Chip Chester
Diamond
- Joined
- Dec 13, 2007
- Location
- Central Ohio USA
Duh... deleted after re-reading original post. Never mind.
Chip
Chip
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Synchronized hydraulic cylinders?
- Thread starter W. Carter Marcy
- Start date
- Replies 35
- Views 21,453
steve10778
Aluminum
- Joined
- Nov 22, 2010
- Location
- ohio
you need a flow divider, they are mfg in many flavors. A common type is made by mounting 4 gears on a common shaft in a housing that creates positive displacement. flow in = flow out equally across all four devices.
You then would use 4 pilot operated check valves to resynch the single acting cylinder at the top of the stroke. I.e. one cylinder is leading the other three, it hits the end of its stroke, the pressure rises in the line, then the check valve opens to allow the fluid to drain back to tank until the other three meet the end of their stroke. Fluid power handbook should have an example of this. Basically you would use a pump, 4 cylinders, an 8 way flow divider (4 devices) and 4 pilot operated check valves. Maybe a relief valve in there somewhere too. Enerpac may have a flow divider to work with their fixturing line of products.
good luck!
steve
You then would use 4 pilot operated check valves to resynch the single acting cylinder at the top of the stroke. I.e. one cylinder is leading the other three, it hits the end of its stroke, the pressure rises in the line, then the check valve opens to allow the fluid to drain back to tank until the other three meet the end of their stroke. Fluid power handbook should have an example of this. Basically you would use a pump, 4 cylinders, an 8 way flow divider (4 devices) and 4 pilot operated check valves. Maybe a relief valve in there somewhere too. Enerpac may have a flow divider to work with their fixturing line of products.
good luck!
steve
JWaldo
Aluminum
- Joined
- May 4, 2011
- Location
- Northern Virginia, USA
I may be under thinking this.
Do you know what a set of parallel rulers look like? (They are used on nautical charts to walk a bearing line to a compass rose to get a bearing). You need 2 of them - except bigger.
2 square frames. Link each corner of frame 1 to the same corner of frame 2 with a 30"+ piece of flat. Now, with one frame on the floor, the other, when it rises, is kept parallel to the floor. I agree that there is some lateral motion to the moving frame. Should be able to handle that with a captive channel on the bottom of the lifting surface. (like angle iron welded into a box frame with the top flat out - capture it in a piece of Z channel on the bottom of your platform)
Ignore periods in ''' drawing ''' below.
------------------------------ Attached to sliding channel on bottom of lifting platform
..\.............................. \
...\...............................\
....\.............................. \
.....\...............................\
......\...............................\
.......\...............................\.
-------------------------------------- Attached to floor
Yes, it moves --> that way as it rises - hence the need for the sliding channels in the bottom of the lifting platform (or slots with bolts, or rollers of some sort, or etc.)
Strictly mechanical. Probably some friction issues if you don't use a lot of grease (or rollers).
FWIW
Thanks,
Jim.
Edited - all the spaces in the diagram dissapeared when posted. Had to replace with '.'s
Do you know what a set of parallel rulers look like? (They are used on nautical charts to walk a bearing line to a compass rose to get a bearing). You need 2 of them - except bigger.
2 square frames. Link each corner of frame 1 to the same corner of frame 2 with a 30"+ piece of flat. Now, with one frame on the floor, the other, when it rises, is kept parallel to the floor. I agree that there is some lateral motion to the moving frame. Should be able to handle that with a captive channel on the bottom of the lifting surface. (like angle iron welded into a box frame with the top flat out - capture it in a piece of Z channel on the bottom of your platform)
Ignore periods in ''' drawing ''' below.
------------------------------ Attached to sliding channel on bottom of lifting platform
..\.............................. \
...\...............................\
....\.............................. \
.....\...............................\
......\...............................\
.......\...............................\.
-------------------------------------- Attached to floor
Yes, it moves --> that way as it rises - hence the need for the sliding channels in the bottom of the lifting platform (or slots with bolts, or rollers of some sort, or etc.)
Strictly mechanical. Probably some friction issues if you don't use a lot of grease (or rollers).
FWIW
Thanks,
Jim.
