Hydraulic Cylinder won’t go back down

Ivan1547 · Sep 20, 2020

Hello. I have a electric manlift.

When you actuate the main lift, it powers 3 cylinders to raise. The problem is the middle cylinder won’t retract with the other 2.

How do I release the pressure here and drop the boom?

WranglerX · Sep 20, 2020

How is cylinder plumbed in with all the rest.... If its under separate control, I think have a valve issue and not a cylinder issue....

Dale

Ivan1547 · Sep 20, 2020

Good question. I am not sure. Here is a pic of the cylinder.

AWSubie · Sep 20, 2020

I have a towable T350 lift and in the operations and safety manual there is an emergency manual descent procedure where at the main hydraulic block there is a valve that can be manually pressed which will allow the cylinders to bleed down but you must be very careful of course. Ensure that no one is around the booms because they will descend fairly quickly.

If you don’t have your operations manual the JLG site will probably have it just search for your model.

AWSubie · Sep 20, 2020

Here is a procedure I found on the JLG site for the model 45ic, not sure what model yours is.

Ivan1547 · Sep 20, 2020

I lifted the boom a little and tried the manual descent.

It dropped the 2 cylinders but the middle one is still engaged.

Is there a way to safely bleed this cylinder so it drops?

AWSubie · Sep 20, 2020

Because your lower and upper cylinders are working I am thinking that one of the holding valve cartridges is defective on your mid cylinder.

the only way to safely bleed the cylinder would be to place a strut between the lower and mid boom to control movement of the mid boom while cracking open a holding valve cartridge.

This may sound silly but do you have a very large tree nearby that you could support the upper and mid Boom from overhead?

One more thought, have you inspected the hydraulic lines to be sure none are leaking? The purpose of the holding valves is to “lock” the cylinder in the event of a line burst.