Figure 3.3 gives an overview of a basic hydraulic system.
A typical hydraulic power system includes the following components:
1. Electric motor
2. Hydraulic pump
3. Strainers and filters
4. Pressure gauge
5. Pressure relief valves
6. Check valve
7. Direction control valve
8. Hydraulic actuator
9. Reservoir
1. Electric Motor: An electric motor is used to drive the pump.
2. Hydraulic Pump: Hydraulic pumps convert mechanical energy from a prime mover (engine or electric motor) into hydraulic (pressure) energy.The pressure energy is used then to operate an actuator. Pumps push on a hydraulic fluid and create flow.
3. Strainers and Filters: To keep hydraulic components performing correctly, the hydraulic liquid must be kept as clean as possible. Foreign matter and tiny metal particles from normal wear of valves, pumps, and other components are going to enter a system. Strainers, filters, and magnetic plugs are used to remove foreign particles from a hydraulicliquid and are effective as safeguards against contamination.
Strainers: A strainer is the primary filtering system that removes large particles of foreign matter from a hydraulic liquid. Even though its screening action is not as good as a filter’s, a strainer offers less resistance to flow.
Filters: A filter removes small foreign particles from a hydraulic fluid and is most effective as a safeguard against contaminates. They are classified as full flow or proportional flow:
(a) Full-Flow Filter: In a full-flow filter, all the fluid entering a unit passes through a filtering element. Although a full-flow type provides a morepositive filtering action, it offers greater resistance to flow, particularly when
it becomes dirty.
(b) Proportional-Flow Filters: This filter operates on the venturi principle in which a tube has a narrowing throat (venturi) to increase the velocity of fluid flowing through it. Flow through a venturi throat causes a pressure drop at the narrowest point. This pressure decrease causes a sucking action that draws a portion of a liquid down around a cartridge through a filter element and up into a venturi throat.
4. Pressure Gauge: A pressure gauge tells us the pressure of fluid going
into the valve.
5. Pressure Relief Valves: Relief valves are the most common type of pressure-control valves. The relief valves function may vary, depending
on a system’s needs. They can provide overload protection for circuit components or limit the force or torque exerted by a linear actuator or rotary motor. The internal design of all relief valves is similar. The valves consist of two sections: a body section containing a piston that is retained on its seat by a spring(s), depending on the model, and a cover or pilot-valve section that hydraulically controls a body piston’s movement. The adjusting screw adjusts this control within the range of the valves. Valves that provide emergency overload protection do not operate as often because other valve types are used to load and unload a pump. However, relief valves should be cleaned regularly by reducing their pressure adjustments to flush out any possible sludge deposits that may accumulate. Operating under reduced pressure will clean out sludge deposits and ensure that the valves operate properly after the pressure is adjusted to its prescribed setting.
6. Check Valve: Check valves are the most commonly used in fluidpowered systems. They allow flow in one direction and prevent flow in the other direction. They may be installed independently in a line, or they may be incorporated as an integral part of a sequence, counterbalance, or pressure-reducing valve. The valve element may be a sleeve, cone, ball, poppet, piston, spool, or disc. Force of the moving fluid opens a check valve; backflow, a spring, or gravity closes the valve.
7. Direction Control Valve: Directional-control valves are devices used to change the flow direction of fluid within a pneumatic/hydraulic circuit. They control compressed-air flow to cylinders, rotary actuators, grippers,and other mechanisms in packaging, handling, assembly, and countless other applications.
8. Hydraulic Actuator: A hydraulic actuator receives pressure energy and converts it to mechanical force and motion. An actuator can be linear or rotary. A linear actuator gives force and motion outputs in a straight line. It is more commonly called a cylinder but is also referred to as a ram, reciprocating motor, or linear motor. A rotary actuator produces torque and rotating motion. It is more commonly called a hydraulic motor or motor.
9. Reservoir: A reservoir stores a liquid that is not being used in a hydraulic system. It has many other important functions as well.
1.It also allows gases to expel and foreign matter to settle out from a liquid.
2.It functions as a cooler.
3.It functions as a “coarse strainer,” providing sedimentation of impurities.
4.It functions as an air and water separator.
5.It functions as a foundation for pumps, etc.
A properly constructed reservoir should be able to dissipate heat from the oil, separate air from the oil, and settle out contaminates that are in it. It should be high and narrow rather than shallow and broad. The oil level should be as high as possible above the opening to a pump’s suction line. This prevents the vacuum at the line opening from causing a vortex or whirlpool effect, which would mean that a system is probably taking in air.Most mobile equipment reservoirs are located above the pumps. This creates a flooded-pump-inlet condition. This condition reduces the possibility of pump cavitation; a condition where all the available space is not filled and often metal parts will erode. Most reservoirs are vented to the atmosphere. A vent opening allows air to leave or enter the space above the oil as the level of the oil goes up or down. This maintains a constant atmospheric pressure
above the oil.