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How Do You Run Your Hydro?


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#46 TUDOR OFFLINE  

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Posted April 02, 2012 - 01:25 AM

Close, but not quite there.

The pressure increases directly according to load. As a for instance, you want to pull a stump. The chain is around the stump, the throttle is at 1/2 and you slowly apply drive. The pressure increases to a low level as the tractor takes up the slack. Once the slack is out, the tractor starts to take up the strain and the pressure rises quickly. At this point, either the wheels spin or, more likely, the relief pops due to lack of horsepower from the low drive speed. Advancing either the drive control or the throttle will make more horsepower available which will temporarily reduce the pressure, followed immediately by a rise in pressure again (it didn't really drop that much) to the relief setting, or the wheels spin. Repeated increases in flow will generate the same results until either the wheels do spin, or the stump moves. Throughout these attempts, the pressure remains very close to the relief setting, until the wheels break traction. At that point it drops dramatically and the horsepower from that additional flow takes over and the tractor digs holes.

If the stump starts to give before the tires do, the same thing applies. With forward motion available to make use of the flow, the pressure begins to drop and more horsepower goes to motion instead of heat over the relief valve. As the stump continues out of the ground with reduced resistance, the pressure drops in tandem until only enough is required to drag the stump along the ground. About the same as simply moving the tractor.

In the above scenario, the pressure spiked when it came under max load, even though there was only a little flow. Advancing either the throttle or the drive control has little effect at max pressure unless the wheels can turn. The additional horsepower produced by the hydro goes over the relief valve as heat.

Second scenario, towing a 10 cu-ft cart with a level load of dirt (1000 lb+).

Throttle at 1/2 and by advancing the drive slowly, the pressure will rise immediately to what is required to get the rig moving, then it will fall off some as inertia is broken and will settle to accomodate the slow advance of the drive control with the resultant accelleration. When the limit is hit with the drive control and there is no more accelleration, the pressure will drop a little more as horsepower takes over the duty of maintaining speed. A sudden increase in throttle at this point will drive the pressure back up to accommodate the accelleration to the new cruise level, where it will once again drop back to the required (slightly higher due to higher speed) cruising pressure and the horsepower again does its thing.

In this scenario, the pressure increased in tandem with the application of drive speed, with both the drive control and the throttle, and dropped back when speed became stable.

There are so many variables involved with pressure, load, horsepower, speed and terrain, that it is difficult to lay out precisely what will occur. As operators, we learn quickly what does and does not work and automatically adjust to all of these variables to some extent at the beginning, and we get better at it as we gain experience until it becomes second nature. Explaining it and keeping all of those variables accounted for is a lot tougher than actually doing it while operating the tractor. An increase in grade will cause an immediate increase in pressure, as will coming to the end of pavement and transitting to sand, both with no change in throttle setting or the drive control. The governor will, of course, open the throttle to get more horses hooked to the wagon for the increased load.in both situations.

For your last question, I'm not sure how much the pressure will change, if at all, since the horsepower is doing the work at steady speeds. Torque accellerates, horsepower maintains. A 500 lb load isn't all that much anyway. GTs weigh anywhere from 500 to over 1000 lb and then there are the operators, ballast, and any attachments added to that weight. Your 1855 weighs over 1000 lb, empty, and won't even notice carrying or pulling another 500. My 1655 weighs over 2400 with me on the seat and a 4000 lb trailer is barely noticeable, to me, at 2/3 throttle. The pressure may say something different with that load, but it won't be much. I've moved heavier loads with that tractor.

Edited by TUDOR, April 02, 2012 - 01:41 AM.

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#47 coldone OFFLINE  

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Posted April 03, 2012 - 09:32 PM

Close, but not quite there.

The pressure increases directly according to load. As a for instance, you want to pull a stump. The chain is around the stump, the throttle is at 1/2 and you slowly apply drive. The pressure increases to a low level as the tractor takes up the slack.(Low resistance to flow?) Once the slack is out, the tractor starts to take up the strain and the pressure rises quickly.(High resistance to flow?) At this point, either the wheels spin or, more likely, the relief pops due to lack of horsepower from the low drive speed.(low flow rate?) Advancing either the drive control or the throttle will make more horsepower (flow?) available which will temporarily reduce the pressure,(how do you get a drop in pressure with an increase in flow?) followed immediately by a rise in pressure again (it didn't really drop that much) to the relief setting, or the wheels spin. Repeated increases in flow will generate the same results until either the wheels do spin, or the stump moves. Throughout these attempts, the pressure remains very close to the relief setting, until the wheels break traction. At that point it drops dramatically(less resistance to flow?) and the horsepower from that additional flow takes over and the tractor digs holes.


