Ch. 7 - CHAPTER 7 Linear Actuators Fluid Power Circuits and...

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1 CHAPTER 7 Linear Actuators Fluid Power Circuits and Controls, John S.Cundiff, 2001 Introduction | Linear actuators are commonly used in modern manufacturing plants. z Hydraulic cylinder to tilt a ladle of molten metal, z A pneumatic cylinder to install a rivet z Set of cylinders to close a box of frozen chicken. | Mobile industrial and agricultural machines also use cylinders to lift, dig, dump and position loads.
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2 Introduction | Concept of Linear actuators: z Fluid at a given pressure and flow is pumped into cylinder z Fluid pressure pushes against the piston, causing it to extend. z Velocity is a function flow rate z Force is a function pressure. Analysis of Cylinders in Parallel and Series | If two independent cylinders in different locations extend at the same time. | When cylinders are connected in parallel, the cylinder having the lowest pressure will extend first. | Consider two cases z Cylinder 1 z Cylinder 2
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3 Analysis of Cylinders in Parallel and Series Analysis of Cylinders in Parallel and Series | Cylinder 1 (Refer Fig 7.1) z No load extension of cylinder 1 requires 80 psi pressure. z Back pressure is 20 psi. z Using force balance to calculate friction force, P C1 A C1 = F f1 + P r1 A r1 z By calculation A C1 = 7.07 in 2 , A r1 = 5.3 in 2 F f1 = 80(7.07) – 20(5.3) = 459.6 lb f z Total pressure at the cap end to extend the load is P C1 = (F f1 + F L1 + P r1 A r1 )/A C1 = 646 psi
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4 Analysis of Cylinders in Parallel and Series Analysis of Cylinders in Parallel and Series | Cylinder 2 : (Refer Fig 7.1) z No-load extension of Cylinder 2 requires 65 psi z Back pressure is 15 psi. z Using force balance to calculate friction force, P C2 A C2 = F f2 + P r2 A r2 z By calculation A r2 = 3.68 in 2 and A C2 = 4.91 in 2 . F f2 = 65(4.91) – 15(3.58) = 263 lb f z Total pressure to extend the load is P C2 A C2 = F f2 + F L2 + P r2 A r2 = 615 psi
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5 Analysis of Cylinders in Parallel and Series | Consider a fixed displacement pump, refer figure 7.2 | Relief valve is set at 2000 psi. | When the DCV is shifted , the pump builds up pressure to 615 psi. | Fluid flows to Cylinder 2, causing it to extend fully. | When full extension is reached, pressure builds to 646 psi, Cylinder 1 extends and at full extension pressure builds to 2000 psi. Analysis of Cylinders in Parallel and Series | Parallel circuit supplied by a pressure- compensated pump. (Refer Figure 7.3) | The pump is set to maintain 2000 psi; thus 2000 psi is available when DCV is shifted. | Maximum pressure required is 646 psi for Cylinder 1 and 615 psi for Cylinder 2. | Both cylinders will start to move; Pressure will drop to the load pressure. | Flow will increase to Cylinder 2 and decrease to Cylinder 1, pressure will continue to decrease until 615 psi is achieved.
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6 Analysis of Cylinders in Parallel and Series | Consider two cylinders connected in series. | Pressure required to extend Cylinder
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Ch. 7 - CHAPTER 7 Linear Actuators Fluid Power Circuits and...

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