Raising a weight using hydraulics

[roger5]

Hi
I have a weight of around 100lbs that I need to raise by a few inches. Basically what I would like is some kind of compressed-gas device that I can place underneath the weight and:
1. then trigger the gas to expand and raise the weight.
2. push down the weight to restore it to its original position

Is it possible? I thought to do it somehow using hydraulics. From searching the Net, I came across things like hydraulic accumulators. Could these be suitable? Is there a solution?

Roger

 

[FredGarvin]

Do you want it automatic or would having to pump a handle or some device be ok? If so, there are a lot of things out there that do this. Look at the following:

pallet jacks
http://www.materialflow.com/MFG-PRODS/Cascade/CPJ2136Q.jpg

Bottle jacks:

Stacker lifts:
http://www.wescomfg.com/spl682424.jpg

 

[Danger]

Just to clarify something here, Roger, compressed gas systems are not hydraulic... they're pneumatic. Hydraulics involve liquid (usually oil). The biggest difference, other than weight, is that liquid is not compressible. Air cylinders can have a bit of a springiness to them. There are hybrid systems as well, wherein air pressure is used to activate the master cylinder of a hydraulic circuit.
In any event, you're not going to be able to simply push the weight back down to reload the system. There has to be a pressure-relief valve involved.

 

[roger5]

Pneumatic I guess I meant.

What I need some kind of cylinder that extends and lifts a weight. I also need to activate the lifting via some kind of RF signal. I would then manually return the weight to the original position.

 

[roger5]

I forgot to ask: How would the pressure relief valve fit into the equation exactly?

 

[Danger]

Just trace the sequence of events. To start with, you have a load sitting on top of your hoist. Then you (remotely) activate your hoist by pumping air into it. In order to lower that load, you then have to allow the air to bleed out in a regulated manner. That's what I mean by a pressure relief valve.

 

[roger5]

Ok, I get it. So here's the thing: Is there any way to have the mechanism self-contained in the cylinder? What I mean is, to do without some kind of external tank to provide the pressure source of air or whatever?
What I am thinking is the cylinder is pressurized enough to raise the weight, but is prevented somehow from extending. That's where the the remote activation comes in. The energy to compress the gas (to reset the sytem) would come from pushing the weight down to the original position.

 

[roger5]

Another question: Say I have to have an external tank providing air (or some other gas). Would the system be able to work in a self-contained way, ie. without having to introduce air from outside the system (the system being the tank and cylinder)?

 

[Integral]

http://www.smcusa.com/"

http://www.bimba.com/"

Check out these links for commercially available pneumatic products.

If you do enough poking around these sites you can learn a lot.

You will need a control valve, so be sure to check those out.

No, you cannot capture and reuse the air. Just like water doing work to drive a turbine you must do work on it before you can use it again.

 

[Danger]

Roger, it sounds very much as if what you want is a spring. I believe that there is a way to achieve your goal using an accumulator as you suggested in your original question.
A cylinder attached to an accumulator, with no valving, should work if it's pressurized enough to lift the load, but not to the full capacity of the accumulator. Manually pushing it back will force the air or liquid into the accumulator, raising the pressure in it. A mechanical latching mechanism can then hold it in position until the next time it's triggered.
Check with the others about this, though, because there might be factors that I'm overlooking.

 

[roger5]

It's starting to sound like what I need. Any chance you could send a sketch? I don't understand how the spring fits into the equation?

 

[brewnog]

Yeah a cylinder/accumulator system would theoretically do what roger wanted, but I'm a bit concerned. I'd like to know why this arrangement is needed; it's inherently more dangerous than a system which would be non-pressurised when at rest. Having seen the aftermath of some relatively low-pressure, low-flow pneumatics having failed after being loaded for extended periods at rest, I'd have to have a really good reason not to use something based on the arrangement first suggested by Danger and Fred.

Roger, why are you so averse to using a compressor/storage tank and a control valve?

 

[Danger]

Good point, Brewnog.
Roger, as for the spring, there isn't one (unless it's a spring-operated accumulator). I was merely pointing out that you want your cylinder to behave the way a spring would.

 

[brewnog]

Well you could use a cylinder and accumulator as a spring, but I don't know why you'd need or want to.

 

[Dreamedideas]

Why not use a worm drive with two identical collapsible containers (that are able to withstand 100+ lbs of pressure) that holds the same amount of fluid. The worm drive of course would be between the two conatainers powered by an electric motor that is conected to a remote toggle switch that can reverse the polarity. you have no need for any valves because of the worm drive. making sure that the size of the tubing used to connect the two containers to the drive is only about 10% of the size of the container or less (the smaller the tubing the more durable it needs to be) but the worm drive needs to be the same size as the tubing. Plus the smaller the tubing the more weight you can lift. (A worm drive is a lot like a drill bit)