Ch. 12 - CHAPTER 12 PROPORTIONAL VALVES Fluid Power...

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1 CHAPTER 12 PROPORTIONAL VALVES Fluid Power Circuits and Controls, John S.Cundiff, 2001 Introduction ± Proportional valves were developed for applications where the precision of a servo valve is not needed, but more accuracy is needed than a conventional valves.
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2 Introduction Types of Proportional Valves ± Types of Proportional valves: ± Force-Controlled ² When a conventional solenoid is energized, the plunger travels it’s full stroke and a given force is developed at the moment actuation occurs. ² With a Force-Controlled proportional valve, provision is provided to increase the force output by the solenoid proportional to input current signal.
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3 Types of Proportional Valves ± Stroke-Controlled ² With a Stroke-Controlled valve, the stroke distance is proportional to the input signal. ² Both types provide an opening of the valve proportional to the magnitude of the milliamp current applied to the valve. Types of Proportional Valves ± Force produced by solenoid is almost a linear function of input current.
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4 Types of Proportional Valves ± Proportional Pilot- Operated Relief Valve ² A functional diagram of Pilot-operated relief valve with a force solenoid replacing the manually adjusted pilot spring. Types of Proportional Valves ± Proportional Pressure Reducing Valve ² Cross-sectional view of proportional pressure reducing valve.
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5 Types of Proportional Valves ± Proportional Directional Control Valve ± It has many of the same features of conventional four- way, three position DCV. ± Graphic symbols have orifices to indicate that the spool has been machined to allow metering of the flow. ± Spool in a proportional DCV can be machined with different shaped notches in the spool lands. Types of Proportional Valves ± Typically these are triangular notches. ± When the spool is shifted, openings are produced as shown in Fig 12.7.
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Types of Proportional Valves ± Note the matched notches, flow is metered when the spool is shifted in both directions. ± Overlap is generally 10% of total spool travel. Types of Proportional Valves ± In most valves, spool movement stops just short of full open position so that some metering function is maintained. ± Because metering notches are
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Ch. 12 - CHAPTER 12 PROPORTIONAL VALVES Fluid Power...

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