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Hi Guys, Can someone explain what is difference between the two. ?
Hydrostatic Oil vs Hydraulic Oil
- Thread starter shahidmustafa197
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there isn't one.
MolaKule
Staff member
Hydraulic fluid is the energy transfer medium in all hydraulic systems and it has additional functions such as heat transfer, contamination removal, sealing, and lubrication.
Here are some hydraulic oils:
ATF
Hydrostatic
Power Steering Fluid
UTTF
They are all hydraulic oils, but have different viscosities and different additive packages, depending on the application.
Here are some hydraulic oils:
ATF
Hydrostatic
Power Steering Fluid
UTTF
They are all hydraulic oils, but have different viscosities and different additive packages, depending on the application.
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JTK
$100 Site Donor 2025
To dig a little further, many hydrostatic drives today also share the same oil as the differential and drive system. Those tend to spec more viscous 40 or 50wt oils, where hydrostatic drives that are separate from a gearbox tend to use hydraulic oil, ATF or 20wt motor oils.
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Can anyone go into more detail and explain the technical of hydrostatic drives meaning? . What is the term hydrostatic mean? Does UTTF comes under Hydrostatic oils category?
A quick Google search shows hundreds of websites and videos on that topic.
its basically variable propulsion with a fluid and pump the other option is some sort of clutch or belt drive.
Hydro= water/ fluid
Static= Motionless and/ or in equilibrium or in this case equal pressure. *I guess I should say equal flow. Pressure will change depending on load.
A static load is technically motionless (in static equilibrium) so the definition can be a little confusing at first. Angled and load bearing beams on a skyscraper for example.
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A hydraulic system means the fluid is driving the system. Such a system can be either hydrostatic or hydrodynamic.
A hydrostatic system involves low-frequency actions, like the controls of a lawn mower. Pressures come to equilibrium in a fraction of a second, while the inputs are slower than that, a half-second delay in the controls just feels normal, so high-frequency effects are not important in the design.
A hydrodynamic system is more complex, and control becomes more complicated/interesting. Air-flow around a fast-moving car or airplane, or the wake of a boat, include important hydrodynamic effects, as well as hydrostatic effects. If one wrote equations describing the motion of an element of fluid, they would have both static and dynamic terms. Even engine oil has to be more concerned with this than we do, because they operate at thousands of rpm and oil splashing (why you don't overfill your crankcase) or shock waves can be a concern.
Therefore we need some sort of "plain old" hydraulic fluid, one that won't wreck our seals. "Hydrostatic fluid" should mean fluid that's designed for low-frequency applications like lawn mowers.
A hydrostatic system involves low-frequency actions, like the controls of a lawn mower. Pressures come to equilibrium in a fraction of a second, while the inputs are slower than that, a half-second delay in the controls just feels normal, so high-frequency effects are not important in the design.
A hydrodynamic system is more complex, and control becomes more complicated/interesting. Air-flow around a fast-moving car or airplane, or the wake of a boat, include important hydrodynamic effects, as well as hydrostatic effects. If one wrote equations describing the motion of an element of fluid, they would have both static and dynamic terms. Even engine oil has to be more concerned with this than we do, because they operate at thousands of rpm and oil splashing (why you don't overfill your crankcase) or shock waves can be a concern.
Therefore we need some sort of "plain old" hydraulic fluid, one that won't wreck our seals. "Hydrostatic fluid" should mean fluid that's designed for low-frequency applications like lawn mowers.
It depends on the manufacturers recommendation. My compact tractor uses the same trans oil in the gear transmission and the Hydrostatic transmission. The movers use what ever engine oil that meets the temperature of the climate and operating temps on the viscosity charts.
The easiest analogy I have for a hydrostatic system is a bicycle...
Think of the pump as the front chain ring - as you increase the displacement (move to a larger chain ring) you pump fluid faster for a given input speed (chain moves faster) and move to a faster gear ratio. If the pump is in neutral, it spins, but doesn't pump fluid (the chain is around the hub, but off the chain rings ;-))
Think of the motor as the rear cassette - as you increase the displacement (move to a larger sprocket) you gain tractive effort, but reduce output speed. If you decrease motor displacement, you increase speed, but reduce output force "tractive effort"
Think of the fluid like the chain...in an ideal case, the same fluid goes around and around in a loop just like the chain - in a real system there is loop flushing, and control losses, but that would be a more advanced topic.
A hydrostatic transmission is just a fluid based CVT
Think of the pump as the front chain ring - as you increase the displacement (move to a larger chain ring) you pump fluid faster for a given input speed (chain moves faster) and move to a faster gear ratio. If the pump is in neutral, it spins, but doesn't pump fluid (the chain is around the hub, but off the chain rings ;-))
Think of the motor as the rear cassette - as you increase the displacement (move to a larger sprocket) you gain tractive effort, but reduce output speed. If you decrease motor displacement, you increase speed, but reduce output force "tractive effort"
Think of the fluid like the chain...in an ideal case, the same fluid goes around and around in a loop just like the chain - in a real system there is loop flushing, and control losses, but that would be a more advanced topic.
A hydrostatic transmission is just a fluid based CVT
What are you using this in? In a small tractor, usually you need UTTF or UTF like Spirax S4 TXM which is fine for a hydrostatic transmission, the hydraulics, final drives, and wet brakes. I wouldn't use plain hydraulic oil in a tractor due to lack of additives for the brakes and final drive, but I would use UTF in a simple hydraulics system in a pinch as the additives won't likely bother anything.
I believe some bulldozers (and maybe other heavy equipment) have HST's with its own oil, seperate from the final drives, or other hydraulics. I would follow what ever specs the manufacturer recommends those HST's as they could be quite specialized?.
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