Synthetic Hydraulic Fluids

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Synthetic fluids on the whole have excellent fire resistant properties. Many of these fluids may be used at high temperatures, and some are quite expensive. Such fluids are named after their base stocks, that is, the predominant material, and their formulations are chemically involved. Phosphate ester base fluids are used in both aircraft and industrial […]

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Petroleum Base Fluids

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Petroleum base oils are by far the most commonly used hydraulic fluid. Petroleum, a complex mixture of chiefly hydrocarbons, must be highly refined to produce a fluid with viscosity characteristics suitable for hydraulic control systems. Such mineral, turbine, or light oils, as they are often called, have a long history of satisfactory performance as a […]

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Disadvantages of Hydraulic Control

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Although hydraulic controls ofl’er many distinct advantages, several disadvantages tend to limit their use. Major disadvantages are thie following: 1. Hydraulic power is not so readily available as that of electrical powe:r This is not a serious threat to mobile and airborne applications but moist certainly afi’ects stationary applications. 2. Small allowable tolerances results in […]

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Advantages of Hydraulic Control

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There are many unique features of hydraulic control compared to other types of control. These are fundamental and account for the wide use of hydraulic control. Some of the advantages are the following: 1. Heat generated by internal losses is a basic limitation of any machine. Lubricants deteriorate, mechanical parts seize, and insulation breaks down […]

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Fail-Safe Circuits

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Fail-Safe Circuits

Fail-safe circuits are those designed to prevent injury to the operator or damage to the equipment. In general, they prevent the system from accidentally falling on an operator and also prevent overloading of the system. In following sections we shall discuss two fail-safe circuits: One is protection from inadvertent cylinder extension and other is fail-safe […]

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Speed Control of a Hydraulic Motor

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Speed Control of a Hydraulic Motor

Figure 1.12 shows the speed control circuit of a hydraulic motor using a pressure-compensated FCV.The operation is as follows: – In a spring-centered position of the tandem four-way valve, the motor is hydraulically blocked. – When the valve is actuated to the left envelope, the motor rotates in one direction. Its speed can be varied […]

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Speed Control of a Hydraulic Cylinder

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Speed Control of a Hydraulic Cylinder

The speed control of a hydraulic cylinder circuit can be done during the extension stroke using a flow-control valve (FCV). This is done on a meter-in circuit and meter-out circuit as shown in Fig. 1.11. Refer to Fig. 1.11(a). When the DCV is actuated, oil flows through the FCV to extend the cylinder. The extending […]

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Cylinders in Parallel

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Cylinders in Parallel

Figure 1.10 shows a hydraulic circuit in which two cylinders are arranged in parallel. When the two cylinders are identical, the loads on the cylinders are identical, and then extension and retraction are synchronized. If the loads are not identical, the cylinder with smaller load extends first. Thus, the two cylinders are not synchronized. Practically, […]

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Locked Cylinder Using Pilot Check Valves

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Locked Cylinder Using Pilot Check Valves

A check valve (Fig. 1.9) blocks flow in one direction but allows free flow in the opposite direction. A pilot-operated check valve permits flow in the normally blocked opposite direction when pilot pressure is applied at the pilot pressure port of the valve. Pilot-operated check valves are used to lock the cylinder, so that its […]

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