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1. In what year was FMVSS 121 introduced?
a.
1997
b.
1998
c.
1975
d.
1957
2. When a truck has no air pressure in its tanks, which warning devices are activated when the ignition key is turned on?
a.
a buzzer
b.
red light
c.
a dash gauge
d.
all of the above
d
3. What legislation mandates every required standard of a highway truck air brake system?
a.
OSHA
b.
FMVSS 105
c.
FMVSS 121
d.
NHTSA
4. If a truck is FMVSS 121 compliant, which of the following air reservoirs must be incorporated into the air brake
circuit?
a.
wet tank and purge tanks
b.
front brake and rear brake tanks
c.
supply, primary, and secondary tanks
d.
wet tank, supply tank, and air start tanks
5. When the emergency/parking brakes are released on an air-brake equipped highway tractor-trailer combination with a
three valve system, which dash control button(s) MUST be depressed before you can move the rig?
a.
system park only
b.
trailer supply
c.
tractor park
d.
all of the above
d
6. Which of the following are function(s) of slack adjusters used on truck air brake systems?
a.
multiply force applied to the S-cams
b.
define shoe to drum freeplay
c.
convert linear force to rotational force
d.
all of the above
d
7. Which types of foundation brakes are used on air-brake equipped trucks and trailers?
a.
S-cam-actuated
b.
air disc brakes
c.
air wedge-actuated
d.
all of the above
d
8. In a truck air brake system, which sub-circuit is primarily responsible for actuating front axle service brakes when the
system is functioning normally?
a.
primary circuit
b.
secondary circuit
c.
supply circuit
d.
wet circuit
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ANSWER:
b
9. In a typical FMVSS 121 compliant tractor-trailer, when you actuate the trailer hand control valve which circuit supplies
air to the trailer service brakes when the system is functioning normally?
a.
primary circuit
b.
secondary circuit
c.
supply circuit
d.
park/emergency circuit
ANSWER:
b
10. When a FMVSS-121 compliant tractor-trailer combination is moving down the highway at a speed of 50 mph, which
of the following circuits MUST be charged with air?
a.
service brake circuit
b.
primary circuit
c.
secondary circuit
d.
hold-off circuit
ANSWER:
d
11. Which of the following pressure values are FMVSS-121 compliant for governor cut-out and cut-in pressures?
a.
cut-out at 135 psi and cut-in at 115 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 115 psi and cut-in at 85 psi
12. Which of the following service application valves is sometimes referred to by truck drivers as a trolley valve or spike?
a.
trailer hand valve
b.
trailer supply valve
c.
foot valve
d.
treadle valve
ANSWER:
13. Which of the following best describes the functions of a tractor protection valve (TP)?
a.
pressure protects the tractor air supply in the event of loss of pressure in a trailer
b.
routes trailer supply air and service application signal to the trailer pneumatic circuits
c.
blocks service signal air to the trailer until trailer air supply is activated
d.
all of the above
14. When a FMVSS-121 compliant tractor-trailer is running down a highway and the driver applies the service brakes,
which of the following is true at the time of the brake application?
a.
only the service application circuit is charged with air
b.
only the hold-off circuit is charged is charged with air
c.
both service application and hold-off circuits are charged with air
d.
hold-off circuit is exhausted and service application circuit is charged with air
ANSWER:
15. If you have to make an adjustment to air system cut-out pressure, where should the adjustment be made?
a.
governor
b.
unloader valve
c.
dryer purge valve
d.
pressure protection valve
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16. An air brake equipped highway tractor features single dash air pressure gauge with two needles, one green and the
other red. What does the red needle display?
a.
service brake application pressure
b.
primary circuit pressure
c.
secondary circuit pressure
d.
hold-off pressure
17. What is the primary function of a relay valve?
a.
remote controlled service brake valve
b.
relays pressure from the primary circuit to the secondary circuit
c.
relays governor signal pressure to the unloader pistons
d.
routes hold-off air to the hold-off chambers
18. How is the relay (secondary) section of an FMVSS-121 compliant dual-circuit foot valve actuated when the air brake
circuit is functioning properly?
a.
pneumatically
b.
mechanically
c.
both mechanically and pneumatically
d.
by foot pressure alone
19. Which valves on a current FMVSS-121 compliant highway tractor are used to balance front and rear braking force
under varying operating conditions?
a.
quick release and relay valves
b.
automatic ratio and bobtail proportioning valves
c.
manually-switched front axle limiting valves
d.
relay and inversion valves
b
20. What is the function of a quick-release gladhand when used?
a.
easier to couple and uncouple than a polarized gladhand
b.
speeds service brake release timing
c.
speeds hold-off air dump at park
d.
pressure protects the hold-off circuit
b
21. What is the most common brake drum nominal dimension used on heavy-duty trucks?
a.
