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Converting from PTO pump to electric dump

21K views 28 replies 5 participants last post by  JA123 
#1 ·
A friend has an 80's Chevy 1 ton dump truck with a PTO driven hydraulic pump driving a 6.5" x 2" x 36" cylinder. The cylinder seems to be single acting with the body acting as the reservoir. It has a small hose going to the bottom of it and a larger hose to the top, with a fill plug near the top.
The problem seems to be the GPM of the electric pumps I've found, they seem to be around 1.5GPM, and if I've calculated properly it would take 5 minutes for a full cycle. I'm using this calculator Speed for a Hydraulic Cylinder - Calculates Extended Speed, Retracted Speed, Extend Time, Retract Time, Cycle Time

Does that seem right, and are there 12V pump systems that have higher GPMs? I've been looking at something like this NorTrac 12 Volt DC Hydraulic Power Unit — Lift-Hold-Lower Applications, Model# YBZ5-F2.1B1W2/WUAAT1 | Hydraulic Power Units| Northern Tool + Equipment or this NorTrac Single-Acting Dump Trailer Power Unit — 12 Volt, Model# YBZ5-F2.1D1W2/WUCTT1 | Hydraulic Power Units| Northern Tool + Equipment or this
NorTrac Double-Acting Dump Trailer Power Unit — 12 Volt, Model# YBZ5-F2.1B1A61/WUUTT2 | Hydraulic Power Units| Northern Tool + Equipment

Any problem using one of the dual acting pumps with a single acting cylinder, since it has two hoses? Coming down wouldn't need much pressure.
 
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#2 ·
I'm suspecting that the 6.5" dimension refers to the outside diameter of the reservoir and the 2" dimension refers to the bore diameter of the cylinder. The 36" dimension should be the length of stroke.

Plug those numbers into your equation and you'll come up with a more satisfactory (30 seconds for full extension) answer. I note that both of those pumps come with reservoirs that are not needed for your friends application with the reservoir as part of the cylinder. However, their design suggests that they will not work with a separate reservoir and perforce, must use the on that is included.

Likewise, a double acting pump (reversible rotation) is redundant. Gravity works for lowering the dump box. Don't make a simple task any more complicated than it needs to be.

What's wrong with the PTO driven pump?
 
#3 ·
I'm suspecting that the 6.5" dimension refers to the outside diameter of the reservoir and the 2" dimension refers to the bore diameter of the cylinder. The 36" dimension should be the length of stroke.

Plug those numbers into your equation and you'll come up with a more satisfactory (30 seconds for full extension) answer.
Not sure I understand. You are correct that 6.5" is the outside dimension of the cylinder, so yes the bore would be somewhat smaller, but the cylinder rod is 2 inches, so the bore would have to be larger than 2 inches, right? My assumption, possibly wrong, is that the cylinder body is the tank, not a separate tube around the cylinder.


I note that both of those pumps come with reservoirs that are not needed for your friends application with the reservoir as part of the cylinder. However, their design suggests that they will not work with a separate reservoir and perforce, must use the on that is included.
I haven't found any 12V setups without a reservoir.

Likewise, a double acting pump (reversible rotation) is redundant. Gravity works for lowering the dump box. Don't make a simple task any more complicated than it needs to be.
I wasn't sure how to handle the other line from the cylinder if using a pump with it's own reservoir so I thought I could just hook it up to the double acting pump for the down force, thinking pressure would be low because of gravity assist.

What's wrong with the PTO driven pump?
He's putting in a new drivetrain which doesn't have a PTO.
 
#4 ·
what type of drive train? , you can get a engine driven PTO pump which looks like a a/c pump ( about $600) . otherwise if its 4wd see if a np205 transfer case can be adapted , as for the cylinder , I would double check to see if there is a tank somewhere ( near the pto pump or inside the frame rails they ussually are not big , about the size of a milk carton ) , I haven't seen a cylinder that stores fluid in it for its own use ( not saying they do not exist ) Just never seen one in a dump truck application because of fluid expansion from the pumping heat .
 
#5 ·
The A/C type pump is more expensive than a 12V, and would need a lot more hose as well, plus a valve. He's taking out the NP 205 T case and putting it in another vehicle, he's putting in a drivetrain with a NP 203. Also he doesn't like the fact that the T case has to be in neutral to run the pump so you cant dump while moving.
Here's a pic of the cyl, note the large diameter hose going to the top of the cylinder, and the fill plug near the top.
Both hoses go directly to the pump
 

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#6 ·
One way cylinder rods are only slightly smaller than the cylinder bore. There isn't a provision to make them into 2-way cylinders. If the rod is 2" diameter, the bore is probably 2.25" or 2.5". The space between the cylinder and the outer wall is the reservoir.

