Hydrostatic versus Hydro
1 - 12 of 12 Posts
Joined
·
4,342 Posts
Hydro [hydraulic drive] is an engine driven pump pushing oil through a [hydraulic] traction motor which is then geared to the axle. Hydrostatic is a belt driven or shaft driven transaxle where a variable displacement piston pump is controlled by a swash plate to control the flow of oil to a integral drive motor. No external cooling and no hydraulic pto provisions with this setup. I'm sure others here can offer more comparisons and advantages/drawbacks for either system.
Joined
·
3,283 Posts
Our Case/Ingersoll tractors have a directly connected to the engine large volume output positive displacement pump. The pump output goes into a hydraulic control valve that allows a variable flow and pressure to go to the drive motor. Any flow and pressure that isn't used by the drive motor is bypassed back to the hydraulic reservoir.This is the design of a hydraulic drive system. Movement of the control valve to reverse from forward brings the valve to full bypass which is neutral, reverses the flow of oil to the drive motor which causes the drive motor to turn in the opposite direction.
A hydrostatic drive system utilizes a variable output pump and a drive motor. The hydrostatic pump is designed so it can change the amount of flow and pressure to the drive motor from the point of no flow or pressure to full output to the drive motor and reverse the flow and pressure to the drive motor. Hydrostatic drive and motor can be in one integral unit or separate pump and wheel motor combinations. The torque output of a hydrostatic pump is much less due to its design as it has variable flow and directional outputs. They put out a lot of flow but not near as much pressure as a hydraulic drive system does. A hydrostatic pump does have a small positive displacement pump in it called a charge pump. This pump keeps a flow of oil around the drive pistons in the swash plate and is bypassed back to the reservoir. When the swash plate angle is zero, there is no flow or pressure to the drive motor. When the swash plate is turned in the positive direction, the drive motor will turn in the forward drive direction. The more positive the movement, the faster the drive motor will turn. When the swash plate is returned to the zero position the drive motor will stop turning. When the swash plate is moved to the negative direction the drive motor will turn in the reverse direction.
The design of a swash plate with pistons is difficult to describe, a picture in a parts or service manual will provide a better explanation/description of how it functions. The swash plate turns all the time the pump is turning.
A hydrostatic drive system utilizes a variable output pump and a drive motor. The hydrostatic pump is designed so it can change the amount of flow and pressure to the drive motor from the point of no flow or pressure to full output to the drive motor and reverse the flow and pressure to the drive motor. Hydrostatic drive and motor can be in one integral unit or separate pump and wheel motor combinations. The torque output of a hydrostatic pump is much less due to its design as it has variable flow and directional outputs. They put out a lot of flow but not near as much pressure as a hydraulic drive system does. A hydrostatic pump does have a small positive displacement pump in it called a charge pump. This pump keeps a flow of oil around the drive pistons in the swash plate and is bypassed back to the reservoir. When the swash plate angle is zero, there is no flow or pressure to the drive motor. When the swash plate is turned in the positive direction, the drive motor will turn in the forward drive direction. The more positive the movement, the faster the drive motor will turn. When the swash plate is returned to the zero position the drive motor will stop turning. When the swash plate is moved to the negative direction the drive motor will turn in the reverse direction.
The design of a swash plate with pistons is difficult to describe, a picture in a parts or service manual will provide a better explanation/description of how it functions. The swash plate turns all the time the pump is turning.
So that’s a great answer but it’s to much for my damaged brain. So everyone I have talked to says hydro is really strong versus hydrostatic , so my next question is who still makes hydro driven, and why is so many hydrostatic driven tractors being sold.
Joined
·
15 Posts
The Cost !!
Joined
·
3,113 Posts
The hydrostatic GT's I have seen only have one hydraulic circuit other than the drive and that is for the lift cylinder, and some don't have that. There is not an option to hook a log splitter, chipper/shredder or hydrovac to these GT's. Like you can with a CCI if you have the optional rear hydraulic PTO.
