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CrestonM 
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 Topic: Off-Color Hydrostat Question
Posted: 06 Jan 2021 at 11:23am |
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Thanks Doc, I’ll keep working on finding the right fittings to carry out this test. That would get the best results the quickest
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DrAllis
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Posted: 05 Jan 2021 at 11:35am |
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You get a gauge plumbed into the pump test port. You find out your max stall pressure (at wide open throttle) isn't at spec (5,000 psi or so ??). Your next step is to disconnect the wheel motors by disconnecting hoses and plugging them. Then, retest the pump at max stall wide open throttle. If the max stall pressure is still low, the problem is the hydro pump. If the stall pressure now reaches spec, the problem is one or both drive motors.
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CrestonM
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Posted: 05 Jan 2021 at 10:35am |
Dave, thank you again for your excellent replies and stellar explanations! You really make it easier to understand for novices such as myself. I looked at the machine yesterday and here's what I notice...you are right about field and road mode being high/low ratio. However, there is no parallel/series valve I see. There is an output hose and a suction hose coming from the pump, each goes to a Tee, then into the wheel motors. The high/low ratio is changed by swash plates in the variable speed wheel motors. A lever in the cab has 2 positions...field and road. The linkage controlled by the lever goes down to the motors and moves the swashplates.
Doc...I have a high enough PSI gauge that the book calls for, but have been struggling to find the right reducer to adapt it where it will thread into the pump.
Edited by CrestonM - 05 Jan 2021 at 10:37am
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DaveKamp
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Posted: 01 Jan 2021 at 12:57am |
Creston... you've got several symptoms, and they all share a common circumstance...
Study the circuits... I'll bet that you'll find FIELD and ROAD mode to be an equivalent of HIGH and LOW ratio...
I don't know about your machine, but FREQUENTLY, a system that does this, is done by virtue of a hydraulic valve that performs a parallel/series switch.
In FIELD mode, you want a low ground speed, but plenty of motive force. In this mode, the hydrostatic pump unit's output goes to a TEE, where the branches split fluid flow to right and left wheel motors. The wheel motors effectively run independant of eachother, and will allow differential action between the two (left and right can go different speeds in a turn).
In ROAD mode, you want high ground speed. In this mode, the hydrostatic pump flows fluid into ONE of the wheel motors, then out and into the IN of the other wheel motor, then back to tank. In doing so, the hydraulic VOLUME to each wheel motor's supply is effectively DOUBLED, rather than divided between the two motors. This results in higher speed on each motor, but with less wheel force available.
The way this is handled hydraulically, is with a specially-plumbed spool valve with two positions- parallel (field) and series (road).
When the hydraulic valve shifts from one mode to the other, there's a bit of a hydraulic 'shock' that occurs during the shift, and there's usually a pressure relief valve either in the valve, or built into the supply plumbing going TO that valve, because the hydrostatic shock can either break, or hydraulically 'jam' the valve spool.
Now, while it makes sense to do so, that check valve doesn't necessarily need to bypass BOTH valves... it really only needs to bypass ONE, in order to prevent damage and valve jamming.
In the case of your machine, it very well may be that the check valve has crud in it, and in the process of normal operation, has managed to become slightly unseated, thus bypassing a little volume, even though the pressure isn't excessive.
I think Dr. Allis's suggestion of taking pressure readings is a good idea... the OTHER thing I'd do, is go looking at that Field/Road valve, and associated plumbing, pop it apart for an internal look-see. If there's crud in that check valve, or in the valve spool or it's actuator (electric? mechanical?) isn't fully seating the valve in one or the other positions (like, the detent isn't holding, or crud is preventing the spool from making it to the detent), then a simple scrubbing out of gak, and reassembly, and a serious hydraulic flushing would be my best suggestion.
FWIW... crud inside a hydrostatic system is a bad thing... and machines tend to accrue crud... with compounded interest...
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DrAllis
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Posted: 31 Dec 2020 at 6:39pm |
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You were told back in August to get a pressure gauge connected to the hydro to see what it was actually doing. So, what kind of pressures are you seeing at FULL THROTTLE when the machine quits moving ????