The large diameter hose is the fluid supply for the pump.
 
#8 ·
The space between the cylinder and the outer wall is the reservoir.
So there is a separate tank around the pressure cylinder? Like this drawing I made?
 

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#9 ·
A PTO can be used on a NP-203 as well ,but if they want it to dump while its moving then the PTO would have to go on the transmission...and if its an automatic,no way to mount one to it--only the SM465 4 speed had PTO covers ..
I assume that is the case and why you want an electric pump instead..
 
#11 ·
#12 ·
Disconnect that big hose from the original pump and drain the reservoir. Raise the open end so that it is closer to the top of the cylinder and install a screened breather. The now empty reservoir needs to breath a bit with changes in temperature.

Use the new pump and reservoir as designed.
 
#13 ·
OK, one last question, I hope. Another person has an electric dump and the bed comes crashing down pretty hard. I don't know what type of cylinder he has or pump setup. We are trying to avoid that happening with this one. Currently it comes down reasonably slowly, do you think it would perform the same with the new pump setup?
 
#14 ·
That you will have to try it and see if it comes down too fast.

There are two manuals listed in the ad. Manual A shows a non-adjustable flow control in the schematic for the lowering operation. Manual B does not indicate a flow control at all.

Get the pump that goes with manual A.
 
#15 ·
Good catch, manual A part number matches the part number in the ad, not sure why they included the other manual.
Thanks so much for your help, you saved me from making a mess of this project by trying to turn it into a double acting cylinder :banghead3 I suppose it could have worked assuming no pressure was put to the tank when the cylinder was fully retracted, but I'd rather not have to find out the hard way.
 
#16 ·
You wouldn't be able to convert it to 2-way operation anyway. The top end of the cylinder vents into the reservoir with no access to install a fitting for the line to make it retract.
 
#17 ·
Right, it wouldn't be a dual action cylinder, but if I had gotten a dual action pump as I originally intended I thought it might have still worked as a single acting cylinder, with gravity bringing the bed back down and the pump pushing fluid into the tank but not actually pushing on the cylinder, (since it can't.)
 
#18 ·
My friend hooked up the new pump and said it started working but when the cylinder was all the way up or nearly so pressurized fluid started coming out the cylinder tank vent, (not the tank on the new pump, the one built onto the cylinder which was supposed to be empty). I'm not sure how pressure could get into the tank, I would think if the cylinder seal leaked it would leak outside around the piston.
 
#19 ·
The piston is inside the cylinder. The piston rod is the part that comes out and is slightly smaller than the piston or the piston would come right out of the cylinder.

There is a slight leakage around the piston seals when pressure is applied. Since there is little space above the piston, any fluid that collects will be pushed out of the vent when the piston is close to the end of stroke. It's not really under pump pressure. It just needs to escape fast enough for the piston to keep moving to the end, just like pushing your hand into a full glass of water. There isn't enough room in the glass for both and spillage is going to occur.

That's why it is a good idea to vent the cylinder all the way back to the tank. Seals do wear in the long term.
 
#20 ·
That's why it is a good idea to vent the cylinder all the way back to the tank. Seals do wear in the long term.
So you're saying we should run a hose from the cylinder vent back to the new pump tank? Could we plug the vent and use the old return flow hose?
I guess it didn't leak with the old system because the pump was pulling any excess fluid from the tank?
 
#22 ·
I guess I'm not understanding how the venting works. I've attached a drawing showing how I thought it works, the vent and low pressure return hose both go into the tank. Are you saying the vent actually goes into the cylinder, as I've drawn in the second drawing?
 

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#23 ·
Second drawing. The space above the piston is enclosed and must be vented or the air in it will be compressed, requiring additional hydraulic pressure in order to raise the piston to full stroke. The line may also be cross drilled to vent the reservoir chamber as well.

It could also be similar to the first drawing, but with an additional venting port on the cylinder that vents into the reservoir.
 
#24 ·
So if I put some air pressure into the vent and got air flow out of the tank return hose I could tell if the cylinder vents into the tank, correct?
 
#25 ·
Yup! And if the cylinder is extended, it may retract with the air pressure if the hose from the pump is not connected.
 
#26 ·
As an update, after cycling it a few times and pushing out the air and extra fluid, (he over filled it), it seems to be working fine. The tank on the new pump isn't really big enough so he's not getting full extension on the ram but he thinks it's enough to dump a load. If not we'll look into installing a larger tank or plumb a second tank to the first one. Not sure why there was fluid coming from the cylinder vent at first but it's not happening any more.
 
#28 ·
Worked fine other than the reservoir being a bit too small. He ended up buying another dump truck so didn't end up using this setup more than a few times.
 
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