The effect of Heat on Liquids
As you know, liquids expand when they are heated. Hydraulic oil is no different. When placed in a completely closed vessel and heated, it will exert great pressure on the vessel. Because liquids are virtually incompressible, a very small rise in temperature (and expansion) can exert enormous pressure on cylinders, accumulators, and closed reservoirs. These internal pressure can also cause much internal system damage.
Heat also cause hydraulic oil to thin out. Sometimes the oil may thin out enough to reduce the maximum pressure which the pump in a system can develop. In many cases, heat causes seals and packing to leak because of the lowered oil viscosity. Heat also causes the oil to deteriorate. Unnecessary heating of the oil in hydraulic system must be avoided. If it cannot be avoided, cooling should be provided.
Hydraulic Power Systems
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| Fig. 1-12. A basic hydraulic system |
Now that you have studied a lot of preliminary information, let’s take a look at a hydraulic power system. A hydraulic power system is a closed piping circuit in which a liquid under controlled pressure is used to do work. The basic hydraulic system shown in Fig. 1-12 is composed of the following elements:
A reservoir to store the hydraulic fluid.
A pump to provide fluid pressure to the system.
A pump to provide fluid pressure to the system.
A control valve to direct the fluid flow.
An actuating unit, such as a cylinder.
Suitable hydraulic fluid.
Piping or tubing to circulate the fluid through the system.
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| Fig. 1-13. A basic hydraulic system with accessories |
The basic hydraulic power system is usually made more complex by the addition of several other component, as shown in Fig. 1-13. These additional components enable the system to accomplish a greater range of work, and they permit the system to function with greater reliability. The following components make up the modified base hydraulic power system:
A reservoir to store the hydraulic fluid.
A pump to provide fluid pressure to the system
A pump to provide fluid pressure to the system
A filter to remove dust, chips, and other foreign particles from the fluid
A pressure regulating valve, which keeps the fluid pressure in the main part of the system at the proper level
An ACCUMULATOR, which acts as a cushion and prevents great fluid pressure variation in the entire system
Check valves, which permit fluid flow only in the desired directions.
A hand pump for operating the system manually if necessary
A pressure gage, which indicates the amount of fluid pressure in the system
A relief valve, which prevents the system pressure from rising too high if the pressure regulating valve fails
A control valve to control the flow of fluid to the actuator
An ACTUATING UNIT, such as a cylinder, which does some kind of useful work when acted upon by a hydraulic fluid under pressure
PIPING or TUBING to circulate the fluid through the system
A suitable HYDRAULIC FLUID
PIPING or TUBING to circulate the fluid through the system
A suitable HYDRAULIC FLUID
Most of these components are discussed in detail in the following lessons of this unit.
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