Cheers,
Gordy
As far as the engineering is concerned, the hydrostatic and hydro are essentially the same thing but they go about it in different ways. The reason why they say that hydro is "Stronger" than hydrostatic is because companies typically use cheap and easy to install hydrostatic transaxles nowadays since they're an all-in-one unit and all you have to do is spin a pulley or shaft input to power them. This gives the impression that they are typically weaker, from experience I can say there's a bunch of very strong hydrostatic transaxles out there so the sentiment is misplaced IMO.
I would imagine the few times an all hydro system has been used and designed they aren't using bespoke pumps and motors so the motors tend to be higher quality industrial motors and would be overrated for their use, similar to our Case GTs. Hydrostatic transaxles on the other hand are a lot more specialized and designed more around being "good enough" for their use case.
@Gordy I have seen plenty of hydrostatic transaxles with a "PTO" output and it functions just like on ours except it's always on and always in one direction because it's a straight output from the hydro pump within the transaxle. I have seen them used for a bunch of things but they are typically used for cylinders since their flowrate and pressure usually isn't anything to get excited about.
Most GTs and lawn mowers use TuffTorq units from what I've seen. Here is a link for you to poke around on and see some specs for their transaxles units. TuffTorq is a pretty good company that typically does things right from what I have seen.
I would imagine the few times an all hydro system has been used and designed they aren't using bespoke pumps and motors so the motors tend to be higher quality industrial motors and would be overrated for their use, similar to our Case GTs. Hydrostatic transaxles on the other hand are a lot more specialized and designed more around being "good enough" for their use case.
@Gordy I have seen plenty of hydrostatic transaxles with a "PTO" output and it functions just like on ours except it's always on and always in one direction because it's a straight output from the hydro pump within the transaxle. I have seen them used for a bunch of things but they are typically used for cylinders since their flowrate and pressure usually isn't anything to get excited about.
Most GTs and lawn mowers use TuffTorq units from what I've seen. Here is a link for you to poke around on and see some specs for their transaxles units. TuffTorq is a pretty good company that typically does things right from what I have seen.
First off gentlemen thank you for the responses.
Bob sorry for being short with you didn’t mean it, just sucks my TBI, I Loved reading, loved it. Your response I would have been all over it.
MrDD that response was a little bit easier on my brain, thanks, next question , on my John Deere 790is that a hydro system, I know it’s not a hydrostatic like my John Deere 345.
Bob sorry for being short with you didn’t mean it, just sucks my TBI, I Loved reading, loved it. Your response I would have been all over it.
MrDD that response was a little bit easier on my brain, thanks, next question , on my John Deere 790is that a hydro system, I know it’s not a hydrostatic like my John Deere 345.
Joined
·
3,283 Posts
Hi Woody184,
We are good! It is difficult to describe the inner workings of a hydrostatic system. I had experience with them as a power equipment mech in the 70s and later on while in the US Army although I was an aircraft mech, crew chief, flight engineer and weapons systems mech.
Your JD 790 is a nice tractor and it has a manual transmission with a clutch, a hydraulic system with a positive displacement pump, all in the same housing using the same fluid. It also has a separate 2 speed transaxle and transfer case if it has all wheel drive.
We are good! It is difficult to describe the inner workings of a hydrostatic system. I had experience with them as a power equipment mech in the 70s and later on while in the US Army although I was an aircraft mech, crew chief, flight engineer and weapons systems mech.
Your JD 790 is a nice tractor and it has a manual transmission with a clutch, a hydraulic system with a positive displacement pump, all in the same housing using the same fluid. It also has a separate 2 speed transaxle and transfer case if it has all wheel drive.
Joined
·
3,113 Posts
What brand? I have seen some JD's with multiple quick connects front, middle and rear. But that is just multipel lifts and or pivots cylinders for the front blade. I also know some JD's with the shaft driven rear end had an optional PTO shaft out the rear.@Gordy I have seen plenty of hydrostatic transaxles with a "PTO" output and it functions just like on ours except it's always on and always in one direction because it's a straight output from the hydro pump within the transaxle. I have seen them used for a bunch of things but they are typically used for cylinders since their flowrate and pressure usually isn't anything to get excited about.
Cheers,
Gordy
1 - 12 of 12 Posts
Join the discussion
