fluid Power Industry and the people who work in this industry with your ignorant statments.

Gary wrote:

quote:

I am working on two jobs now that require a mechanical engineer, and PLC person, and let me tell you, I find a good person in these fields as often as I find a good knowledgeable hydraulic person, NOT OFTEN.

And I was trying to build up the TRAINED/DEDICATED persons in the Mechanical and Electrical field and have to learn from Gary that all their training was of little use.

Oh well. at least there is at least ONE KNOWLEDGEABLE HYDRAULIC PERSON ON THE PLANET and if you don't know who he is, just ask Gary.

Gary, you need to be passing on all that knowledge so it won't be lost when you can no longer remember what it was you forgot.

I wrote down all the dumb stuff I know, or at least thought I knew, and some dumb person actually put it on the internet for all the smarter persons to read. You can see my unintelligent writings here:
http://www.hydraulicspneumatics.com/200/eBooks/

Oh well, that is the REAL WORLD OF FLUID POWER and from 99% of the feedback I read, Fluid Power is destined to stay on the back burner in most of the world.

Gary wrote:
quote:
I am working on two jobs now that require a mechanical engineer, and PLC person, and let me tell you, I find a good person in these fields as often as I find a good knowledgeable hydraulic person, NOT OFTEN.

And I was trying to build up the TRAINED/DEDICATED persons in the Mechanical and Electrical field and have to learn from Gary that all their training was of little use.


Answer: I never made the statement anyone’s training was of little use, which is your twisted mind talking.



Oh well. at least there is at least ONE KNOWLEDGEABLE HYDRAULIC PERSON ON THE PLANET and if you don't know who he is, just ask Gary.


Answer: Again, never stated that I was the only knowledgeable person in hydraulics, I did state there are many people that have hydraulic knowledge and Fluid Power is doing just fine.



Gary, you need to be passing on all that knowledge so it won't be lost when you can no longer remember what it was you forgot.


Answer: I do not need you to tell me what I should be doing in regards to anything.



I wrote down all the dumb stuff I know, or at least thought I knew, and some dumb person actually put it on the internet for all the smarter persons to read. You can see my unintelligent writings here:
http://www.hydraulicspneumatics.com/200/eBooks/

Answer: So you produced some basic hydraulic writings and some may read them and learn something, good for you. However, your work is not the Holy Grail of hydraulic knowledge, just some basic stuff that has been out there for years, rewritten in a different format.



Oh well, that is the REAL WORLD OF FLUID POWER and from 99% of the feedback I read, Fluid Power is destined to stay on the back burner in most of the world.


Answer: You have no idea what the real world is regarding fluid power, there are MANY of us that work all around the world and we do just fine, if not leading the industry in ideas and technology. You’re the one sitting on the back burner being negative about the Fluid Power Industry with the ramblings of a person time as passed by with knowledgeable hydraulic people.

Fluid Power is doing great, and if I expect to hold my own, I need to be smarter, and take more training; otherwise, some very capable people now working in the industry will pass me by, much like what they have done to you. Stop insulting the hard working people in Fluid Power by telling them, electrical is taking over the world, Fluid Power is on the back burner, and only the ramblings of an old man can save them.

And,Would you believe Gary believed this and wrote a paper on it?

"Accumulators Store, Contain and Discharge Pressure."

Had it on his web site "Tech Page" for DownLoad at one time. Funny it's missing now.