Red colored statements are questions. I am not sure I understand how horse power and flow rate work together. Does an increase in HP (more throttle) increase the amount of flow and pressure or does it just increase the flow rate in a hydrostatic system. Assuming the stump is not moving, the tire arent spinning, and the relief hasnt popped yet.

If the stump starts to give before the tires do, the same thing applies. With forward motion available to make use of the flow, the pressure begins to drop and more horsepower goes to motion instead of heat over the relief valve. As the stump continues out of the ground with reduced resistance, the pressure drops in tandem until only enough is required to drag the stump along the ground. About the same as simply moving the tractor.

Would the flow rate equate to ground speed in this scenario? More flow equals more speed? would the pressure be constant assuming a constant load and grade?

In the above scenario, the pressure spiked when it came under max load, even though there was only a little flow. Advancing either the throttle or the drive control has little effect at max pressure unless the wheels can turn. The additional horsepower produced by the hydro goes over the relief valve as heat.


So would flow equate to available torque? More flow equals more torque to the drive motor? assuming relief valve not popped yet

Throttle at 1/2 and by advancing the drive slowly, the pressure will rise immediately to what is required to get the rig moving, then it will fall off some as inertia is broken and will settle to accomodate the slow advance of the drive control with the resultant accelleration. When the limit is hit with the drive control and there is no more accelleration, the pressure will drop a little more as horsepower takes over the duty of maintaining speed. A sudden increase in throttle at this point will drive the pressure back up to accommodate the accelleration to the new cruise level, where it will once again drop back to the required (slightly higher due to higher speed) cruising pressure and the horsepower again does its thing.

Still cant wrap my head around this part. The rest of it I think I have.


There are so many variables involved with pressure, load, horsepower, speed and terrain, that it is difficult to lay out precisely what will occur. As operators, we learn quickly what does and does not work and automatically adjust to all of these variables to some extent at the beginning, and we get better at it as we gain experience until it becomes second nature. Explaining it and keeping all of those variables accounted for is a lot tougher than actually doing it while operating the tractor. An increase in grade will cause an immediate increase in pressure, as will coming to the end of pavement and transitting to sand, both with no change in throttle setting or the drive control. The governor will, of course, open the throttle to get more horses hooked to the wagon for the increased load.in both situations.


I agree! maybe we should try the crawl, walk, run form of teaching. In electronics my great instructors started by teaching us the very basics of a circuit. Battery, wire, and resistor. Then as we got proficient in understanding that they started adding in more variables (components)

Bob, Thank you for taking your time to help me understand and learn. Thats one of the things I love about this site and this hobby, we have very knowledgeable people who take the time to help us learn something new.

Edited by coldone, April 03, 2012 - 09:35 PM.

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#48 TUDOR OFFLINE  

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Posted April 04, 2012 - 03:21 AM

Some reading for you to help understand.

http://www.edgeroame...s/hydraulics01/

Some formulae to work with.

http://www.hydraulic...ef_formulas.htm

Okay, basics it is! (My son tuned me up many years ago about this. It seems that I had 2 teaching modes, kindergarten level and advanced. No intermediate level!!! I've been trying ever since, so please bear with me! I mean no insult!)

There are 2 components for getting work out of a hydraulic system, flow and pressure. Flow is generated by the pump, and pressure is generated by the work being done. An increase in flow will cause an increase in pressure due to the extra work created by accelleration.

Examples:

- A bicycle air pump is a positive displacement pump. With your thumb placed loosely over the hose outlet, operate the pump at a steady speed. The air flows past the thumb at a steady rate without much pressure. Pump it a second time at a much faster rate. The pressure increase can be felt as the air tries to escape through the same space at a faster rate. Under the right circumstances, you can also feel the heat generated on your thumb as the air flows through the restriction.

- The same occurs with a garden hose. Without the thumb over the end of the hose, the flow of water kind of just falls to the ground. Clamp the thumb on the end of the hose, point it at your wife 20' away........ and enjoy making your own supper. The restriction causes the pressure in the hose to increase over what is available with the end of the hose open.