16.5-inch
b.
18.5-inch
c.
18-inch
d.
19.5-inch
22. Which of the following type of heavy truck foundation brakes can be actuated by a power screw?
a.
S-cam drum brakes
b.
wedge brakes
c.
disc brakes
d.
driveline brakes
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23. When should you cage a spring brake chamber?
a.
before attempting to remove and replace it
b.
when making a brake adjustment
c.
before performing a chassis lubrication
d.
both A and B
24. Which of the following factors can affect the timing of service brakes?
a.
relay valve crack pressures
b.
hose and tubing diameters and length
c.
replacing a 45-degree fitting with a 90-degree fitting
d.
all of the above
25. Technician A says that in the event of a total failure of the primary circuit in an FMVSS-121 compliant tractor-trailer
combination, the rig is designed to be brought safely to a complete stop. Technician B says that in the event of a total
failure of the primary circuit the relay section of the treadle valve will be actuated mechanically. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
26. Which of the following factors best accounts for brake feel in an air brake system?
a.
resistance of foot valve spring force versus foot pressure
b.
actual system pressure at the moment of application
c.
relative strength or weakness of the driver’s boot
d.
resistance of service application pressure versus foot pressure
27. What is the potential energy of an air brake system?
a.
the mechanical force applied to the treadle valve by a driver’s boot
b.
the volume of air contained in all air reservoirs combined
c.
a combination of pneumatic and mechanical force applied to the foundation brakes
d.
compressed air
28. Technician A says that for an air brake system to be FMVSS-121 compliant, there must be a minimum of 3 air
reservoirs on a truck. Technician B says that some OEMs use a single air tank, divided into 3 separate chambers each with
its own dump valve to meet FMVSS-121 requirements. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
29. Technician A says that current air brake systems are designed to bring a fully loaded tractor trailer combination safely
to a complete standstill in the event of a complete failure of either the primary or secondary circuits. Technician B says
that in an emergency, a tractor-trailer combination can be driven a few miles providing only the secondary circuit has
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failed. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
30. When a tractor spring brake assembly is charged with air on both its service and hold-off chambers, what results is
known as:
a.
service braking only
b.
park braking only
c.
compounding
d.
proportioning
31. Which of the following is true of hold-off pressure in current truck and trailer air brake systems?
a.
maintained at 60 psi
b.
regulated at 90 psi
c.
subject to chassis system pressure
d.
dumped when service brake is applied
32. A system air pressure loss occurs on a trailer resulting in a gradual pressure bleed down. Which of the following will
occur FIRST?
a.
service brakes on trailer apply
b.
tractor-protection valve cuts service signal to the trailer
c.
tractor-protection valve cuts the trailer supply
d.
spring brakes on trailer begin to apply when pressure drops to 60 psi
33. A driver is bringing a tractor-trailer combination to a gradual stop using the trailer service brakes only. A vehicle cuts
him off and he reacts by hitting the treadle valve with panic stop force. Which source circuit supplies the trailer service
signal from the tractor at the time of the panic application?
a.
primary only
b.
secondary only
c.
both primary and secondary
d.
trailer onboard supply
34. What is the minimum compressed air reservoir volume dedicated to the air brakes required by an FMVSS-121
compliant highway tractor?
a.
4 times total brake chamber volume
b.
8 times total brake chamber volume
c.
12 times total brake chamber volume
d.
24 times total brake chamber volume
35. What is the minimum compressed air reservoir volume dedicated to the air brakes required by an FMVSS-121
compliant highway trailer?
a.
4 times total brake chamber volume
b.
8 times total brake chamber volume
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c.
12 times total brake chamber volume
d.
24 times total brake chamber volume
36. Which of the following pressure value ranges are FMVSS-121 compliant governor cut-out pressures?
a.
