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Pneumatic Exam with complete solution
An object's inertia determines how much force is needed to lift or move the object or to change its speed or direction of movement. - ANSWER- True Most pressure gauges in a pneumatic system measure only pressure that is higher than the atmospheric pressure surrounding them. - ANSWER- True In a pneumatic system, mechanical energy is produced by the motor. - ANSWER- False Pascal's Law states that when a gas is confined under pressure in a closed container, the pressure is equally transmitted in all directions by the gas - ANSWER- True If the volume of a confined quantity of gas remains the same, the change in the pressure of the gas varies directly with a change in the absolute temperature(T) of the gas. If the temperature increases, then the pressure of the confined gas increases. - ANSWER- True In a pneumatic system, the force that permits a small amount of pressure to move a larger object is called pneumatic leverage or force multiplication. - ANSWER- True Bernoulli's Law states that, in an ideal system, if air velocity increases, the kinetic energy of the air also increases, while the total energy of air does not remain constant. - ANSWER- False
A pneumatic system is quite different from a hydraulic system. It differs not only in the components it contains, but also in the flow paths through the system. - ANSWER- True The three types of symbols used in drawing pneumatic circuit diagrams are pictorial, cutaway, and schematic. - ANSWER- True In a pneumatic timing circuit, the timing is a function of the size of the restriction and the volume of the reservoir, however, the magnitude(pressureO of the air signal also affetcs timing. - ANSWER- True Industrial technicians usually designs symbols for special pneumatic devices. - ANSWER- False To understand the operation of many special pneumatic devices, obtain the manufacturer's service bulletins, which describe their operation. - ANSWER- True A system that uses a gas for transmitting force is called - ANSWER- pneumatic system A force is a push or a pull exerted on an object to change its position or movement and in a pneumatic system this force is exerted by - ANSWER- compressed air In a pneumatic system, the force in pounds is exerted by air pressure acting on the area of a moving piston in a cylinder. What equation is used to determine the amount of work done by a cylinder? - ANSWER- force x piston travel The amount of work done by a cylinder that exerts a force of 120 in-lb and a 10-in. stroke is - ANSWER- 100 ft-lbs In a pneumatic system, Power is defined as the amount of work(foot-pounds) done in a given length of time(seconds or minutes), or foot-pounds per minute. What equation is used to determine the amount of power? - ANSWER- work/time can be described as the rapid intermingling of the molecules of one gas with another. - ANSWER- diffusion is the ideal type of airflow in a pneumatic system because the air layers move in nearly parallel lines. - ANSWER- streamline
(Do all calcs in psia) - ANSWER- 2132 psig What would the output force be if a 100-lb force is applied to a piston having an area of 20 in2 and transferred to a piston having an area of 50 in2? Pressure= Force/Area - ANSWER- 250 lb of force An air compressor functions by creating a partial vacuum at its inlet and it reduces the air's volume, increasing air pressure. - ANSWER- True Air compressors can be classified into two seperate type: Positive displacement and Dynamic. - ANSWER- True Reciprocating compressors are manufactured in many varieties, and are ususally driven by electric motors. The motors can be connected to the compressor directly or by v-belts or speed reducers. - ANSWER- True The discharge valve on a reciprocating or piston compressor is opened when the air is compressed in the cylinder to a pressure high enough to force the valve open. - ANSWER- True The movable part of a discharge valve is frequently held against the seat by compressed air. - ANSWER- False The cooling efficiency of an air-cooled compressor with finned tubes can be improved by using a fan to force air over the fins. - ANSWER- True Compressor lubrication is only accomplished by splash methods. - ANSWER- False Large or heavy-duty compressors rely mainly on pressurized lubrication. - ANSWER- True Relieving all internal pressure on a compressor is called unloading. - ANSWER- True Sliding vane, dry screw, wet screw, liquid ring, and impeller are positive- displacement rotary air compressors. - ANSWER- True The wet rotary-screw compressor uses timing gears. - ANSWER- False
In a liquid-ring compressor, the liquid forms a flexible interior compression chamber. - ANSWER- True The three-stage compressor consists of three individual compressing impellers (of different sizes ) mounted on a speed increaser. - ANSWER- True Most centrifugal compressors are equipped with intercoolers and aftercoolers to prevent the air temperature from decreasing excessively. - ANSWER- False Control of centrifugal compressor output varies, but it can be grouped into four major methods: speed variation, suction throttling, discharge throttling, and recirculation. The most efficient method is speed variation. - ANSWER- True Compressor capacity is usually specified in terms of cubic feet per minute. ACFM is actual cubic feet per minute and is also referred to as free air capacity. - ANSWER- True SCFM is standard cubic feet per minute. - ANSWER- True ______ compressors confine the air within a