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Discussion Starter #1
Is this normal?

This is a 34 year old Italian 85hp agricultural tractor with a zillion hours on it

My hydraulic pressure is good when cold; even at low engine speed, I get 200 bar, 2,900 psi
But as the oil gets hot I only get full pressure if I increase engine speed.

Full engine speed is 2200, which [supposedly] corresponds to a pump speed of 1380rpm
I like to run the hedge cutter with an engine speed of 600 / 800; but I only get full hydraulic pressure at 1000 rpm after it gets hot.
In practice the operating pressure is usually around 100 bar, 1400 psi, but when the cutter blades hit some heavy material or a lot of small material bunches up, the hydraulic motor will stall. At low rpm and 100 bar max pressure, it stalls a lot. at 1000rpm and 200 bar available pressure, it usually chews through.

So the question is, is this more or less how these machines usually work, or is the pump shot?
 

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The pump may be worn.

Oil viscosity lowers as the oil temperature increases. With lower viscosity, the fluid can more easily move through the clearances in the pump from the high pressure areas to the low pressure areas, thus reducing available pump flow in the process. Higher pump speed overcomes the loss of flow to internal leakage, but the increased flow generates more heat as the fluid passes through the same clearances.

Two options, rebuild the pump now, or add a cooler to stall off the rebuild until some time in the future.

I'd add a cooler for the time being until down time is less critical. The pump may not be all that worn and the work load is what is causing the heat problem. With a cooler on line, the problem may well go away entirely and the rebuild may not be needed for several years.
 

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Discussion Starter #3
I hadn't even thought of rebuilding; how would that be done?

I actually took the pump out today, I thought I would get a new one, maybe with a little more capacity.
Things like that are 1/2 price in the UK and I wanted to get it done before Brexit...

I was sure it's worn out, but it turns very smoothly, so now not so sure.

It turns out that it's an oddly set up thing with a weird little 9 tooth spline; smaller capacity ones have splines like that but this one is 29cc, 1.8ci.
So a new one would be difficult, and an OEM part is likely to be insanely expensive.

I was thinking of a cooler, and have yet to come up with a reasonable plan for placing one. I tend to rub up against things like trees and such.
 

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Put the cooler in front of the radiator behind the grill. If space is available use standoffs to keep it separated from the rad.
 

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Discussion Starter #5 (Edited)
It's air cooled, no radiator.
The front end gets bonked a lot, a protection grill is another project I mean to get to one day, but even then space is limited by the FEL cross beam.
Maybe it could be wedged in somewhere between the fuel tank at the nose, and the engine cooling air intake that's behind it.
It would be tough though.
Is it normal to cool the pressure line? That's where the heat is, but pressure too.

Just checked my supplier; doesn't list coolers.
Ebay has some but they're used parts from other machines, no way to tell if any would fit or if they're made for the pressure I have.
 

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Agreed. Put the cooler on a low pressure line, usually the return line. That's where the higher temperature will be.

Aftermarket coolers for automatic transmissions work. For 11 gpm, the tube cross section area should be about 0.8 sq-in (1"diameter). If the tubes on available coolers are too small to handle the flow, get several of them and Tee them to work in tandem, or use a flow divider to divert some of the return flow to the cooler while the rest goes back to tank.

A 12V fan can be ducted to blow air through the cooler(s).

Search - hydraulic oil coolers .

Or possibly check at a (big) truck recycler.
 

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Discussion Starter #8
My return line feeds the 3-point lift and then dumps into the case.
So when the lift operates, the return line is pressurized.
Suction line could be used. I worry a little about flow constriction, but I suppose it's just a question of sufficient cross section.
A fan is an obvious solution, but makes the thing a lot bigger. I'd have to make a new, smaller fuel tank to make room.

I'm still looking for a pump, the 9-tooth spline can be ordered only on pumps a bit smaller.
Min rpm for pumps I found is listed at 500, 800, or even 1,000. Yet power / flow graphs show a straight line [that starts from the min flow number].
My engine has a gear reducer to the pump, so when I run at 600 the pump is making only 400.

This is turning into a non-trivial effort.
 

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Discussion Starter #9
It turns out there is an error in the repair manual; pump rpm is 1.27 higher than crankshaft rpm.
Pump is 14 cc [0.85 ci]for the EU, and the US model [were there any?] 19cc [1.16 ci].

I checked by marking the pump gear + crank, then rotating.
Double checked by running oil through the old pump while turning it by hand.

I found new old stock 19cc pump on ebay Italy, a bit pricey at 250 euros, and maybe the UK shop can get me a bolt-in pump for 1/2 that.

This is a lot easier, and not more expensive than an oil cooler, as cool as a cooler would be.
I can always go back to the cooler later.
 

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How about the motor on the trimmer? Before buying new you should do a pressure/flow test on pump. All you need is a gauge and needle (flow control). Break the line just before the trimmer motor, install big needle valve and an upstream gauge. Open needle valve fully and do some trimming until it gets hot. Then with motor unloaded, turn in needle valve. Watch pressure and note if/when motor slows.
 

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Discussion Starter #11
Thanks for your input.

