ABSTRACT Pneumatic system is a system that uses compressed air to transmit and control energy. Some applications of the system in real world is in controlling train doors, automatic production lines and mechanical clamps. Pneumatic system is widely used due to its high durability and reliability, simplicity, safety and high adaptability to harsh environment. Through the experiments conducted,a pneumatic system is set up and operated, operation of a 3-way, 2position directional control valve is verified and one-cycle reciprocation system is tested.
OBJECTIVES 1. Set up and operate a pneumatic system using the Conditioning Unit, a directional control valve and a cylinder. 2. To verify the operation of a 3-way, 2-position directional control valve. 3. Set up and operate a one-cycle reciprocation system.
THEORY Definition Electro-pneumatic term is defined from words of electro, which mean electrical and pneumatic, which mean air pressure. The electro-pneumatic system is an integration of electrical and mechanical components with compressed air source. Components Electro-pneumatic controllers have a pneumatic power section. In an electro-pneumatic control, the signal control section is made up of electrical components, for example, the proximity switches, and the relays. The directional control valve behaves as an intermediary between the electrical signal control section and the pneumatic power section in the controller. Switch There are three (3) types of electrical switches used in the design of electro-pneumatic circuit. They are: i) Normally-opened (NO) contact switch. ii) Normally-closed (NC) contact switch. iii) Changeover contact switch. Relay Relay is an electrical device that contains a coil and one or more contact switches. Solenoid Valve Solenoid valve is an electro-mechanical device that built-in with a coil (solenoid) and a pneumatic/hydraulic directional control valve (DCV). Proximity Sensor
Proximity sensors are commonly used to monitor a process condition in a machine. For instance, sensor is used to ensure the raw part was placed on a fixture, height of raw material within control, etc. There are three types of proximity sensors: 1. Inductive sensor – able to detect metal, especially mild steel. 2. Capacitive sensor – able to detect most parts except low-density product. 3. Optical sensor – able to detect bright surface reflectively except black / rough surface. PROCEDURE (A)
Set up and operate a pneumatic circuit 1. Conditioning Unit, directional control valve and cylinder are mounted on the work surface and connected as shown. The Conditioning Unit is connected to the NC (normally non-passing) port of the directional control valve.
2. On the Conditioning Unit, the main shutoff valve and the branch shutoff valve at the manifold are opened. A tip is screwed to the rod of the cylinder. 3. The regulator adjusting knob is pulled up to unlock the regulator and it is turned clockwise to set the pressure at 200 kPa on the regulated Pressure Gauge. 4. The motion of the cylinder is observed and recorded.
(B)
Verify operation of a 3-way, 2-position directional control valve 1. The status of the trainer is verified according to the procedure. 2. The circuit is connected as shown. The Conditioning Unit is connected to the NC (normally non-passing) port of the directional control valve.
3. The main shutoff valve and the branch shutoff valve at the manifold are opened and the pressure regulator is set at 100 kPa on the regulated Pressure Gauge. 4. The reading indicated by the Pressure Gauge is recorded. 5. The button on the directional control valve is pushed and the reading indicated by the Pressure Gauge is recorded with this position of the button. 6. The shutoff valves is closed. 7. The circuit is modified by connecting the Conditioning Unit to the NO (normally passing) port of the directional control valve. 8. The shutoff valve is opened and the pressure regulator is set at 100 kPa on the regulated Pressure Gauge. 9. The reading is recorded. 10. The button on the directional control valve is pushed and the reading is recorded with this position of the button. 11. The Conditioning Unit is connected to the OUT port of the directional control valve. 12. The shutoff valves are opened and the regulator adjusting knob is slowly turned clockwise until some noise generated by compressed air can be heard. 13. The port where the compressed air flows is observed. 14. The button on the directional control valve is pushed and the observation is recorded. 15. The circuit is modified by connecting the Flow Control Valve to the NC port of the directional control valve and the Conditioning Unit to the NO port. 16. The required shutoff valves are opened the pressure regulator is set at 200 kPa on the regulated Pressure Gauge. 17. The Flow Control Valve is opened partially by turning the control knob three turns counterclockwise. 18. The flow rate indicated by the flow meter is recorded. 19. The button on the directional control valve is pushed and the observation is repeated. The flow rate indicated by the flow meter while the button is pressed is recorded.
