I have designed a hydraulic pump specifically to move or raise multiple cylinders exactly the same distance irregardless of load or uneven load. I designed and tested it in Solidworks we built the prototype and after some slight adjustments and a dump valve redesign the pump works perfectly. The prototype has undergone 14 days of continuous cycling (lifting 250 lbs 8" with 4 1.25" cylinders) My pump is driven with a 12Vdc motor or cranked by hand. My problem is how do bring something like this to market?

Interesting, how do you know that multiple cylinders are moving exactly the same distance?

I am still skeptical, 250 lb is insignificant.

If this really works better get started on a patent and then look for a pump manufacturer that may be interested in buying the rights. The capital equipment cost for build a pump would be very high so I doubt would be able to get the money for this.

We built a test fixture with 4 dial indicators located on the 4 corners. and I know the weight is insignificant but the whole works was designed to be portable for demonstration purposes

If the dial indicators are not feedback devices then how can you be sure the 4 corners will stay at the same position? I am familiar with Temposonic MDT rods providing position feedback.
Then one can correct for errors but to think that the errors simply not happen is dreaming. Things wear. Even the best servo valves have tolerances of a few percent.

I'm sorry I did mot give you all the design criteria. We where approached to design a system that could move 4 points simultaneously a distance of 54 inches with a tolerances of +- .015 for a maximum of 500 cycles. The max weight is 1000lbs but it must remain level in any position between 0 and 54 inches and it is a shifting load.

Oooppss!!!!!!
Here is a challenge to the rest of the forum.
Where did Dave go wrong????

There are 20 people on this forum all day and no one knows the answer. Hmmm.

This message has been edited. Last edited by: Peter Nachtwey,

I wonder how he lower the load after a lift cycle?

quote:

Originally posted by AKKAMAAN:
I wonder how he lower the load after a lift cycle?

That is a good question.

My question is more basic. How will the pump keep the different actuators level even when the load changes with out feed back?

yes, raising the load evenly is one thing but lowering it evenly is all about gravity force and will need another form of control....

no feed back.....Well I thought we(you) already ventilated that problem...0.015" tolerance over 54" is about 0.03%....and thats the volumetric efficiancy pump-valve-cylinder have to make combined....each one of them average third root of (100-0.03)/100= third root of 0.9997.....basically no leaks at all....pressure only average 142psi...hmmmm...cool...

Where to use it with that light load?
how will the system do if we increase load to more useable 100-100000 times?


EDIT
Is it possibly so we have 4 pump units, one per cylinder??
EDIT 2
Woops....I calculated the pressure on 1.5" bore...should be 1.25"....pressure average 203.7 psi.....

This message has been edited. Last edited by: AKKAMAAN,

It is possible that Dave has some very efficient pumps with no leakage. I believe that one can always approach perfection given enough resources. The problem I am thinking about can't be solved by mechanical precision.

quote:

o feed back.....Well I thought we(you) already ventilated that problem...0.015" tolerance over 54" is about 0.03%

I almost thought the AKKAMAAN had found my refutation.

quote:

EDIT
Is it possibly so we have 4 pump units, one per cylinder??

Feedback is still required.

I think there is one very obvious thing that everyone has over looked. Perhaps it isn't that obvious. I will post my refutation tomorrow. It will be interesting to see what Dave has to say.

quote:

I think there is one very obvious thing that everyone has over looked

Ummmm...I'll have a stab at it being β.

"The bulk modulus for hydrocarbon-based hydraulic fluids is approximately 250,000 PSI, (17,240 bar) which results in a volume change of around 0.4% per 1,000 PSI (70 bar)"


So...

"Springy" oil columns of 54 inches + uneven cylinder loads = out of tolerance?

Regards Woody

quote:

Originally posted by Woodygb:

quote:

I think there is one very obvious thing that everyone has over looked

Ummmm...I'll have a stab at it being β.

"The bulk modulus for hydrocarbon-based hydraulic fluids is approximately 250,000 PSI, (17,240 bar) which results in a volume change of around 0.4% per 1,000 PSI (70 bar)"


So...

"Springy" oil columns of 54 inches + uneven cylinder loads = out of tolerance?

Regards Woody

You nailed it!

Woody got it!!! The worst case is when the cylinder is extended. The bulk modulus of oil is usually MUCH lower than 250000 psi and may be only half that depending on how much air is entrained in the oil as it returns to the tank.
The worst case is when the bulk modulus of oil is low.

So, how big can the error be worst case? That would be when the cylinder has 54 inches of oil in it and the load is all on one actuator. Woody, you should be able to easily now since you have been working with the bulk modulus of oil for the last two weeks.

If all 1000 punds is put on one cylinder it will go down due to the compression of oil. 1000 pounds on a 1.25 inch diameter induces 815 psi. 1000lbf/((π/4)*1.25^2) So how much will the oil compress as a result? The magic formula is:
ΔP=β*ΔV/V
divide the top and bottom by the cylinder area
ΔP=β*ΔL/L
Solve for ΔL
ΔL=ΔP*L/β
so assume the bulk modulus of oil , β, is 200,000psi which is optimistic. In practice is can be much lower and I never use a value as high as Woody suggested.
ΔL=(815psi*54in)/200,000psi)=0.22in just due to compression of oil!!!!!

So another "flow makes it go" application bites the dust.

I wonder what Dave is thinking now.

This message has been edited. Last edited by: Peter Nachtwey,

quote:

I never use a value as high as Woody suggested.

I got lazy and used the first Google quote I came across.

Rather than looking up the one you gave me... β := 200000

Woody

Most will tell you that even 200000 is on the high side. I use it because it is a nice round number easy to remember. I can do math in my head with round numbers.