Hydraulic power unit

[mmiller]

I'm building a lift table for working on my cubs. I originally planned to use a manual hydraulic cylinder from an engine lift to power it, but that presents some problems getting to the release valve and handle when the table is in the lowered position.

Does anyone know a source for an economical electric/hydraulic power unit with a ram with about 10" of travel? The units I've seen so far would cost as much as buying a commercially made table.

 

[kweaver]

Think junkyards and treasure hunt I found my Barnes power unit years ago for $25 that I'm now using on my pipe bender.

Semi trucks (cab overs) use a hand pump that they plumb to their cylinder.

You may want to use a hand pump with a tank added to it for more volume. I've converted jacks to remote pumps but they are kinda slow. A portable Port-a-Power would be another choice.

This use to be a cheap place to get stuff but the net has upped their price and exposure


Another choice

 

[mmiller]

Thanks Ken. Great idea about the semi trucks. One of my favorite things is scrounging around junkyards.

 

[kweaver]

Michael - Here's some of my stash to give ya some ideas ...
Portapower on my tractor

Air over hydraulic on my shop press (first used on home-made tractor 3pt)

Jack pump I converted to a remote pump (first used on my press)

Semi truck style pump

and my $25 Barnes 110v

Then of course there's the regular engine driven hydraulic pumps and valves ... and a 12v linear actuator

 

[mmiller]

Ken, tell me about that air/hydraulic unit. Does the air valve control the ram in both directions or do you have to lower the ram with a manual bleed valve like a conventional hyd. jack?

 

[kweaver]

They're for single acting cylinders with bleed back for retraction. In the pic the handle is in the "pump" position, flip it to the left of pic and it bleeds back. Those suckers aren't cheap either if you buy them new but they sure are handy if you can get a used one. Their design is simplicty in action. I've got a 5x5" H-beam across the top of my press and I've used it to bend 2x2" barstock with a 4.5" bore cylinder. It bows the H-beam too ...

Good for pressig out stubborn spindles too

 

[kweaver]

I've taken a Chevy starter and made a drive pump motor with it before. A guy needed a boom lift on his truck so I built one that swiveled (similar to the fixed one on my TOY in Pipe Bending section). Pull off the nose cone and make a disc to bolt back on in it's place with a bearing to support the armature. Turn the armature shaft to fit bearing and put a small sprocket on the end. Get a small displacement pump and put a sprocket on it and it's ready to go. It wont be for continuous duty since the starter will get hot but it's basically the same drive (less sprockets) as 12v units. That setup can be used with a 2 spool valve to have power both ways.

 

[mmiller]

I've done that with a starter motor to power an automotive compressor. We used to let the air out of our tires and drive our vans on the sand at Cape Hatteras. The motor/compressor was used to pump the tires back up when we came off the beach. Worked great...you just had to squirt a little oil in the air intake once in awhile to keep the compressor lubed.

 

[kweaver]

Michael - Get an old 2 cylinder Chrysler A/C compressor they had a crankcase oil bath
I used a GM stumpy compressor for 4 years on my air over lift system on my tractor before it finally gave out with no oil, sucking in dust. It was used almost everyday doing something as can be seen in the Off Topic Tractors section.

That would probably be your cheapest way to go if you can't find something used/priced right.

 

[mmiller]

Ken, Good ideas. A DA cylinder with a power unit would be very cool, but a portapower setup would be sufficient. Time to start scrounging.

 

[kweaver]

Michael - I had a mini brain storm @ 4am this morn to come in here and throw at ya but I got sidetracked with Matt's problem then I finally got 4 hours sleep after 3 days running on 1 hour per morning ... anyway

How about using a second hydraulic cylinder as a pump ? I glanced at the cylinder on my bender laying diagonal and it struck me, why not fill it with fluid in the extended posistion then plumb it to your closed cylinder. You could use a come-a-long to draw in the rod to force out the fluid filling the working cylinder pushing it out. A metal (strong one) could be made like a press with the second cylinder being pushed closed with a hydraulic jack if the come-a-long idea doesn't work real easy.