60 – 90 psi
b.
90 – 115 psi
c.
115 – 135 psi
d.
120 – 150 psi
37. What governor cut-out pressure is recommended by the ATA (American Trucking Association) TMC (Technology
and Maintenance Council) for highway trucks?
a.
115 psi
b.
120 psi
c.
125 psi
d.
130 psi
38. Which of the following terms is often used to describe a truck safety pressure relief valve?
a.
emergency relay valve
b.
quick release valve
c.
pop-off valve
d.
inversion valve
39. What pressure is a pop-off valve set to trip at in most highway truck applications?
a.
governor cut-out pressure
b.
governor cut-in pressure
c.
125 psi
d.
150 psi
40. When an inversion valve is activated, which of the following occurs?
a.
some hold-off air is exhausted
b.
service air is dumped
c.
tractor protection valve closes
d.
park/emergency circuit brakes are fully applied
41. When a properly functioning treadle valve is actuated by foot pressure, which of the following will determine what
pressure is metered out to actuate the primary and secondary service circuits?
a.
mechanical force applied to the treadle
b.
actual travel of the primary piston
c.
actual system pressure at the time of the application
d.
mechanical force applied to the relay piston
42. Technician A says that the relay section of a dual circuit foot valve is actuated mechanically under normal operation.
Technician B says that the primary piston of a foot valve is actuated mechanically under normal operation. Who is
correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
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43. Technician A says that a relay piston in a foot valve responds to pneumatic signal from the primary section of the
valve, by metering out into the secondary circuit the same pressure that acts on it. Technician B says that the further a
primary piston travels through its stroke in a dual circuit foot valve, the more pressure is applied in opposition to foot
pressure. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
44. Technician A says that a trailer service brake signal is always sourced from the tractor primary circuit. Technician B
says that a trailer service signal can only pass through a tractor protection (TP) valve when it is in its ON state. Who is
correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
b
45. Technician A says that most current highway tractors use a 3-line TP valve. Technician B says that a 2-line TP valve
will remain OFF (closed) until the trailer air supply dash button is depressed. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
b
46. What are S-cam type foundation brakes mounted to?
a.
axle spindle
b.
brake drum
c.
wheel hub
d.
spider
d
47. Technician A says that when air is charged to a trailer with a spring brake priority system, it is directed to the hold-off
chambers of the spring brakes BEFORE the reservoirs are charged. Technician B says that when a trailer is equipped with
a spring brake priority system the air tanks must be fully charged with air before the parking brakes can be released. Who
is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
48. How many anchor pins are used for a pair of S-cam actuated brake shoes?
a.
one
b.
two
c.
four
d.
eight
49.
In an S-cam foundation brake, where would you find brake shoe rollers?
a.
riding the S-cam profiles
b.
on the shoe anchor
c.
S-cam bushings
d.
return spring clips
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50. What term is used to measure the aggressiveness of friction facings?
a.
inertia resistance
b.
coefficient of friction
c.
frictional tribology
d.
kinetic resistance
b
51. Technician A says that truck brake shoe edge codes are used as an exact measure of their coefficient of friction.
Technician B says that the first letter of an edge code indicates the coefficient of friction of the friction facing when cold.
Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
b
52. Technician A says that a closed-anchor brake shoe web encloses the anchor pin it pivots on. Technician B says that
most current truck S-cam brake systems use closed-anchor brake shoes. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
53. Where should grease be applied on an S-cam brake system components?
a.
S-cam profile contact face
b.
cam roller contact face
c.
cam roller pocket race
d.
all of the above
54. In current practice in a truck service facilities, when should a truck brake drum be machined?
a.
when heat checked
b.
when heat discolored
c.
when scored
d.
only when new
d
55. What is the maximum permitted service oversize dimension permitted for a standard 16.5 inch brake drum?
a.
0.060-inch
b.
0.090-inch
c.
0.120-inch
d.
0.180-inch
56. Technician A says that dual-actuated wedge brakes have better mechanical braking efficiencies than comparable S-
cam actuated brakes. Technician B says that dual-actuated wedge brakes tend to require less servicing than comparable S-
cam actuated brakes. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
57. Technician A says that air disc brakes have higher mechanical braking efficiencies than S-cam actuated, drum brakes.
Technician B says that air disc brakes offer better control than equivalent drum brakes. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
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58. Given that energy forms can only be altered not eliminated by mechanical action, what is the energy of motion
ultimately converted to by a vehicle brake system?
a.
brake dust
b.
sound
c.
kinetic energy
d.
heat
d
59. A multiple trailer train combination consisting of a tractor and two trailers is spec’d to haul close to maximum loads.
