Hydraulic system components

Pilot Pressure Auxiliary pressure used to actuate or control hydraulic system components. 

Hydraulic components (application and function of all hydraulic system components)... 

The application of maintenance decision diagram for hydraulic systems components is shown in Table 6 taking as an example of application the analysis of the Electric Motor A.C. 

Typical clearances employed on hydraulic system components range from 15 0 pm for low pressure components, down to about 5 pm for high pressure components (or even less for miniature valves), as shown in Table 5.10. Most components will have critical areas, which are particularly subject to clearance problems. Examples include ... 

Control of quality and state of engine parts, components of electric, pneumatic, hydraulic systems, load-bearing elements Investigations of parts and units failure causes... 

The bulk of hydrauhc fluids is specified and purchased on bid. Specifications and approval fists are issued by some manufacturers of hydraulic pumps and system components that require lubrication as well as power for control signal transmission. U.S. government military specifications for hydraulic fluids are fisted ia Table 12, and ASTM tests that are applicable to hydraulic fluids iaclude the foUowiag ... 

To transmit and control power through pressurized fluids, an arrangement of interconnected components is required. Such an arrangement is commonly referred to as a system. The number and arrangement of the components vary from system to system, depending on the particular application. In many applications, one main system supplies power to several subsystems, which are sometimes referred to as circuits. The complete system may be a small, compact unit or a large, complex system that has components located at widely separated points within the plant. The basic components of a hydraulic system are essentially the same regardless of the complexity of the system. Seven basic components must be in a hydraulic system. These basic components are ... 

This is the energy source for hydraulic systems. It converts electrical energy into dynamic, hydraulic pressure. In almost all cases, hydraulic systems utilize positive displacement pumps as their primary power source. These are broken down into two primary sub-classifications constant-volume or variable-volume. In the former, the pumps are designed to deliver a fixed output (i.e. both volume and pressure) of hydraulic fluid. In the later, the pump delivers only the volume or pressure required for specific functions of the system or its components. 

Most hydraulic systems use a positive displacement pump to generate energy within the system. Unless the pressure is controlled, these pumps will generate excessive pressure that can cause catastrophic failure of system component. A relief valve is always installed downstream of the hydraulic pump to prevent excessive pressure and to provide a positive relief should a problem develop within the system. The relief valve is designed to open at a preset system pressure. When the valve opens, it diverts flow to the receiver tank or reservoir. 

A similar action takes place in a fluid power system in which the fluid takes the place of the projectile. For example, the pump in a hydraulic system imparts energy to the fluid, which overcomes the inertia of the fluid at rest and causes it to flow through the lines. The fluid flows against some type of actuator that is at rest. The fluid tends to continue flowing, overcomes the inertia of the actuator, and moves the actuator to do work. Friction uses up a portion of the energy as the fluid flows through the lines and components. 

Fluid power equipment is designed to reduce friction as much as possible. Since energy cannot be destroyed, some of the energy created by both static pressure and velocity is converted to heat energy as the fluid flows through the piping and components within a hydraulic system. As friction increases, so does the amount of dynamic and static energy that is converted into heat. 

As the pump provides flow, it transmits a force to the fluid. When the flow encounters resistance, this force is changed into pressure. Resistance to flow is the result of a restriction or obstruction in the flow path. This restriction is normally the work accomplished by the hydraulic system, but there can also be restrictions created by the lines, fittings or components within the system. Thus, the... 

Cleanliness in hydraulic systems has received considerable attention recently. Some hydraulic systems, such as aerospace hydraulic systems, are extremely sensitive to contamination. Fluid cleanliness is of primary importance because contaminants can cause component malfunction, prevent proper valve seating, cause wear in components, and may increase the response time of servo valves. Fluid contaminants are discussed later in this chapter. 

A hydraulic system must have a reserve of fluid in addition to that contained in the pumps, actuators, pipes and other components of the system. This reserve fluid must be readily available to make up losses of fluid from the system, to make up for compression of fluid under pressure, and to compensate for the loss of volume as the fluid cools. This extra fluid is contained in a tank usually called a reservoir. A reservoir may sometimes be referred to as a sump tank, service tank, operating tank, supply tank or base tank. 

Clean hydraulic fluid is essential for proper operation and acceptable component life in all hydraulic systems. While every effort must be made to prevent contaminants from entering the system, contaminants that do find their way into the system must be removed. Filtration devices are installed at key points in fluid power systems to remove the contaminants that enter the system along with those that are generated during normal operations of the system. 

The conversion of hydraulic force to mechanical work generates excessive heat. This heat must be removed from the hydraulic fluid to prevent degradation of the fluid and possible damage to system components. 

