Step-up hydraulic cylinder?

[snubengr]

Hello:

Today I came across a website for a 'step-up hydraulic cylinder'. Apparently it has a high-speed, low force mode and then when it encounters resistance it switches to a low-speed, high force mode. I'm assuming that it must work by somehow altering the active pressure area of the piston, but how would this work? Any input is appreciated.

The website is:

http://www.simson.ch/English/Hydraulic_Cylinders.html

Cheers,

Denande

 

[alexit]

I believe they are two concentric cylinders connected by a check valve(s), the inner moves quickly along the long stroke until it encounters more pressure which opens the check valve(s), the inner cylinder is hydraulically locked to the outer cylinder at this point. Now the inner and outer act as one large piston, moving together.

Alex

 

[Barry1961]

You can do this with a single rod cylinder by plumbing both ports together for high speed low force. With this the rod extends with a force equal to the area of the rod times the pressure and has the increased speed due to the fluid on the rod side being added in. The bigger the rod the greater the extend force but the slower the extend speed.

After the rod contacts something substantial and the pressure rises you then switch to the "normal" plumbing for your high force slow speed.

This works well on hydraulics but not very well with air.

Barry1961

 

[snubengr]

Thanks for the quick reply, but I'm still missing something.

Isn't the pressure in the cylinder constant? If so, what determines when the secondary (outer I guess) cylinder is activated?

Cheers,

Denande

 

[EdDanzer]

This concept is used in log splitters. A double pump is used, with an unloading valve and check valve to limit the large volume pumps out put pressure.

 

[Barry1961]

The pressure in the cylinder will be dependant on the on the "load" on the cylinder piston and the flow of the supply. This load can be from a meter out flow control or from a force on the rod.

Dual pressure pumps are common for applications like this but they do not reduce the volume like advertised on the web page. I think they are just plumbing the ports together for a quick extend. They could be using a flow meter, pressure switch, load cell, linear transducer, motor current sensor or other device to tell when the rod hits something.

Barry1961

 

[toolmantwo]

Denande

Think what you have found is a HYD cylinder that has two sizes of cylinders in line with one (Small bore) that will telescope inside the other (large bore) to drive the rod.

No check valves are needed. If the resistance is low the small bore is driven fast. If the resistance is high the large bore is driven slower, yet develops higher pressure (all using the same pump). Some farm tractors have used this concept for loaders. The difference in the surface area of the pistons determines the force developed.

To visualize this, think of the larger bore cylinder as a helper for the small, yet it draws oil from the same source and thus the travel is slower

 

[Mandrake22]

The web site makes the following comment:

Moreover, the control system can be simplified due to the integrated control valves.

This would indicate that it works at least similar to Barry1961's supposition. Note the plumbing connecting the ports. We make machines using the high/low, dual pump concept. This cylinder looks interesting for us.

 

[budt]

Try these web sites to see one way of getting fast approach and high tonnage from an air operated cylinder.

http://www.multicyl.com/multicyl.htm

http://www.tox-de.com/e/products/powerpackage/index.htm

Bud Trinkel

http://www.fluidpower1.us

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com

http://www.fluidpower1.us

 

[toolmantwo]

Denande

I just looked at the website you posted and I may be wrong in total Ha Ha. Sorry for the confusion. That type of operating method must be more complex being they have a patent.