Throughout axles in the rig, where would you find the lowest relay valve crack pressures if the rig is spec’d for balanced
braking?
a.
rear axles on the pup trailer
b.
rear axles on the lead trailer
c.
tractor drive axles
d.
tractor steer axle
60. If the service chamber of a 30/30 spring brake chamber has an application pressure of 50 psi acting on its service
diaphragm, how much linear force is delivered to the slack adjuster?
a.
150 lbs
b.
300 lbs
c.
1500 lbs
d.
3000 lbs
61. If a spring brake assembly has 90 psi acting on the hold-off diaphragm and no air pressure acting on the service
diaphragm, how much linear force is delivered to the slack adjuster?
a.
2000 pounds
b.
200 pound
c.
1800 pounds
d.
none
d
62. When 1000 pounds of linear force is delivered to a 6-inch slack adjuster, how much brake torque is produced at the S-
camshaft?
a.
50 lb–ft
b.
100 lb–ft
c.
500 lb–ft
d.
1000 lb–ft
63. Technician A says that Rockwell automatic slack adjusters generally use stroke-sensing adjustment on the release
stroke. Technician B says that Gunnite slack adjusters use clearance-sensing adjustment on the apply stroke. Who is
correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
64. Technician A says that automatic slack adjusters are required to be fitted to all currently manufactured highway
tractors and trailers. Technician B says that it is recommended that an automatic slack adjuster is not adjusted after being
put in service. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
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Class:
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65. When under severe braking, the wheels of a trailer lock causing it to spin around while the tractor remains in a
straight-ahead position, the condition is known as:
a.
jackknife
b.
trailer swing
c.
plow-out
d.
brake fade
b
66. 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
67. Aerodynamic tractor-trailer rigs should have what effect on vehicle braking?
a.
Make the rig easier to stop
b.
Require increased stopping distance
c.
Should not influence braking
d.
Influence braking only at low speeds
b
68. Which of the following terms is used to describe an air brake treadle valve on a CMVSS 121 compliant highway
tractor?
a.
foot valve
b.
service brake valve
c.
dual circuit application valve
d.
all of the above
d
69. Technician A says that brake chambers convert air pressure into rotary force. Technician B says that slack adjusters
convert rotary force into linear force. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
d
70. When S-cam brakes are properly adjusted, which of the following conditions will result in the most service brake
torque?
a.
highest pressure in hold-off chambers
b.
maximum service brake pressure
c.
highest vehicle road speed
d.
shortest distance from the brake treadle valve
b
71. What would occur if all of the air leaked out of one hold-off chamber while a vehicle was moving down the highway?
a.
service brakes would apply on the affected wheel
b.
service brakes would apply on the whole rig
c.
spring brake would apply on the affected wheel
d.
parking brakes would apply on the whole rig
72. Which of the following is true of an automatic slack adjuster?
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a.
signals driver when brakes need adjusting
b.
automatically defines the amount of brake force required
c.
automatically sets the amount of hold-off chamber force
d.
adjusts brake free stroke as friction surfaces wear
d
73. Which of the following correctly describes the function of an automatic slack adjuster?
a.
converts linear force to torque
b.
acts as a lever to increase mechanical advantage
c.
resets brake free stroke as friction linings wear
d.
all of the above
d
74. Which of the following best describes the role of an air compressor?
a.
a motor
b.
an engine
c.
an air pump
d.
an air cleaner
75. Which of the following components functions to control the compressor effective cycles?
a.
treadle valve
b.
safety pop-off valve
c.
inversion valve
d.
governor
76. What is primarily used to cool air compressors on most truck air brake systems?
a.
engine coolant
b.
water
c.
ram air
d.
alcohol injection
77. How many supply tanks would a typical tractor-trailer semi-combination rig be equipped with?
a.
one for the entire rig
b.
one for the tractor, one for the trailer
c.
one for each drive axle
d.
