A hydraulic manifold is a component which regulates fluid flow between pumps and actuators and other components in a hydraulic system. It is like a switchboard in an electrical circuit because it lets the operator control how much fluid flows between which components of a hydraulic machinery. For example, in a backhoe loader a manifold turns on or shuts off or diverts flow to the telescopic arms of the front bucket and the back bucket. The manifold is connected to the levers in the operator's cabin which the operator uses to achieve the desired manifold behaviour.
A manifold is composed of assorted hydraulic valves connected to each other. It is the various combinations of states of these valves that allow complex control behaviour in a manifold.
A hydraulic or hydrostatic drive system or hydraulic power transmission is a drive- or transmission system that use of a hydraulic fluid under pressure to drive machinery.
Such a system basically consists of:
Generator part of the transmission, in general a hydraulic pump, driven by an electric motor, a combustion engine or a windmill.
Valves, filters, piping etc. to guide and control the system
Motor part of the transmission a hydraulic motor or hydraulic cylinder to drive the machinery.
Hydrostatic means that the energy comes from the flow and the pressure, but not from the kinetic energy of the flow.
These valves are usually very heavy duty to stand up to high pressures. Some special valves can control the direction of the flow of fluid and act as a control unit for a system.