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# ELT 791 - Hydraulics & Pneumatics

Credits: 3
Lecture Hours: 3
Lab Hours: 0
Practicum Hours: 0
Work Experience: 0
Course Type: Voc/Tech
The basic principles of fluid power and the operation and application of fluid power components are introduced. In the lab we will evaluate valves along with linear and rotary actuators. In addition, pneumatic position control servomechanisms are evaluated.
Corequisite: ELT 792
Competencies
1. Summarize common PHYSICS QUANTITIES used in hydraulic and pneumatic applications
1. Define the following dimensional quantities
2. Label typical English units of measure for each of the dimensional quantities listed above
3. Show a commonly used equation for each of the dimensional quantities listed above.
4. Illustrate each of the dimensional quantities listed above
2. Differentiate FORCE AND PRESSURE
1. Define a solid and a liquid
2. Discuss compression of solids and liquids
3. Describe how force is transmitted through a solid and a liquid
4. State Pascal’s Law as it applies to a liquid in both words and in equation form
5. Explain the difference between “Force” and “Pressure”.
6. Describe the following pressure gages, explain how they work, and compare their accuracy
3. Outline basic ACTUATOR, INTENSIFIER AND ACCUMULATOR OPERATION
1. Define a hydraulic actuator
2. List the most common type of linear actuator and rotary actuator
3. Draw a pictorial of a hydraulic cylinder and label its parts
4. Explain how a hydraulic cylinder functions
5. Associate Pascal’s Law to hydraulic cylinders regarding mechanical force multiplication
6. Draw a pictorial of a hydraulic intensifier
7. Explain what an intensifier does and how it functions
8. Illustrate hydraulic transmission of energy
9. Draw a pictorial of a simple hydraulic accumulator
10. Explain the purpose of an accumulator and how it functions
11. Perform calculations relating Force, Pressure, and Area with hydraulic cylinders and intensifiers
4. Contrast HYDRAULIC PUMP DESIGNS AND OPERATION
1. Draw a simple piston type positive displacement pump and label its parts
2. Define “positive fixed displacement (PFD)II as it applies to pumps
3. Explain how the piston type pump functions
4. State the fundamental operating principle which explains how all PFD pumps work
5. Draw a pictorial of a simple rotary (vane) type pump
6. Explain how the rotary (vane) type pump functions
7. Draw a pictorial of a simple gear type pump
8. Explain how the gear pump functions
9. Draw a pictorial of a simple gerotor type pump
10. Explain how the gerotor type pump functions
5. Summarize basic OPERATION OF A HYDRAULIC CIRCUIT
1. Describe what determines system operating pressure in a hydraulic circuit which uses a PFD pump
2. List the two basic factors that determine resistance to flow in a hydraulic circuit using a PFD pump
3. Describe how heat is generated in a hydraulic system
6. Differentiate FLOW RATE AND FLOW VELOCITY
1. Define viscosity and its unit of measure
2. List the three factors that determine a liquid’s viscosity
3. Explain how viscosity is measured
4. Describe how the velocity of a liquid flowing through a pipe is related to its flow rate.
5. Identify the English units of measure for Flow Rate and Flow Velocity
6. Identify the two variables that determine Flow Velocity in both words and as stated in an equation
7. State the recommended maximum Fluid Velocities in Feet per Second at the following points in a hydraulic system
8. Describe how bends in hydraulic pipes/plumbing effects heat generation
9. Define pressure differential and explain its significance in a hydraulic system
10. List three design features which must be considered to minimize heat generation in a hydraulic system
7. Outline the EFFECTS OF ATMOSPHERIC PRESSURE AND ALTITUDE ON PUMP OPERATION
1. Describe how a barometer is used to measure atmospheric pressure
2. Explain how altitude affects atmospheric pressure
3. Explain the difference between absolute and gauge pressure
4. Calculate absolute pressure given gauge pressure and ambient atmospheric pressure
5. Explain how a pump and atmospheric pressure work together at the suction side (inlet) of a pump
6. Define vacuum
7. Describe a vacuum gauge and how it measures vacuum
8. Explain how Inches of Mercury translates into Pounds per Square Inch
9. Explain the difference between Inches of Mercury Gauge vs.Inches of Mercury Absolute
10. Compute Inches of Mercury Absolute given Inches of Mercury Gauge and Ambient Atmospheric Pressure (in Inches of Mercury).
