Mod for hydraulic pump?

[Tchamp]

I have a 2001 PT 2422 that has the Subaru engine 25 hp. It came new with the 22 hp but since was upgraded.

My auxillary pto - steering pump assembly is a 8 gpm 2500 psi gear pump.
My question is when I replace the pump assembly which is weak, I am thinking of putting a 10 gpm 2500 psi pump to replace the old. The difference in the required hp for the 10 gpm on the new pump is 3 hp which I already have from the new 25 hp Subaru. The attachments from Power Trac are rated from 8- 12 gpm.
I shouldn’t have to worry about power loss for the rest of the machine since it was running on 22 hp from the factory.

I’m thinking that I can upgrade my pump, and in return have better flow for a more diverse attachments from the aftermarket, brush hog, stump grinder, etc and have better results from that which I already have since the pumps on the attachments are rated for 8-12 gpm.

Am I thinking on the right track? Looking for any input before I do this in about 2 weeks. The only downside I can think of is when starting the motor i may have to put a higher amp battery and or a high output starter to spin it over faster.

 

[agjones]

You may have considered /some any of the following already...

For baseline comparison, you might want to check w Terry the cost to rebuild/swap the existing pump.

Confirm that the 2001 22hp version used 2500psi as the working pressure. 2000psi is also possible.

In general, you seem on the right track, consider: that more flow will produce more heat (potential power loss) in the hydraulic system and the stall point on that engine is hovering over your head anytime you are working close to max psi.

The mini skidsteer standard, 10 gpm@3000psi things like dingos use with engines in a similar power curve perform well. They generally give up travel for power.

 

[Tchamp]

You may have considered /some any of the following already...

For baseline comparison, you might want to check w Terry the cost to rebuild/swap the existing pump.

Confirm that the 2001 22hp version used 2500psi as the working pressure. 2000psi is also possible.

In general, you seem on the right track, consider: that more flow will produce more heat (potential power loss) in the hydraulic system and the stall point on that engine is hovering over your head anytime you are working close to max psi.

The mini skidsteer standard, 10 gpm@3000psi things like dingos use with engines in a similar power curve perform well. They generally give up travel for power.

I hav thought about the heating issue and am going to install a larger oil cooler to compliment the other one that is on there as well. My oil capacity is only 5 gal on this unit so I really want to keep the oil cool .

I have confirmed with terry and he said that I could probably run up to a 12 gpm pump as long as I was willing to trade off the speed . I chose 10 gpm because I didn’t think I would be losing any of the speed it was originally designed for. But I am liking the idea of more POWER lol

 

[agjones]

Sounds good. Smart to add cooling capacity, especially in Georgia!

Increased flow on that circuit is faster tool speed (work), your force remains limited to 2500 psi.

 

[Tchamp]

Sounds good. Smart to add cooling capacity, especially in Georgia!

Increased flow on that circuit is faster tool speed (work), your force remains limited to 2500 psi.

Yes, I can adjust the pressure settings up some if I choose but don’t think it’s necessary. I will have to reset them because when I was diagnosing the pump I actually tried to increase The max pressure on the check valves so they aren’t spot on at 2500 now I don’t know where they are because the pumps max output was 1500 psi. I could adjust the pressure down on them but it stopped at 1500 with the pressure regulator check valvewhen I adjusted them upward. I also switched them around to see if it would make a difference which it did not.

 

[BigDaddyEureka]

+1 on agreeing that you're on the right track thinking this through. The only thing that hasn't been discussed is "tank turns" - or how often the total volume of the tank flows through working system per unit time. If your tank turns get too low then heat will build up even faster. You've thought of an improved cooler - an excellent idea! - and in general PT tends to run fairly large tank turns so you're probably going to do fine.

A very coarse rule of thumb is that for a high duty cycle machine like a medium wheel loader, you want your tank turns between 5 and 10 per minute. If you get down to 3 you either need a VERY large and effective cooler relative to the system volume or you need to reduce the duty cycle somehow to give the cooler time to catch up and manage the total thermal mass in the tank / system. If you get below 1.5 you run the risk of temperature-related cavitation due to boiling the oil in the circuit before it reaches the cooler. THIS IS NOT GOOD, and booger to troubleshoot, and to be avoided at all costs. More than 10 tank turns / minute is nice, but sometimes excessive and can be a problem in low ambient conditions (far north, Siberia, etc.) because you never really get the machine up to operating temperature and the thick oil isn't great for certain pumps.

Probably more than you wanted, but thought i'd offer what I know. Seems like you're on the right track so far!

 

[agjones]

+1 on agreeing that you're on the right track thinking this through. The only thing that hasn't been discussed is "tank turns" - or how often the total volume of the tank flows through working system per unit time. If your tank turns get too low then heat will build up even faster. You've thought of an improved cooler - an excellent idea! - and in general PT tends to run fairly large tank turns so you're probably going to do fine.

A very coarse rule of thumb is that for a high duty cycle machine like a medium wheel loader, you want your tank turns between 5 and 10 per minute. If you get down to 3 you either need a VERY large and effective cooler relative to the system volume or you need to reduce the duty cycle somehow to give the cooler time to catch up and manage the total thermal mass in the tank / system. If you get below 1.5 you run the risk of temperature-related cavitation due to boiling the oil in the circuit before it reaches the cooler. THIS IS NOT GOOD, and booger to troubleshoot, and to be avoided at all costs. More than 10 tank turns / minute is nice, but sometimes excessive and can be a problem in low ambient conditions (far north, Siberia, etc.) because you never really get the machine up to operating temperature and the thick oil isn't great for certain pumps.

Probably more than you wanted, but thought i'd offer what I know. Seems like you're on the right track so far!

Great info thx for the depth.

 

[Tchamp]

Great info thx for the depth.

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.

 

[MossRoad]

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.

You have to remember that you have 2 continuously running PTO pumps (the MAIN PTO and the AUX PTO/STEERING/FEL pumps), PLUS the tram pump.

Whether you're doing any work or not, the pumps are always pumping oil through the system. They cannot be turned off. And they are always generating heat just by friction moving through the systems. Add work to the load, like a brush cutter or mower motor, and the heat starts to build just from the blades pushing air. Then throw some grass or brush resistance to the blades and the heat increases rapidly.

So you can figure the total flow of both your MAIN and AUX PTO pumps into your tank return cycles that are being discussed. I think my MAIN is 8GPM and my AUX is 4GPM, but I'd have to check with Terry to be sure. So that would be 12 GPM through the tank. The tank on my machine is 10 gallons.

I'd need over a 50 gallon tank to get a bit over 4 of these tank turnovers.

 

[MossRoad]

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.

If you pump 10 gallons through a pump from a 5 gallon reservoir, you're going to drain the tank twice a minute. That is correct math.

 

[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.