O/T Engineering question

[JAMMAN]

I'm going to build an oil flow tester that needs to build 100PSI+ of oil at a rate less than a gallon a minute. I was looking into fancy vari-speed drives and HP oil pumps from racing apps but would it be possible to pressurize a 3 to 5 gallon container with....air? If I put 100PSI of air pressure on top of 2 gallons of 50weight in a 5 gallon container, am I going to get 100PSI of oil pressure?

[jbel]

OK here goes.....

 

I just measured a 5 gallon pail to be 12 inches in diameter. If we assume that the taper on the bucket is negligible then the surface area of liquid at any level in the bucket is A = pi * r^2 = pi * 6 ^2 = 113 in^2.

 

Now, if you put a lid on and pressurize the bucket to 100 PSI the force on the liqiid is 113(in^2)*100(lb/in^2)= 11300 lb

 

Let me just say that this is a big number.

 

Your PSI output is dependent on the surface are of your output orifice. For instance if you are using 3/8" ID tubing out of your bucket the surface area is 0.11 in^2.

 

So the pressure would be 11300(lb)/0.11(in^2) =

102727 PSI.

 

This is a really HUGE number. As a matter of fact this is down right dangerous. The cool thing about hydraulics is that you can build up huge pressures with a little bit of force and a big surface area. You can do your own calculation using this framework and find out what you need the pressure to be. You will also need to maintain the same pressure as the bucket is draining. Some kind of regulator on the line may help.

 

Good luck and dont get hurt!!!!!!!!

[jbel]

Here's another way to think of it.

 

Think of 100 PSI as 100 Pounds per Square Inch. If you have 113 square inches per my last post your force will be 100 pounds in each of those square inches, or 100 pounds added 113 times.

 

This is 11300 pounds of force.

 

All that force has to go somewhere when you open the valve on the bottom of the bucket. What ever your surface area across the valve or tube or whatever you use coming from the bucket will govern the pressure, or Pounds of Force per Square Inch.

 

You are dealing with 11300 pounds of force that has developed. This is DANGEROUS. Think twice before trying this or get help in person from someone who is farmiliar with hydraulics.

 

Consider this a friendly warning!!!!!

[Müřlıń®]

quote:

---

If I put 100PSI of air pressure on top of 2 gallons of 50weight in a 5 gallon container, am I going to get 100PSI of oil pressure?

---

Don't think so.

 

If you are looking to make a hydrolic unit that outputs oil at 100 PSI@1gal a minute, you can do this by buying a self contained unit or building your own from a few parts from Granger.

 

All my old hydrolic machines use pressure valves to regulate the oil pressure. This is done by a ball/spring check valve on a pump.

 

The motor runs at a constant speed.

 

You just restrict the flow and adjust the pressure valve to where you are getting your 100PSI@1GPM

 

 

Murlin

[jbel]

All of what I have said above neglects internal forces in the fluid and minor losses.

 

Where is that darn Bernoulli equation when I need it?

 

+1 to Murlin for the pressure valve and the observation that the situation just isn't practical

[Müřlıń®]

PS...if you just want to test the flow off a given line, a 5-gal bucket with marks a gal a part and a watch would tell you your flow...

 

quote:

---

Where is that darn Bernoulli equation when I need it?

---

LOL

 

Murlin the simpleton...

[BernieT]

I don't want to cause a rift here but you need to speak to an hydraulic engineer or someone who knows his physics.

 

To answer your question - yes , 100 psi of air above 2 gallons of oil will give you 100 psi of oil in any size container. However , 100 psi in a container not rated for more than 100 psi could explode or rupture and cause serious damage!

 

Look into 'Accumulators'. They are designed to do just what you want. The principle is to keep the volume and surface area of air at pressure to a minimum - just enough to pressurize the oil.

 

BE CAREFUL!!!!

[BernieT]

Another analogy. When you release water from the bottom of your air compressor - that water is under the same pressure (psi) as the tank air.

[crazy^millman]

You mean this equation:

 

 

Here is the link: Bernoulli's equation

 

HTH

[Müřlıń®]

My bad... I thought he wanted to build a hydrolic system....

 

I was just thinking that using air for this would be very ineffecient.

 

First off you would loose pressure when you depressurized and tested the flow.

 

A simple pressure tank would not give a consistant pressure due to pressure loss...this is why I said no it wouldn't work.

 

I guess it would depend on how presision you really wanted to be....

 

 

Murlin teh disclaimer not a physics major of hydrolic engineering

 

[ 06-12-2004, 07:16 PM: Message edited by: Murlin ]

[McRae]

Relaitivly low cost option for a pump. (less than $1000)

 

www.schydraulic.com

[L Hanft]

Bernoulli's law won't do you much good, you really need Pascal's law. Here is a link to a page that explains Pascal's principal ans some exqamples. Pascal's Law - fluid dynamics

[jbel]

L Hanft,

 

That is a fantastic link with lots of practical applications.

I was reading at the top about Pascal's Law and it seems like it could be derived from Bernoulli. Presure in = Pressure out. or Force/Area in = Force/Area out. Couldn't you just equate these in the post from Millman?

[jbel]

P.S.

 

Jamman

Sorry about the thread hijack

[JAMMAN]

No prob, I'm learning a lot! Anyway, solved the problem today. We have a mechanical pump from Riverside engines we are bolting on to one of our "fuel pump" stands to check oil flow. I'll post results.

[L Hanft]

If you take a close look at Pascal's Law surface area plays a key role in the application. This is why a simple hydraulic jack can be pumped with a screw driver (cause we can't find the @#$&^ing handle) and lift 10,000 poounds with little effort. Although some aspects of Bernoulli deal with area by way of volume it really is not interchangable. Additionally, fluid in the form of a gas ie air is compressible while hydraulic fluid is not compressible. For instance a syringe full of air can be plugged at the needle end and the air compressed by applying pressure with the plunger, the air will compress a considerable amount. Replace the air with a similar volume of hydraulc oil and apply the same pressure to the plunger and the results will be very different. If you look at the restrictions for applying Bernoulli's law, incompressibility limits the practical use.