More torque for my Power trac?

woodlandfarms · Mar 9, 2009

The whole thing sounds pretty great.

As we discussed in an earlier post, just a reminder... If you happen to blow one of the motors, please remember to go to the wife and say "I blew a wheel motor, but they don't make that kind anymore so I have to buy 4 new ones".

Doesn't sound like the above excuse will be necessary, I really look forward to hearing how it works in a pushing / pulling / ground engagement activity. I am intrigued at what will happen when you meet an imoveable object.

BobRip · Mar 9, 2009

I am glad it is working so far. We want a complete parts list and more details once you think it is really good. I am not sure I would do this, (it seems like a lot of getting into the hydraulics), but I sure would like that torque. Actually after 8 years, I am pretty used to it and mostly satisfied. Great job, keep the findings and details coming.

J_J · Mar 10, 2009

Stray,

Do you have a two section VSP pump, or two VSP pumps, or just two outlets from one pump, all at 3000 psi.

It also seem like we are not all talking about the same pump. Just how many different pumps are in , say the PT-425/422, and are they all single pumps with two outlets, independent of each other, or what. One has to know all the facts to make an educated guesstimate. From all that I have read, we are not talking about the same pump. I know that my VSP pump is different than others.

From what I gather so far is, that you are modifying the hydraulic circuit, and changing the series/parallel circuit into a four motor series circuit, each with a running psi of 1500, and do you have 3000 psi on each outlets, or 3000 psi on one outlet.

I don't think you are running them parallel, because the motors are I believe 1500 psi motors, and you will damage them. If you are running all four motors in a single series line, you have divided the pressure for each motor, at around 750 psi. Now, as far as traction, if one wheel spins/slips, each motor is getting the same flow, but you have lost 25 % of your power. I think also when turning/steering, that you will notice a difference. since all motors will be turning the same rpm, with little differential action.

An example: 2, 15 cu in ,1500 psi motors in series 3000 psi pump pressure, each motor will develop 3,583 in lbs.
times two for the normal circuit. total of 14,332 in lbs

4, 15 cu in, 1500 psi motors in series 3000 psi pump pressure, each motor will develop 1,791 in lbs
times four for a total of 7166 in lbs

4, 15 cu in, 1500 psi motors in parallel, 3000 psi pump pressure, each motor will develop 7166 in lbs
times four for a total of 28,664 in lbs

We know the motors are 1500 psi motors, but the pump putting out 3000 psi, the motor will try and develop that much torque until the motor is destroyed.

Feel free to correct any of my figures.

BobRip · Mar 10, 2009

J_J said:
Stray,

Do you have a two section VSP pump, or two VSP pumps, or just two outlets from one pump, all at 3000 psi.

It also seem like we are not all talking about the same pump. Just how many different pumps are in , say the PT-425/422, and are they all single pumps with two outlets, independent of each other, or what. One has to know all the facts to make an educated guesstimate. From all that I have read, we are not talking about the same pump. I know that my VSP pump is different than others.

From what I gather so far is, that you are modifying the hydraulic circuit, and changing the series/parallel circuit into a four motor series circuit, each with a running psi of 1500, and do you have 3000 psi on each outlets, or 3000 psi on one outlet.

I don't think you are running them parallel, because the motors are I believe 1500 psi motors, and you will damage them. If you are running all four motors in a single series line, you have divided the pressure for each motor, at around 750 psi. Now, as far as traction, if one wheel spins/slips, each motor is getting the same flow, but you have lost 25 % of your power. I think also when turning/steering, that you will notice a difference. since all motors will be turning the same rpm, with little differential action.

An example: 2, 15 cu in ,1500 psi motors in series 3000 psi pump pressure, each motor will develop 3,583 in lbs.
times two for the normal circuit. total of 14,332 in lbs

4, 15 cu in, 1500 psi motors in series 3000 psi pump pressure, each motor will develop 1,791 in lbs
times four for a total of 7166 in lbs

4, 15 cu in, 1500 psi motors in parallel, 3000 psi pump pressure, each motor will develop 7166 in lbs
times four for a total of 28,664 in lbs

We know the motors are 1500 psi motors, but the pump putting out 3000 psi, the motor will try and develop that much torque until the motor is destroyed.