Edited - all the spaces in the diagram dissapeared when posted. Had to replace with '.'s
BobRenz
Stainless
- Joined
- Jun 30, 2012
- Location
- Minnesota, USA
There isn't any cheap and simple way to synchronize four hydraulic cylinders. Your simplest, and probably cheapest, solution is with 4 jackscrews. depending on the load, they could all be driven by a common roller chain operating a sprocket modified to also be a feed nut.
Just make a scissor lift guide arrangement, The linkages if well made will keep the force equally on all 4 corners forcing a level rise. maintaining precision on 4 hydraulic cylinders is going to be costing north of 5 figures. Equally using 20 tons of enpac rams and a hand pump to go up 30" is going to take a life time or 2. If the load is only just over a ton or 2 you can't beat srew threads or other mechanical options, even if there powered just by one "lift" cylinder.
What your doing is like going to the corner store going round the far side of the moon in the process. Rather than just walking directly there or jumping in the car. Its a nice theretical chat, but is going to be a stupid waste of money + a maintenance nightmare in use.
What your doing is like going to the corner store going round the far side of the moon in the process. Rather than just walking directly there or jumping in the car. Its a nice theretical chat, but is going to be a stupid waste of money + a maintenance nightmare in use.
W. Carter Marcy
Aluminum
- Joined
- Dec 15, 2002
- Location
- Troy, NY, USA
Only going up 3 inches...
Mud
Diamond
- Joined
- May 20, 2002
- Location
- South Central PA
What about flow divider valves? I think they are only made for 2 outlets, but maybe 3 could be ganged to serve 4 cylinders. It's above my pay grade to explain how they work, but I have one on the fork positioner on my forklift to synchronize the 2 cylinders so the forks don't go off center when spreading or returning. It's a little spool valve screwed into a rectangular valve block. When researching it I found a bunch of different types, some meter in both directions, some in only one direction.
Gary E
Diamond
- Joined
- Jan 2, 2006
- Location
- Houston, TX
How about 4 scissor jacks... one for each corner of the load..
Then adapt or buy them allready adapted with a motor they looked like 12 volt starter motors from a small car...
Some wire and a switch....
or get fancy with limit switches that stop it at both up and down positions...
Hydraulics are nice... but... they will LEAK eventually and I'd bet they'l cost more
Then adapt or buy them allready adapted with a motor they looked like 12 volt starter motors from a small car...
Some wire and a switch....
or get fancy with limit switches that stop it at both up and down positions...
Hydraulics are nice... but... they will LEAK eventually and I'd bet they'l cost more
9100
Diamond
- Joined
- Nov 1, 2004
- Location
- Webster Groves, MO
Look at a hydraulic press brake. They only have two cylinders, but they must move perfectly in unison. They use a large cylinder with a smaller one built into it which feeds the other end. You could do something similar with multiple double rod cylinders linked together. This is a variation on the idea of one cylinder driving four, which I think has the best chance of success. An 8" air cylinder on 100 PSI air will produce 5000 pounds of force that can push 4 smaller hydraulic cylinders. A caveat here. Air and hydraulic cylinders don't like to be used as pumps. This is especially true of air cylinders with O ring seals. If you are thinking about doing it, ask for the full explanation before you waste time and money. Hu's idea will work if you do it right, but you must put the seals on the cylinders and push rods through them as he says. This is one of those "ask me how I know" issues. Believe me, I do know from grim experience.
Bill
Bill
QUOTE'
" Right now I have it so that the cylinders bottom out at full stroke at the required lift height, which levels the unit perfectly. they just don't bottom out at the same time."
That indicates that the load is not symmetrical. If it were the rams would rise at the same speed.
The idea of double acting cylinders, feed the downstream cylinders from the rod end of the cylinder won't work. That would be an "intensifier. ie., increased pressure from the smaller area, but reduced flow, and where do you get the additional fluid hen you have extended the first cylinder?
