Archive for May, 2010

Hydraulic Servo Valve Port Shape

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Hydraulic Servo Valve Port Shape

Servo valve bodies are machined with three common port shapes as shown in Fig. 11.13. The effect of port shape on flow is shown in Fig. 11.14. A full annulus port gives the highest flow per unit of spool displacement or, correspondingly, per unit of current input to the torque motor. The valve flow characteristics …

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Jet Pipe Hydraulic Servo Valve Spool

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Jet Pipe Hydraulic Servo Valve Spool

The jet pipe design (Fig. 11.12) is less sensitive to contamination than the flapper nozzle. This design uses fluidics technology. A nozzle, attached to the armature, directs a stream of fluid (pressure Ps) at two receivers. When the nozzle is centered (no current through the armature coils to cause it to turn), the two receivers …

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Double Flapper Nozzle Shifting Servo Valve Spool

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Double Flapper Nozzle Shifting Servo Valve Spool

A diagram of the double flapper nozzle is shown in Fig. 11.10. Supply pressure (the setting of the relief valve or the setting of a pressure compensated pump) is supplied to the points identified with Ps (Fig. 11.10). Fluid flows across the fixed orifices and enters the center manifold. Orifices are formed on each side …

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Hydraulic Servo Systems

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Hydraulic Servo Systems

There are four basic servo systems as shown in Fig. 11.7. The two servo-actuator systems are (1) valve-motor and (2) valve-cylinder. These systems are often referred to as servo motors and servo cylinders. The recommended procedure is to mount the valve directly on the actuator. This avoids a column of compressed fluid in the lines …

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Hydraulic Servo Valve Feedback

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Feedback is an intuitive concept. Each time we reach for an object, we slow our hand as it approaches the object so that it is captured with minimal impact. There is visual feedback that our brain uses to control the arm and ensure that it reaches the target and stops. An equipment operator, for example …

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Hydraulic Pilot-Operated Check Valve

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Hydraulic Pilot-Operated Check Valve

The pilot-operated check valve is shown in Fig. 7.11. For flow in the forward direction, this valve operates just like a normal check valve. Pilot line pressure holds the valve open for fluid in the reverse direction. If the pilot line is pressurized (for example, if there is pressure at P0 in Fig. 7.10), the …

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Hydraulic Presses Machines Circuit

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Hydraulic Presses Machines Circuit

Presses are used for molding, shaping, shearing, and many other operations. Some of the older manufacturing plants have lines of presses connected in parallel as shown in Fig. 7.9. To give perspective to the problem, let us assume that the press cylinder has a 30-in. bore and 10-in. stroke. It needs to close in 30 …

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Gear-Type Hydraulic Flow Divider

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Gear-Type Hydraulic Flow Divider

The gear-type flow divider functions like two gear motors with their shafts rigidly attached. We will consider first the case in which both motors have the same displacement. Since their shafts are attached, they both have to turn at the same speed; consequently, the same flow goes through both sides. Except for leakage, which is …

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Orifice-Type Hydraulic Flow Divider

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Theoretically, the orifice on both sides of the flow divider can be adjusted so that the ?P across the orifice plus the load ?P is equal on both sides. Then, the flow from the pump will divide equally, and both cylinders will extend at the same time. If the cylinders are the same size, they …

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Servo Valve Electrical Circuit

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Servo Valve Electrical Circuit

Some explanation of the electrical circuit required for a servo valve is presented here to help readers understand how the servo valve in the servo pump operates when it is used in a closed-loop transmission.  The key features of the electrical circuit for a closed-circuit, closed-loop hydrostatic transmission are shown above the dotted line in …

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