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CrestonM
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Posted: 31 Dec 2020 at 11:09am |
Hey guys, I've got another question about these wheel motors. I think the relief valves are stuck partially open. I've been busy with my day job and harvest, so haven't had much time to work on this. Once I start the machine and throttle up, I have to rock the hydro lever back and forth a bit to get the machine moving. If I just push it forward, the machine creeps slowly like it's trying to move, but just can't get going. Once I rock the machine with the hydro a few times, it will take off and the acceleration/deceleration works smoothly...in field gear. If I move the motor swashplates to "road" mode, I have no movement, but the pump still sounds like it has a load on it. Go back to the swashplates being in "field" mode...if I'm travelling on flat ground, it does fine, but the minute I go up a slight incline, the machine slows to a stop (pump still sounds like it has a load and charge pressure is good) but the only way to get moving again is to back up and go another way, downhill or on flat ground. To me it sounds like relief valves, but I wanted to get your thoughts.
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shameless dude
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Posted: 11 Sep 2020 at 3:36am |
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don't get this one stuck!
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CrestonM
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Posted: 10 Sep 2020 at 10:22pm |
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That’s the truth! Don’t know how cold you’ve been but we had highs in the 40s yesterday. 60 today and supposed to be 80s this weekend, so a little more normal thankfully!
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Michael V (NM)
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Posted: 09 Sep 2020 at 11:48pm |
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I'd like to come over an help,,,just seems like there is something that needs to be done around here....last couple days it's a pretty good job jus staying warm....
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CrestonM
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Posted: 09 Sep 2020 at 10:17pm |
 Michael V (NM) wrote:
I've been following this, glad to see you got it moving! |
Thanks, Michael! I'm pretty glad as well. Why don't you run over and help me get all the other little bugs worked out?
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CrestonM
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Posted: 09 Sep 2020 at 10:15pm |
JohnColo wrote:
Glad to read you got her moving. If you drive it the 40 miles back home, you might consider washing the windshield.. Got any cotton to harvest this year?
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Yeah John window's a little dusty! That's on my to-do list, along with about a hundred other little things on the machine. The whole cab interior needs a serious cleaning. Would be great to get the A/C working, but that might be a "next summer" project. So far no cotton to harvest yet...I've only done custom work so far, and the guy I work for hasn't found any work yet, but hopefully some will pop up soon.
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Michael V (NM)
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Posted: 08 Sep 2020 at 5:52pm |
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I've been following this, glad to see you got it moving!
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JohnColo
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Posted: 08 Sep 2020 at 2:31pm |
Glad to read you got her moving. If you drive it the 40 miles back home, you might consider washing the windshield.. Got any cotton to harvest this year?
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JPG AUSTRALIA
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Posted: 07 Sep 2020 at 6:41am |
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Great outcome,you got off lightly😀
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CrestonM
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Posted: 07 Sep 2020 at 2:14am |
Hey guys! Made a little more progress... hooked up another gauge to verify my charge pressure in the cab was reading correct, and it was. I tried what you suggested Dave and throttled up and tapped on the motors on one of them I heard a slight noise so maybe that was the brake releasing? I got back in the cab and tried moving the machine forward and backward, but it acted as if it was still struggling. So I carefully rocked it back and forth with the hydro and with each rock it moved a little more. After doing that 4-5 times, it took off driving and was very responsive. Even at idle it drives well now. So I guess things were just stuck from sitting 25+ years, and just needed more coaxing. But the knowledge y'all, and especially Dave, have provided to me about hydrostatic drive systems is invaluable!
Here is the link to the photo file again, I added a short video just now of it driving. Not the greatest video, but hopefully will get good footage at cotton harvest, if I get the rest of the machine ready by then.
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DaveKamp
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Posted: 01 Sep 2020 at 10:51pm |
Just to clarify-
CHARGE PUMP pressure is so named, because it exists to assure that the 'hydrostatic loop' between motor and pump has been 'charged full' of hydraulic fluid.
So imagine you have a variable pump driving a motor, with no reservoir, just a full pump, full hoses, and full motor. This system will work in theory, and for a short while in practice, but without some source trying to bring in 'more', the circulating loop will suffer several problem, including, but not limited to overheated fluid, aeration, and leakage loss.
SO the designers added that 'charge pump' as another device who's function is to draw from the reservoir, and PUSH MORE into the hydrostatic circuit (usually, through the variable pump's incoming feed, which of course changes with swash-pump direction.
Important to note that the charge pump, in most cases, will pressurize BOTH SIDES of the hydrostatic circuit (through check valves), so that when the engine is started, the hydrostatic loop, in NEUTRAL, will be pressurized on BOTH sides, to a certain amount.
This is important with automatic-spring-brake setups, as this basic pressure is usually sufficient to overcome the brake springs, and affect a release.
Creston, if your machine is NOT getting sufficient charge pump pressure to release the brakes, it is probably due to a charge pump pressure relief/bypass valve that's stuck open (particularly common when an auxiliary circuit driven by charge pump output is bypassing)... or a charge pump section, or it's suction filter, that is somehow obstructed... and as someone else noted, you might not have it throttled up high enough.
