4 stage DA telescopic cylinder mis staging on retract..

[speedshop]

Howdy,
Need help in problem solving: have a 21",4 stage, double acting, telescopic hydraulic cylinder, 56" stroke, 6" dia main body with both ports on main barrel. cylinder hooked up to a 12v DC haldex/barnes power pack with a 2 position, four way electric valve ( 2 coils on one cartridge,push & pull).
system installed on a 2008 toyota tundra dump bed made from scratch.
system extends fine, but mis stages on powered retract by first stage retracting first but for a bit and locks up.
when partially extended and retracting, first stage retracts while the other 3 smaller stages extends at the same time. When fully extended, cylinder locks during first stage retract. video & pics of problematic cylinder in action available upon forwarding your email. files too large to upload to forum. help!

[Doug Hanson]

Away till Dec 2. Maybe someone else on the forum can help till then. Try un-pinning the rod end of the cylinder and stroking it a few times from stop to stop to get all the air out.

[speedshop]

Thanks Doug, I'll hang in there and keep troubleshooting. Anyway, got a response from a retired elevator repair guy and he confidently assumed that the 'back to back U cup seal' needs replacing judging from just the pic and explanation earlier. I now have 2 videos of the problematic cylinder for anyone to see and hopefully, recognize the problem:

YouTube - cylindernoretract.MOV

YouTube - cylinderpartiallyextendedretractwrong.MOV

I have just tested the dump system with its first actual load today: 1,925kg (almost 2 tons) of semi loose, sticky construction dirt. system worked flawlessy extending fully with most of dirt still sticking to bed at 65 degree angle. I had to hop on the bed to add weight to assist in gravity retract which was smooth but awfully slow. from full extend, gravity retract had to start by 'tugging' down on the bed for the first stage to start descending then gravity takes over.
Have more videos & pics available upon requests. keep you posted.....

[Doug Hanson]

OK speedshop, back from holidays.

Cool videos, that is a wierd a problem while powering down. Double acting multi stage cylinders are a little tricky. The way your is configured, I believe it only power retracts on the largest stage which I call the first stage. Rock trucks that have 3 stage hoist cylinders usually have just one stage that power retracts to get the box back over center to the point that gravity can retract the rest of the way. They are a bit different though, the porting is to the rod end. Same idea though.
Double acting cylinders can be built to power retract all the way, but they are usually ported through the rod end and can have 'mis staging' issues. It is possible to have a double acting multi stage cylinder power retract all the way and be ported through the barrel, but it would be really complicated to manufacture (trombone flow tubes, or double walled stages, or drilled passages in the walls of the stages).
The way that your cylinder is built, you basically have a double acting single stage cylinder arranged in mechanical series with a single acting multi stage cylinder in which the extend ports are plumbed parallel, and the retract port for the single stage cylinder is on it's own.
There also apears to be a valve problem. For some reason, the extend side oil is being trapped. Because the extend side of the double acting single stage cylinder is plumbed parallel to the extend side of the single acting multi stage cylinder, as the retract side of the piston is pressured up, forcing the main stage piston down, it is trying to reduce the oil volume on the extend side of the piston, this is causing the other stages to extend. When they are fully extended, there is no where for the oil to go, and everything locks up.
I've run into suppliers selling cartridges of one manufuacturer (yours looks like Sterling) with bodies of another manufacturer, and there is nothing wrong with this except that sometimes the numbers stamped on the bodie do not corrispond with the numbers for the porting on the cartridge as indicated in the literature.
So lets start here, do you have the part number for your cartridge? it should be right on the hex of the cartridge?
Well get that part working right, and then there will be one other problem, when retracting, once the first stage power retracts fully, the pump will need to be able to shut off, but still allow the control valve to route return oil back to tank and at a controlled rate so as to not drop too fast. For the pump shuttling off, you could use a limit switch, or a pressure switch, or have two lowering buttons on the control, whichever is your prefference.
You mentioned that it gravity returns alright, how was the plumbing arranged for this? Just venting the extend line directly to tank, or was it going through your control valve?

[speedshop]

Thanks for the reply. You are right about the first stage being only double acting while the other three are single acting. Here is an image of the sterling/parker 3/4way tandem solenoid spool valve I am using: .

I am suspecting something is amiss in the plumbing and/or the valve itself. I ruled out the cylinder after having it bench tested at a local hydraulic shop. the first stage can actually power retract and extend freely now from a full extension unlike my previous test/video. Here is the video of the cylinder being bench tested at a local shop: http://www.youtube.com/watch?v=uEA-LTzwvBE

Though the first stage is working as it should, the other three stages still seem to 'creepingly' extend while on continous power retract mode as evident by this video: http://www.youtube.com/watch?v=6KdcOEknlLA
Is this normal? I think I can live with this as long as the first stage is working right. will follow your advice with the secondary switch to gravity retract after the first stage is done retracting. Gravity retract thru the 3/4way valve is fine, but awfully slow on the first stage originally.
My plumbing could be an issue due to having 3 seperate reservoirs supplying hydraulic oil to the pump by vacuum thru clear hosing. The pump does whine loudly than normal, indicating a presence of a vortex in the pump, introducing air. Plan to add an inline booster pump to eliminate this delimma. Forced to use seperate reservoirs due to space constraints in enlarging the pump tank. Back to the drawing board with this project...will keep you posted....bob

[speedshop]

...found these identification numbers on the barrel by accident when bench testing at shop:

533492-8
391246-64
SK391246-71

would like to know where and what application it came from originally. can you decipher?
also, here is a top view of the setup before the 3/4 valve was installed.

wish me luck....bob

[Doug Hanson]

Sorry, the numbers on the cylinder don't mean anything to me. I think it is a dump cylinder out of an underground haul truck like a Toro or Jarvis-Clark. Here is a link to your control valve though:
http://www.sterling-hydraulics.com/files/pdf/g0457.pdf
Looks like you have your valve plumbed up right. Pump to port 2, Tank to Port 4, Cyl ports to port 1 and 3.
The problem must be one of the following:
1. There may be a velocity fuse valve in the base cap port on the cylinder, if you look in the port is there any kind of poppet in there. These are used on scissor lifts to keep them from dropping if a hose breaks.
2. The retract oil volume is to high for the valve, flow forces are shifting the spool to close. This usually causes chatter though. The retract flow of oil can be calculated if you know the flow from your pump, the diameter of the cylinder barrel, the diameter of the first stage.
3. There is a design flaw with this cylinder and as the first stage is fully retracted, the piston is blocking the path of the oil flow for the other stages to escape through the port.
4. The cylinder was rebuilt and someone left a rag in the barrell (it' sounds funny but I've seen it happen, i've also found a grinding disc in a barrell once)

As for testing the cylinder, the smaller stages extend while the large stage power retracts do to back pressure at the extend port. When the first stage is retracting, there is a whole lot more oil coming out of the cylinder than there is going in (difference in displacement due to the stage diameter).
While the cylinder was stalled out in power retract and the smaller stages where creeping out, this is also due to back pressure at the extend port. The back pressure in this case is from oil flow from their relief valve across the return filter. I didn't hear a piston pump compensating, so it is either a gear pump and relief they are using, or it could be a piston pump, but they were using a relief valve to adjust pressure and not an adjustable compensator, as you would hear the pump destroking. If the largest stage was fully retracted and left to stall out, the power extend line blocked, and the stages creeping out, that will be due to bypass on the first stage piston seal. This piston seal is often just one or more cast iron rings.