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My apologies, as once again.....it's not an antique...

B

Bob Bancroft

Well-known Member
Location
Aurora NY
It seems that most(if not all) hydrostatic drive units use a gerotor type charge pump- while the rest of the machine most likely uses a gear pump for operating cylinders.
Why, on both?
 
The gear rotor charge pump as its name implies, "Charge Pump" pumps oil to another pump most likely a swash plate type pump used in hydrostat systems. A Swash plate type pump has a variable output thus giving the machine different speeds by pushing the pedal or lever farther or pulling the lever or pedal and reversing the oil flow to the drive motor allowing the machine to back up.
Swash Plate Type Pumps
 
The reason a swash plate type pump needs a charge pump is because the swash plate pump is always in the neutral (non-pumping) position and may not have enough suction to pull oil into its cavities to pump. So the charge pump does this for it.
 
Thank you for the replies. I apparently wasn't clear with my question. I wasn't asking why a "charge" pump was needed. I was asking why the charge pump for a hydrostatic drive is typically a gerotor- as opposed to the gear pump, which is typically used for hydraulic system(valves/cylinders).
 
I am 90% sure the charge pump on our L2 Gleaner is a gear pump. There is just one pump, for power steering, hyd and the hydro.
 
You were clear with your first question, many of us skim read and the result is an answer not connected to your question. As to g-rotor pumps..they are compact and fit well in the confines of a swash plate hydrostatic pump. A regular gear pump for charge would add bulk. I haven't seen high volume high pressure pumps in g-rotor, maybe g-rotors are less efficient??
 
I would say it is due to the neat way it can be adapted to the input shaft in most cases. A gear pump would have to be offset to one side or the other. However, like in the large frame IH hydrostatic tractors, they use the same style gear pump for the charge of the hydrostatic drive as they use for the balance of the hydraulic system.
 
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