3rd 6 Flashcards
In a pneumatic system what provides the force that performs work?
compressed Air
How much work is done by a piston that exerts a force of 15lbs through a distance of 10in?
150 in-lbs
Heating a gas in a solid rigid container will ____ the ____ of the gas.
increase; pressure
Two cylinders having different diameters are connected by an air line. A force is applied to the smaller piston. The larger piston exerts a force on a load and moves it. The force on the load is ____ the force applied to the small piston, and the distance load moves is ____ the distance the small piston moves.
greater than; less than
When air flowing in a pipe reaches a section where the diameter is reduced, the speed of the air ____ and its pressure ____.
increases; decreases
A reciprocating compressor is one kind of ____ compressor
positive- displacement
In a typical reciprocating compressor, the intake valves are forced open by:
atmospheric pressure
The purpose of the intercooler between the two stages of a two stage compressor is to reduce the ____
power needed to run
The purpose of lubricating oil in a compressor is to reduce friction between the moving parts and:
improve the cooling of compressor
The advantage of unloading a compressor is to allow it to
Run without delivering air
Single-stage sliding- vane compressors can produce pressures up to
50 psi
Rotary screw compressors run at speeds ranging from ____ to ____ rpm
3,000 ; 12,000
Impeller compressors deliver air at ____ volume and ____ pressure
high; low
Compared to other compressors, centrifugal compressors
more power
Most effective way to reduce output of a centrifugal compressor is ____, but may not work if the reduction is too ____
speed variation; large
Water often collects in pneumatic systems because when air is compressed its ____ decreases
moisture capacity
Most common way to remove water vapor from the air leaving a compressor is to:
cool the air
Water cooled after coolers are typically used with ____ capacity compressors that run ____ hours a day
large; 10 or more
A desiccant removes water from air by ____ it.
absorbing
The main purpose of a receiver in a pneumatic system
maintain pressure during peak demand
The operation of an internal separator depends on
rapid change in the direction of air flow
Of the particles listed, the smallest are the ____ particles
aerosol
A filter can stop 100% of the particles down to a specific min size. Known as the filter’s ____ rating
absolute
An advantage of wetted filters over dry
can be cleaned many times
A fine mist lubricator should be used in a system if air flow is ____ and/or distance to the equipment is ____
intermittent; long
Laminar air flow in a system is made turbulent by
constrictions in pipe
Greater pressure losses occur if air is at ____ pressure, because of greater ____
low; friction
When used as a compressor discharge line, a pipe run should slope ____ in the direction of flow by 1in for every ____ ft
downward; 10
When should you use pipe joint compound in connecting NPT- threaded pipe?
Either
-if joint can’t be tightly fitted
Or
- never
[Never got the correct answer]
If an air hose is not completely depressurized when you disconnect it, the danger is a sudden
blowing of dust or chips
A four way valve has four
connecting ports
The ____ valve is a good throttling device and is suitable for high pressure service. It causes ____ pressure losses in the line
needle; high
The spool in a valve controls the flow of air by ____ from one piston to another. In a high pressure system, the spool is ____ to move
sliding; easy
An advantage of 4-way valves over 2-way and 3-way is that they
simplify controls
A valve has 5 connecting ports, 2 of which are exhaust ports. The valves is a
4-way
The cracking pressure of a simple poppet type relief valve is determined by the
spring adjustment
A diaphragm type relief valve responds very quickly to a pressure change because of its
larger pressure sensitive area
The only purpose of a pressure relief valve is to
prevent damage
An increase in pressure on a secondary side of a pressure regulating valve ____ the valve
slightly closes
The best way to guard against excessive pressure on the secondary side of a pressure regulator is
use a regulator with a built in relief valve
The thrust that can be applied when a rod of a single rod, double-acting cylinder is moving out of a cylinder is ____ the thrust that can be applied when the rod is moving in
greater than
An internal spring is sometimes used to return the piston in a ____-acting ____ rod pneumatic cylinder
single; single