A hydraulic loader with 2 cylinders WILL have the same pressure on both cylinders, I don't care how much weight is on one side of the bucket or the other. Guages on both cylinders will read the same, as they are plumbed in parallel, teed to feed both cylinders. If one ram has leaky cups, both will drop in synch. If your valves close off both advance and retract, then, no, the cylinders will not lose pressure, as there is no place for the leakage past the cups to go
My company lifted 500 ton turbo generators with centralized Enerpac, and they lifted evenly. BUT, the 4 corners were uniform in weight.
"You then would use 4 pilot operated check valves to resynch the single acting cylinder at the top of the stroke. I.e. one cylinder is leading the other three, it hits the end of its stroke, the pressure rises in the line, then the check valve opens to allow the fluid to drain back to tank until the other three meet the end of their stroke."
" it hits the end of its stroke, the pressure rises in the line, then the check valve opens to allow the fluid to drain back to tank ."
That is impossible. The pressure cannot rise in that line, if they are all in parallel. The same pressure on all 4. IF one ram were smaller area, it would lift quicker, but the pressure on all 4 will be the same, and in an hydraulic system, you do not dump fluid from one cylinder to allow the others to catch up. If you DID have a valve open on a common rail system, as you are describing, if your "check valve" opened, you would lose pressure to all you cylinders. One is faster than the others, and I think you are referring to something called, properly, a "buffer valve", if it opens, system pressure falls off, you quit lifting, simply dump back to the reservoir.
JWaldo,
Also known as a "Walking Beam" conveyor. We had them to move 35 ton coils into the Pickle Line infeed.Couple hundred year old idea. Nothing new under the Sun, though we might just dream up what we never saw. Re-invent the wheel.
"There isn't any cheap and simple way to synchronize four hydraulic cylinders.'
Bullshit! 4 identical cylinders ARE self synchronizing. Even IF one is dumping fluid past the cup and all over the deck, all 4 will have the same pressure in them, and I have had a LOT of "professionally rebuilt" AND new Enerpac rams, 100 ton, leak like hell on first use trying to lift the corner of a 400 ton weight, not capacity, EOT. Carry that sumbitch down 60 feet, get another and hope that one will see the job through.
Hydraulic lifting devices were much better when there was competition. Now, I think Enerpac has gobbled them all up, take it or leave it.
I have been involved in hydraulics since 1962. School, even. And we have people who want to conjure up mechanical contraptions, OR tell you it will cost 5 figures to lift half a ton 3 inches. Airbags, 500 each? Can't get the air in each one the same pressure? One corner lifts quicker? Back to Square One.
Scissors like mechanical device? 500 pounds? How do you lift it high enough to get a 1 piece lifter under it? 2 devices, split, how do you lift each side to install? Pinch bar? Then a chain or something to drive them both. Synchronized? Fat chance.
I have said my piece. Your original idea is the best solution.
George
" Right now I have it so that the cylinders bottom out at full stroke at the required lift height, which levels the unit perfectly. they just don't bottom out at the same time."
That indicates that the load is not symmetrical. If it were the rams would rise at the same speed.
The idea of double acting cylinders, feed the downstream cylinders from the rod end of the cylinder won't work. That would be an "intensifier. ie., increased pressure from the smaller area, but reduced flow, and where do you get the additional fluid hen you have extended the first cylinder?
A hydraulic loader with 2 cylinders WILL have the same pressure on both cylinders, I don't care how much weight is on one side of the bucket or the other. Guages on both cylinders will read the same, as they are plumbed in parallel, teed to feed both cylinders. If one ram has leaky cups, both will drop in synch. If your valves close off both advance and retract, then, no, the cylinders will not lose pressure, as there is no place for the leakage past the cups to go
My company lifted 500 ton turbo generators with centralized Enerpac, and they lifted evenly. BUT, the 4 corners were uniform in weight.
"You then would use 4 pilot operated check valves to resynch the single acting cylinder at the top of the stroke. I.e. one cylinder is leading the other three, it hits the end of its stroke, the pressure rises in the line, then the check valve opens to allow the fluid to drain back to tank until the other three meet the end of their stroke."
" it hits the end of its stroke, the pressure rises in the line, then the check valve opens to allow the fluid to drain back to tank ."