I would throttle it up, and then lightly tap around the wheel motors, perhaps a little vibration might knock free something lightly stuck, and get you going...
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Johnwilson_osf
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Posted: 01 Sep 2020 at 9:42pm |
Creston, Wow. Keep up the good work. Perseverance pays off. I am really impressed by your can-do attitude to make these old machines run. Not having any cotton ground up north here, makes the post all that more interesting to see how things are done there. DaveKamp, Wow. Great explanations. Thank you for not only answering Creston's questions, but also answering why. This is the stuff I love to read on this forum, because I know someday I am going to be looking at something, and will have a better understanding of it, because of what I read on this forum.
Looking forward to seeing that big beast move. Great job
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Allis Express: Eastern PA on Rt 80
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CrestonM
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Posted: 01 Sep 2020 at 8:53pm |
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Progress has been a little slow lately... didn’t get to work on the machine this past weekend, but rummaging around the shop I did find a 10,000# gauge. Service manual says an 8,700# gauge will suffice so this ought to work. Hopefully this weekend I can hook it up and see what the pressures are at the motors.
Edited by CrestonM - 01 Sep 2020 at 8:54pm
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DrAllis
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Posted: 28 Aug 2020 at 7:15am |
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Each and every "hydrostatic" drive system has test ports or plugs to remove to connect a 5 to 6,000 psi gauge for FORWARD and REVERSE circuits. You know you have correct charge pressure ?? Get or read on-line a service manual written to actually test these pressures on that particular brand of pump/motor combo. Take the results and go from there. The swash plate in the pump (and motors if equipped with a swash plate) are positioned by pilot pressure which comes from the charge pressure circuit. So, there should be a place to measure if the pilot pressure is even trying to move the swash plate. In short, you can't diagnose much of anything without gauges connected in the proper places. If this was in a Shop that worked on these units everyday, the diagnosis would have been made in an hour or less. MACK is very correct on the disconnecting of any drive motor. With no load it is very possible to overspeed it and blow it up if enough oil flow with pressure is delivered to it from the pump.
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CrestonM
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Posted: 28 Aug 2020 at 6:39am |
MACK wrote:
DON't unlock motor from wheel and run it!!!!!. It will over speed the motor and destroy it's self. MACK |
What is your recommendation to solving the problem at hand?
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MACK
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Posted: 27 Aug 2020 at 9:02pm |
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DON't unlock motor from wheel and run it!!!!!. It will over speed the motor and destroy it's self. MACK
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DrAllis
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Posted: 27 Aug 2020 at 7:06pm |
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Many of todays skidloaders and the like have brakes that are inside each drive motor. Brakes are spring applied when the engine is off and when engine fires and charge pressure is built, a brake release switch can be activated and charge pressure overcomes the brake spring to release them.
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CrestonM
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Posted: 27 Aug 2020 at 6:30pm |
Thanks for another great explanation, Dave! I will try your suggestion tomorrow. I will disengage the hubs and try running it for a while and see if anything changes.
Re-reading the brake section... "machine is equipped with powered disc brakes, between the hydrostatic motor and torque hubs. The braking system is always locked when engine is not running. The brake system requires at least 180# of charge pump pressure to release the brakes, therefore park brakes are always set when engine is dead".
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DaveKamp
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Posted: 26 Aug 2020 at 7:19am |
Okay, so you DO have variables in both the pump, AND the motors.
Most systems would just have variable displacement elements in one, or the other... frequently just on the pump end, as a simple wheel motor is much more compact and simpler to plumb... and a WHOLE lot less expensive.
Your pump, and your wheel motors, are basically the same guy inside... there's a rotating spool with a series of pistons (like the cylinder on a revolving pistol), and the pistons roll against an adjustable swashplate.
You have variation at the pump side, and also at the motor side. The pump swashplate side is probably direct mechanical via that blue lever. The wheel motors are more likely controlled by hydraulic ('pilot') pressure. Notice on the blue wheel motor, there's two smaller lines, going to a metal block... where on the pump, there's a smaller block, with pivot and lever. That lever acts on the swashplate, varying the direction and volume of fluid. What Sundstrand did, was make a small double-acting piston that takes place of that lever, so that it could be hydraulically modulated instead.
Before digging into anything too deep, what I would suggest, is that you start it up again, and repeat your tests... and listen to the engine.
