hydraulics vs hydrostatics?

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jklingel

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Obviously, I am new to this stuff. Why, if both terms refer to the movement of fluids, do I see reference to hydraulic oil AND hydrostatic oil? I also seem to see references in various threads to hydraulic pumps and "hydrostats", which are apparently pumping fluid. Thanks. Confused in Frb.
 

skidsteer.ca

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John
Hydraulics go to move the boom lift and bucket tilt or to your aux couplers.
Hydrostatics are what drives your wheels.
Both generally use the same oil and the same reservoir and the systems are tied to each other, but serve 2 different purposses.
Hydraulics are a fixed displacement pump feeding hyd cylinders or attachments, where as hydrostatics are variable displacement pumps supplying fixed displacement motors. (generally)
Hope tha helps a bit.
Ken
 
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jklingel

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John
Hydraulics go to move the boom lift and bucket tilt or to your aux couplers.
Hydrostatics are what drives your wheels.
Both generally use the same oil and the same reservoir and the systems are tied to each other, but serve 2 different purposses.
Hydraulics are a fixed displacement pump feeding hyd cylinders or attachments, where as hydrostatics are variable displacement pumps supplying fixed displacement motors. (generally)
Hope tha helps a bit.
Ken
Ken: Roger that. Thanks. One more mystery solved. john
 

Tazza

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Ken: Roger that. Thanks. One more mystery solved. john
Exactly what Ken said.
Basically hydraulics are for lift/tilt and hydrostatics refer to your drive system. The drive system uses a variable displacement pump. This makes for a MUCH smoother ride and when you don't need oil it won't pump any. This reduces load on your engine and lowers the heat generated as oil is only pumped when you need it.
I have seen hydraulic drive machines and they buck around like mad, hydrostatic drive on the other hand is smooth.
 

skidboy

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Exactly what Ken said.
Basically hydraulics are for lift/tilt and hydrostatics refer to your drive system. The drive system uses a variable displacement pump. This makes for a MUCH smoother ride and when you don't need oil it won't pump any. This reduces load on your engine and lowers the heat generated as oil is only pumped when you need it.
I have seen hydraulic drive machines and they buck around like mad, hydrostatic drive on the other hand is smooth.
Bobcat call their oil hydrostat oil and not hydraulic oil.This is because their recommendation is for a 15/40 oil,not a hydraulic oil.
 
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jklingel

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Bobcat call their oil hydrostat oil and not hydraulic oil.This is because their recommendation is for a 15/40 oil,not a hydraulic oil.
Got it. Thanks for the clarification. Interestingly, there was a discussion earlier about using engine oil for hydraulic oil. That was a new one on me, but when I got my new JD I RTFM'd and saw that the same oil is "recommended" everywhere in the machine; engine, hydraulics, chain case. Others can be sub'd, of course, but one oil was always on the recommended list. Supreme 50 Plus or something. Interesting to me, anyway.
 

Bandit1047

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Jan 13, 2008
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Got it. Thanks for the clarification. Interestingly, there was a discussion earlier about using engine oil for hydraulic oil. That was a new one on me, but when I got my new JD I RTFM'd and saw that the same oil is "recommended" everywhere in the machine; engine, hydraulics, chain case. Others can be sub'd, of course, but one oil was always on the recommended list. Supreme 50 Plus or something. Interesting to me, anyway.
I was watching RFDTV last night and they had two lubrication specialist from John Deere on the show. They talked about their hydraulic lubricants and their super 50 motor oil. You can go to www.johndeere.com and learn about their lubricants. I have not been on it, but plan on going to take a look. Joe
 

thetool

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Mar 22, 2008
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This is one of my favorite subjects, so I'll chime in.
The way I unerstand it, a hydrostatic system is one which is a function more of pressure than flow. Hence, "static", or stationary, with pressure being the applied force.
Hydrostatic systems, relative to hydraulic systems are generally low flow, high pressure, where components(pumps and motors) can be designed for low rpm, high torque, and use the same power source as does the hydraulic system which makes it ideal for the drive.
There are still hydraulic drive machines-like mini-excavators with fixed-displacement gear pumps and hydraulic drive motors(high rpm with planetary gear reduction).
Hydraulic systems rely more on flow than pressure. Higher flow equals faster linear motion(stroking a cylinder). Pressure is still required for digging or lifting force, but pressures are generally lower than hydrostatics sharing the power unit.
And there are load-sensing hydraulic systems that use variable-displacement pumps that are similar in design to hydrostatic pumps, which require complex controls but get you closer to the best of both systems.
I believe the future of our stuff is no more distinction between these two system types. Everything bigger than a walk-behind is going to have variable-displacement, load-sensing pumps that operate the drive as well as the work equipment with no more engine-lugging, black smoke, fuel inefficiency, and requiring engineering degrees and tall dollars to repair.
 
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jklingel

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Feb 8, 2008
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This is one of my favorite subjects, so I'll chime in.
The way I unerstand it, a hydrostatic system is one which is a function more of pressure than flow. Hence, "static", or stationary, with pressure being the applied force.
Hydrostatic systems, relative to hydraulic systems are generally low flow, high pressure, where components(pumps and motors) can be designed for low rpm, high torque, and use the same power source as does the hydraulic system which makes it ideal for the drive.
There are still hydraulic drive machines-like mini-excavators with fixed-displacement gear pumps and hydraulic drive motors(high rpm with planetary gear reduction).
Hydraulic systems rely more on flow than pressure. Higher flow equals faster linear motion(stroking a cylinder). Pressure is still required for digging or lifting force, but pressures are generally lower than hydrostatics sharing the power unit.
And there are load-sensing hydraulic systems that use variable-displacement pumps that are similar in design to hydrostatic pumps, which require complex controls but get you closer to the best of both systems.
I believe the future of our stuff is no more distinction between these two system types. Everything bigger than a walk-behind is going to have variable-displacement, load-sensing pumps that operate the drive as well as the work equipment with no more engine-lugging, black smoke, fuel inefficiency, and requiring engineering degrees and tall dollars to repair.
Good to know. Thanks. j
 
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