1 1 Hydraulic machinery and pump Hydraulic machinery are machines and tools which use fluid power to do wectric motor (by volume). They are powered by an electric motor or an engine, connected through gears, belts, or a flexible elastomeric coupling to reduce vibration. Common types of hydraulic pumps to hydraulic machinery applications are; Gear pump: cheap, durable, simple. Less efficient, because they are constant displacement, and mainly suitable for pressures below 20 MPa (3000 psi). Vane pump: cheap and simple, reliable (especially in g-rotor form). Good for higher-flow low-pressure output. 3 3 Axial piston pump: many designed with a variable displacement mechanism, to vary output flow for automatic control of pressure. There are various axial piston pump designs, including swashplate and checkball. The most common is the swashplate piston pump: A pump that is normally used for very high pressure at small flows. Piston pumps are more expensive than gear or vane pumps, but provide longer life operating at higher pressure, with difficult fluids and longer continuous duty cycles. Piston pumps make up one half of a hydrostatic transmission. Control valves Directional control valves route the fluid to the desired actuator. They usually consist of a spool inside a cast iron or steel housing. Directional control valves are usually designed to be stackable, with one valve for each hydraulic cylinder, and one fluid input supplying all the valves in the stack. The spool position may be actuated by mechanical levers, hydraulic pilot pressure, or solenoids which push the spool left or right. The main valve block is usually a stack of off the shelf directional control valves chosen by flow capacity and performance. Some valves are designed to be proportional (flow rate proportional to valve position), while others may be simply on-off. The control valve is one of the most expensive and sensitive parts of a hydraul
