IET 260 Morehead State University Hydraulics and Pneumatics Worksheet

IET 260: Hydraulics and Pneumatics Chapter 10: Hydraulic Conductors and Fittings Qingzhou Xu q.xu@moreheadstate.edu (606) 783 9598 LC Room 105E There are not too many to talk about. Please read by yourselves. IET 260: Hydraulics and Pneumatics Chapter 11: Ancillary Hydraulic Devices Qingzhou Xu q.xu@moreheadstate.edu (606) 783 9598 LC Room 105E Oil Reservoir or Tank A tank serves not only as a storage space but also the location where the oil is conditioned. A tank serves the following functions: 1. Permit foreign substances to settle to the bottom 2. Allows entrained air to escape from oil 3. Prevent localized turbulence in reservoir 4. Promote heat dissipation through reservoir Oil Reservoir or Tank Oil to Pump Returning Oil Hot Oil Filter This tank does not function well because the hot oil will flow back to the hydraulic system. Short circuit of the returning oil Oil Reservoir or Tank Baffle Plate Oil to Pump Returning Oil Hot Oil A baffle plate is placed in the center and its height is about 70% of the height of the oil level. The baffle plate is used to prevent the short circuit of the same returning oil, promoting efficient heat dissipation. Oil Reservoir or Tank: Sizing The size of a tank has to be able to contain all the oil of a fluid power system. An empirical relation is a tank having a capacity of three times the flow rate: Tank Volume = 3  Pump Flow Rate (gpm) For example, if the pump’s flow rate is 10 gpm, the tank’s size needs to be ~30 gallon. Accumulator An accumulator is a device that stores potential energy and provides a temporary second source of fluid power for a hydraulic system. It is important for reducing energy loss, decreasing pressure fluctuation, avoiding hydraulic shock and responding to emergency power need. There are three types: 1. Weight-loaded or gravity type 2. Spring-loaded type 3. Gas-loaded type Accumulator: Weight-Loaded Dead Weight Wdead P= Apiston A weight-loaded accumulator is basically a vertical cylinder. It produces a constant pressure regardless of its volume filled with the oil. Its main disadvantage is its large size and heavy weight. Accumulator: Spring-Loaded kx P= Apiston A spring-loaded accumulator is a cylinder, which is operational in any direction. Its output pressure depends on the displacement of the mechanical spring. That is, its output pressure varies with its volume filled with the oil. Accumulator: Gas-Loaded Non-Separator-Type Inert Gas nRT P= V Oil A gas-loaded non-separator-type accumulator is a seamless container. It has to be working vertically. Its output pressure is a function of the oil-occupying volume and temperature. Its main advantage is convenient to use; its main disadvantage is gas absorption. Accumulator: Gas-Loaded Separator-Type: Piston Gas nRT P= V Oil A gas-loaded piston-type accumulator is a seamless container separated by a piston. It has to be working in any direction. Its output pressure is a function of the oil-occupying volume and temperature. Its main disadvantage is unable to respond to pressure change because of the inertia of the piston and the friction of the seals. Accumulator: Gas-Loaded Separator-Type: Diaphragm Gas nRT P= V Oil A gas-loaded diaphragm-type accumulator is a seamless container separated by a an elastic barrier. It can work in any direction. Its output pressure is a function of the oil-occupying volume and temperature. Its main advantage is light-weight and has no mechanical friction, enabling it for airborne applications. Accumulator: Gas-Loaded Separator-Type: Bladder Gas nRT P= V Oil A gas-loaded bladder-type accumulator uses a elastic bladder in a seamless container. It can work in any direction. Its output pressure is a function of the oil-occupying volume and temperature. Its main advantage is that the light-weight bladder enables quick response to pressure change and hydraulic shock. Accumulator’s Applications: Auxiliary Power Source 850 psi 1. The accumulator is charged after the cylinder fully retracts. 