Dump truck hydraulics

[fka tree grower]

My 1995 F350 dump is run by an electric power up - power down system. I would really like to disable the power down function, so the body would drop as fast as the hydraulic resistance would allow. It would seem that I could cut into the hydraulic line, install a single acting, open center valve with return line cut into the reservoir, replace the electric switch with an off-on one, and be in business. As they say, if it sounds too good to be true, it probably is. What am I missing?

 

[muddstopper]

It might just be a matter of disableing the electric pump motor for down feed. I suspect this could be done at the control cord, but without seeing how your system works I cant say for sure. My dump is home made but, I used a solenoid valve for the raise and lowering. The way I have it wired, it has power up and for down the solenoid just switches without the pump running. The shifting of the valve allows the oil to flow thru the valve and the bed just gravity feeds down with no power. I have never needed power down, but if I ever did, I would just have to install a jumper wire to make the pump motor run when I activate the down button.

 

[Texasmark]

I agree on the bypass. To do any kind of pressure in the first place.....lift the bed of the truck..... you need a displacement/gear pump, aka 2 stars working together with no space around for fluid to do anything but go the way of the Outlet Port. That means that the pump would have to turn to let the fluid out and the question there is how many reduction gears between the pump and the shafts of, and the resistance of, the driving motor. Going from input to output you are reducing rpms and increasing torque, nice energy transfer. In reverse you are using pressure induced torque to generate rpms and that's a different story. Leastwise as the way I see it. Somewhere in the back of my mind I have a corollary but I don't remember the details.....been too long.

On the valve, I'd make it as large as is reasonable to allow for the maximum amount of flow to mitigate the pressure that the outlet line will see, or ensure that you are using a high pressure routing hose to the sump if very long and restrictive. Other thing I'd ensure that the return fluid is introduced at the bottom of the reservoir, or at least as near the bottom as is practical as it will reduce the turbulence and air entrapment that would be encountered by dumping it on top of the sump oil level........ Bubbles introduced in the sump could make your lift pressure mushy...air compresses, fluid doesn't.

HTH,
Mark

 

[Steve_Miller]

If you were to switch it to a single acting, are you planning on converting your cylinder to a single acting or just letting it suck the fluid back into the cylinder on the way down? If you are planning on it just sucking air into the retract side then you may need a bigger tank as now the retracted side will no longer be replacing the fluid back to the tank anymore when the extend side is being filled. You may have to put some type of flow control to limit the speed down if it is too fast as well.

Steve

 

[fka tree grower]

Thanks for the replies. All three of you have confirmed my belief that it is probably too good to be true. My real preference is for a totally different truck with 7.3 diesel and a PTO powered lift. I will be better off waiting until that truck comes up for sale.