Mod for hydraulic pump?

[ponytug]

Not sure if possible to have the flow you are describing, if my pump is a 10 gpm and I have a 5 gal reservoir then it will only move the fluid through twice in 1 Min Time, am I correct?

I know that the fluids get pretty warm pretty fast on my unit I have, I was attributing it to the weak pump and the small reservoir.

I think that @BigDaddyEureka makes a great point on considering tank turnover for heating, and @MossRoad makes an excellent point that the PTO pump is only part of the math.

I believe all PTs have very low turnover times, hence the reason they all have big oil coolers. I also believe that the rule of thumb comes experience and is based on assuming heat loss from the oil tank to the outside passively, so it isn't exactly applicable to Power-trac, although to me it does highlight the need for functioning oil coolers.

For the few that have had fan failures, their descriptions of their experiences suggest that, yes, the oil gets hot quickly, supporting the rule of thumb.

All the best,

Peter

 

[marrt]

Somewhere on here, I did a calculation and write up about the HP needed for the 425 (I have two 425’s). It's been a while, but if I remember correctly, the 425 needs a full 25 HP when under a full load, such as mowing a slope for example. This makes sense as the 425 has a 25 HP engine, right? Well, not really. The 25 HP rating for the Subaru EH72 is peak horsepower. The continuous horsepower rating is much lower…around 19 HP if I remember correctly. Consequently, I concluded the engine is underpowered for mowing applications.

I went through this study because my engine had failed and I needed to get a new one. I had always suspected the engine was underpowered and wanted to confirm my suspicion. I ended up dropping in a 32 HP Subaru engine because, at the time, it was the only engine available that would mostly fit (still required a LOT of custom modification though). The difference in tractor performance is night and day (I also increased the displacement of the wheel motors).

Now, I'm not recommending you replace your engine again. I’m just suggesting a larger output hydraulic pump may not solve your problem. Unless you are stalling the existing hydraulic motor (or pushing it to the point where the pressure reliefs open) it’s possible the “weak” impression is more a function of engine output than pump output. There’s a lot of issues involved here and it’s hard to make a firm assessment without understanding more about your specific situation. But the easiest way to get more “power” for an attachment is to increase the displacement of the attachment motor (at the expense of motor speed). So, you may want to ensure the fundamental performance problem isn’t engine power, rather than pump output.

 

[MossRoad]

And don't forget that the tramp pump adds to the heat and turnover through the tank as well. It's not a lot, as it's just the makeup for the charge pump in the tram pump, but it is there to consider. Also, just a reminder, that only the oil going through the charge pump is filtered, as I recall.

 

[MossRoad]

We've had this discussion before, but where in the system is the oil cooler plumbed?

 

[cqaigy2]

In my case, going from Subaru 22HP to Kohler 25HP engine was a game changer for me. I can mow uphill and if i start to lose traction, i raise the implement just a bit up, and continue on. With the 22HP, in the same situation, engine bogged down and i'd have to turn the PTO off, to get a bit more HP to the tram circuit.

 

[Tchamp]

Somewhere on here, I did a calculation and write up about the HP needed for the 425 (I have two 425’s). It's been a while, but if I remember correctly, the 425 needs a full 25 HP when under a full load, such as mowing a slope for example. This makes sense as the 425 has a 25 HP engine, right? Well, not really. The 25 HP rating for the Subaru EH72 is peak horsepower. The continuous horsepower rating is much lower…around 19 HP if I remember correctly. Consequently, I concluded the engine is underpowered for mowing applications.

I went through this study because my engine had failed and I needed to get a new one. I had always suspected the engine was underpowered and wanted to confirm my suspicion. I ended up dropping in a 32 HP Subaru engine because, at the time, it was the only engine available that would mostly fit (still required a LOT of custom modification though). The difference in tractor performance is night and day (I also increased the displacement of the wheel motors).

