Basic Hydraulics. Module 4: Flow Control Valves & Pressure Relief Valves. Academic Services PREPARED BY. January 2012

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1 Basic Hydraulics Module 4: Flow Control Valves & Pressure Relief Valves PREPARED BY Academic Services January 2012 Applied Technology High Schools, 2011

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3 ATM 1122 Basic Hydraulics Module 4: Flow control valves and pressure relief valves Module Objectives After the completion of this module, the student will be able to: 1. Explain the functions of flow control valves. 2. Distinguish between the different types of flow control valves 3. Identify the symbols of different flow control valves 4. Explain the function of Pressure relief valve. 5. Identify the symbol of a Pressure relief valve. 6. Simulate a hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve. 7. Explain the operation of the hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve 8. Assemble the hydraulic circuit that controls the speed of a double acting cylinder by using a two way flow control valve Module Contents Module Objectives Flow Control Valves: The one way flow control valve Two way flow control valve Pressure Control Valves Pressure relief valve Practical Task I Practical Task II Embossing machine Procedure of solution:... 6 References... 8

4 ATM 1112 Basic Hydraulics 1 Flow Control Valves: The flow control valve is used to control the speed of a cylinder or a motor by controlling the amount of fluid flow rate passing through it. As explained in Module 1, the flow rate is the volume of fluid that moves through the system in a given period of time. Flow rates determine the speed at which the output device (e.g., a cylinder) will operate. The flow velocity of a fluid is the distance the fluid travels in a given period of time which is the extension speed of the cylinder. Q v A v : Extension velocity of a cylinder ( m / s ) Q : Flow rate ( 2 A : Area ( m ) 3 m / s ) 1.1 The one way flow control valve The one way flow control valve (Fig.4.1.a) is used to control the flow rate in the hydraulic circuit only in one direction (throttling part: from A to B), and allows a free flow in the opposite direction (from B to A). Throttling is achieved by adjusting the valve screw The ISO symbol of this valve is shown in Fig.4.1.b. (a) one way flow control valve (b) ISO symbol of the one way flow control valve Fig.4.1: (a) One way flow control valve. (b) ISO symbol of one way flow control valve. Adjusting throttle screw 2 Module 4: Flow control valves & pressure control valves

5 ATM 1122 Basic Hydraulics 1.2 Two way flow control valve Adjusting throttle screw The two way control valve (Fig. 4.2) provides a constant flow rate in the case of variable loads. This valve has two ports (A) and (P) and adjusting throttle screw. The ISO symbol of this valve is shown in Fig.4.2.b Fig 4.2 (a) Two way flow control valve Fig 4.2 (b) ISO symbol of two way flow control valve 2 Pressure Control Valves These valves are used to control and regulate the pressure in the hydraulic system. 2.1 Pressure relief valve Pressure relief valve (Fig.4.3.a) is used mainly as safety valve. It prevents the maximum permissible pressure in the hydraulic system from being exceeded. If the maximum pressure is reached at the valve inlet, the valve outlet is opened and the oil will flow out to the tank. The valve remains open until the built-in spring closes it after reaching the preset pressure in accordance with the spring characteristic. The ISO symbol of the pressure relief valve is shown in Fig.4.3.b where: P: input pressure, T: tank port (a) (b) Pressure relief valve ISO symbol of the pressure relief valve Fig.4.3: (a) Pressure relief valve. (b) ISO symbol of the pressure relief valve Module 4: Flow control valves & pressure control valves 3

6 ATM 1112 Basic Hydraulics 3 Practical Task I 3.1 Controlling the speed of a double acting cylinder using a two way flow control valve. Background: The function of a two way flow control valve is to maintain a constant speed of the actuator under variable loads. Required components: SR Name Qty 1 Double acting cylinder 1 2 Two way FCV 1 3 Check valve 1 4 4/2 way valve 1 5 Power pack 1 Fig 4.4 Shows a schematic diagram of the hydraulic circuit that controls the speed of a Double Acting Cylinder using two way flow control valve. 4 Module 4: Flow control valves & pressure control valves

7 ATM 1122 Basic Hydraulics Procedures 1- Prepare the components according to components list. 2- Install all components according to hydraulic circuit shown in Fig 4.4 (All components should be firmly fixed). 3- Connect hydraulic hoses according to the hydraulic circuit, (Check that all return lines are plugged and all hose lines are firmly plugged in). 4- Check all parts are connected properly to each other. 5- The operating pressure should not exceed 20 bar. 6- Switch on the hydraulic power pack. 7- Start the circuit, then adjust the two way flow control valve and note what happens within the circuit. 8- Switch off the hydraulic power pack. 9- Make sure that the circuit pressure is zero (free of pressure). 10-Dismantle the circuit and tidy up. Module 4: Flow control valves & pressure control valves 5

8 ATM 1112 Basic Hydraulics 4. Practical Task II 4.1 Embossing machine A special machine is used to emboss graphic symbols on metal foil. The foil is fed through the embossing machine. The advanced motion of the stamp must be capable of being varied in accordance with the fed speed as shown in Fig.4.5 The return motion must always be executed as a rapid traverse. A One way flow control valve is used to control the speed of the stamp, while a pressure relief valve is used to prevent the weight of the stamp from pulling the piston rod out of the cylinder. A 4/2 way valve is used to switch between advance and return motion. Fig.4.5 Embossing machine sketch 3.2 Procedure of solution: 1. Draw the hydraulic circuit diagram for the task. 2. Simulate the hydraulic circuit using FluidSim software. 3. Assemble the circuit practically and check its operation. 4. Write down your observations. 6 Module 4: Flow control valves & pressure control valves

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10 ATM 1112 Basic Hydraulics Work sheet 1- State the function of the one way flow control valve. 2- Draw the I.S.O. symbol of the one way flow control valve Name the main parts of the one way flow control valve State the function of the two way flow control valve? 5- Draw the I.S.O. symbol of the two way flow control valve State the function of pressure relief valve References 1. Festo Didactic hydraulic basic level textbook TP Oil Hydraulic Systems, S.R. Majumdar, Different websites. 8 Module 4: Flow control valves & pressure control valves

11 ATM 1122 Basic Hydraulics Student notes Module 4: Flow control valves & pressure control valves 9