closed space and compress it by decreasing the volume of the space. - ANSWER- Positive-displacement ______ compressors accelerate the air with rapidly turning rotor blades and this increase in airflow causes the air pressure to be raised slightly. - ANSWER- Dynamic A compressor that compresses air at only one end of a cylinder is called a ______ compressor. - ANSWER- single-acting A compressor that draws in air at atmospheric pressure and compresses it in two or more strokes is called a ______ compressor. - ANSWER- multistage When a compressor has more than one stage, air is usually cooled after it has discharged from the first stage and before it is compressed in the next stage. This is called ______ and this results in less power required to compress the air. - ANSWER- intercooling In a water-cooled intercooler, the most efficient and commonly found flow arrangement is when the fluid and gas flow in opposite directions and is commonly described as_________. - ANSWER- counterflow
The centering of a three-position, four-way pneumatic valve is usually accomplished by springs located at each end of the control element. - ANSWER- True Limiting the pressure of the compressor output with a pressure control valve is done in either of two ways. The first involves starting and stopping the compressor. The second involves unloading the compressor intake or discharge valves. - ANSWER- False Pressure regulators are usually located at air stations (or outlet points) or on individual pieces of pneumatic equipment. - ANSWER- True Cracking pressure is the pressure at which the valve initially closes. - ANSWER- False Applications that have larger flows or that require a smoother relief control may use diaphragm relief valves. - ANSWER- True The constant air bleed in a precision regulator prevents the diaphragm from modulating and helps to ensure a high degree of accuracy at low airflow rates through the regulator. - ANSWER- True If a large, high-volume air line must be regulated, a pilot-controlled regulator, or booster relay, can be used. - ANSWER- True Control valves used in pneumatic systems are identified by several different methods to include: number of primary system connecting ports and. - ANSWER- number of control positions, type of control element, method of operation A pneumatic needle valve has high pressure losses, because the _______ is smaller than the inlet and outlet connections of the valve. - ANSWER- valve seat Automatically operated pneumatic control valves can be actuated by several methods. The most common of these is by __________. - ANSWER- electric solenoid When larger volumes of air at high pressures are required, _________ valves are almost always used. - ANSWER- pilot-operated solenoid
_______ valves are used to simplify pneumatic circuits. Although they may seem slightly more complicated, they reduce the total number of controls in a system. - ANSWER- Four-way In a nonactauated two-position, four-way valve, air flow can flow in ______ directions. - ANSWER- two _________ valves reduce and control the pressure of the compressed air in the system to a level that is safe for equipment operation. - ANSWER- Pressure- regulating _______ valves have limited use in pneumatic systems. They open at a preset pressure and exhausts the air until the pressure drops below the set pressure. - ANSWER- Safety ________ valve opens and discharges excess air into the atmosphere if the compressor controls fail to shut down the compressor when the maximum working pressure of the system is reached. - ANSWER- Relief In some applications a regulator has to be mounted in an out-of-the-way place to function properly, or to offer good control of the air. For these application a ___________is used. - ANSWER- pilot-controlled regulator A federal law states that when an air hose is used to blow off chips, its nozzle pressure may not exceed _____psi. - ANSWER- 29 A pneumatic motor converts the movement and pressure of a stream of compressed air directly into mechanical energy. - ANSWER- True The pressure of the compressed air admitted to the pneumatic motor determines its force or torque output. - ANSWER- True Pneumatic motors are only classified by their principle of operation. - ANSWER- False Pneumatic motors are all of the positive-displacement type, which means that they have a mechanical seal somewhere between the inlet and outlet ports. - ANSWER- True The horsepower output of pneumatic motors is the product of the shaft speed and torque. - ANSWER- True
To operate properly, pneumatic motors need a starting or breakaway force, commonly called _________, that is great enough to start rotation while under a full load. - ANSWER- torque The shaft output speed of a fixed-displacement motor can be changed only by: - ANSWER- changing the pressure and flow rate of the compressed air supplied to the motor Categories of motor torque include: - ANSWER- starting, stalling, and running The construction of pneumatic motors is restricted to a few basic designs that include: - ANSWER- Vane, radial-piston, and axial piston To reverse the direction of rotation in a pneumatic motor, you ______________. - ANSWER- reverse the airflow In a piston-type rotary actuator, reciprocating linear motion is converted to reciprocating rotary motion through the use of ___________. - ANSWER- rack and pinion gear Rotary air tools (drills, grinders, and so on) are generally driven by__________. - ANSWER- vane motors The ______ of the air determines the piston speed and also the pneumatic output.
