Return to center

ParkerFly · Nov 9, 2009

Can someone explain to me how you make a hydraulic cylinder return to center? For example, you pull a lever and the cylinder extends, but when you let off that lever it springs back to neutral and the cylinder automatically retracts back to its center position.
I appreciate any insight into this. Thank you,

Justin

kennyd · Nov 10, 2009

That would require some type of special valve-probably not commonly available.

Can you please tell us the application you need it for? We may have other options/suggestions.

J_J · Nov 10, 2009

Need more data, but I will give you some ideas. Basic centering could be done with an electric valve and switches. Then you have sensors like lasers, magnetic, pressure. Are you considering a double rod cylinder, like in boat motor steering. How about Power steering like on a car.

On my Power-Trac, I have a cable that controls my hydraulic transmission. It goes through an assembly called a Hydroback, which keeps the lever centered so the machine does not move in neutral. When I push on the pedal, the transmission shifts one way, and when I press the other side of the pedal, it shifts the other way. When I am not pushing the pedal, the valve is in neutral. The Hydroback has opposing springs to keep the cable centered within a certain range.

Can some of you PT owners explain how the hydraulic shift for your transmission works. It must work something like a spring loaded valve.

ParkerFly · Nov 10, 2009

kennyd said:
Can you please tell us the application you need it for? We may have other options/suggestions.

It's currently in operation on a tractor pulling sled. The pan under it pivots to steer the sled. It is on an electric solenoid and returns to center (straight) when you let off the switch. I was just curious if anyone knew how it was doing that. Thanks.

J_J · Nov 11, 2009

Are you talking about the cylinder returning to center, or the pan returning to center?

ParkerFly · Nov 11, 2009

The cylinder returning to center. When it returns to center the pan is centered, and that's what made me wonder how you can make a cylinder return to center like that.

Wayne County Hose · Nov 11, 2009

Short, expensive answer, an LVDT. Linear variable displacement transformer. Usually computer controlled. Off the end of the cylinder is a spool that goes through a coil. The coil sends a signal to the computer and the computer would fire the motor/pump and electronically spool the valve to return the cylinder to it's predetermined point. Could be center, fully stroked, retracted, or anywhere inbetween. You can calibrate it to wherever you need. A simpler way may be to use micro switches to trigger an indicator light or shut the motor off when the cylinder is where you want it.

J_J · Nov 11, 2009

Do you have a picture of the cylinder? I am getting old, so please explain about the cylinder returning to center. Do you mean that there is a cylinder with one shaft and one piston in the middle of the shaft ? Or do you mean a cylinder with two rods coming out each side of the cylinder.

This a double rod cylinder.

https://www.surpluscenter.com/item.asp?UID=2009111109204037&item=9-6847&catname=hydraulic

ParkerFly · Nov 11, 2009

It's just a standard cylinder. Cross 4" bore 8" (I think) stroke. By return to center, I mean that the cylinder returns to the center of its stroke (extended 4") when you let off the button to cycle it.