one for each trailing axle
78. When a driver is using the trailer hand brake valve to stop a rig and then stomps on the treadle valve, what is the
source of the trailer service control signal?
a.
tractor primary circuit
b.
tractor secondary circuit
c.
trailer reservoirs
d.
trailer hold-off circuit
79. 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
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80. Technician A says that most air brake system safety pop-off valves trip open at 150 psi. Technician B says that a
safety pop-off valve should be fitted to the system supply tank. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
81. Technician A says that the system safety pop-off valve should be set at a lower pressure than governor cut-out.
Technician B says that system pressure should be maintained at a constant 120 psi. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
82. When secondary circuit signal air is routed to through the trailer service signal circuit, which brake valve is
responsible?
a.
tractor foot valve
b.
trailer hand valve
c.
tractor protection valve
d.
inversion valve
83. Technician A says that methyl hydrate is a de-icing fluid. Technician B says that alcohol is introduced into brake
systems to lubricate pneumatic valves. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
84. 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
85. What service braking is actuated by the primary circuit on a typical tandem drive axle, air brake equipped tractor?
a.
front brakes
b.
drive axle brakes
c.
emergency braking only
d.
all tractor axles
86. What service braking is actuated by the secondary circuit on a typical tandem drive axle, air brake equipped tractor?
a.
front axle brakes
b.
drive axle brakes
c.
emergency braking only
d.
all tractor axles
87. Technician A says that the tractor secondary circuit is actuated by the relay piston in a treadle valve. Technician B
says that when a treadle valve is functioning properly, the relay piston is actuated pneumatically. Who is correct?
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Class:
Date:
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
88. What is the reason for using different relay valve crack pressures in a tractor trailer semi combination?
a.
intensify tractor braking
b.
ensure the tractor brakes actuate ahead of the trailer brakes
c.
ensure the trailer brakes actuate ahead of the tractor brakes
d.
balance the braking on the tractor and the trailer
89. What is the function of the quick release valve in the hold-off circuit?
a.
accelerates parking brake application
b.
accelerates parking brake release
c.
minimizes air dump on brake release
d.
prevents application air exhaust
90. Which of the following is another way of describing the parking brake circuit?
a.
service circuit
b.
emergency circuit
c.
primary circuit
d.
secondary circuit
91. Technician A says that the only means of stopping an air brake equipped, semi-trailer combination is by actuating the
service application circuit. Technician B says that unless the hold-off circuit is fully charged with air, a semi-combination
rig cannot be moved. Who is correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
92. What amount of braking force is a spring brake chamber capable of delivering?
a.
about half that of a full service application
b.
exactly equal to a full service application
c.
two times the equivalent of a full service application
d.
mechanical force cannot be compared to pneumatic force
93. What controls a trailer parking brake circuit?
a.
the yellow diamond shaped dash valve
b.
the red octagonal shaped dash valve
c.
the driver
d.
all of the above
94. Technician A says that an inversion valve only plays a role when a rig has suffered a significant loss of air. Technician
B says that the inversion valve acts as an accumulator to provide additional air for emergency braking. Who is correct?
a.
Technician A only
b.
Technician B only
Name:
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c.
Both A and B
d.
Neither A nor B
95. What are the compounded forces that an anti-compounding valve limits?
a.
service and hold-off air pressure
b.
primary and secondary air pressure
c.
mechanical and hydraulic force
d.
mechanical spring and pneumatic service application forces
96. 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
97. Technician A says that dual-actuated wedge brakes have better mechanical efficiency than air-actuated S-cam brakes.
Technician B says that air-actuated S-cam brakes provide better stopping power than air-actuated disc brakes. Who is
correct?
a.
Technician A only
b.
Technician B only
c.
Both A and B
d.
Neither A nor B
98. What is the current required stopping distance for an FMVSS-121 compliant tractor-trailer semi-combination rig?
a.
150 feet or less
b.
250 feet or less
c.
350 feet
d.
425 feet
99. Which of the following would be more likely to meet the FMVSS-121 2010 shorter stopping distances?
a.
increased air reservoir volume
b.
increased air pressures
c.
disc brakes
d.
wedge brakes
100. When must a low pressure warning switch activate an alert?
a.
at system cut-in pressure
b.
as system cut-out pressure
c.
when actuation pressure is 5 psi
d.
when system pressure drops to 60 psi