- Most folks with a GT also have a floor jack. When you roll it under the truck, close the valve and lift the handle, you're ready to put this hydralic system to work. Let go of the handle, and most of them will drop to their limit because there is very little load to develop pressure. This is low resistance to flow. Pump it a few strokes until it almost makes contact with the bottom of the vehicle and see how far the handle falls on its own. As soon as it contacts the vehicle, the handle will stop due to increased pressure being required to raise the vehicle. A few more strokes and the pressure increases with each one until you need 2 hands to pump because the jack is taking up the load that the springs normally carry. This is high resistance to flow. At the top of the stroke, additional pumping only serves to pop the relief valve since there is no other place for the oil to go. The same thing happens if the vehicle is heavier than the jack is rated for, only it won't get to full stroke before the relief pops. All the extra pumps go over the relief unless the load is lightened. Because the relief valve is a restricted orifice, a higher rate of flow will increase the relief pressure to a small degree.The statement made above was erroneous in fact, not in results. With an increase in flow, there is the possibility of a small amount of movement of the rear wheels due to this slight increase in pressure before the relief can dump the extra flow. Any movement of the wheels of a GT will result in a slight drop in pressure until the wheels stop again. With the gear reduction involved, it doesn't take much movement of the rear wheels to equal 1 revolution of the pump. With the hydro in a GT, sufficient increase in flow will usually cause the rear wheels to break traction if the load will not move.

This equation is the foundation of this discussion.

Horsepower = (Pressure/1714) X Flow (gallons/minute)

This one shows that there is no rpm involved in generating torque, only pressure and motor displacement are required.

Torque = Motor Displacement X Pressure/ (24 X Pi)

Given a hydro pump that will flow 12 gpm at full throttle (3600 rpm) and an engine idle speed of 1200 rpm;

Idle = 0 - 4 gpm over the fullrange of the drive control
1/2 = 0 - 8 gpm over the full range
Full = 0 - 12 gpm over the full range

It takes approximately 2 horsepower to move a GT over the ground at speed, and a lot less to creep. ANY position off neutral with the drive control will create flow. If there is flow, then there can be resistance to flow. This resistance is measured as pressure and that results in torque. Relief pressure results in the maximum torque available.

It takes more torque to break inertia to get something moving than it does to keep it moving. Think about the effort to hand push a car to get it moving and then the effort to keep it rolling on a flat surface. In the winter, I try really hard to not have to stop at traffic lights at icy intersections. I may slow down to a creep, but I try to keep moving to avoid the start up inertia.

Once moving, the amount of flow will determine how fast you can go. In the stump pulling scenario, inertia also came into play with more flow. Even the oil has inertia, and an increase in flow will cause a small spike in pressure above the relief setting that may be enough to get motion on the wheels. With motion, there will be a slight reduction in pressure and horsepower can go to work until the wheels stop due to increased traction (compaction from the chains) and the relief redirects the additional flow, or the tires break traction. If the tires break traction, pressure drops. A spinning wheel has very limited traction and it doesn't take as much pressure to overcome the limited traction and enough horsepower (flow at pressure) will keep them spinning. Without the relief valve popping due to high pressure, the oil only has one place to go, through the motor to turn the wheels.

An increase in throttle at the same drive control position or an advance of the drive control will result in more flow, and, if the wheels don't turn, more oil over the relief with a small spike in pressure to deal with the inertia. That small spike may be less than 5 psi or more than 100 psi, depending on how much additional flow is involved, and it is transitory (a fraction of a second) in nature.

At a very low flow rate with high pressure, the leakage due to internal clearances of the pump and motor may be enough to keep the relief from popping. If the relief hasn't popped and nothing else moves, an increase in flow will pop the relief.

Barring relief pressure, flow rate relates directly to speed. At a steady speed on level ground, the pressure will remain the same. An increase in flow will cause accelleration (work) which will raise the pressure until the new speed is established and it will fall back to a new and slightly higher steady pressure due to the extra work being done.

I think that I've covered all of your questions, just maybe not in the order that they were asked. Any more? Ask away! I'll try to answer as best that I can.
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#49 coldone OFFLINE  

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Posted April 04, 2012 - 05:39 AM

I think you gave me the missing piece, "Horsepower equals flow at pressure". I think its equivalent in electronics is the watt. I can relate those two.
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#50 TUDOR OFFLINE  

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Posted April 04, 2012 - 01:02 PM

I think you gave me the missing piece, "Horsepower equals flow at pressure". I think its equivalent in electronics is the watt. I can relate those two.


Hunh! If i'd paid attention to your last post, I could have saved myself about 4 hours of typing last night!

Pressure relates to voltage.
Flow relates to amperage.
Torque relates to ohms, more or less. What it takes to overcome resistance to work
Horsepower relates to wattage.

1 Horsepower = 746 watts

Starting current for a motor is invariably higher than running current and doesn't quite relate to hydraulcs except that heat is a by-product. In hydraulics, pressure (voltage) is the variable for starting and flow (current) is the constant. Bass-ackwards to electrical circuits. Pressure and flow (voltage and current) are both variables in hydrostatic drives.

Better?

I've forgotten some of the formulae for electricity that I learned a half century ago because I rarely use them and tend to think in the terms that I have been using more or less constantly over the past 40 years. I'm a retired steel plant millwright.