2. The accumulator can then be used as the secondary power to drive the cylinder. Accumulator’s Applications: Auxiliary Power Source 850 psi Because the charged accumulator is always ready when needed, the use of the accumulator allows the intermittent operation of the pump. Accumulator’s Applications: Leakage Compensator 800 ~ 900 psi Because of oil leakage, the pressure will decrease below 800psi some time later. Pump is stopped Accumulator’s Applications: Leakage Compensator 800 ~ 900 psi Because of oil leakage, the pressure will decrease below 800psi some time later. An accumulator can be used to help the pressure in 800~900psi for a long time. Pump is stopped Accumulator’s Applications: Leakage Compensator Pilot-control contact switch: When P < 800 psi, pump on When P > 900 psi, pump off 950 psi 800 ~ 900 psi Accumulator’s Applications: Leakage Compensator 800 ~ 900 psi 950 psi When P < 800 psi, pump on Accumulator’s Applications: Leakage Compensator When P > 900 psi, pump off 950 psi The accumulator will compensate the oil leakage until the system pressure drops below 900 psi. In this way, the pump does not need to keep on. Accumulator’s Applications: Emergency Power Source Because of safety requirement, the cylinder has to be in the retraction position even if the normal supply of oil pressure is lost. 850 psi Such an application needs to use an accumulator as an emergency power source. Accumulator’s Applications: Emergency Power Source Accumulator’s Applications: Emergency Power Source Accumulator’s Applications: Emergency Power Source 850 psi Accumulator’s Applications: Hydraulic Shock Absorber To Power Application 850 psi Accumulator’s Applications: Hydraulic Shock Absorber To Power Application 850 psi Sealing Devices 1. O-ring 2. V-ring 3. Cup-packing Sealing Devices: Single-Acting Cylinder V-type or cup-type ring faces high pressure High Pressure Atmosphere Sealing Devices: Double-Acting Cylinder V-type or cup-type rings face both the high pressures High Pressure High Pressure Sealing Devices: Single-Acting Cylinder Muptiple V-type or cup-type rings can be used to ensure seamless sealing. High Pressure Atmosphere Heat Exchanger Because various forms of energy loss are inevitable, the oil in a hydraulic system can become very hot. Heat exchanger is necessary. Air-Cooled Water-Cooled IET 260: Hydraulics and Pneumatics Chapter 12: Maintenance of Hydraulic Systems Qingzhou Xu q.xu@moreheadstate.edu (606) 783 9598 LC Room 105E We also skip this chapter. Please read by yourselves. IET 260: Hydraulics and Pneumatics Chapter 13: Pneumatics Air Preparation and Components Qingzhou Xu q.xu@moreheadstate.edu (606) 783 9598 LC Room 105E Equation of State for Ideal Gas Idea gas is defined as a body of randomly-moving, non-interacting (perfect elasticity), point (negligible size) particles. PV = nRT m = RT mmolar Where P is the absolute pressure, T is the absolute temperature, and R is the universal gas constant. By re-arranging: PV m = R T mmolar For a confined gas volume: PV = const . T That is: P1V1 P2V2 = T1 T2 Air Compressors Like hydraulic pressure pumps, there are three types of compressors: gear, vane and piston. A compressor increases the pressure of a gas by reducing its volume. Because gas is compressible, a compressor always has a gas tank with it. Thus, the prime mover of a compressor can work in an intermittent way. Electrical Motor Compressor Gas Tank Air Compressors: Sizing of Gas Tank The tank size of a compressor depends on the pressures and flow rate requirements of a power system and the compressor’s flow rate. It can be decided by the following empirical formula: VTank = 14.7t (QTank − QCompressor ) Pmax − Pmin ( ft3 ) Where t is the time during which the tank needs to supply the required amount of air (minute), Pmax is the maximum pressure level and Pmin is the minimum pressure level of the tank during the time of period. Air Compressors: Capacity Rating The capacity of a compressor is generally rated in the cfm of free air, which is defined as the air at one atmosphere (14.7 psi) and 68°F. The unit is also called a standard cubic feet per minute (scfm). P1V1 P2V2 = T1 T2  P1 V2 =   P2  T2   V1  T1  V2  P1  T2  V1 =    t  P2  T1  t  P1  T2 Q2 =    P2  T1  Q1  Air Compressors: Capacity Rating The capacity of a compressor is rated 300 scfm. What is its flow rate at 250 psi and 90°F?  P1  T2 Q2 =    P2  T1 At the standard condition: P1 = 14.7 psi T1 = 68 F + 460 = 528 F Q1 = 300cfm  Q1  At the pressured condition: P2 = 250 psi + 14.7 psi = 264.7 psi T2 = 90 F + 460 = 550 F Q2 = ?  