Now, I'm not recommending you replace your engine again. I’m just suggesting a larger output hydraulic pump may not solve your problem. Unless you are stalling the existing hydraulic motor (or pushing it to the point where the pressure reliefs open) it’s possible the “weak” impression is more a function of engine output than pump output. There’s a lot of issues involved here and it’s hard to make a firm assessment without understanding more about your specific situation. But the easiest way to get more “power” for an attachment is to increase the displacement of the attachment motor (at the expense of motor speed). So, you may want to ensure the fundamental performance problem isn’t engine power, rather than pump output.

My problem is the pto pump is putting out 1500 pounds pressure at peak output on engine, no stalling problems on engine or lack of power on drives. I have a power rake and it doesn’t have the power on the loader cylinders to pick up the unit when I use for more than 5 min I don’t know what my pressures are then, but when cold ambient temp 68 outside I have max 1500 pounds pressure out of my pump.

 

[BigDaddyEureka]

Catching up with the post stream here...let me ask another question. Are the pumps we're talking about variable displacement or fixed displacement? You can tell by looking for either a pilot hydraulic line (a tiny thing) running to the pump or a wire (for an electrohydraulic or EH) system. I suspect that PT uses a cable on the pedals to stroke the pump's pinnel plate in some of their models, and that's OK too (if kinda old school).

On tram circuits, often there is a variable displacement pump. At idle the pinnel plate is in neutral and even thought the pump is spinning (because it has to - it's mechanically connected to the motor) it's not actually doing much if any work. When you engage the drive, the pinnel tips one way or the other to cause a variable amount of flow to the circuit. So it's kinda weird on the tank turns calculation. Technically at neutral you have infinite tank turns (X gallons of tank / ZERO flow of gal / min) but at full pinnel (or stroke) you get the full rated flow. In part this is where duty cycle comes from for tank turns. Sure you'd turn the tank REAL FAST at full stroke, but how often and for how long do you really tram at full flow? Now that said I've noticed that lots of tramming DOES get things toasty pretty quickly on my PT-425, but not concerningly so thus far. It's not like I drive it miles at a time at full wampum....is more like zip to a pile and zip to someplace else kind of a thing.

That said, to some degree you really should design for the worst case situation that was described earlier. So if you are at full tram, full pto, and somehow full work tool effort on the lift / tilt (how? it's probably possible...) your tank turns get realllllllly small and things get hot. Quick. Like dang hot. But in theory that shouldn't happen too often or too long so often a manufacturer will kinda cheat the calculation a bit.

A fixed displacement pump - like a gear pump, a vane pump, or some low-cost piston pumps - operate in an open loop system where they pump all the time regardless of the control positions and just bypass back to tank when there's no flow to a working circuit. That will also produce a relatively low tank turns calculation too, but since the work being done isn't much (just some flow up and down and around but no real effort) you can run your tank turns down a bit lower than I wrote earlier but it can get risky without a good cooler. On some large yellow machines I'm aware of where the tank turns are a bit on the lower side and you're @riding the cooler@ it pays off to periodically pulse the electric cooling fan backwards to blow the crap out of it so you don't get caught out on heat buildup.

On the very largest wheel loaders - like in mining applications - the drive to the ground is usually either mechanical or electrical, not hystat. One of the big reasons for that is in that size of machine the resulting hydraulic tank size would affect the payload capacity of the machine...because that would be a LOT of oil! Those things are really interesting...but that's a story for another time.

 

[ponytug]

We've had this discussion before, but where in the system is the oil cooler plumbed?

IIRC: different places different years different models. My 1445 has it downstream of the PTO attachment.

All the best,

Peter

 

[ponytug]

My problem is the pto pump is putting out 1500 pounds pressure at peak output on engine, no stalling problems on engine or lack of power on drives. I have a power rake and it doesn’t have the power on the loader cylinders to pick up the unit when I use for more than 5 min I don’t know what my pressures are then, but when cold ambient temp 68 outside I have max 1500 pounds pressure out of my pump.