(C)
Setting up and operating one-cycle reciprocation system 1. The one-cycle reciprocation circuit is connected as shown. A tip is screwed to the cylinder rod.
2. Magnetic Proximity Switch PX1 is mounted on the Double-Acting Cylinder so the switch is activated when the cylinder rod is fully extended. 3. DC Power Supply is turned on. 4. The START pushbutton PB1 is shortly depressed. Pilot lamp L1 should turn on when the electric circuit is working. 5. With my hand, the cylinder rod is pulled until it is fully extended. Pilot lamp L1 and the pilot lamp of SOL-A should turn off if the circuit is operational. 6. The cylinder rod is retracted and the tubes are connected at the cylinder ports. 7. The Flow Control Valves are closed by turning the control knobs fully clockwise. By turning the knobs two turns counterclockwise, each valve is opened. The mark on the knobs is referred to help set the correct position. 8. The shutoff valve and the branch shutoff valve at the manifold is opened and the pressure regulator is set at 400 kPa on the regulated pressure gauge. 9. The cylinder cycle is started by momentarily depressing the START pushbutton PB1. The motion of the cylinder rod is observed. 10. The set screw on Magnetic Proximity Switch PX1 is loosened until the clamp is loose enough to slip over the cylinder tie rod. The set screw is tightened after the switch is positioned approximately at the middle of the cylinder.
11. The cylinder cycle is started by momentarily depressing PB1 while observing the extension of the rod. 12. Relay contact CR1-A in rung 1 are removed. The circuit operation and its ability to fully extend the cylinder rod is observed. 13. The Magnetic Proximity Switch PX1 is repositioned at the rod end of the cylinder and the DC Power Supply is turned on. 14. The cylinder cycle is started by momentarily depressing the START pushbutton PB1 and the reaction time of the piston rod is measured. The results are entered in appropriate cell and the measurement is repeated to validate the result. 15. The shutoff valves on the Conditioning Unit and the Quick Exhaust Valve is inserted between Flow Control Valve FCV1 and the cylinder as shown. The tube used between Quick Exhaust Valve and the cylinder must be as short as possible. The IN port of the Quick Exhaust Valve must be ensured to be connected to the Flow Control Valve.
16. Shutoff valves are opened and step 14 are repeated.
DATA COLLECTION EXPERIMENT 1: INTRODUCTION TO PNEUMATIC Observation 1. At initial condition the rod of the cylinder didn’t extend when the circuit is completed. 2. The rod of cylinder is extended when the button of directional control valve is pushed. 3. The rod of cylinder is extended when the button of directional control valve is pushed for 5 seconds and released. 4. The cylinder is back to its initial position when the button is released for both cases. EXPERIMENT 2: DIRECTIONAL CONTROL VALVES (DCV); NC VS NO VALVE CONFIGURATION Observation A.
Conditioning Unit’s hose connected to NC port of DCV. Initial Reading : 0 kPa Final Reading : 100 kPa
B.
Conditioning Unit’s hose connected to NO port of DCV. Initial Reading : 100 kPa Final Reading : 0 kPa
EXPERIMENT 3 (A): DIRECTIONAL CONTROL VALVES (DCV); SELECTION CAPABILITIES OF DCV. Observation 1. The compressed air flow through the NO port of the DCV. 2. The compressed air flow through the NC port when the button of DCV is pushed. EXPERIMENT 3(B):DIRECTIONAL CONTROL VALVES (DCV); SELECTION CAPABILITIES OF DCV. Observation 1. Flow Meter reading before button of DCV is pushed : 150 litre per meter 2. Flow Meter reading after button of DCV is pushed : 15litre per meter EXPERIMENT 4&5: Introduction to Electrical Control of Pneumatic Systems & Basic Electrically Controlled Pneumatic Circuits Observation
1. Pilot Lamp L1 and Pilot Lamp SOL-A turned on when START button PB1 is pushed. 2. Both LI and SOL-A turned on when the cylinder rod is extended. 3. The cylinder is extended once the START button is pushed, but did not retract and stays in the extended position. 4. The cylinder rod stops at one cycle only. 5. After modification (adding PB2-NC contact), pressing the PB2 will retract the cylinder back to its original position. 6. Time taken for the cylinder rod to be retracted is faster with the Quick Exhaust Valve. RESULTS AND DISCUSSION