14.7 psi  550 F    300cfm = 17.35cfm  Q2 =    264.7 psi  528 F  Air Conditioners: Air Filter A filter is used to remove contaminants in the air before it reaches pneumatic components, such as valves and actuators. Air Conditioners: Pressure Regulator A pressure regulator is used to achieve a constant pressure for a pneumatic system. Air Conditioners: Pressure Indicator A pressure indicator is used to indicate the pressure. Pressure Indicator FRL Combined Unit of Filter, Regulator and Lubricator (FRL) Air Control Valves B A B A P P Exhaust Exhaust A B A B P Ex P Ex A B Four-way, two-position directional control valve P Ex Air Control Valves A B A B 2 4 P Ex P 1 3 In pneumatics, the pressure port is numbered (1). The exhaust port is numbered (3) and the second exhaust port is numbered (5) if existing. The other two are numbered (2) or (4). Air Control Valves A P Exhaust 1 A B Ex1 P Ex2 A B Exhaust 2 A Exhaust 1 B P Exhaust 2 B 2 4 P 3 1 5 Air Control Valves A B A Ex1 P Ex2 Ex1 P Ex2 A B B Ex1 P Ex2 A B Ex1 P Ex2 Air Motors One-Directional Bi-Directional IET 260: Hydraulics and Pneumatics Chapter 14: Pneumatics Circuits and Applications Qingzhou Xu q.xu@moreheadstate.edu (606) 783 9598 SSC Room 212F Air Pressure Loss in Pipeline As in the case of liquid, an air flow also suffers energy loss due to friction. The energy loss is calculated by the following empirical formula: cLQ 2 Pf = 3600  CR  d 5 where c is an experimentally determined coefficient, CR is the compression ratio of the pressure in pipe over the atmospheric pressure. Pneumatic Circuits: Operation of Single-Acting Cylinder No Pump Shown. The triangle represents pressured air source Supply Line No Return Line Release to Air FRL Pneumatic Circuits: Operation of Single-Acting Cylinder Pneumatic Circuits: Operation of Single-Acting Cylinder Pneumatic Circuits: Operation of Double-Acting Cylinder Pneumatic Circuits: Operation of Double-Acting Cylinder Pneumatic Circuits: Operation of Double-Acting Cylinder 100 psi 10 psi Pneumatic Circuits: Operation of Double-Acting Cylinder 100 psi 10 psi Pneumatic Circuits: Operation of Double-Acting Cylinder 100 psi 10 psi The End IET 260: Hydraulics and Pneumatics Chapter 15: Basic Electrical Controls for Fluid Power Circuits Qingzhou Xu q.xu@moreheadstate.edu (606) 783 9598 LC Room 105E Electrically-controlled fluid power systems are most powerful and useful in industry. Electrical Control Devices: Push-Button Switch Push-button switch is the switch can be opened or closed by a push. There are four common types: 1) Single-pole, single-throw, normally open SPST-NO 3) Double-pole, single-throw DPST-NO/NC 2) Single-pole, single-throw, normally closed SPST-NC 4) Double-pole, double-throw DPDT-NO/NC Electrical Control Devices: Limit Switch Limit switch is the switch used to open and/or close circuit when actuated, often at the end of extension and/or retraction of a cylinder. Hydraulic Symbol Limit Switch This limit switch is closed to shut off the hydraulic circuit. This limit switch is closed to shut off the hydraulic circuit. Electrical Control Devices: Limit Switch 1) Normally open 2) Normally closed LS-NO When activated LS-NC When activated Electrical Control Devices: Pressure Switch Pressure switch is the switch that open or close, based on the pilot pressure. PS-NO PS-NC Hydraulic Symbol Electrical Symbol Electrical Control Devices: Solenoid Solenoid uses electromagnet to generate a push or pull force to operate hydraulic valve. Hydraulic Symbol Electrical Symbol Electrical Control Devices: Relay Relay is a switch whose contacts open or close when their coils are energized. High Voltage Normally Closed Contacts Normally Open Contacts Low Voltage Low Voltage High Voltage Normally Closed Contacts Relay Coils Normally Open Contacts Electrical Control Devices: Timer A timer is used to control the time duration of a working cycle. 1) Normally open (closed when energized) 2) Normally closed (open when energized) 3) Normally open (open when energized) 4) Normally closed (closed when energized) Ladder Diagram: Five Basic Rules L1 1. Place control (input) devices on the left and load (output) devices on the right. 2. Place one, and only one, load per rung. START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 3. Number all the connectors in order from left to right and top to bottom. 2 4. Number all the rungs in order from top to bottom. 