Dump trailer hydraulics

[jenkinsph]

Usually if the pump runs in both raise and lower it is double acting, if it lowers quietly with the pump not running it is single acting. On my PJ dump with scissor lift it is double acting this also holds the dump body firmly in place against the frame. I would hope you have a cam lock to hold the bed in place if your cylinder is only a single acting arrangement.

 

[1gr8bldr]

Help me understand why one hose is a typical hydraulic hose, high pressure and the other just a low pressure

 

[bcp]

Help me understand why one hose is a typical hydraulic hose, high pressure and the other just a low pressure

Sounds like a single action system, using the rod end of the cylinder as a reservoir.

Bruce

 

[pmsmechanic]

To me it looks like you have pressure up and gravity down. Whoever plumbed the system put a low pressure hose on the fill port of the reservoir and attached it to the pressure down port of the hydraulic cylinder. Kind of ingenious as the pressure of the cylinder going up helps to pressurize the reservoir and help the hydraulic pump do it's job. If you over fill the reservoir it will just go into the top side of the cylinder instead of dumping on the ground. By the sounds of it you need to add a bit of oil. I would prop up the box so it doesn't come down on you and take off the low pressure hose at the reservoir. Add enough oil so that the pump pressures the hydraulic cylinder all the way to the top of it's cycle lifting up and you should be good.

 

[jenkinsph]

bcp is correct, the fluid is sucked into the rod end as the cylinder is lowered or retracted. This doesn't require a high pressure hose, very similar to a syringe under very low pressure. I take it your pump doesn't run when lowering the dump bed.

 

[Arc weld]

My old 3 ton dump truck hoist used the cylinders as a reservoir but also had a vented cap on the steel hyd. tank. Maybe this system needs a vent in order to fully extend? If it's single acting, the pump shouldn't run when lowering.

 

[jenkinsph]

My old 3 ton dump truck hoist used the cylinders as a reservoir but also had a vented cap on the steel hyd. tank. Maybe this system needs a vent in order to fully extend?


If it's single acting, the pump shouldn't run when lowering.

I mentioned this in post 21 but the OP hasn't responded

 

[timster2]

You may want to check the condition of the lift cylinder. The original owner may have plumbed that line to the tank to allow oil bypassing the piston seals to go back to the tank rather then leak on the ground. That would explain the low pressure line from the rod side to tank. For the piston to act as part of the oil reservoir the line would have to be lower than the oil level in the tank in order to suck the oil back to the rod side when the body is lowered.

 

[1gr8bldr]

Usually if the pump runs in both raise and lower it is double acting, if it lowers quietly with the pump not running it is single acting. On my PJ dump with scissor lift it is double acting this also holds the dump body firmly in place against the frame. I would hope you have a cam lock to hold the bed in place if your cylinder is only a single acting arrangement.

I will listen for the pump on the let down today

 

[1gr8bldr]

I will listen for the pump on the let down today

Motor runs going up but not down. It lifts fast at the beginning, but gets super slow at the top, not quite lifting enough to get the load to slide on it's own.