That is impossible. The pressure cannot rise in that line, if they are all in parallel. The same pressure on all 4. IF one ram were smaller area, it would lift quicker, but the pressure on all 4 will be the same, and in an hydraulic system, you do not dump fluid from one cylinder to allow the others to catch up. If you DID have a valve open on a common rail system, as you are describing, if your "check valve" opened, you would lose pressure to all you cylinders. One is faster than the others, and I think you are referring to something called, properly, a "buffer valve", if it opens, system pressure falls off, you quit lifting, simply dump back to the reservoir.
JWaldo,
Also known as a "Walking Beam" conveyor. We had them to move 35 ton coils into the Pickle Line infeed.Couple hundred year old idea. Nothing new under the Sun, though we might just dream up what we never saw. Re-invent the wheel.
"There isn't any cheap and simple way to synchronize four hydraulic cylinders.'
Bullshit! 4 identical cylinders ARE self synchronizing. Even IF one is dumping fluid past the cup and all over the deck, all 4 will have the same pressure in them, and I have had a LOT of "professionally rebuilt" AND new Enerpac rams, 100 ton, leak like hell on first use trying to lift the corner of a 400 ton weight, not capacity, EOT. Carry that sumbitch down 60 feet, get another and hope that one will see the job through.
Hydraulic lifting devices were much better when there was competition. Now, I think Enerpac has gobbled them all up, take it or leave it.
I have been involved in hydraulics since 1962. School, even. And we have people who want to conjure up mechanical contraptions, OR tell you it will cost 5 figures to lift half a ton 3 inches. Airbags, 500 each? Can't get the air in each one the same pressure? One corner lifts quicker? Back to Square One.
Scissors like mechanical device? 500 pounds? How do you lift it high enough to get a 1 piece lifter under it? 2 devices, split, how do you lift each side to install? Pinch bar? Then a chain or something to drive them both. Synchronized? Fat chance.
I have said my piece. Your original idea is the best solution.
George
ADFToolmaker
Cast Iron
- Joined
- Mar 12, 2012
- Location
- Hamilton, New Zealand
This is a really interesting thread, lots of good ideas coming out. One thing that I want to help clear up though. The op is correct that one cylinder will usually move to the end of its stroke before the others in his application, even though the pressure is the same in each cylinder. The reason is in the geometry. If two people carry a piano up a flight of stairs, do they both feel the same weight? No, the poor guy on the bottom carries more, the vertical component of the force vector swings toward him. It's the same on a platform as the op described, unless the load is exactly the same on each corner, and I mean exactly, one cylinder can move easier, and even if the difference is slight, it will go first. As soon as this happens the force vector swings to the lagging cylinder, just like the guy under the piano, and the force imbalance gets worse and is not corrected until the leading cylinder gets to the end of it's stroke.
But....If the cylinders have a spring return, and the spring is large compared to the force imbalance from the load, as the lead cylinder moves further, it experiences a greater force than the laggaing cylinders, and they have a chance to catch up and keep an even stroke.
But....If the cylinders have a spring return, and the spring is large compared to the force imbalance from the load, as the lead cylinder moves further, it experiences a greater force than the laggaing cylinders, and they have a chance to catch up and keep an even stroke.
9100
Diamond
- Joined
- Nov 1, 2004
- Location
- Webster Groves, MO
Mount four double acting cylinders with twice the required stroke on the corners with the cylinders on top and the rods down. Pressurize the bottoms of the cylinders with air. I use a strut pump available from aircraft supply houses like Wag-Air for a reasonable cost. These are simple hand cycled boosters that run off circa 100 PSI air. The air will serve the same purpose as ADF's springs, but will be adjustable. As the cylinders extend, the volume reduction in the bottom end will increase the pressure, performing a balancing function. If one corner tends to get ahead or behind, trim the air pressure to compensate. You will need to incorporate stops because the cylinders will not be bottoming at full height. An easy way to do that is to put a loose sleeve on the rod inside the cylinder.