 

[dcurrin]

Michael,
Air over oil cylinders or compressors use a large surface area side on the air side and small surface area on oil side. The ratio is where you get the conversion of pressures. ie 100psi air at 10 sq in (inlet side), could make 1000psi on oil side at 1 sq in. Volume is a function of length.

This compressor would have two different bore sizes on the same cylinder (perhaps axis/centerline). with a few check valves and control valves you could allow for several cycles to lift your table. I used to use a piston pin press that worked this way... It probably had a 2" air side and ??1/4" oil side it cycled atuomatically very fast. Special valving was built in it to automatically recycle the air piston for another stroke...

Have fun scrounging. A few machine tools opens the possiblities quite a bit.

Cheers
Dudley

Do you still need loader frame pictures??

 

[mmiller]

Great ideas Ken and Dudley. It reminded me I have an extra floor jack. I could use the guts of that to operate a pumping cylinder. Kinda like a big, homemade porta power setup. By using the right size cylinder I should be able to get a good lifting speed. Lots of possibilities.

Dudley, I have a pretty complete machine shop in my garage, so fabrication is not much of a problem. Yes, still would like some loader pics. I've got an idea of how I'll make my frame, but it's always good to look at a lot of designs. Thanks!

 

[kweaver]

Michael - If you've got a machine shop then I can show you the simple make up of my air over pump. I've often thought abought making one to see if it's as easy as it looks. No special valving needed I think a pump from a 2 ton bottle jack would be the only complicated part needed. I've even got some aluminum tube for the air cylinder pump side if you need it.

 

[mmiller]

Ken, I'd like to see it. I usually like a fabbed-up solution to an off-the-shelf (expensive) solution.

 

[kweaver]

Michael - I may get a chance to take it a part for pics in a day or two. This weekend is a mess , Kathy's brother was found dead from a heart attack.

I can tell you from what I seen before when I took it a part 20 years ago to see what made it tick was that it had a spring on the bottom side of the piston to act as a return. The "connecting rod" was driving the pump plunger and the cylinder wall had a slit in the side to dump the air pressure at the end of the power stroke. Simple huh !

 

[mmiller]

Ken,
I'm sorry to hear about Kathy's brother. Take your time on the pics; I'm headed out to DC this evening for a week of work, so I can't work in the shop for awhile anyway.

That does sound simple...reminds me of the gas cylinder on a Garand.

 

[kmcconaughey]

KENtucky, sorry to hear about Kathy's brother.

 

[mmiller]

Ken,

Don't worry about getting pics of the air-over-hydraulic unit; the situation has changed. I bought a used heavy duty lift table very similar to the one I was designing. The new problem is it needs repair, but I figured even if I spent $500 getting it going I would come out ahead on materials and labor when all is said and done.

It appears to need a new solenoid valve and a relay, which shouldn't be hard to do, but before I buy any parts, I wanted to be sure I understood the way this thing is plumbed.

Hydraulics is not my forte, having only theoretical exposure to the field. So, I made a diagram of the unit and am trying to decipher how it works. I'll post the diagram in my next post. If you or anyone else would care to critique it for me, I would much appreciate it.

 

[mmiller]

Here's the diagram.

All of the red lines are steel high pressure lines. The green line is a low pressure return line.
This is apparantly a SA cylinder, but I haven't seen one with two lines entering the base of the cylinder like this.

My theory is this:
When the pump is running and the solenoid is not engaged, fluid is circulated from the pump outlet through the base of the cylinder and through the solenoid valve and back to the reservior.
When the solenoid valve engages, flow is stopped at the valve, allowing pressure to build in the cylinder, extending the ram, and the table lifts.
When the solenoid is disengaged, the pressure drops in the cylinder, allowing it to return to lowered position.

If this is how it works, then I've got more questions:
What would control the speed of the cylinder on lowering? Might the solenoid valve also have a flow rate control function? If this is a SA cylinder, why the need for a low pressure return line? Does this return line play a role in the rate of lowering? I've shown a device in the schematic between the pump outlet and the cylinder that I think is a check valve or directional flow valve. That would seem to fit with my theory of operation.

OK, so am I anywhere close or totally off base here? All comments welcomed, even the "I can't believe you're that stupid" kind.