When the governor routes air to the compressor unloader circuit, what happens?
a. the compressor drive disconnects
b. the compressor intake valves are held open
c. system air pressure is at its lowest
d. all of the above
What pressure is a pop-off valve set to trip at in most highway truck applications?
a. 125 psi
b. governor cut-out pressure
c.governor cut-in pressure
d. 150 psi
How often should truck air tanks be drained during normal operation?
a. weekly
b. at each PM service
c. daily
d. monthly
When the differential between governor cut-out and cut-in pressures is less than 20 psi, which of the following will more probably result?
a. unloader valve failure
b. lower than specified system pressures
c. extended intervals between compressor effective cycles
d. increased compressor cycling frequency
Technician A says that if the electrical supply to an air dryer is interrupted, the dryer purge valve will immediately cease to function. Technician B says that the heater used in many air dryers is cycled by a thermostat. Who is correct?
a.Technician A only
b. Technician B only
c. Both A and B
d. Neither A nor B
a buzzer
b. red light
c. a dash gauge
d. all of the above
Where does the governor sense air pressure?
a.compressor discharge
b.supply tank
c.primary tank
d. air dryer
a. 85 – 100 psi (5.8 – 7 bar)
b. 95 – 115 psi (6.6 – 7.9 bar)
c.110 – 120 psi (7.6 – 8.3 bar)
d. 100 – 105 psi (7 – 7.2 bar)
a.cut-out at 115 psi and cut-in at 85 psi
b.cut-out at 135 psi and cut-in at 90 psi
c.cut-out at 110 psi and cut-in at 80 psi
d. cut-out at 135 psi and cut-in at 115 psi
What is primarily used to cool air compressors on most truck air brake systems?
a.alcohol injection
b.ram air
c.engine coolant
d.water
a.dryer purge valve
b.governor
c.pressure protection valve
d.unloader valve
In what year was FMVSS 121 introduced?
a.1957
b.1997
c.1975
d.1998
Which of the following best describes the role of an air compressor?
a.an engine
b.an air pump
c.an air cleaner
d.a motor
Technician A says that most truck compressors today are seldom rebuilt in the field today. Technician B says that it most cases it is cost effective to rebuild compressors in the shop rather than stock rebuilt/exchange units. Who is correct
a.Technician A only
b.Technician B only
c.Both A and B
d.Neither A nor B
When must a low pressure warning switch activate an alert?
a.when system pressure drops to 60 psi
b.as system cut-out pressure
c.when actuation pressure is 5 psi
d.at system cut-in pressure
Which of the following pressure value ranges are FMVSS-121 compliantgovernor cut-out pressures?
a.60 – 90 psi
b.115 – 135 psi
c.90 – 115 psi
d.120 – 150 psi
Which of the following terms is often used to describe a truck safety pressure relief valve?
a.
emergency relay valve
b.
pop-off valve
c.
quick release valve
d.
inversion valve
What is the function of the compressor on a truck air brake system?
a.compress ambient air
b.clean ambient air
c.dry ambient air
d.all of the above
a.Technician A only
b.Technician B only
c.Both A and B
d.Neither A nor B
Which of the following components functions to control the compressor effective cycles?
a.safety pop-off valve
b.inversion valve
c.treadle valve
d.governor
b.check the primary circuit gauge needle and subtract from system pressure
c.low air pressure warning switch
d.check the actuation pressure gauge needle
What are S-cam type foundation brakes mounted to?
a.spider
b.wheel hub
c.brake drum
d.axle spindle
a.wet circuit
b.supply circuit
c.primary circuit
d.secondary circuit
What are the compounded forces that an anti-compounding valve limits?
a.
service and hold-off air pressure
b.
mechanical spring and pneumatic service application forces
c.
primary and secondary air pressure
d.
mechanical and hydraulic force
Technician A says that the steering column mounted, hand control valve actuates the tractor service brakes without applying the trailer brakes. Technician B says that the hand control valve sources its air from the tractor secondary circuit when functioning normally. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
a.
secondary circuit
b.
park/emergency circuit
c.
supply circuit
d.
primary circuit
a.
all tractor axles
b.
front brakes
c.
drive axle brakes
d.
emergency braking only
a.
by foot pressure alone
b.
pneumatically
c.
both mechanically and pneumatically
d.
mechanically
Air continuously leaks from the exhaust port of a tractor relay valve when the park brakes are released. What should be done?
a.
replace the relay valve
b.
replace the park/emergency quick-release valve
c.
repair the exhaust valve
d.
check the related spring brake chambers for hold-off pressure back-flow
a.
all tractor axles
b.
emergency braking only
c.
front axle brakes
d.
drive axle brakes
Assuming a major air leak in tractor-trailer combination that will result in complete system air pressure loss, which of the following sequence of events will occur FIRST?
a.
tractor inversion valve actuates
b.
spring brakes start to apply when hold-off air drops below 60 psi (4 bar)
c.
trailer supply button pops out
d.
tractor protection valve trips to OFF
Technician A says that when a supply reservoir is completely drained, air pressure in the primary circuit should drop to zero. Technician B says that when the secondary reservoir is completely drained, pressure in the primary reservoir should drop to zero. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
How many anchor pins are used for a pair of S-cam actuated brake shoes?
a.
eight
b.
four
c.
two
d.
one
a.
front brake and rear brake tanks
b.
wet tank, supply tank, and air start tanks
c.
supply, primary, and secondary tanks
d.
wet tank and purge tanks
a.
hold-off pressure
b.
service brake application pressure
c.
secondary circuit pressure
d.
primary circuit pressure
In an S-cam foundation brake, where would you find brake shoe rollers?
a.
on the shoe anchor
b.
S-cam bushings
c.
riding the S-cam profiles
d.
return spring clips
What is the function of a quick release valve when used in a front service brake circuit?
a.
speeds up application time
b.
speeds up release time
c.
intensifies service pressure
d.
all of the above
Who is responsible for defining OOS criteria on highway trucks?
a.
ATA
b.
OSHA
c.
CVSA
d.
FMVSS