Here is a quote from the August 2010 issue of Hydraulics & Pneumatics
. A hydrostatic transmission (HST) exists any time a hydraulic pump is connected to and dedicated to one or more hydraulic motors. Versatility is achieved by making either or both the pump and motor(s) variable displacement. The result is a continuously variable transmission (CVT).
So, hydrostatic transmissions are a vital part of many hydraulic systems but are not quite like a single component like a cylinder or pump. Instead, they are a subsystem made up of components.
In this article, our resident expert, Jack Johnson, gives a clear and concise explanation of that they are and what they do. The article can be found on our website also under the title Understanding Hydrostatic Transmissions
If you get a chance to review this article, you might also be interested in taking a look at Jack's new book which is featured in the article. This book can be purchased at the H&P Bookstore