John

There are some links between torque and pressure as well as speed and flow rate. Run some numbers through this to get a feel for what is related to what and how. http://www.surpluscenter.com/Hydraulic.htm#calc

As far as the stalling, it would be a help to put in a gage before each motor input to assess what might be going on. In a low load situation (like running on level ground) changing the motor size should have slight effect on the pressure required, but moreso on the travel speed. You've changed motors right? Any idea what the input pressures are to each motor? AS a temporary measure, you could direct the return flow to a pail and see what happens to the flow as the motors are loaded too. Be carefull to secure both the line and the pail though.

I checked the calculator above and as I said 10 gpm will take a little more then 16 hp to run at 2400 psi. You should do more then just move your machine. Your circuit is? One valve in series with the other valve which then goes back to the tank maybe through a filter first. You then control the direction of each motor by its spool valve. The surpluscenter calc. shows about 238 rpm at 10 gpm. Not as nice as my Excel spreadsheet program that you can download above but it does work.
You get this working you may want to get something like this to prevent breakage.

surpluscenterrelieve

Camdigger,
No, I have not changed motors, they are still the 9.7 cid char-lynns that came off a paver.

Strange as this may sound, if I understand you correctly, then my issue seems all the more baffling. If bigger motors would only affect travel speed in low load appliations, then it wouldn't appear as if changing them would play any role in getting my machine to actually move from a level, stationary position. I assumed that the amount of displacement was related to the torque it could generate, and thus, their ability to move the machine.

I have not yet had a pressure gauge on the system and it looks like I really should do that. Because somehow I am generating enough pressure out of a 10 gpm pump and a 17hp engine to stall out the engine before it will actually turn the motors.

Bigger volume pump = more torque. If you have the same volume you will get slower speed porportionally to the change of volume, but the same power. Power = Torque * speed (in rpm)Power in is determined by the flow and pressure coming from the pump. Assuming this is fixed and your pump is making 16 hp. The torque you get from the hydraulic motors will increase as the speed decreases, and vice versa. The product of the two will be the power.

Now to confuse it more...the motors will only take the pressure that is needed to turn them. If they will turn xx rpm the pressure will equalize to turn xx rpm. The flow required for this condition might only take 500 psi but the same flow volume from the pump. So the pump might only be making 5 hp as it idles around.

The same thing applies in your 315 hp silverado. The engine will make 315 hp at xx torque and 5000 rpm. How many time do you run it at 5000 rpm (never or it would blow up) the truck in normal operation is only making a fraction of the rated hp. maybe 150 (guessing)

Changing to bigger motors will be like down shifting a car.

I would do the gauge thing first though to make sure you don't have anything else going on.

You're exactly right Gator

There is a combination of displacement and pressure that generates torque. BUT, if you don't have enough torque to move the machine unloaded, you will NEVER be able to do any work with it.

So if you need 25% of the maximum torque to make the machine move on level ground, that leaves 75% to do any additional work like dozing, tillage, or hauling. If you're loaded 125% to make the machine move.... You can't get much work done. Hence the qualifier LOW LOAD.

I'm curious what the motors Kohn has were doing on the paver? Running an auger, conveyor, or main traction drive?

is there a chance that the governor on the engine isn't picking up the load.

The motors are char-lynn s series motors with the number 103 1004 008. I believe they came off the auger on the paver, but since I didn't pull them I can't say for sure. The guy who did get them told me they definitely were not the from the drive wheels.

I guess I keep coming back to the same notion though. It seems most of what I'm reading here says that the engine and pump should be strong enough to move a machine of this size, at least on flat ground. And since I know that oil is flowing through the system fine, and I know the wheels on the machine will rotate just fine, I keep coming back to wondering if the motors themselves are just too small. If I am reading Gator and camdigger's responses above correctly, using bigger motors would be "like downshifting a car" which should give me much higher torque at lower rpms right? Which seems to be what I need here.

keep in mind that your relief valve should bypass unneeded pressure and let the engine keep running.

PRESSURE (PSI):
CONTINUOUS: 1,900 PSI / INTERMITTENT 2,300 PSI
TORQUE (LB-IN.):
CONTINUOUS: 2,567 LB-IN. / INTERMITTENT: 3,072 LB-IN.
FLOW (GPM):
CONTINUOUS: 15 GPM / INTERMITTENT: 20 GPM
SPEED (RPM):
CONTINUOUS: 353 RPM

I just got these specs for your motors. You set your relief valve at 2000 psi no more then 2300.

As Tom was saying. Your engine may need richer fuel or as he was saying the governor checked. Never thought about that.

However your hydraulic motors are a little weak for digging and moving dirt. Still should run the machine around just fine as is. I don't have the picture in my mind of your circuit.




pdf file hydraulic circuits

you could back off your hydraulic relief valve till the fluid is just running back to the tank. then as you crank down on the relief valve see how the engine reacts. with a gage in line it will tell you what presser kills the engine and if the governor is working or not.

Hello, Did you ever get this figured out?