- ANSWER- flow rate The retraction stroke of a double-acting pneumatic cylinder has ______ as the extension stroke because the rod takes up some of the surface area of the piston.
- ANSWER- less power The _______ pneumatic cylinder has a power stroke in one direction only. - ANSWER- single-acting Most pneumatic cylinders used for industrial applications have the heads or caps held in position by four or more ______ that may be studs or long bolts. - ANSWER- tie rods Various piston rings or seals are used in pneumatic cylinders,. The piston seal that is most often used is the formed ring seal and is usually made of _______ taht resemble semi-hard rubber. - ANSWER- synthetic material
When you install a new pneumatic cylinder in an existing system, the procedure includes: - ANSWER- all of the above ______ devices slow down the piston as the cylinder approaches the end of its stroke and this slowdown reduces the possibility of shock. - ANSWER- Cushioning The best way to conduct plant maintenance is with a planned maintenance program and this program is related to the scheduling of lubrication and normal adjustments. - ANSWER- True Preventive maintenance corrects sources of trouble before they become major problems. - ANSWER- True The best way to check and maintain the compressor and all associated equipment on a regularly scheduled basis is with a alarm. - ANSWER- False If a filter element is damaged during cleaning, it should be repaired and placed back in service. - ANSWER- False Clogged filters are common cause of pressure drop at tool points. - ANSWER- True Excessive line pressure is just as bad as insufficient line pressure and results in accelerated wear, possible overstressing, and premature failure of parts. - ANSWER- True Whenever you work on a part of the circuit that does not require pneumatic power, always make certain that the shutoff cock is completely open and that the system is pressurized. - ANSWER- False Scheduled maintenance on portable tools should be the responsibility of a single individual rather than the operator. - ANSWER- True The best time to make a maintenance check of the compressor room is at the end of the shift. - ANSWER- False The first thing to check for when troubleshooting a pneumatic system is to determine if there is any air pressure in the supply system. - ANSWER- True
The intake air filter should be checked at least _______ to see that no foreign materials are partially blocking the intake. - ANSWER- daily Belt-driven compressors are usually driven by two or more V-belts and they should be checked _______ for proper tightness. - ANSWER- weekly Compressor intake and discharge valves and their seats should be thouroughly cleaned ___________. - ANSWER- every 6 months to 1 year Pneumatic system drains and moisture traps should be checked ___________. - ANSWER- daily The intervals at which pneumatic cylinders should be completely overhauled depends on. - ANSWER- type of cylinder, severity of operation, and the duty cycle Probably the greatest cause of early failure of pneumatic tools is ___________. - ANSWER- lack of lubrication Referring to the _________ on the schematic drawing is the most positive way to identify system components. - ANSWER- bill of materials The ____________ section of operations manauls gives the parts breakdown of each component and this breakdown identifies the individual parts in the compnent and shows how they are assembled. - ANSWER- component and parts lists The ____________ section of the operations manual should contain a complete system schematic as well as all subsystem schematic and detailed drawings. Drawings of special linkages or assemblies of one or more components are also included in this section. - ANSWER- drawings and schematics Possible causes of an open circuit in a solenoid coil include. - ANSWER- physical damage to the coil, arcing, and heat Most of the problems in pneumatic logic circuits are caused by pipe scale and. - ANSWER- dirt, thread sealant, and other materials
