A primer on hydrostatic system filtration. Comprising a closed loop variable displacement pump and a fixed or variable displacement motor.
Filtration for this system is multiple. Some systems you will see a couple of these filters, some you will see all of them, and others you will see none.
The reservoir breather. A spin on 25 micron nominal filter will make a good breather. Spin on’s used as a breather are generally 3 times as efficient in filtering air as filtering oil. If it’s a moist area, use a glass media as opposed to cellulose, or use a desecant breather.
Suction strainer on the charge pump. I personally do not like to use suction strainers. If the reservoir is in a clean state, with an appropriate breather, leave out the strainer. If you must use a strainer, do not use a filter finer than 25 micron nominal. It is more preferable to use 100 mesh. Be sure to size this filter for the appropriate volume of oil and use the lowest bypass setting possible.
