travel pump

[KentT]

MR,

I think what we're really wrestling with here is the difference between series and parallel circuits, when everything else is constant.

For example, I've been assuming the travel pump has 16 GPM max flow, since that is the maximum spec (continuous) for ONE of these wheel motors. If the above explanation of a series circuit is correct, does that mean that the pump could safely produce up to 32 GPM without exceeding spec on any component, since that flow is divided into two series circuits? I doubt that, but...

For the purpose of this discussion, I'm going to assume the pump puts out 16GPM max. (According to the HP formula at the above link, 16GPM at 3000 PSI equates to 27.984 HP. So, I'm guessing that this system with 25HP in, will output something a bit less than 16GPM at 3000 PSI.)

Looking at the performance chart for the White CE-230 wheel motors, it certainly seems to illustrate Stray's understanding.

Also, I think each circuit has the wheel motors in series, but the two wheel motor circuits are parallel. If the two circuits cut this flow in half -- i.e. down to 8 GPM at 3000 PSI -- then each wheel motor is effectively working at 8 GPM, but only 1500 PSI. According to the wheel motor performance charts this yields a maximum of 2691 lb-in of torque, and 122 RPM.

However, if the wheelmotors were in parallel, as Stray suggests, they'd each have 4 GPM at 3000 PSI maximum, which yields a maximum of 5385 lb-in of torque, but only 41 RPM -- twice the torque, but 1/3 the RPM.

Note that all these numbers are max values, as I interpret the chart, and based on the stated assumptions. His experiment could be interesting!

 

[MossRoad]

If two wheel motors are in series, the first motor gets 8GPM in and then dumps it out to the second motor. Each motor in the circuit gets 8GPM.

There are two series circuits, each with two motors.

The two series circuits are hooked in parallel.

If the pump puts out 16GPM, 8GPM goes to circuit one and 8GPM goes to circuit two, IF the loads are balanced(what does a flow divider do?).

If one tire in circuit one spins, the second tire in circuit one still gets 8GPM. Same thing for circuit two.

However, if both tires in circuit one spin, will the parallel design blow all the fluid to the circuit that is spinning?(again, what does a flow divider do and is there one that divides the flow to each of the two circuits?).

 

[KentT]

</font><font color="blue" class="small">( However, if both tires in circuit one spin, will the parallel design blow all the fluid to the circuit that is spinning?(again, what does a flow divider do and is there one that divides the flow to each of the two circuits? )</font>

According to the little bit I'm learning about hydraulics, the flow should increase to the circuit where the tires are spinning)...

I don't know if there is a flow divider, nor how it would work, if there is one. Note that it would need to divide the flow in both directions, since the flow is reversed to provide reverse...

Next question that comes to mind -- are the wheel motors plumbed the way they are to load-balance and facilitate steering -- especially when sharply articulated? When the left front wheel slows down because it is on the inside of a circle, the right rear tire speeds up to travel further -- and vice versa....

 

[J_J]

I think if one tire spins, there is almost zero pressure in that circuit. Pressure is developed when there is resistance in the circuit. I have a pressure gauge in my lift circuit, and I notice that when I am not lifting anything, there is almost no pressure. As soon as I lift a heavy load, the pressure jumps right up to 2750, which is where the relief valve is set.

On the wheel motors , when you have exceeded the capacity of the motors, the relief valve will start to let you know by the whining noise I believe the psi and the gpm are dictated by the foot controls.

The rated psi of a fixed displacement pump is variable by the rpm. At 1500 rpm, you might have only 1500 psi, and 4 gpm. and at max rpm, you might have 3000 psi, and 8 gpm. If the circuit is not using that fluid, it is sent back to the tank at almost zero pressure.

 

[stray]

Guys I've been looking at this schematic. With it I’ll attempt to figure what valves, fittings and hoses I need. Any info about this will be helpful.

 

[toolz_not_toyz]

Hrm. I see four motors, a pump, a bunch of hoses, and a bunch of fittings. Unless their integral to the motors or other large components there aren't any valves in that diagram. /forums/images/graemlins/confused.gif

Wouldn't you just swap the pump and the motors and reuse the existing hoses and fittings?

Doh! Hang on. You're on the plan to put all of the motors in parallel right? There's an upper and lower port on the pump. 2 motors connected to the upper, 2 connected to the lower. You need to find out what that's all about. Two options are:

1) Put everything on one port and use a proportioning valve of some sort .
2) Combine both ports using a proportioning valve.

Neither of these may be a good idea though. Are the upper and lower ports of the pump tied together or is the pump really like two pumps in one housing? I think that's the big question.

 

[MossRoad]

There are no valves in the drive circuit because the variable volume pump is the valve... so to speak.

When you step on the pedal to go forward, the angle of the swash plate moves a bit and some fluid is directed out the forward port while the rest goes out the return port. Step down a little more and the swash plate angle increases, more fluid goes out the forward port, less goes out the return port, etc...

Let off the pedal and the swash plate angle goes back to zero and all the fluid goes out the return port.

Now step on the reverse pedal and the angle of the swash plate goes negative a bit. Some fluid goes out the reverse port while most goes out the return port. Step on reverse some more and the angel of the swash plate goes more negative and more fluid goes out the reverse port and less goes out the return port, etc....

 

[KentT]

To put them in parallel, I think you'd have the 4 return lines on one port and the 4 supply lines on the other port -- rather than the return line of one motor becoming the supply line for the other one in that circuit.

So, you'd need a 4-way splitter for each of the two ports on the pump...

 

[stray]

So it looks like all one would need to just change to the low speed will be 2 each 4 way splitters and 2 more hoses. That’s 8 all together (2 for each motor). There are already 6 for the wheel motors now. Reroute the two from pump to pump and add 2 new ones. Now that is fairly cheep but I suggest we add an electric solenoid valve (not sure if we will need 1 or 2. It is just according to what is available and cost effective) so we can have the best of both worlds. Also the valve may serve as the splitters. I have some more investigating to do. I will be back at work Friday night where my hydraulic books are. This is beginning to be a good discussion. You guys really get me to thinking. Thanks a bunch.

 

[MossRoad]

If you do it and it is successful, we will forever call it the STRAY MOD! /forums/images/graemlins/grin.gif