Feel free to correct any of my figures.

Stray, I know everyone here appreciates the risk you are taking for the benefit of us all. I wonder if you should limit your engine speed when operating in this mode. Or better yet put a relieve valve in this mode set at 1500 PSI. Of course you may loose all or most of the advantage.

J_J · Mar 10, 2009

I believe that someone said this before, and , it would be interesting to know what the psi is on each wheel motor under full power, and with one or two motors slipping.

MossRoad · Mar 10, 2009

Could he use a pressure gauge teed into the system between the disconnects that he installed?

J_J · Mar 11, 2009

MossRoad said:
Could he use a pressure gauge teed into the system between the disconnects that he installed?

;Yes. you could tee a gage in just about anywhere

stray · Mar 11, 2009

Here is a fact about hydraulics. When pressure is put to a series of motors (hyd oil into the first. out of the first, into the second, then back to reservoir) the pressure is divided between the motors. One may get 50 percent and the other may get the other 50. But now with no load on the second motor and all of it on the first (say the first wheel stalled and the second off the ground) then the first is receiving all available pressure. In reality the first wheel stalls, some hyd oil leaks through and the second free spins some.
So it would be safe to say that the first wheel is receiving at least 90 percent of the pressure.

Now on my PT if you have both rear wheels off the ground and pushing till the machine stalls both front wheels then the 2 front motors are receiving full pressure minus the leakage. Now if you have the system with all 4 motors in parallel and stall all four of then the four receive full pressure minus the leakage. The 4 motor parallel system has the sad fact that there can be twice as much internal motor leakage losing more pressure through leakage than the 2 series system. With this said then I will make the statement that there is less potential of hurting a hydraulic motor in the 4 motor parallel system than the 2 motor 2 series factory set up system. This increase in total motor leakage is one fact why trying and testing is necessary to tell if this set up will be worth it. I am still undecided but am enthused that it will be a nice and useful thing to have. So far tests are looking good. If I had the pt set up where I could switch systems easily (say solenoid valves rather that quick disconnects) then it would be easier and quicker to tell about the outcome. AS it is, it is going to take a while to give a sure non bias account.
Thanks Guys for all you interest. To tell the truth it is half the reason I am doing this.

J_J · Mar 12, 2009

Stray.

I am very interested in the results of your endeavors, trying to make something better or more usable. I am, skeptical on certain things. Do you happen know the pump relief pressure? When you say stall the first motor in series, that is where the relief valve should work to prevent the wheel motor destruction. If you get two gal of fluid through the first motor, then the second motor will see two GPM. It is possible that the wheel motors have a bypass valve in them, or a relief valve, so the hydraulic fluid could continue downstream. It would be nice to have a bunch of pressure gages, and a GPM flow gage in the system.

So here is what I am thinking, in a two motor series/pump situation. The pump is capable of putting out 3000 psi, and since the motors are in series, the available pressure is developed across both motors. No matter which one stalls, the relief will cut in and relieve until the stall situation goes away. If the wheel motors are held in a stall position very long, the hydraulic fluid will heat up fast. These motors were not selected for 4 motor series operation. If you are thinking of 4 motor parallel operation, you still have a 3000 psi pump, but the relief is still set at the 1750 psi or somewhere close, to protect the motors as if they were in the series configuration. In my opinion, I don't think you will get the torque you desire, using what you have now. Also in the parallel setup, if one wheel is off the ground, the pressure and GPM will try and go through that motor, the path of least resistance.

There is a guy on the INTERNET by the name of Casey that has a hydraulic software program that will allow one to setup/design a system and see the results before building, and those, what if scenarios.

stray · Mar 13, 2009

Good point about the relief valves. I do need to know that. Does anyone know if the wheel motors on the old style PT422s have relief valves installed in the wheel motors themselves? If no one knows I can call terry and fine out I guess. I was hoping one of you all knew for sure. It looks like having them was an option for the 400 serious. Come to think of it i have the old one i broke the shaft in. I could look at it. Hu. Thanks JJ