johara1
Platinum Member
can any one tell me the max. pressure and the gal. per min. on the old 422 and 425? i was planning a mod. new travel motors with more torque and a internal brake /forums/images/graemlins/cool.gif
travel pump
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MossRoad
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I thought it was rated at 8GPM and 2500 PSI, but that may be the PTO pump and not the variable volume pump that supplies the power to the wheels. Might want to give Terry a call at Power Trac.
KentT
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Pondering this, since I'd like more low-end torque on my old PT425 also, are these correct assumptions:
1. To increase low-end torque with the existing wheel motors, you'd have to increase the pressure from the pump, while maintaining at least the same volume.
2. If you replace wheel motors for ones with more low-end torque, without replacing the current pump, you'd sacrifice top-end speed, since the new wheel motors would require more volume per RPM, and would generate less RPMs total.
3. Likely the best solution would be to replace both the wheel motors and pump at the same time. Wheel motors that produced more torque -- requiring more volume -- and a pump that corresponding produced more volume -- all at similar pressure levels to the existing circuit.
Are these correct assumptions?
If so, would adjusting the bypass valve to generate more pressure from the existing pump (WARNING -- immediately voids the PT warranty) make a noticeable increase in torque? It seems that Tazewell anticipated someone trying this, based upon the warning stickers on the tunnel...
1. To increase low-end torque with the existing wheel motors, you'd have to increase the pressure from the pump, while maintaining at least the same volume.
2. If you replace wheel motors for ones with more low-end torque, without replacing the current pump, you'd sacrifice top-end speed, since the new wheel motors would require more volume per RPM, and would generate less RPMs total.
3. Likely the best solution would be to replace both the wheel motors and pump at the same time. Wheel motors that produced more torque -- requiring more volume -- and a pump that corresponding produced more volume -- all at similar pressure levels to the existing circuit.
Are these correct assumptions?
If so, would adjusting the bypass valve to generate more pressure from the existing pump (WARNING -- immediately voids the PT warranty) make a noticeable increase in torque? It seems that Tazewell anticipated someone trying this, based upon the warning stickers on the tunnel...
RegL
Platinum Member
" If so, would adjusting the bypass valve to generate more pressure from the existing pump (WARNING -- immediately voids the PT warranty) make a noticeable increase in torque? It seems that Tazewell anticipated someone trying this, based upon the warning stickers on the tunnel... "
Seems to me, With the 1430 anyway, that the wheel motors bypass before any bypass valve. I'm not quite sure how that happens, weather the motors have bypass circuits in them or the fluid just leaks past the seals at high pressure. Happens more when the fluid is hot.
Seems to me, With the 1430 anyway, that the wheel motors bypass before any bypass valve. I'm not quite sure how that happens, weather the motors have bypass circuits in them or the fluid just leaks past the seals at high pressure. Happens more when the fluid is hot.
Bob999
Platinum Member
<font color="red"> 3. Likely the best solution would be to replace both the wheel motors and pump at the same time. Wheel motors that produced more torque -- requiring more volume -- and a pump that corresponding produced more volume -- all at similar pressure levels to the existing circuit.
</font>
If you put a larger pump on it will then take more power at maximum load. I would presume that the existing arrangement is designed to balance total power available with the power required for the sum of the three pumps at some design operation condition. Assuming that PT did a reasonable job of engineering then putting a larger pump on without increasing total power available would likely lead to engine overload and possible stalling under high load conditions.
</font>
If you put a larger pump on it will then take more power at maximum load. I would presume that the existing arrangement is designed to balance total power available with the power required for the sum of the three pumps at some design operation condition. Assuming that PT did a reasonable job of engineering then putting a larger pump on without increasing total power available would likely lead to engine overload and possible stalling under high load conditions.
KentT
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It seems to me that you should be able to do with hydraulics what you can with gears -- i.e. increase the numerical gear ratio to increase low-end power, at the expense of top end speed...
I'm just not sure how this is done with hydraulic circuits. That's why I'm essentially asking for help understanding how to do this.
As it is, I can stall the engine (when fluids are cool and thick) because I don't have enough low-end torque to spin the wheels and there is no clutch to slip...
I'm just not sure how this is done with hydraulic circuits. That's why I'm essentially asking for help understanding how to do this.
As it is, I can stall the engine (when fluids are cool and thick) because I don't have enough low-end torque to spin the wheels and there is no clutch to slip...
Bob999
Platinum Member
<font color="red">It seems to me that you should be able to do with hydraulics what you can with gears </font>
The variable displacement pump used on the PT for powering the wheels takes the place of gears in a mechanical transmission. A "first" gear effect is achieved by moving the treadle a very small amount. This results in a very low volume of fluid being pumped and a very slow wheel speed. It allows the user to climb a steep hill without stalling the engine. A "second" gear effect is achieved by moving the treadle a slightly larger amount. This increases the volume of fluid being pumped and results in a slightly greater wheel speed.
So, to be more correct, a variable displacement pump is much more like a continuously variable transmission in a car than a transmission with a specific number of gears.
Only the drive pump on the PT is variable displacement which allows the volume of fluid pumped at any speed to be varied by moving the treadle. The power take off pump and auxiliary pump are gear pumps and they do not have a capability to vary the the volume of fluid pumped--except by varying the engine speed.
The variable displacement pump used on the PT for powering the wheels takes the place of gears in a mechanical transmission. A "first" gear effect is achieved by moving the treadle a very small amount. This results in a very low volume of fluid being pumped and a very slow wheel speed. It allows the user to climb a steep hill without stalling the engine. A "second" gear effect is achieved by moving the treadle a slightly larger amount. This increases the volume of fluid being pumped and results in a slightly greater wheel speed.
So, to be more correct, a variable displacement pump is much more like a continuously variable transmission in a car than a transmission with a specific number of gears.
Only the drive pump on the PT is variable displacement which allows the volume of fluid pumped at any speed to be varied by moving the treadle. The power take off pump and auxiliary pump are gear pumps and they do not have a capability to vary the the volume of fluid pumped--except by varying the engine speed.
MossRoad
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You could replace the wheel motors with ones that provide more torque, but the top end speed would be cut.
OR
You could put on tires with a smaller diameter to effectively change the gearing, but that would sacrifice ground clearance.
OR
You could sell the PT425 and buy a PT1430. /forums/images/graemlins/grin.gif
If you up the pressure on the reliefs, you could possibly damage the pump. It might be worth getting the specs for the pressure from the pump manufacturer and then checking your system to see what the actual pressure is. Just remember that running it at it's maximum pressure will probably shorten its life, over time.
OR
You could put on tires with a smaller diameter to effectively change the gearing, but that would sacrifice ground clearance.
OR
You could sell the PT425 and buy a PT1430. /forums/images/graemlins/grin.gif
If you up the pressure on the reliefs, you could possibly damage the pump. It might be worth getting the specs for the pressure from the pump manufacturer and then checking your system to see what the actual pressure is. Just remember that running it at it's maximum pressure will probably shorten its life, over time.
MR,i think the pump pressure should be checked and set to the max. thats how it was set at the factory.after years of use and abuse,and the dirt PT. leaves in the tank you should check the pressure, it will drop due to wear.i do remember i think it was up around the 3-4000 range,i do remember it was on here long ago.if you can notice the power when its cold to hot,if it's a lot you might want to check it.