Edited by TUDOR, April 04, 2012 - 01:28 PM.

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#51 Michiganmobileman OFFLINE  

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Posted April 04, 2012 - 08:28 PM

I am playing catch up tonight on this thread although it has not been too long since I was last here :confuse: . The main participants here (and you know who I mean guys :smilewink: )may not know it but you are providing a very good education to me (and probably many more) on the mysterious world of hydraulics. Your patient discussions back and forth on this subject are very "clarifying", and I especially appreciate the relation to electrical terminology. I honestly feel I have absorbed and understood more about the basics of hyd. systems after following this thread than I have on my previous research forays in cyber space. GOOD JOB GUYS!! :thumbs: :thumbs: :thumbs: Keep it up. Thanks
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#52 HowardsMF155 ONLINE  

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Posted April 09, 2012 - 11:25 PM

Howard, if you're going to plow 3 or 4 acres, at least take an IR temperature gun to monitor the hydro. It's one thing to pull a huge load on wheels a hundred feet on a level hard-packed surface, It's something else to pull a constant heavy load for a couple of hours. A quick temp check every 15 minutes or so until it stabilizes will do your confidence in the machine wonders. As long as it stabilizes at 180* or less, you're good. Normal is 140* - 160*, over 195*, get the plow out of the ground and drive around at full throttle for a bit to cool it off. The only cooler for that tranny is the fan and the fins.


Just as a follow-up, I mowed my lawn this weekend in 75-80 *F temperatures. The hydro tank was about 120* at the end of it. Apparently I don't work the hydro too hard while mowing.

#53 TUDOR OFFLINE  

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Posted April 10, 2012 - 12:25 AM

  • No, that's all implement work, the same as snowblowing. The tractor is just for riding on with those jobs. Pushing snow with a plow isn't much worse and even loader work is not all that hard for heat buildup in a hydro. Ploughing the ground is where the hydro gets a workout and generates serious heat.

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#54 middleageddeere OFFLINE  

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Posted May 28, 2012 - 09:33 PM

Wow, this opened my eyes...I have always run my 317 as low RPM as possible, trying to "save" the old, original engine and drive shaft. Looks I better just replace that drive shaft and rev her up! Thanks guys.

#55 KC9KAS OFFLINE  

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Posted July 31, 2012 - 05:28 PM

Anything that is hydrostatic is designed for the engine to be run at full throttle when in use. I won't say I always follow this but that is how they are designed to be run as it at full RPM that the pump and motor of a hydro system have the appropriate operating pressure.

I just read in the manual for my "new to me" WH D-200 that the engine should be ran at "full throttle".
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#56 twostep OFFLINE  

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Posted August 01, 2012 - 10:45 AM

my 682 manual says to mow at full throttle but to engage the deck at low rpm to prevent extra stress on the drive belt.
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#57 retiredarmyguy OFFLINE  

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Posted August 02, 2012 - 01:50 PM

Every hydro manual I have seen recommends operating the engine at 3/4 to full throttle to maintain hydro oil temp.
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#58 skunkhome OFFLINE  

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Posted October 06, 2012 - 06:55 PM

Simplicity, AC, DA, Agco Allis instructions for 7100/900 series tractor, states that throttle should be at 1/4 to 1/2 while initiating movement. for mowing it should be set at 3/4 to full throttle. No instruction for pulling ground engaging implements. Earlier models with same transmission specify 3/4-full throttle for ground engaging implements with exception of the 10" moldboard plow which calls for full throttle which is essentially the same as the geared tractors. I think I'll keep my plowing on my geared shuttle tractor.

Edited by skunkhome, October 24, 2012 - 08:33 AM.

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#59 Dieselcowboy OFFLINE  

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Posted March 12, 2013 - 05:23 PM

Will lugging an engine hard really lead to premature ware and oval the cyls?

#60 OldBuzzard OFFLINE  

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Posted March 13, 2013 - 10:15 AM

Will lugging an engine hard really lead to premature ware and oval the cyls?

 

Yer dern tootin' it will.

 

A good friend of mine found that out the hard way when he 'wore out' a JD 750 (Yanmar 3-cyl diesel) in a little over 2 years by mowing with it at 1/2 throttle and too high a gear.

 

I had told him time and time again to open up the throttle so that the tach was in the "Rated PTO Speed" range, but he just wouldn't listen.  He thought he was 'saving the engine' by not running it at near full throttle.  It got hard to start, started having major blow by, and eventually got so bad that it wouldn't start even with ether.

 

After a $3,000.00 overhaul and a talk with the mechanic, he finally decided I was right.


Edited by OldBuzzard, March 13, 2013 - 10:18 AM.

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