11. Describe how atmospheric pressure is used in two phases at the suction side of a pump
8. Differentiate PUMP CAVITATION AND PSEUDO-CAVITATION
1. Define cavitation (true cavitation).
2. List two ways that cavitation affects pump life
3. Identify how true pump cavitation can be detected and prevented
4. Explain how temperature and vapor pressure affect boiling and how these factors relate to cavitation.
5. Explain the difference between dissolved air in a liquid vs. entrained (undissolved air
6. Define pseudo-cavitation
7. Compare and contrast pump true cavitation with pseudo­cavitation
8. Identify how pump pseudo-cavitation can be detected and prevented
9. Determine if a pump can be operated at a given altitude when given a pump’s suction specification at sea level
10. Explain how a pump’s rotational speed (in RPM) affects its suction specification
11. Define Flooded Suction, Head Pressure, Lift, Suction, and Suction Pressure
9. Examine HYDRAULIC CYLINDER PARAMETERS
1. Calculate a hydraulic cylinder’s rod area when given its rod diameter
2. Calculate a hydraulic cylinder’s piston area when given its piston diameter
3. Define cylinder stroke
4. Calculate cylinder volume in terms of cylinder stroke and piston area
5. List the two variables that determine cylinder rod
6. Calculate cylinder rod speed/velocity speed/velocity
10. Examine HYDRAULIC MOTOR PARAMETERS
1. Define mechanical torque
2. List the two variables that determine mechanical torque
3. Calculate mechanical torque
4. Define hydraulic motor torque
5. List the two variables that determine hydraulic motor torque
6. Calculate hydraulic motor torque
7. Define hydraulic motor displacement
8. Calculate hydraulic motor displacement
9. Calculate hydraulic motor shaft speed in RPM in terms of flow and motor displacement
10. List the two variables that determine hydraulic motor horsepower
11. Calculate hydraulic cylinder horsepower in terms of flow and pressure
12. Calculate hydraulic motor horsepower in terms of shaft speed (RPM) and torque
11. Summarize how valves are used to CONTROL HYDRAULIC ENERGY
1. Define a valve
2. List the three main uses of valves (what they control).
3. Draw a pictorial of a Pressure Relief Valve and explain how it functions
4. Describe how a Pressure Relief Valve is used to control hydraulic pressure in a circuit using a Positive Fixed Displacement (PFD) pump
5. Draw a pictorial of a double-acting cylinder and explain how it functions
6. Draw a pictorial of a 4-way directional control valve (using a blocked center spool) and show how it can control the direction of a double-acting cylinder
7. Draw a pictorial of a flow control valve (needle valve) and explain how it functions to control actuator flow in a hydraulic circuit consisting of a PFD pump, hydraulic cylinder, and relief valve
8. Explain the terminology - “normally open(NO)” and “normally closed(NC) ” as it applies to flow control valves
9. Draw the hydraulic schematic diagram ANSI symbols of the following
12. Use CHECK VALVES in hydraulic circuits
1. Draw a pictorial of a check valve and label its parts
2. Draw the schematic diagram symbol of the check valve
3. Explain how the check valve functions and its purpose
4. Show how a check valve may be connected across a flow control valve in a hydraulic circuit to increase cylinder rod speed during the return stroke
5. Show how the check valve is used in a circuit containing an accumulator
6. Show how the check valve may be used as a simple pressure relief valve
7. Explain the problem of DCV spool leakage and cylinder drift when a hydraulic cylinder is used to suspend a heavy load and how a check valve cannot completely solve the problem
13. Use PILOT OPERATED CHECK VALVES & LOAD LOCK VALVES in hydraulic circuits
1. Draw a pictorial of a pilot operated check valve (P.O.C.V) and label its parts
2. Draw the schematic symbol of the P.O.C.V
3. Explain how a P.O.C.V. operates
4. Explain what is meant by a 5:1 ratio P.O.C.V
5. Show how to connect the P.O.C.V. to solve the cylinder drift problem of suspending a heavy load (mentioned above).
6. Explain how to make a “Load Lock Valve” from two P.O.C.V.s
7. Show how to connect a Load Lock Valve to lock a horizontally mounted double-acting cylinder
14. Use ACCUMULATORS in hydraulic circuits
2. Draw the three accumulator schematic symbols used to indicate the methods of loading
3. Describe the construction and operation of the three types of accumulators
4. Describe the construction and operation of the three types of hydro-pneumatic accumulators (the piston, diaphragm, and bladder types).