For my home grown molding machines I needed hydraulic power for a few seconds closing the molds and cycling the transfer cylinders with just holding pressure between cycles. A small pump with an accumulator and a pressure switch would work, but cost more than I wanted to spend, so I got about 4" bore, 18" stroke cylinders from Grainger and pressurized the rod end with the aforementioned strut pump. I mounted a frame on the rod end with an adjustable switch controlling the pump. When the hydraulic pressure drops, the cylinder retracts and trips the switch, running the pump until it extends and turns it off. That gave me an inexpensive accumulator and pressure control in one unit.
The reason for mounting the cylinders rod down is so any air that leaks past the seal will bubble out in the reservoir when the unit is lowered, making it self bleeding. From time to time, you will want to release the air to blow out any fluid that gets into the bottom of the cylinder.
The "Prince" brand cylinders Grainger sells were inexpensive and gave good service.
Bill
For my home grown molding machines I needed hydraulic power for a few seconds closing the molds and cycling the transfer cylinders with just holding pressure between cycles. A small pump with an accumulator and a pressure switch would work, but cost more than I wanted to spend, so I got about 4" bore, 18" stroke cylinders from Grainger and pressurized the rod end with the aforementioned strut pump. I mounted a frame on the rod end with an adjustable switch controlling the pump. When the hydraulic pressure drops, the cylinder retracts and trips the switch, running the pump until it extends and turns it off. That gave me an inexpensive accumulator and pressure control in one unit.
The reason for mounting the cylinders rod down is so any air that leaks past the seal will bubble out in the reservoir when the unit is lowered, making it self bleeding. From time to time, you will want to release the air to blow out any fluid that gets into the bottom of the cylinder.
The "Prince" brand cylinders Grainger sells were inexpensive and gave good service.
Bill
NeilJ
Aluminum
- Joined
- Jul 29, 2008
- Location
- Melbourne, Australia
If you Google "phasing cylinders" there is good info about synchronizing cylinders.
Example: http://www.dependabledistributors.com.au/images/brochures/103-Phasing Cylinders..pdf
Commonly, agricultural seeders and cultivators use one cylinder on each wheel, and remain level while raising and lowering.
From the link it seems each cylinder must be a different size. There is usually a method (groove machined in the barrel wall or built-in valve) to allow all cylinders to fully extend without manual bleeding.
Neil
Example: http://www.dependabledistributors.com.au/images/brochures/103-Phasing Cylinders..pdf
Commonly, agricultural seeders and cultivators use one cylinder on each wheel, and remain level while raising and lowering.
From the link it seems each cylinder must be a different size. There is usually a method (groove machined in the barrel wall or built-in valve) to allow all cylinders to fully extend without manual bleeding.
Neil
Toms Wheels
Titanium
- Joined
- Dec 30, 2005
- Location
- Jersey Shore
Short of the equalizing valves that come to mind while watching Mega-mover on TV. Here is a way if you have ability to machine or have machined a set of cylinders.Four double acting cylinders, Just number I choose to start with. A single hand pump plumbed to cylinder a 3+ diameter piston with a 1 " rod, all cylinder have the same 1 " D rod. the base in of the cylinder takes 7.065 cuin of oil to move one inch, the rod side of that cylinder would displace 6.28 cuin of oil when moved 1 inch, That amount of oil would be pushed to the second cylinder which has a bore diameter of 2.828" and would move on inch with the 6.28 cuin of oil pushed from the rod end of the #1 cylinder, it would displace 5.495 cuin of oil from the rod end which is plumbed to the base of cylinder #3 which has a bore of 2.449, and would move 1 inch with the oil from cylinder #2, the rod end of #3 would displace 4.71 cuin oil plumbed to cylinder #4 which would have a bore of 2.236" and would move one 1" with the oil from piston 3,
The common pressure of the porta power systems is common of 10K psi max, so these cylinder sizes are large, I used those just as the idea. If you had air pressure of 100 psi, you could built a simple air over oil with a 4" piston and no hand pump needed.
I believe that this could be a cost effective choice, just need someone to make the cylinders for you.
The common pressure of the porta power systems is common of 10K psi max, so these cylinder sizes are large, I used those just as the idea. If you had air pressure of 100 psi, you could built a simple air over oil with a 4" piston and no hand pump needed.
I believe that this could be a cost effective choice, just need someone to make the cylinders for you.
