
Conventional wisdom has been that the hydraulic reservoir was required for:
First: reservoirs are poor heat conductors and ineffective at cooling hydraulic fluid.
Second: modern filtration and cleanliness practices remove the need to “settle†particulates.
The primary purpose of modern reservoirs is to allow the suspended air contained within the fluid to dissipate, before being drawn back into the pump.
In the past, this has been accomplished by having a very large reservoir with baffles to allow the fluid to relax in order to relieve the suspended air.