can anyone help troubleshoot my dump bed?

[cochino12]

Just recently bought this dump bed truck. The dump works but it is very slow, I mean very slow. Lowering it is slower than raising it. I dont know anything about hydraulics, is there anything obvious here that I can adjust for speed? any ideas?

Thanks

[Sheepdip]

There should be a needle/throttling valve off the bottom of your cylinders in the line that returns to the hydraulic tank. It throttles both ways actually but by being in the return line it keeps the bed from slamming down from the weight where it is needed most.

Be careful and safe while adjusting it, some have a little screw, allen or otherwise to lock them where you like it.

[mongocanfly]

That's a really odd setup...unusual to have double acting cylinders on a dump bed..most use single acting cylinders and the weight of the bed is what makes it come down
You could also be limited by the pump output.and/or valve size...that's 2 sizable cylinders ..and like sheepdip says..there could possibly be a flow control valve that can be adjusted...I'm not really seeing one in the system though..
If I see it correctly ,the pump valve control goes into the bottom of the cylinders..then at the other end of the cylinder it goes back into the round pipe crossmember...and I'm assuming then back to the tank the pump is attached to..
Thing is you dont want a dump bed moving to fast...
how long does it take to fully dump..and then to lower?

[1976gmc20]

I'm guessing that electric-hydraulic pump is just too small for those two big cylinders. The one that I set up that way was for a 3/4 ton dump flatbed and it had one cylinder about half that size. It was a kit with pump, scissors, lines, and cylinder.

If your truck is a four speed you might think about converting to a PTO pump. I set up a complete system from scratch for my log loader so it isn't that hard or expensive.

As far as coming back down, your plumbing looks a little weird to me. It looks like you have two oil tanks, one on the pump and one in that round crossmember. It's like the bed and lift was designed for a PTO pump and somebody grafted in the electric pump/tank using only one line. Maybe you have an air lock or an oil lock. Lots of times those 2 way cylinders were set up to use the "down" side (usually not powered for this purpose) as an extra oil reservoir: the oil from the other side goes into the tank when it's going up and then gets sucked back up into the top of the cylinder when it's going down.

[Killer Bee]

not familiar with this setup specifically but a few things stand out from your pictures that I would check..

first thing, make sure the hand lever on the control valve is transmitting full range of motion.. you may even be able to manipulate the valve stem manually to extend the range of motion for noticeable difference in performance..

• control lever moved to raise position should start the electric motor and open the passage from the pump to the cap (lower) end of the cylinders
  
• lever in the neutral position should block the hydraulic passage and motor should turn off
  
• lever in the lower position motor should remain off while hydraulic passage from the cylinders is throttled back to the reservoir..

that's a generic explanation of a basic system, of course there are many variables by manufacturer, different types of load holding systems, counter balance valves, pilot operated controls, check valves, orifices, etc.

based on the single hose outlet from the hpu (hydraulic power unit) this appears to be a simple single acting, dual cylinder system.. the two vent/filler caps is probably a result of not plugging the unused bung.. these units can be mounted horizontally or vertically... the pump suction riser inside the reservoir is replaced/relocated for the desired mounting orientation and the vent/filler is relocated/plugged as required.. if this an older used system before your ownership, might be a good idea to remove the reservoir for cleaning and inspection and make sure the suction screen on the pump inlet tube is clear..

there may also be deceleration adjustment on the manifold that controls the return of fluid to the reservoir.. these can vary by manufacturer..

I would also remove all of that black pipe, the street ell, the threaded union,etc. on the high pressure side of the system and replace with forged steel fittings rated for the hydraulic pressures in your system.. those cast WOG (water, oil, gas) fittings are typically rated for 200-300 psi where that hydraulic system could easily be 1000-3000 psi.. I would also check and replace as necessary all of the hoses connected from the HPU to the cap end of the cylinders..

the slack hoses hanging down from the rod (upper) end of the cylinders should be simply to vent the rod end of the cylinder.. why they are plumbed back to what appears to be a transverse mounted reservoir built in to the cylinder anchor points which looks like a large diameter tube or pipe, I'm not sure.. but the hose on the driver's side appears to be severed almost in two above the shock absorber area.. something just dawned on me, that reservoir where the two rod end hoses return to should have a vent on it, maybe somewhere along the line the HPU ended up with both filler/breather caps and that reservoir got the plug?? this may be a source of slow performance, the driver's side cylinder is vented through the severed hose but the passenger side is still air tight? so again, not sure why they were plumbed to a reservoir but typically they would just have an air vent fitting and if either of them start dripping, indicates the cylinder piston packing leaking internally..

speed = flow.. so as mentioned above, maybe the HPU is not properly sized for the cylinders? maybe the old unit failed and was replaced with a smaller one? I have worked on several different types of those 12vdc package units, some of them have optional pump displacements available..

those cylinders may be larger than necessary? force = pressure x area.. you can get the approximate diameter of the piston by checking the diameter of the packing gland at the rod end where you can see the cylinder wall I.D. take that to get the radius and pi x radius squared (sorry don't know how to express that with my keyboard) x system pressure should give you an idea of force or capacity of those cylinders.. just from looking at them from your pictures they appear to be at least 6" diameter on the outside so lets's use 5" for piston diameter.. 2.5 x 2.5 = 6.25 x 3.14 = 19.625 x 1000psi = 19,625 lbs of force.. if this is anything close to the size of your cylinders and system pressure, might be a little overkill to have 40k lbs of lifting force on a light duty truck dump?? and if those cylinders are that big, it takes a lot of fluid to fill them up and may contribute to slow operating speeds..

there are a lot of other things that could be factors here but from the brief description and those pictures that should either lead you to the problem or at least get you closer to it.. you're welcome to pm me with your number if you have some more questions, happy to help if I can.. good luck!

[1976gmc20]

Well, just to add to the above: if any oil is getting past the cylinder packing, then it is getting routed into the second hydraulic tank when the cylinder is fully extended, and then it is going - well, apparently nowhere but rather just filling up that tank. That could cause problems, and also if that tank is not vented so the cylinders can suck air or oil back when retracted/lowered.

I'm going to guess there is a plug in the bottom of that round tank that previously or at least by design would have had a suction line leading directly to a PTO driven pump. It was common to use the non-pressurized side of double acting cylinders to store extra oil so the tank could be smaller. It seems like at the very least there should be a cross-feed line between the round tank and the pump/tank to equalize the oil or air coming out of the "top" of the cylinders.


I used to use black pipe for static portions of the high pressure side of the pump without any problems, but I reckon that's no guarantee that it is truly safe. I had if I recall correctly a 20 gpm pump that could produce up to 2000 psi. I had plenty of hoses blow out before I finally managed to replace everything with brand new hose, but the steel pipe never failed.