The main purpose of an exhaust flow control metering valve on a pneumatic cylinder is to
limit return stroke speed
A cylinder that must be free to pivot requires a(n) ____ mounting
trunnion or clevis
You can determine whether a control valve can deliver air enough for a cylinder by calculating the ____ required by the valve
capacity coefficient
The highest torque a pneumatic motor can exert on a load is its ____ torque
stalling
The HP of a pneumatic motor varies with the ____ and the ____ of the motor shaft
speed; torque
The highest power output of a pneumatic motor occurs when its speed is
medium
An axial-piston pneumatic motor transmits force from the piston to the output shaft by means of:
cam plate and gears
Air pressure of 100psi can create hydraulic pressure of 1000psi if the air piston drives a ____ hydraulic piston
smaller diameter
The designation 52Y indicates the device is a ____
circuit breaker, anti-pump auxiliary
The accepted industry standard for showing relay contacts on circuit diagrams is to show the contacts assuming the relay is
de-energized
Protective relay zones of protection are overlapped to:
avoid leaving unprotected areas
A well designed protective relay system should provide 3 basic operational characteristics
all above
The method of symmetrical components consists of reducing any unbalanced 3 phase system of vectors in 3 ____ systems
balanced
In high current arcs in excess of 100 amps, the voltage across the arc is nearly constant at an average of around ____ volts per foot
400
Open circuits on power occur more frequently than short circuits
T or F
False
The current flowing out at the polarity marked terminal on the secondary side is substantially in phase with the current flowing in at the polarity marked terminal on the primary side
T or F
True
The ground and neutral point on a 3 phase system are on the same point
T or F
False
Circuit diagrams show ____ of the currents and voltages. [Eliminate 1]
magnitude
Plasma is defined as the state of matter in which electrons are removed from atoms or molecules, creating electronically conducting gas
T or F
True
The plasma performs what function when breaking a circuit?
flow between two open circuits
Why must air in the breaker’s high air pressure system be very dry?
because it is the insulating medium between contacts
What is the purpose of SF6 gas in air blast circuit breakers?
insulate the support column current
The purpose of the blast valve is to blow the arc from the stationary to the arcing probe. It also cools and lengthens the arc so it will extinguish at the next zero current
T or F
True
Which element is used as a time delay?
disk
Relays reduce the number of alternate links to avoid equipment damage or limit damage to a single unit
T or F
True
The links in a power system chain are: generator, power transformers, switchgear, transmission lines, distribution circuits and the utilization apparatus
T or F
True
What is the most vulnerable portion of the power system chain
transmission lines
Operating characteristic curves is a graph depicting the relationship of quantities that will cause the relay to operate
T or F
True
What is the advantage of the induction cap
instantaneous operating with ability to monitor several electrical quantities
What are the 4 basic types of electromagnetic relay operating elements
All above
A device when energized by suitable currents, voltages, or both, responds to magnitudes and relationships of those values to indicate or isolate an abnormal condition. This best describes protective relays
T or F
True
The difference between primary and backup relaying is that the primary is the SECONDARY defense and isolates a greater portion of the chain
T or F
False
Speed of an actuator may be regulated with a
flow control valve
When the flow control valve controls the amount of oil going in the actuator, the application is
meter-in
In applications where the load might tend to “run away”, the flow control application should be
meter-out
When the flow control is teed off supply line from the pump and determines the actuator speed by metering a portion of the pump delivery to tank, the application is
bleed-off
The light spring in a bypass flow control valve holds the pressure compensator normally
closed
The light speed in a restrictor type flow control holds the pressure compensator normally
open
Flow through a pressure compensated flow control valve is subject to change with variations in oil ____
temperature
Deceleration valves are usually used in a meter-out configuration
T or F
True
The use of proportional valves requires the equipment contain ____ controls
electronic
