I just can't believe this, guys think , the pump feeds the first motor, it turns... OK, great right? But the out side now has no pressure correct? AH yes no pressure because the motor is turning thus used up most if not all the pumps pressure to it to turn, now the out side has no pressure because it's on its way back to the tank via cooler or what have you, so to answer who ever's question will they both turn the same, maybe with no load in theroy, but not in real life.
As for the motor seals , if you block off the return side flow be it either side as I think these motors are bi- directional you will cause internal case pressure ,blowing out the seal. This is why some have case drains in apps that are known to cause this .
So things are not as simple as they appear or we would all be driving hydrostat cars.
And sorry for the caps not ment to yell just get attention I haven't figured out how to underline the text...
skyrydr2,
All a pump does is move oil in a continuous circle. Pressure is something that is created when you try to interfere with the movement of that oil.
Yes, oil enters the first motor and if that motor has a hard time rotating the wheels, then a certain amount of pressure will be created by that resistance. Theoretically speaking, you are correct in saying that the oil exiting the first motor has no pressure because the first motor is no longer asking it to perform work.
However, that oil is now entering the second motor and if that second motor asks for the oil to perform work, then the pressure in the line between the first and second motor will also rise accordingly. This is called "back pressure" because pressure is not a one-way street. The force is equal in all directions in the hydraulic hose/line. Pumps don't create a specific amount of pressure that is "used up" in one device and leaving all other devices helpless. Look at a backhoe with bucket, boom, stick and swing cylinders.
The pump can supply oil to all five or six cylinders when necessary and can apply whatever pressure is needed to dig a bucket of dirt and swing it to one side for emptying. All those cylinders are in parallel with one another. It's the Operator who consciously apportions the volume of oil diverted to each cylinder during the digging process in order to obtain a full bucket but all three cylinders on the hoe get pressure in varying amounts. One cylinder doesn't "use up" the pressure and leave nothing for the other two.
As for your claim about motor seals.......... it is absolutely possible to stop a motor from rotating and that is no different than blocking off one motor port. A stalled motor allows no oil to flow through it and the seals are designed to withstand this pressure. As an example, the Case rototiller is driven by a hydraulic motor. I have often had my tines encounter a rock, root or hard clay that stopped the tines from rotating. When that happens, the relief valve opens up at 2200 PSI and squeals like a stuck pig until I take corrective action. If seals blew out every time this happened, no one would buy those tillers.
Case and Ingersoll are famous for hydraulically powered attachments such as Bush Hog type mowers, finishing mowers, snocasters, mower decks, chipper/shredders, vacuums, double-acting log splitters and roto tillers.
I gave you two links showing an articulated FEL using a pair of 200 series Case trans-axles. Both axles drive this machine in whatever direction the operator wants it to go. Many others have built similar machines. No one runs the motors any other way but in series.