When the engine grunts, that means the hydrostatic pump is applying a load. The pump is pulling fluid from one side of the circuit (and the charge pump, as needed), and sending it to the other side of the system. IF the pump were stalled (meaning, there's no where for the fluid to go), it would pull the engine down really hard. A simple grunt suggests to me that you have flow through, and the wheel motors' swashplates are still in a neutral state.
Yes, the swashplate angle changes direction and displacement, and when displacement is high, volume will be high, but pressure capacity will be low. Reducing swashplate angle reduces volume of displacement, hence raising pressure potential. Realize however, that output pressure is load-dependant... a high pressure pump, working against no load, develops no pressure.
It may be that the swashplates are in neutral, and fluid is just bypassing. In the variable motor setup, they've incorporated a bypass circuit to prevent drastic overpressure on coast, because not doing so makes for a very dangerous, jerky machine. They've identified that it has 'hydraulic' braking, it could mean one of two things, that they're using the wheel motor as a dynamic brake (by stalling it's output with the swashplate), or by an additional brake feature that is activated by pilot pressure. Without looking up the build sheet for your pump assembly AND one of the wheel motors, and seeing a hydraulic diagram, its pretty difficult to tell... and the function of the 5th hose (two for motor supply, two for pilot pressure) is probably a bypass return...
My bet, is that it's been sitting long enough that the control cylinders for wheel motors aren't providing action YET, because they've been sitting for a while.
IF you can unlock the hubs and run it with the wheel motors disengaged from the wheels, I'd suggest you do that for a while, and move the levers around (all of them) to coax any air bubbles out, and get the wheel motor control lines operative.
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CrestonM
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Posted: 25 Aug 2020 at 8:04pm |
Hey guys...added a couple more photos to the shared album above. My machine is 40 miles away, but I was able to go look at one that's closer... the wheels are powered by Sundstrand 22-4015 hydraulic motors with 5 lines, not 4 like I previously thought. In the recently added photo, you can see the lines. I can identify the 2 big lines and return line, but the 2 smaller blue lines I'm not sure about.
Also...Mack...an IH 915 combine was close by, and I looked...it has the same hydro pump like you said. Pretty neat!
Edited by CrestonM - 25 Aug 2020 at 8:07pm
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MACK
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Posted: 24 Aug 2020 at 9:22pm |
There is a lot of info on youtube about Sundstrand. As always youtube may not be 100% accurate . JD and MF also used same hydro. MACK
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MACK
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Posted: 24 Aug 2020 at 9:10pm |
IH used that same hydro in their combines for a lot of years. A local IH dealer might help you out. Have worked on them myself, but been a while. They have a forward and reverse relief valves. If it does the same forward and reverse, tells me problem is not in the relief valves. Good luck. MACK
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CrestonM
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Posted: 24 Aug 2020 at 5:44pm |
Dave, thank you for that very thorough explanation! It's starting to make some sense to me. Reading from the operator's manual, it says the hydrastatic pump (not sure why they spell it hydra instead of hydro) is the Sundstrand variable displacement motor for forward-neutral-reverse. It says the motors (2) are Sundstrand variable displacement. There is a lever to control the motors, placing them into working and road range. I'm guessing this moves a swashplate in the motors to change the speed of the motors, but also changes the torque level?
There is a troubleshooting section with 4 possible causes of no movement, and all point to low charge pressure, low fluid, and out of adjustment control linkage, but everything there is good.
The machine has hydraulic turning brakes, but no park brake arrangement according to the book. It says the hydro is the brake, which makes sense.
Here are a few photos I took a while back...it's kinda hard to see but the motors on the wheels have the 4 hydraulic lines you were talking about. I haven't traced them all to their sources yet, except for the big ones. Nearly every function on the machine is hydraulically powered in some way, so there is a huge maze of blue hoses, making tracing difficult.
Trying to save file manager space...here's a link to a shared Google Photos file. If it doesn't work, let me know. One photo shows the cab controls...the 2 on the left are the focus...the top one moves linkage to the drive motors to switch from field to road range. The one under it is the forward-N-reverse lever. I have verified the linkages are free and working, and I even disconnected the hydro lever at the pump and moved the servo lever by hand (I think it's a servo lever?) The PTO is next to the hydrostat pump, and it is activated by charge oil pressure from the hydrostat pump.
Edited by CrestonM - 24 Aug 2020 at 5:59pm
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DaveKamp
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Posted: 24 Aug 2020 at 2:27pm |
there's several possibilities, and you've given us JUST ENOUGH information to pile up a bunch of guesses.