I have a similar issue on 30 degree slopes trying to mow uphill. Adding heavier weight oil didn't change my issue (which granted is an unusual case for me), which leads me to believe that, like your 425s, for me it is a total HP issue, rather than an oil leakage in the pumps or motors. But more HP is more waste heat just by pumping oil around the various circuits, which means more cooling, which requires HP...

Your low pressure does suggest to me that the pump is worn, and I think that you are doing the right thing trying to replace it. A bigger pump will consume more HP, which may mean lower speeds or stalling under other conditions, but that is something that I think is your call for your uses.

All the best,

Peter

 

[MossRoad]

Catching up with the post stream here...let me ask another question. Are the pumps we're talking about variable displacement or fixed displacement? You can tell by looking for either a pilot hydraulic line (a tiny thing) running to the pump or a wire (for an electrohydraulic or EH) system. I suspect that PT uses a cable on the pedals to stroke the pump's pinnel plate in some of their models, and that's OK too (if kinda old school).

On tram circuits, often there is a variable displacement pump. At idle the pinnel plate is in neutral and even thought the pump is spinning (because it has to - it's mechanically connected to the motor) it's not actually doing much if any work. When you engage the drive, the pinnel tips one way or the other to cause a variable amount of flow to the circuit. So it's kinda weird on the tank turns calculation. Technically at neutral you have infinite tank turns (X gallons of tank / ZERO flow of gal / min) but at full pinnel (or stroke) you get the full rated flow. In part this is where duty cycle comes from for tank turns. Sure you'd turn the tank REAL FAST at full stroke, but how often and for how long do you really tram at full flow? Now that said I've noticed that lots of tramming DOES get things toasty pretty quickly on my PT-425, but not concerningly so thus far. It's not like I drive it miles at a time at full wampum....is more like zip to a pile and zip to someplace else kind of a thing.

That said, to some degree you really should design for the worst case situation that was described earlier. So if you are at full tram, full pto, and somehow full work tool effort on the lift / tilt (how? it's probably possible...) your tank turns get realllllllly small and things get hot. Quick. Like dang hot. But in theory that shouldn't happen too often or too long so often a manufacturer will kinda cheat the calculation a bit.

A fixed displacement pump - like a gear pump, a vane pump, or some low-cost piston pumps - operate in an open loop system where they pump all the time regardless of the control positions and just bypass back to tank when there's no flow to a working circuit. That will also produce a relatively low tank turns calculation too, but since the work being done isn't much (just some flow up and down and around but no real effort) you can run your tank turns down a bit lower than I wrote earlier but it can get risky without a good cooler. On some large yellow machines I'm aware of where the tank turns are a bit on the lower side and you're @riding the cooler@ it pays off to periodically pulse the electric cooling fan backwards to blow the crap out of it so you don't get caught out on heat buildup.

On the very largest wheel loaders - like in mining applications - the drive to the ground is usually either mechanical or electrical, not hystat. One of the big reasons for that is in that size of machine the resulting hydraulic tank size would affect the payload capacity of the machine...because that would be a LOT of oil! Those things are really interesting...but that's a story for another time.

The tram pump is the variable volume pump.
Older model PT's used what PT called the hydroback cable.
So the foot treadle operated a cable to move the arm on the VVP to control the angle of the swash plate.

Newer PTs use a hydraulic treadle arrangement that got rid of the hydroback cable setup. Then they found that system to be quite sensitive to foot movement, and offered stiffer springs to go under the treadle, as it was pretty touchy.

On the PT425, there is the tram pump (variable volume pump) and two fixed displacement pumps. One is the MAIN PTO pump (provides hydraulic power to implement motors) and the other is the AUX PTO pump. The AUX PTO pump provides power to the steering, then through a power-beyond port to the 3 spool valve bank for the FEL up/down, dump/curl, AUX PTO (the quick attach), then back to the tank.

Don't know how the other models are plumbed.