Synchronizing a slideout for a bus conversion

[Ray2]

I am converting a 40' Prevost bus into a motorhome, I have installed a 12' slideout (yes it was engineered)and need to install hydraulics to move it. The slideout does not touch the floor, so mechanical guides are not practical, so I want to install a hydraulic cylinder on each side. Both ends of the slide can and do move freely from the other side and if one side moves more than a couple of inches than the other, it binds. The slide also needs to move very slowly, so flow dividers can not be used. The slide is not difficult to move, the problem is keeping it going straight. I am linking a picture of something I think will work (using two cylinders in series with two others)but I can not figure out how to maintain and bleed lines A & B that are between the slaves and masters. Any ideas or suggestions appreciated.

 

[budt]

Ray2;

You have over complicated the series circuit. Here is a way to use only 3 cylinders

Connect one port of the Directional Control Valve to the rod end of the left cylinder 1, the cap (Blind) end of that cylinder to the cap end of a second cylinder that is fully extended and has its rod connected to nothing same as your two bolted together cylinder setup, connect the rod end of cylinder 2 to the rod end of cylinder 3, connect the cap end of cylinder 3 to the other Directional Control Valve working port.

You still have the problem of bleeding but it can be done.

A simpler way is to use four flow controls and two cylinders. It is not dead accurate but would work very well for your setup. Any out of synch can be evened up after the first cylinder bottoms out by leaving the directional control valve shifted until the lagging cylider bottoms out.

For flow controlling it is best if the flow path length to a set of ports are the same.


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

http://www.fluidpower1.us

 

[Ray2]

Thanks for the answer Bud,

That is certainly simpler (I'm good at making things more complicated that they should be), but you are right,the two lines between cylinders will be hard maintenance.

Four flow valves??? Sounds interesting, could you expand on this please.

Ray2

 

[budt]

Use only two cylinders and install a Meter Out flow control at each cylinder port. Line length is not important with this setup since you can adjust resistance individually.

I always install the flow controls set them wide open and then cycle the cylinders while disconnected from the work to purge the air. Next, adjust them fully closed and then open each one some small amount, say 1 round. You will know how much to open them by watching a pressure gauge at the pump. If the flow controls are actually controlling flow pressure will be pump relief setting since some pump flow is bypassing to tank because you are not allowing it to all go to the cylinders.

With the cylinders still disconnected from thier work, start cycling them and adjust the speed individually until they are synchronized. If you want them to be as fast as possible keep opening them up evenly until system pressure starts dropping. Then close them some until pressure is at relief valve setting and they are synchronized.

This will be very close to the correct setting though a little tweaking might be necessary after attaching them to the load. Also, the circuit may need some adjusting over time since the orifice can be modified by any bit of trash floating around.


Always move the cylinders full stroke so they are re-synchronized at least one direction of travel each cycle.

This circuit works great for an application like you are doing. It can be a problem in a production line since flow can be modified by many things and some circuits never go full stroke in either direction.


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

http://www.fluidpower1.us

 

[byrdj]

I recall you were looking at a HWH system that used a "synchronizing valve". The function of this valve was to bleed the air out of the lines. I didn't make very good notes back then and I don't think I posted my interpetation of that system. But basically:
1) pressure was applied to the two coupled synch pistons. stroking both to its ? position
2) a check valve in the two coupled pistons allowed oil to pass thru and go the retract side of the power cylinders.
3) with the retract valve open. the fluid on the extend side would be forced to drain.

I don't recall if this was found on the HWH site or was it something I made up

http://home.att.net/~joseph.f.byrd/wsb/media/209474/site1011.GIF

 

[Ray2]

budt, thanks for the response,

I thought about 2 cylinders in series after Bud's response, but having the difference in volume from going from shaft end to the blind end of the other cylinder was about 10% less oil in the second cylinder and would have made a difference of 1.5" of travel. Would the flow controls compensate this?

byrdj,

Good memory, I have been working on this problem for months, so I tried a different approach to my question, my situation is very similar to what the HWH cylinder could do for me, but they will not sell to me; they won't even talk with me. Can't blame them I guess, they are just protecting themself. It's a check valve huh; dam** that makes sense, wonder if I could build that? The wheels are spinning again, danger Will Robinson!!!
Gentlemen, thanks for the responses, your time on this is appreciated, when I am done I will post my results and some pictures.
Ray2

 

[budt]

Take a look at the DCR and Dr Rephasing cylinders at this manufacturer. I think this is what you are talking about

http://www.crossmfg.com/cylinder.html

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

http://www.fluidpower1.us

 

[kcj]

Years ago I saw several versions of the same mechanical synch circuit: The sliding portion had a short section of rack gear teeth, (or roller chain, or series of holes punched in a metal strip) affixed to each end. In this example, the front and rear extremes of the slider, with the rack going left and right, in the direction of slider motion.

A long shaft or tube goes from front to rear, fixed on bearings at each end. Close to each end, there was a gear fixed to the shaft (or a roller chain sprocket), meshed to the rack on the slider.

As one end of the slider moves out xx inches, the rack turns the gear and the shaft. If the other end does not move the same distance, the shaft twists and transfers force and torque from the end trying to lead, back toward the lagging end.

Principle is similar to gear flow divider transferring inergy through the shaft from one section to another.