EXPERIMENT 1: INTRODUCTION TO PNEUMATIC A single acting cylinder has only one entrance port that allows compressed air to flow through. Thus, thrust produce only in one direction. The rod of the cylinder do not extend when we on the system. The button on the directional valve is pressed and the rod cylinder extend. The pressurized fluid inside the cylinder will exert force and make the rod extend. The rod cylinder returns to original position when the button is released. This is because the compressed air is released inside the rod and spring force exerts on rod will make it to retract to initial position. The motion of the rod cylinder shows that it convert fluid energy into linear mechanical motion. EXPERIMENT 2 & 3: DIRECTIONAL CONTROL VALVES In double acting cylinder, a propelling force and a retracting force is produce by the air pressure applied alternately to the surface of the piston. When the main shutoff valve and branch shutoff valve at the manifold is opened, the reading of the pressure gauge is 0kPa. Value about 100kPa is shown by the pressure gauge when the button on the directional control valve is pushed. This flow path configuration corresponds to a normally non-passing because when we leave (do not push the button), no fluid is pass into the cylinder but when the button is pushed, the air is blown inside the cylinder. At this moment, the valve is closed and air cannot pass when the air is at rest. When the operator is energized (push the button), full flow is achieved. After modified the circuit by connecting the Conditioning Unit to the NO (normally passing) port, the pressure gauge shows the reading of 100kPa. When we push the button on directional control valve, the reading shown at the pressure gauge is 0kPa. These flow path configurations correspond to a normally passing valve because valves are fully open when the operator is at rest and air will be at full flow. When the valve is energized (push the button), the valve will closed and no air will pass. Then the circuit is modified by connecting the Conditioning Unit to the OUT port of the directional control valve. The compressed air flow through NO port at initial stage and when the button of directional control valve is pressed the flow is through the NC port. This clearly
indicates that normal configuration of directional control valve is NO (normally passing) which it determined by connect the output hose to Conditioning Unit. The circuit is modified by connecting the flow control valve to the NC port. The flow control valve is opened partially and the flow rate indicate by the flow meter is 150 litre/min. While the button is pushed, the reading shows 15 litre/min. This confirmed that the directional control valve allows the selection of a power source because this system is same like regulator. EXPERIMENT 4&5: Introduction to Electrical Control of Pneumatic Systems & Basic Electrically Controlled Pneumatic Circuits Based on observation and the guide provided, electro-pneumatic basically is a combination between mechanical pneumatic and electrical circuit. The concept in mechanical pneumatic is, the compressed air is supply to system through the shutoff valve and the regulator, from here the shut off valve act as switch to let the air flow through the system. After that the air flow to the regulator, this will allow operator to control the pressure that required by the system. Next, again there is shut off valve to connect and disconnect the pneumatic system. Then the compressed air connected to the spring solenoid by flow tube. From the solenoid it connected to Flow Control Valve then go inside the Double Acting Cylinder. There is another tube coming out from the Acting Cylinder connected to another FCV and going back to the solenoid. Then the mechanical pneumatic system is completed. For the electrical part we construct the circuit according to the ladder diagram given in laboratory manual. The function of this circuit is to control the Double Acting Cylinder position whether fully extend or not. Through this circuit the Magnetic Proximity Switch able to detect whether the Double Acting Cylinder is fully extend or not. If the Double Acting Cylinder was fully extend, the Magnetic Proximity Switch on the Double Acting Cylinder will send the signal through the relay and power up the solenoid to change the direction of the flow. In the solenoid, there is magnet where it will move against the spring when the current is flow inside it. This action will move the valve at the solenoid and change the direction of the air flow to let air go inside the cylinder and retract the position of the piston rod. This can be identified when light indicator light up when the solenoid is power up. The pilot lamp L1 and pilot lamp of SOL-A is turn off when we pull the cylinder rod until it fully extended because the Magnetic Proximity Switch did not detect the piston position inside the cylinder, underneath Magnetic Proximity Switch. CONCLUSIONS As for conclusion, we can set up and operate pneumatic and electro pneumatic system using the equipment provided. The operation of the pneumatic circuit and electro pneumatic circuit can be explained briefly from the aspect of theory and logically. The identification of the pneumatic II system components also can be done. For recommendation, the replacement of the components and equipment that are not really accurate in giving output should be necessary. The objective is achieved.
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