3 5. Label all the components. L2 POWER LINE 1-LS 1-CRA 1 6 1-CRB 2 SOL A Ladder Diagram: Voltage Drop L1 0V START STOP 2. Place one, and only one, load per rung. 1 1-PB L2 24 V 2-PB 1-CR 4 3 5 2 1 1-LS 2 1-CRA 3 1 6 1-CRB Control Devices 2 SOL A Loads Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 6 1-CRB Hydraulic Diagram Electrical Diagram Power Diagram Ladder Diagram 2 SOL A Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 Relay coil engaged 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 Relay coil engaged 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Solenoid engaged Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 Relay coil disengaged 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Solenoid disengaged Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 Relay coil disengaged 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Solenoid disengaged Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 6 1-CRB 2 SOL A The cylinder remains retracted. When the “START” button is pushed: 1) 2) 3) 4) 5) 1-CR is engaged. 1-CRA and 1-CRB are closed. SOL A is engaged. DCV is actuated/its position is shifted. The cylinder starts to extend. 6) When 1-LS is actuated, the current in Rung 1 is off/1-CR is disengaged. 7) 1-CRA and 1-CRB are opened. 8) SOL A is disengaged. 9) DCV is deactivated and return to its initial position. The cylinder retracts. Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 5 2 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 6 1-CRB 2 SOL A Electrical Control of A Cylinder Using A Single Limit Switch 4 5 L1 L2 POWER LINE 1-LS START STOP 1 1-PB 2-PB 1-CR 4 3 2 5 1 SOL A 1-LS 2 6 2 1-CRA Oil In 3 1 2 6 1-CRB SOL A When the cylinder is moving. if the “STOP” button is push: 1) 2) 3) 4) The current in Rung 1 is off and1-CR is disengaged. 1-CRA and 1-CRB are opened. The current in Rung 2 is shut off. SOL A is disengaged. DCV is deactuated and return to its initial position. The cylinder retracts. Reciprocation of A Cylinder Using Pressure or Limited Switches POWER LINE 1-PS 2-PS 1-PS SOL A SOL B SOL B Oil In 2-PS SOL A Reciprocation of A Cylinder Using Pressure or Limited Switches When pressure builds up to 800 psi POWER LINE 800 psi 800 psi 1-PS 2-PS 2-PS is closed SOL A 1-PS SOL B SOL B Oil In 2-PS SOL A Reciprocation of A Cylinder Using Pressure or Limited Switches POWER LINE 800 psi 800 psi 1-PS 2-PS 1-PS SOL A SOL B SOL B Oil In 2-PS SOL A SOL A engaged Reciprocation of A Cylinder Using Pressure or Limited Switches When pressure releases POWER LINE 800 psi 800 psi 1-PS 2-PS SOL A Oil In 2-PS opens SOL B 1-PS 2-PS SOL B SOL A Reciprocation of A Cylinder Using Pressure or Limited Switches When pressure builds up to 800 psi POWER LINE SOL B engaged 800 psi 800 psi 1-PS 2-PS 1-PS 1-PS is closed SOL A Oil In SOL B SOL B 2-PS SOL A Reciprocation of A Cylinder Using Pressure or Limited Switches POWER LINE 1-PS 2-PS 1-PS SOL A SOL B SOL B Oil In 2-PS SOL A Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A At the beginning, both cylinders are fully retracted. 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START Sol A engaged SOL A 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A SOL B SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START Sol A disengaged SOL A 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A 2-LS SOL B 1-LS SOL C 1-LS switched on Sol C engaged Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START SOL A 2-LS SOL B 1-LS SOL C Double-Cylinder Sequencing Circuit 1-LS 2-LS Cylinder 1 SOL A Cylinder 2 SOL B SOL C Air In START One push on “START” button results in: SOL A 1) 2) 3) 4) Cylinder Cylinder Cylinder Cylinder 1 fully extends; 2 fully extends; 1 fully retracts; 2 fully retracts. 2-LS SOL B 1-LS SOL C Box-Sorting Circuit Limited Switch Conveyor Track Box-Sorting Circuit conveyor motor 2 2-LS 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 Box-Sorting Circuit conveyor motor 2 2-LS High Box 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA Both motors are turned on. 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 Box-Sorting Circuit conveyor motor 2 2-LS High Box 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA Conveyor motor 2 is stopped. 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 Box-Sorting Circuit conveyor motor 2 2-LS High Box 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA Conveyor motor 2 is stopped. 