What is a pump dump?

[BeezFun]

I have an aerial lift with a problem I'm trying to debug. One of the components in the electrical logic diagram is a "pump dump". It is some kind of electrically operated valve because it's shown on the electrical schematic with 2 wires going to it, a ground and 12v controlled by a set of relays. Here's where it appears on the hydraulic diagram, it's called a "dump valve" in the parts description. The machine has a DC motor and a gas engine to operate the pump. Any help on what it does would be appreciated, including what it might look like.

 

[oldnslo]

A dump valve unloads the pump back to tank so not running under load and frequently used to allow motor to start unloaded.

 

[TractorTech]

Most likely it is a solenoid valve.

 

[BeezFun]

A dump valve unloads the pump back to tank so not running under load and frequently used to allow motor to start unloaded.

Thanks, that helps me make sense of the logic diagram. I have a parts diagram and don't find that part on it, even though it's' shown in several schematics. I know where the wires for the valve terminate in the control module, but they disappear in a tightly packed mess of looms and oily hoses. So I can't follow the wires to find this valve.

 

[oldnslo]

Can you post some pictures of the pump assembly? That might help a member of this board identify the components. The valve in question could be either line mounted or part of a manifold assembly.

 

[BeezFun]

Here's an overview of where things are, the DC motor and tank are just to the left of the batteries. The DC motor drives a pump that lives inside the tank. The gas engine at the far end drives it's own pump that's external and visible.


Here's a view of DC motor, the contactor is right on top of the motor, it has 2 wires coming out of it. I've tested the contactor and motor by jumpering directly from the battery, both work fine. The red filler cap for the tank is just visible at the right edge of photo and the control board is at the left.



Here's a view of gas engine and its pump.



Photo of gas engine and tank from the other side:

 

[oldnslo]

On the photo of gas engine and pump shows the unloading valve. By the shape of the coil it could be a Delta Power valve. If it is the name should be molded on the coil. If schematic is correct it is Normally closed and energized to open allowing flow in the side ports and out the nose to tank.

The DC unit probably has the valve in that block between the motor and reservoir.

 

[zzvyb6]

But back to basics: When lowering the boom, you don't need the hydaulic pressure supply. You just release the pressure proportional to the control handle (joystick) demand.

I have the JLG version (all electric) and no motor operation (needed) when you are landing the basket. My reference calls it a 'dump valve'.

 

[BeezFun]

On the photo of gas engine and pump shows the unloading valve. By the shape of the coil it could be a Delta Power valve. If it is the name should be molded on the coil. If schematic is correct it is Normally closed and energized to open allowing flow in the side ports and out the nose to tank.

The DC unit probably has the valve in that block between the motor and reservoir.

Thanks, now I understand.

If I understand the operation, the dump valve is energized when I push the button that turns on a hydraulic pump (either motor or gas engine, it doesn't matter), but then something has to deenergize it so it closes. I'm guessing the flow switch is somehow doing that, even though it isn't shown on the logic diagram. So as soon as flow starts, power is removed from the dump valve.

The problem I'm chasing is that when I push the hydraulic button that should turn on the DC motor, it doesn't come on. I've traced it to the wire on the control board that goes to the contactor on the motor, and it's not raising 12v when I push the button, so something in the logic circuit is preventing it.

Here's the logic diagram if you have time to look at it. The resolution isn't great unless you have a larger monitor. Look at the far left two logic streams, one is labeled "DC Motor Run", the other is labeled "Pump Dump". The top horizontal line on drawing is +12v, the bottom line is ground. The connection point labeled "101" always has 12v, in order for the motor to run the connection labeled "14" must be 12v, but it's not. The connection point labeled "116" has 12v, which is energizing the dump valve. My machine doesn't have that device labeled "Battery Management" with the dotted line around it, so connections 14 and 114 are jumpered together.

So my problem comes down to figuring out why that relay labeled "RL8/1" (which is almost impossible to read) isn't closing and putting 12v on connection 114.

 

[BeezFun]

But back to basics: When lowering the boom, you don't need the hydaulic pressure supply. You just release the pressure proportional to the control handle (joystick) demand.

I have the JLG version (all electric) and no motor operation (needed) when you are landing the basket. My reference calls it a 'dump valve'.

Interesting, my motor seems to labor as much when I lower as when I raise. I wonder if that's because it has to run the cage leveling cylinders?