travel pump

RegL · Nov 7, 2005

I'm thinking the only way to increase torque with the existing wheel motors is to increase pressure in the circuit, while speed is a factor of volume..

 Trouble is , even with 2 wheels in series, i have had one of those wheels spin while the other doesn't. I assume fluid leaks by the seals when enough load is applied to the wheel motor. So at a certain pressure and temperature would it not blow through the wheel motor no matter what the max pressure was set at? If anyone ever figures this out he's going to make PT hill people happy everywhere.

BobRip · Nov 7, 2005

There was a thread where we discussed this before. I believe that somebody makes a two speed wheel motor. They switch something (electrically) inside the motor to select the speed/torque range. How this works, I don't know.

I still suggest that if you are running 5w30 weight oil in your transmission that you change to 20W50 synthetic and also add some weight to the rear of the PT.

Bob Rip

stray · Nov 7, 2005

You know that the PT wheel motors are 2 in a serious. The front right and the back left, the front left and the back right. What if one would put them all in parallel line or each in its own circuit. Wouldn’t this make the PT something like twice as slow and geared with more power. What if one could rig it so you could swap back and forth.

Guys I will make this my winter time project. I feel sure that this will work and is what most of us that needs or wants more power will end up doing if we do anything. Give me a month or so to go over the schematics, talk with PT and an engineer or two where I work. I have worked on similar hydraulics systems and I don’t think that the cost for doing this will be near as much as swapping tram pumps or wheel motors. I get back to you all on this one.

KentT · Nov 7, 2005

Stray,

If you could come us with a reasonably cost-effective way to do that, you'd definitiely become a HERO to those of us who own older PTs....

So far, the lack of torque/hill-climbing ability when hot is my only complaint with these great little machines....

Kent

toolz_not_toyz · Nov 7, 2005

How about an even bigger project and possibly a better idea? Convert the PT 42x to electric! Just think, you could add a ton of weight with a bunch of lead acid batteries and also get gobs of torque from electric motors. The only downside is the limited run time. But you could design it so that the whole battery pack could get swapped out. That's what we used to do with our (much larger and much heavier) high reach warehouse forklifts. Heck, one of the battery packs in those things probably weighs more than a PT 425!

BT Reach Truck

BillCroasmun · Nov 8, 2005

Stray,
I'm definitly not an expert on hydraulics but I am trying to picture your concept with visions of water and/or air lines. If you have an air compressor or water pump putting out X lbs or pressure with Y amount of volume down a single line and you then divide the line into two parallel each new line would have half the volume but still the same pressure building up in each line. If I am thinking right, and if hydraulics work the same, putting each wheel on it's own circuit would decrease speed but would not increase torque.

I know I am not factoring in the "stuck and slipping motors" but I still think the total pressure in the line can not exceed what the compressor (or in this case pump) puts out. Hopefully I'm just missing something though...

KentT · Nov 8, 2005

FWIW, I've found this equation:

Torque = Displacement x Pressure / 24 PI

At this link:

Northern Hydraulics

If I understand what they're saying about a "series circuit" then Stray's idea may just work. In defining control valves, they state:

( SERIES TYPE: A multiple spool valve in which the return oil from the first spool is directed to the inlet of the second spool (and from the second to the third, etc.). This type valve permits simultaneous operation of two or more functions with the same oil flow. However, the total pressure requirements of all functions are accumulative. )
If I'm understanding that correctly, the first motor in the circuit "takes" half the pressure and the second motor "takes" the other half... So, if each were plumbed independently, each would get "full pressure" but 1/2 the current volume....

Also, searching the old posts, I found this link: Real Brakes for a PT Topic

In it, SnowRidge links the White wheel motor catalog, and gives the existing White part number of 400230W31222AAA

Using that, I appears that the existing "old wheel motors" are 14.2 cubic inch, 260 continuous RPM, 16 continuous GPM, and produce 4950 lb-in of torque continuous at 3000 PSI.

The next larger size, 15.9 cu in, is 18 GPM, and yields 6250 lb in of torque, a 26.3% increase over the current ones. The 2nd larger size, a 18.3 cu in, is 20 GPM, and yields 7100 lb in of torque, a 43.4% increase.

Does anyone know the specs on the variable displacement travel pump?

BillCroasmun · Nov 8, 2005

OK I think I get it now... The max pressure of the line is fixed by the pump but due to the way the motors operate in series they are effectively splitting that pressure in half. So putting them into a parallel configuration each will receive the full output pressure of the pump. The only question then is can the motors handle the full pressure of the pump? I'm sure if I re-read the thread now this was all probably stated already, just not clickin' in the ol' noggin' till now. /forums/images/graemlins/blush.gif /forums/images/graemlins/laugh.gif

MossRoad · Nov 8, 2005

Here's a link to an old thread but a good thread, on how an HST tranny works and more specifically, how a variable volume pump works.

There was, at one time, a working link to a military manaul on hydraulics, but, unfortunately, it no longer works.

However, I found a link to it here. /forums/images/graemlins/grin.gif

MossRoad · Nov 8, 2005

So putting them into a parallel configuration each will receive the full output pressure of the pump 

Yes, but the flow will follow least resistance, so the slipping wheel will get most of the fluid and the wheel with traction will get very little, so we will remain stuck. Isn't the PT setup considered a series/parallel setup?

KentT · Nov 8, 2005

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 · Nov 8, 2005

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 · Nov 8, 2005

( 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? )

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 · Nov 8, 2005

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 · Nov 8, 2005

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 · Nov 9, 2005

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 · Nov 9, 2005

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 · Nov 9, 2005

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 · Nov 9, 2005

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.