First piece of 'good' info, is Sundstrand 22-2084. that is a variable piston hydrostatic pump.
that suggests to me that your wheel motors are fixed-volume, not variable... as the pump has a swashplate, probably servo operated, rather than direct-(mechanical lever) operated.
Your wheel motors most likely have THREE hydraulic lines going to them, possibly four, but probably three.
In many cases, a hydraulic motor will have a supply, a return, and a bypass drain... the latter is actually ported to a cavity on the outside of the primary, but prior to the secondary motor shaft seal, such that any leakage which sneaks past the motor shaft seal, can be returned to the reservoir. It is this way, because the motor is bidirectional... BOTH sides are pressure ports. SOMETIMES, though, this return feature is done by a pair of duplex check valves or a dragging shuttle plate inside the hydraulic motor, but that's not popular with most as it offers opportunity for air bubbles to be drawn into the hydrostatic circuit loop.
Sometimes, the hydraulic motors don't have a bypass return line... meaning, if they develop a leak, they just leak...
The inclusion of yet-another-line frequently goes to a brake built into the hydraulic motor. When the hydraulic motor is in a non-pressurized state, rather than allowing it to coast, one could simply 'cap off' both hydraulic lines to prevent the hydraulic motor from turning. Unfortunately, a propulsion motor becomes a pump when spun externally (like coasting) and if you 'cap off' hydraulic flow, not only does it enforce a very abrupt stop on the machine, the amount of force applied to the motor, and concurrently, hydraulic pressure appearing at the motor's plumbing, can prove traumatic for the machine, so frequently, hydraulic motors will have a duplex check valve located within the motor that has very high pressure spring relief (i.e., a check valve with 4,000psi cracking pressure) so that a sudden stop of flow will cause the excess pressure to simply bypass around the check valve, and eliminate freewheeling shock.
In many hydraulic motors, there is a mechanical brake, that is mechanically (spring) applied, and requires a certain amount of pressure to release. Sometimes, this pressure is applied through yet another duplex-check-valve (drive forward, or drive reverse, right?) but not through the circuit in such a way that applying forward motion would present enough pressure to release it's own brake (yeah... I demonstrated that in class!)
...So in many cases, the wheel motor will have an extra hydraulic line who's function is strictly to RELEASE the mechanical brake. Frequently, that's just a piston inside a volume that pulls back against a stack of bellville washers leaning against a multi-disk in the end of the hyd-motor).
That pressure gauge you're seeing... is most likely CHARGE PUMP PRESSURE... charge pump is a small pump located in the hydrostatic pump unit that draws in fluid from the reservoir, and CHARGES the hydrostatic pump with fresh fluid. The hydrostatic pump isn't a 'pump' in a normal sense- it takes fluid from one side of a circuit, and passes it to the other... and in a purist sense, doesn't "need" a reservoir to draw from, as whatever comes out of one side of the wheel motor, gets pushed into the other... but our systems operate in a real, not theoretical world. The charge pump 'forces' fluid into the hydrostatic pump, so that there's fresh-and-cool flow INTO the circuit, while that which it displaces is bypassed to the reservoir to cool, de-aerate, and get filtered.
The CHARGE pump usually isn't a HIGH pressure (most of the time, they're under 750psi or so), and they don't have a significant volume, but can be used, because of how they work, as an auxiliary hydraulic supply to operate small cylinders or control functions.
MY BET... is that your machine has wheel motor brakes, and there's either a valve (mechanical, or pilot-operated, or solenoid-electric) that sends CHARGE PUMP pressure down to release the wheel motors...
OR... there's a high-low circuit valve that's in the center (stopped) position.
Hydraulically driven machines with more than one wheel motor, can be set up for different ground ratios by virtue of simple plumbing:
ie.e Two motors, each having a displacement of 10 cubic inches, connected in parallel, require 20 cubic inches of flow from the hydrostatic pump, in order to make ONE motor rotation.
Connect the same motors in series, only 10 cubic inches of flow is required... because that which flows thorugh one motor, flows through the other.
As a result, the two motors in parallel will only travel half the speed, as if they're in series... with the trade-off being tractive force capacity... in parallel, they'll have twice as much force at the ground, right?
The 'gotcha' is that when you're in 'high-range', there is no provision for the motors having different flow rates, so there's no 'differential' action... basically, they're locked. Shift to LOW range (parallel) in order to make a tight turn.
Post pictures of your pump, motors, and controls. The answer is probably there...
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john(MI)
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Posted: 24 Aug 2020 at 11:03am |
You mention the pressure gauge in the cab. Find out where that is connected in the system. Your problem should be after that point.
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