The control and application of fluid power would be impossible without suitable means of transferring the hydraulic fluid between the reservoir, the power source, and the points of application. Fluid lines are used to transfer the hydraulic fluid, fittings are used to connect lines to system components, and seals are used in all components to prevent leakage. This chapter is devoted to these critical system components. 

With the trend toward higher pressures in hydraulic systems, the loads on unbalanced pump and motor components become greater and this, coupled with the need for closer fits to contain the higher pressures, can introduce acute lubrication problems. Pumps, one of the main centers of wear, can be made smaller if they can run at higher speeds or higher pressures, but this is only possible with adequate lubrication. For this reason, a fluid with good lubrication properties is used so that hydraulics is now almost synonymous with oil hydraulics in general industrial applications. Mineral oils are inexpensive and readily obtainable while their viscosity can be matched to a particular job. 

The hydraulic fluid continuously lubricates the components of a hydraulic system, which must, of course, be suitable for this purpose. Many ball and roller bearings are grease-packed for life, or need attention at lengthy... 

The third class of hydraulic fluids discussed in this profile is the polyalphaolefins. Polyalphaolefins are synthetic hydrocarbons that are made by oligomerizing alphaolefins such as 1-decene (see Chapters 3,4, and 5). Aliphatic hydrocarbons are the principal components of both mineral oils and polyalphaolefins, but the array of hydrocarbons with differing molecular weights is much narrower in polyalphaolefins than in mineral oils. Certain polyalphaolefins maintain good operational characteristics at low temperatures and have been proposed for use in hydraulic systems in U.S. military aircraft (Kinkead et al. 1992b). 

Polyalphaolefin Hydraulic Fluids. Polyalphaolefm hydraulic fluids have properties comparable to the most effective components in mineral oil and are used in applications identical to mineral oil hydraulic fluids (Chrisope and Landry 1993 Papay 1993 Shubkin 1993 Wills 1980). Polyalphaolefins are more expensive than mineral oil, and this may limit their use in industry. In addition, polyalphaolefin hydraulic fluids are used in military applications such as aircraft and missile hydraulic systems, tank recoil and hydraulic systems, and aerospace test stands (Shubkin 1993). 

System component Filter beds, media, backwash mechanism, pumps, and controls. The filter beds were sized for hydraulic loading of 81 L/min/m2 (2gpm/ft2). 

Method The process used for oily waste stream after emulsion breaking-gravity oil separation. System component Filter modules sized on the basis of hydraulic loading of 1 L/min/m2. 

Method A packed-bed throwaway system to remove organic pollutants from oily waste stream. System component A contactor system, and a pump station designed for a contact time of 30 min and hydraulic loading of 162 L/min/m2 (4gpm/ft2). 

Terpolymers in which the acrylate monomer is the major component are useful as ethylene-acrylate elastomers (trade name Vamac) [Hagman and Crary, 1985]. A small amount of an alkenoic acid is present to introduce sites (C=C) for subsequent crosslinking via reaction with primary diamines (Sec. 9-2d). These elastomers have excellent oil resistance and stability over a wide temperature range (—50 to 200°C). They are superior to nitrile and chloroprene rubbers. Although not superior to silicone and fluorocarbon elastomers, they are less costly uses include automotive (hydraulic system seals, hoses) and wire and cable insulation. 

Oils used to lubricate machinery, motors, hydraulic systems and other mechanical devices can sometimes contaminate fuel systems. These oils often carry with them low levels of the metals which wear from the lubricated surfaces of the mechanical components. Some common wear metals and possible sources of origin are listed in TABLE 4-12. 

Nuclear Boiler Assembly. This assembly consists of the equipment and instrumentation necessary to produce, contain, and control the steam required by the turbine-generator. The principal components of the nuclear boiler are (1) reactor vessel and internals—reactor pressure vessel, jet pumps for reactor water circulation, steam separators and dryers, and core support structure (2) reactor water recirculation system—pumps, valves, and piping used in providing and controlling core flow (3) main steam lines—main steam safety and relief valves, piping, and pipe supports from reactor pressure vessel up to and including the isolation valves outside of the primary containment barrier (4) control rod drive system—control rods, control rod drive mechanisms and hydraulic system for insertion and withdrawal of the control rods and (5) nuclear fuel and in-core instrumentation,... 

Modifed PTFE can be used in practically all applications, where the conventional polymer is used. In addition to that, new applications are possible because of its improved flow and overall performance. In the chemical process industry, it is used for equipment linings, seals, gaskets, and other parts, where its improved resistance to creep is an asset. In semiconductor manufacturing, modified PTFE is used in fluid handling components and in wafer processing components. Typical applications in electrical and electronic industries are connectors and capacitor films. Other applications are in unlubricated bearings, laboratory equipment, seal rings for hydraulic systems, and antistick components.103... 

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