5. Explain and emphasize the importance of using DRY NITROGEN gas to precharge the hydro-pneumatic accumulators and why compressed air or oxygen gas must NEVER be used
6. Explain how pressure, temperature and volume are related to form the gas laws and how these laws relate to hydro-pneumatic accumulators
7. Describe isothermal and adiabatic charging and discharging of accumulators
8. List three purposes of using accumulators in a hydraulic system
9. Explain how to calculate the pre-charge pressure of a hydro­pneumatic accumulator
10. Define “useable volume”.
11. Show how useable volume is affected by pre-charge
12. Determine the actual useable volume when given an accumulator performance chart and pre-charge pressure
13. Show how to correct the performance chart readings for an accumulator whose volume capacity may be different that what the performance chart was designed for
15. Summarize SPECIAL HYDRAULIC CYLINDERS AND CYLINDER FEATURES
1. Describe the types of hydraulic cylinder seals
2. Describe a hydraulic cylinder cushion’s construction, purpose, and operation in a hydraulic circuit
3. Describe a stroke adjuster’s construction, purpose, and operation in a hydraulic circuit
4. Explain the difference between a cylinder thrust load and tension load
5. Show how a stop tube is used in a cylinder to protect its rod gland bushing
6. Describe the following cylinders according to their construction and use
7. Show how to synchronize the movement of two cylinders
8. Define a 2:1 cylinder
9. Show how to operate a 2:1 cylinder in a regenerative circuit and explain the purpose and operation of this circuit
16. Use NON-COMPENSATED AND PRESSURE COMPENSATED FLOW CONTROL VALVES in hydraulic circuits
1. List the three factors that affect flow through an orifice and describe how they affect flow
2. List the three overall types of variable orifices and describe their constructions and common applications
3. List the factors which affect actuator flow in a hydraulic circuit consisting of a positive fixed displacement (PFD) pump, relief valve, flow control valve, actuator, and operating a work load. Then describe how these factors affect flow as they are vari
4. Draw the schematic diagram of a restrictor type pressure compensated flow control (P.C.F.C.) valve and explain how it operates
5. Draw the schematic diagram of a hydraulic circuit using a restrictor type P.C.F.C. valve connected in a meter-in application and explain how it operates should
6. Draw the schematic diagram of a bypass type pressure compensated flow control (P.C.F.C.) valve and explain how it operates
7. Draw the schematic diagram of a hydraulic circuit using a bypass type P.C.F.C. valve connected in a meter-in application and explain how it operates should
8. Compare the advantages and disadvantages of using a restrictor type P.C.F.C. valve vs. a bypass type P.C.F.C
9. Explain how temperature affects flow in a hydraulic circuit
10. List the two types of temperature compensation techniques for flow control valves and explain how they operate
11. Draw the schematic diagram of a temperature compensated restrictor type P.C.F.C. valve
12. Describe a restrictor type P.C.F.C. valve using a lunge control and explain how it operates
17. Contrast the four popular GENERIC HYDRAULIC CIRCUIT CONFIGURATIONS
1. Draw the schematic diagrams of the following hydraulic circuits using a PFD pump, relief valve, flow control valve, cylinder, work load
2. Explain the operation of each of the four generic hydraulic circuit configurations
3. List the advantages and popular applications for each of the four generic hydraulic circuit configurations
4. Calculate system pressure, flow control valve pressure drop, and work load pressure in each of the four generic hydraulic circuit configurations