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 Box-Sorting Circuit conveyor motor 2 High Box 2-LS 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA Conveyor motor 2 is stopped. 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 Box-Sorting Circuit conveyor motor 2 High Box 2-LS 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA Conveyor motor 2 is turned on again. 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 Box-Sorting Circuit conveyor motor 2 High Box 2-LS 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA 1-CRB 1-CRA SOL A 2-CRB conveyor motor Box-Sorting Circuit conveyor motor 2 High Box 2-LS 1-LS conveyor motor 1 High Box STOP SOL A START conveyor 2-CR motor 1 2-CRA Air In Low Box 2-LS 1-LS 1-CR 1-CRA This system is waiting for next sorting. 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 Box-Sorting Circuit This ladder diagram is from the textbook but it has one critical fault and one minor fault. Where are the faults and how do you fix them? STOP START conveyor 2-CR motor 1 2-CRA 2-LS 1-LS 1-CR 1-CRA 1-CRB 1-CRA SOL A 2-CRB conveyor motor 2 The End Student Name: __________________ HW 7 of ETM 260: Hydraulics and Pneumatics 50 points in total, due on April 26, 2020, Sunday 1. An electrical circuit is used to control the movement of a double-acting cylinder. The directional valve is actuated and the piston rod is in the middle of moving to the limit switch. For some reason, it needs to be stopped at this moment. Please describe in the order of reactions what happen when the “STOP” button is pressed. These reactions may include the on/off of the electrical current, the change in the directional valve position, the change in the fluid flow and the change in the hydraulic cylinder’s movement. Please mark these reactions on the figure. (20 points) 1-LS POWER LINE START STOP 1-LS 1-CR SOL A 1-CR Oil In 2. (b) (a) SOL A 1-CR A double-acting cylinder is controlled by an electrical means. When Pushbutton 2 (START) is pushed and released, analyze and describe in detail the reactions of EACH COMPONENT in the hydraulic and electrical diagrams in the logic sequence. Then, draw a final conclusion what movement the cylinder is doing. You need to mark the reactions on the diagrams. (30 points) 1-LS L1 2-LS L2 1 7 6 START STOP 2-PB 6 1 3 1 A B 1-CRA 5 2 2-CRA SOL B 3 5 1 8 2 P T 4 1 Oil In (a) 5 6 2 4 2 1-CRB SOL A 1-CR 1-PB 2-LS SOL A 2 2-CR 6 2 7 2-CRA 1-LS 8 1 SOL B 2 2-CRB (b) 1 Solution of Homework 5 of IET 260’s Chapters 7 and 8 80 points in total, due on April 9, 2019, Tuesday 1. A hydrostatic transmission, operating at 1,500 psi pressure, has the following data: Hydraulic Pump VD=10 in3 ηv=85% ηm=90% N=1,000 rpm Hydraulic Motor VD=? and TA=? ηv=87% ηm=95% N=1,500 rpm Ask 1) what is the displacement volume? 2) what is the actual output torque of the hydraulic motor? (30 points) Soution: 1) What is the displacement volume? The theoretical flow rate of the hydraulic pump is: QPT = VPD × N p = 10in3 × 1,000rpm = 10,000in3 / m The actual flow rate of the hydraulic pump is: QPA = ηPV × QPT = 85% × 10,000in3 / m = 8,500in3 / m Because all the actual flow rate of the hydraulic pump is used to drive the hydraulic motor, the actual flow rate of the hydraulic motor is equal to the actual flow rate of the hydraulic pump. That is: QMA = QPA = 8,500in3 / m Because the hydraulic motor has internal leakage, the part of the actual flow rate of the hydraulic motor that is really used to drive the motor is equal to the theoretical flow rate of the motor. It is: QMT = ηMV × QMA = 87% × 8,500in 3 = 7,395in3 / m Because QMT = V MD × N M , the displacement volume of the hydraulic motor is: VMD = QMT 7,395in3 / m = = 4.93in3 1,500rpm NM 2) what is the actual output torque of the hydraulic motor? The theoretical torque of the hydraulic motor is: TMT = P × V MD 1,500 psi × 4.93in 3 = = 1,176.95lb ⋅ in = 98.08lb ⋅ ft 2π 2π The actual torque of the hydraulic motor is: TMA = η MM × TMT = 95% × 98.08lb ⋅ ft = 93.18lb ⋅ ft IET 260, Qingzhou Xu 1 2. Figure 1 shows the internal features of a simple pressure relief valve. Please (20 points) 1) 2) 3) What are the cracking pressure, set pressure and pressure override? Why does the set pressure differ from the cracking pressure? What feature in this device can you change to decrease the pressure override? Pset Pressure Override Pcrack Full Pump Flow Fig.1: Internal structure and output characteristic of a simple pressure relief valve. Solution: 1) What are the cracking pressure, set pressure and pressure override? The cracking pressure is the pressure that is large enough to just unseat the poppet and the set pressure is the pressure that makes the valve open to allow a full pump flow. The difference between both is the pressure override. 