Cylinder Retraction

[kjellum]

What stops a double acting cylinder from retracting quickly under load? eg loader not slamming down with a full bucket while being lowered, fork lift not slamming down under load while being lowered.

 

[J_J]

The retract mode of a cyl is fast. The orifice of the valve or ports, hoses limit the flow.

Sometimes you have dead weight plus the hyd flow into the cyl.

More load, the faster the retract..

 

[kjellum]

Makes sense. So I can limit the retract rate by limiting flow, the easiest way would be to restrict the hose size. Is this typically how retraction rate is controlled? eg a boom fork lift or boom truck.

I'm designing a hydraulic system and am having retraction speed challenges.

42' 9000 LB FORKLIFT - Runyon Equipment Rental

 

[J_J]

Using a needle valve , you can dial in the speed of descent.

 

[kjellum]

Thanks J.J.

 

[oldnslo]

Are wanting to control the speed for the complete travel or just prevent slamming at the end of stroke.

Some cylinders offer "cushions" which help decelerate the cylinder at end of stroke to limit the slamming effect.

For overrunning loads a counterbalance valve can be used to prevent "runaway conditions.

For speed control: Some form of flow control is required

 

[kjellum]

I'm looking to slow the speed during the compete travel. Gravity is working against me in this case so I am in a "runaway" condition. Reading about counterbalance valves it looks like this might be the right application for one. This will create back pressure on the cylinder to control retraction.

It seems like a needle valve will give me more fine tune adjustment on the retraction.

The tail lowering is what I'm working on: http://lh6.ggpht.com/-KU-Roo_bFHg/T.../uI33KZ7UdR4/s800/6117802511_5958062cc0_o.jpg

 

[oldnslo]

Counterbalance will prevent the "runaway" and a pressure compensated flow control will provide consistent speeds with varying loads. For hydraulics I prefer meter-in control.

Interesting application you are working on..