18. Use DIRECTIONAL CONTROL VALVES in hydraulic circuits
1. Draw the schematic diagram symbols of a 2-way, 3-way, and 4­way directional control valve (DCV).
2. Show how the 2-way, 3-way, and 4-way DCVs are used in hydraulic circuits
3. List the four most common 4-way DCV spools, draw their schematic diagram symbols, explain their use, and illustrate their operation in hydraulic circuits
4. List the DCV actuators, draw their schematic diagram symbols, and illustrate their operation
5. Explain spring offset and detents as applied to DCVS
6. Explain the following topics as related to DCVS
7. Explain how a deceleration valve is used in a hydraulic circuit
19. Analyze the following PRESSURE CONTROL VALVES
1. Pressure Relief Valve
2. Sequence Valve
3. Directly Operated Counterbalance Valve
4. Remotely Operated Counterbalance Valve
6. Pressure Reducing Valve
7. Brake Valve
8. Draw the schematic diagram symbol for each valve
9. Explain the operation of each valve using a pictorial diagram
10. Identify each valve as normally open or normally closed
11. Identify where each valve’s pilot line(s) is/are connected
12. Identify each valve as internally or externally drained
13. List common applications for each valve
14. Illustrate the operation of each valve in hydraulic circuits
15. Calculate pressures, cylinder forces, and cylinder piston areas for hydraulic circuits using the pressure control valves listed above
20. Illustrate a ‘HI-LO HYDRAULIC CIRCUIT’
1. Draw the schematic diagram of a ‘Hi-Lo Hydraulic Circuit’
2. Explain the purpose of a ‘Hi-Lo Hydraulic Circuit’
3. Describe the operation of a ‘Hi-Lo Hydraulic Circuit’
21. Contrast the three most popular types of HYDRAULIC MOTORS
1. List the three most popular types of hydraulic motors
2. Describe motor drains and explain their purpose
3. Describe a balanced vane motor and how it functions
4. Describe an unbalanced vane motor and how it functions
5. Explain the methods of extending the vanes of a vane motor
6. Describe a external gear motor and how it operates
7. Describe an internal gear motor such as the gerotor motor and how it operates
8. Describe a piston motor and how it operates
9. Explain how swashplate angle of a piston motor affects
22. Use HYDRAULIC MOTORS in hydraulic circuits
1. Calculate motor shaft speed, motor torque, and motor horsepower
2. Connect a hydraulic motor in meter-in and meter-out circuits and explain the characteristics and operation of each
3. Illustrate the techniques of braking hydraulic motors
4. Explain hydraulic motor cavitation and the methods used to prevent it
23. Differentiate OPEN LOOP AND CLOSED LOOP HYDROSTATIC DRIVES
1. Draw the schematic diagram of an open loop hydrostatic drive
2. Draw the schematic diagram of a closed loop hydrostatic drive
3. Explain the difference between the open loop and closed loop hydrostatic drive
4. List the four types of pump-motor combinations used for hydrostatic drives
5. Identify the following parameters for each of the hydrostatic drive combinations as either fixed or variable
24. Compare the special types of ROTARY ACTUATORS
1. List the special rotary actuators.
2. Show a pictorial illustration of each rotary actuator
3. Describe the operation of each rotary actuator.
4. List typical torque and angle of rotation for each rotary actuator
25. Summarize ENERGY TRANSMISSION IN A PNEUMATIC SYSTEM
1. Describe the characteristics of gases
2. Associate the affects of temperature and pressure on gases via the gas laws
3. Explain how air compression and expansion affects gases
4. Describe the pneumatic transmission of energy
5. Explain how a positive displacement compressor operates
6. Describe inefficiencies in a pneumatic system
7. Describe air flow rate in terms of cubic feet per minute (CFM) and
8. Explain how air velocity and critical velocity is related to piping size in a pneumatic system standard cubic feet per minute (SCFM).
26. Illustrate CONTROL OF PNEUMATIC ENERGY
1. Draw the schematic diagram of a pneumatic system showing, the compressor, pressure switch, check valve, receiver tank, safety relief valve, pressure regulator, flow control valve, and actuator
2. Explain how each of the components (listed above) operates in a pneumatic system
3. Explain the difference between a vented and non-vented pressure regulator (refer to Chap. 10 for additional information).
27. Use COMPRESSORS in pneumatic circuits. (Chap. 5)
1. List the compressor types according to “displacement” or “dynamic” grouping
2. Explain how each of the compressor types operate and their uses
4. Illustrate how to select a compressor for a system
5. Describe how to install a compressor
28. Relate AFTERCOOLERS, DRIERS, RECEIVERS AND AIR DISTRIBUTION SYSTEMS
1. Explain the purpose of an aftercooler
2. Discuss the following processes
3. Explain the purposes of an air receiver tank