2) Why does the set pressure differ from the cracking pressure? Because the displacement of the mechanical spring is larger at the fully-open position than at the justunseated (or close) position, the set pressure is bigger than the cracking pressure. 3) What feature in this device can you change to decrease the pressure override? Increasing the length of the mechanical spring can decrease the pressure override. IET 260, Qingzhou Xu 2 2. Servo valves, especially electrohydraulic ones, are high-precision devices and are widely used in automatic controls of modern industry. There are three common types of servo valves: mechanical, jet pipe and flapper. The flapper servo valves are the most responsive and accurate design. Figure 2 shows the internal structure of a flapper-type servo valve. Please (30 points) 1) 2) 3) Describe how it works Why does the magnitude of the control signal determine its output flow rate of the valve? Why does the lasting time of the control signal decide the opening time of the valve? Why does this type of valve need oil filters? P A T B Fig.2: Internal structure of a flapper-type servo valve. Solution: 1) Describe how it works Fig.2’ (b) (a) P A T B P A T B In Figure 2, without control signal, the flapper is located in the center. It generates equal pressures on both ends of the spool. As a result, the spool is in its equilibrium position. The servo valve remains closed. When a control current signal is sent to the torque motor, it generates a torque to turn the coil’ armature out of its balance position. The direction of the torque depends on the current direction of the signal and the rotation angle of the armature depends on the signal’s current magnitude. In Figure 2’(a), The torque motor makes a counter-clockwise rotation and the flapper is pushed closer to the right nozzle and farther away IET 260, Qingzhou Xu 3 from the left nozzle. The restraint on the right nozzle’s flow increases while the restraint on the left nozzle’s flow decreases. As a result, the pressure on the right end of the spool increase while the pressure on the left end of the spool decreases. Now the spool is not in equilibrium anymore. A net hydraulic force moves the spool to the left. As the spool pushes the feedback wire to the left, it generates a torque in the opposite direction to the armature torque. When the spool torque and the armature torque are equal, the movement of the spool stops. This creates the opening for the fluid to flow, as shown in Figure 2’(b). Now, the servo valve is opened. 2) Why does the magnitude of the control signal determine its output flow rate of the valve? Why does the lasting time of the control signal decide the opening time of the valve? The opening’s size of the servo valve depends on the armature torque, which is determined ultimately by the magnitude of the input current signal. The opening’s size decides the output pressure and flow rate. The pressure, flow rate and direction of the fluid will be maintained until the input current signal is turned off. When the signal current is turned off, the coil’s armature returns to its balance position. This returns the flapper to the center. Then, no net hydraulic force is generated on both ends of the spool. The feedback wire brings the spool to its equilibrium position and the servo valve is closed. In this way, an accurate current signal can be used to precisely control the pressure, flow rate and direction of the fluid in the servo valve for a fuild power application. 3) Why does this type of valve need oil filters? For a flapper servo valve, very small-diameter nozzles are used to realize fast response with minimal wasted energy. Because of the small diameter, the nozzles can easily get clogged by contamination. Common oils can result in its failure in several hours if without carefully filtering. IET 260, Qingzhou Xu 4
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