I have a system pressure gauge on the control panel.
It was a hassle to install, but it's been worth the trouble, it tells me a lot.

So when the system gets hot, the max pressure is dependent on rpm with the other things too, like FEL arms.
I don't know how hot the oil gets; I can put a finger on a steel fitting and it feels around 50 to 60C [120 / 140 F]. I'm surprised that such a small temperature rise has so much effect.

Of course, there could be an internal leak in a valve somewhere.

The electric valve block on the hedge cutter is very old, taken from a street sweeping machine.
Most of the ports are normally open, and there's an extra NC solenoid that blocks the return port when work is being done. So plenty of possibilities for problems.

The cutter motor has a few hundred hours on it, and the pump has unknown thousands of hours.

Anyway, I've found a replacement pump for around $150 that's 50% higher capacity.
It took hours and hours; I had a factory part number, the one on the old pump got me nowhere, I found some from size specs but it's hard to work that way. One error and I get a lot of trouble.

Finally, I found a Bosch number that gets results, and found a replacement. It has an Italian name but at that price, is most likely Chinese.
If I used the tractor 20 hours a week for financial gain, I'd go with the Bosch at $300+. For my use, the cheap one.

Even if the problem is elsewhere, the extra volume means I can use a lower engine speed while cutting, and that's worth the money.
There could be issues with the extra oil volume at higher speeds when using the hedge cutter, as the electric valves aren't rated for it. The motor will be ok but I might need to go to larger hoses.

I'm also changing the pulleys + belt between the cutter motor and the crank that drives the teeth, lowering the ratio from 2:1 to 1.5:1 to get more torque.
The extra pump volume will make up for the lost speed and the new belt is rated for the load [the old one wasn't and I broke a few].

I'm working on new, better cutting blades too, but it's a long road with difficult to find material.
 

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I see, I assumed everything was working as normal, just the Trimmer was slow.

The pump is probably Italian, unless they're outsourcing now. 25 Years ago gear pumps were $300.00 to $400.00 CAD. Then the Italians flooded the market with cheap aluminum gear pumps and motors. The design was similar (read...copy) to the Dowty gear pump which could be made entirely in a small shop with a CNC mill. Until recently, they owned the market, now China and Taiwan, are making their copies, and cheaper still. Princess Auto have sales at $89.00 CAD.
 

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Discussion Starter #13
I found a German Rexroth pump for just a little more on ebay.DE, I'm trying to buy it but ebay is sometimes sticky on international sales.
It should drop right in and give me 50% more volume.
Hopefully low rpm pressure will improve too.
 

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A fluid temperature of 180°F (82°C) is on the high end of normal, but it's still normal and everything should work correctly.

I suspect that wear is causing internal leakage to be a bit too much as the viscosity decreases with the higher temps.
 

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Discussion Starter #15
Thanks; that's sort of what I figured.
Of course I'm just guessing about the temp, a finger on an exposed banjo fitting. But it won't fry eggs.

It will be a week or two before I get the new pump, and a lot longer before I need to use the hedge cutter again; but when I get a result, I'll post it here.

I don't have anything else that uses the hydraulics continuously.

I'm still thinking about your recommendation to add an oil cooler; I expect you're right about that.
The temperature I felt was on the return line.
 

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The return line is where the fluid temperature is highest, and where a cooler works most efficiently.
 

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Discussion Starter #18
Thought this thread deserves an update;
After [finally] getting into town and buying new Orings, I installed the new pump; it works very well.
It feels like low speed response is much more crisp [for lack of a better word] at idle, which makes me think it's not just the added volume of the larger pump, but that the old one was worked out and leaking internally a little.
As expected, the FEL is a lot faster.

On the negative side, the back pressure in the system at 2000 rpm when not working is around 50 bar, 700psi, and that would be around 60 liters or 16 US gallons per minute.
Even at my more normal usage 1000 rpm, pressure and volume are both around 1/2 that level, and that eats power and fuel.

It will be a while before I mount the hedgecutter again, which is the only thing I have that really taxes the hydraulics.

I'll post the results when I have them.
 

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On the negative side, the back pressure in the system at 2000 rpm when not working is around 50 bar, 700psi, and that would be around 60 liters or 16 US gallons per minute.
Even at my more normal usage 1000 rpm, pressure and volume are both around 1/2 that level, and that eats power and fuel.

It will be a while before I mount the hedgecutter again, which is the only thing I have that really taxes the hydraulics.

I'll post the results when I have them.
This suggests to me that the hoses are a bit undersized. This link has a printable nomograph for determining the size of hydraulic lines.

It's one thing to have undersized lines for a loader where pressure and flow to the cylinders is periodic and only of a few seconds duration. It's something else again for a hydraulic motor that operates for sustained periods of time. In any event, an undersized return line will offer a constant restriction and require higher pressure to maintain flow.

A flow rate of 16 gpm at 700 psi will eat about 7.5 hp from the engine and fuel to match. More importantly, it also contributes 7.5 hp in heat generation to the system.
 

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What does the pump on the crankshaft run? Power steering? You could also get the return of the steering circuit and run through the radiator if you still have high temperature problems.
 
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