Apparatus systems explained for practical test

Question 1

main components of air brake system

Answer 1

air compressor
governor
air dryer
storage tanks (3-new, 4-old)
treadle valve
brake chambers and slack adjustors
brake linings and drums

Question 2

briefly describe the air compressor

Answer 2

2 cylinder piston type reciprocating compressor that is gear driven and in constant drive with the engine. It is lubricated by engines oil and cooled from engines cooling system. 2 stages loading or unloading

Question 3

briefly describe governor

Answer 3

controls the cut in and cut out pressure in the system by telling compressor when to be in loading or unloading stage. Pressure builds against piston to overcome spring tension to either cut in or cut out. (piston moves up for cut out, down cut in)

Question 4

describe air dryer

Answer 4

A desiccant type filter that removes water, oil and other contaminants from the air system before it reaches the supply tank (wet). Works in 2 cycles- charge cycle and purge cycle

Question 5

explain charge cycle

Answer 5

when compressor is in loading stage (cut in), air flows thru oil separator which removes water, oil and other contaminants. Then it moves up thru the desiccant filter becoming more dry as it moves upward. (removes 95% water vapor). Air exits thru check valve and fills the purge volume between outer shell and desiccant filter, this dry air moves down thru this space to the supply tank

Question 6

explain purge cycle

Answer 6

cut out pressure is reached the compressor unloads and purge cycle begins. Purge valve opens and contaminants in dryer cover, oil separator expel immediately. The air that was flowing up thru desiccant filter changes direction and flows down toward purge valve. The dry air flowing back down reactivates the desiccant material b/c it removes the water vapor that was on it. Full process usually takes 15-30 seconds

Question 7

explain air compressor for eclipse CAFS

Answer 7

GHH Rand rotary screw type compressor model CF75ED. Its driven by a polychain and pneumatic clutch thru the pump transmission by utilizing an extended impeller shaft. Fully encapsulated so it injects oil into itself, where it lubricates, seals, cools and silences the compressor. Max rpm is 8950. Compressor is cooled by tank water w/ norm operating temp 200-225, max 235, shut off automatically at 250* w/ overheat light activating.
3 modes- unload, fixed (150psi), auto

Question 8

explain discharge relief valve

Answer 8

spring loaded, pressure actuated safety device that’s mounted between the discharge and intake side of the pump that protects the nozzle member and components of the pump from high pressure surges by relieving excess pressure from the discharge side of the pump and routing it back to intake side. 2 main components, Pilot Valve and Relief Valve proper. Pilot valve hydraulically controls function of relief valve. Controls pressure from 75-300psi

Question 9

explain intake relief valve

Answer 9

safety valve that dumps excess pressure from the intake side of the pump. It makes it less likely that water hammer will burst a supply line. 2 main components- Pilot valve and Main valve. pilot valve hydraulically controls the main valve. Controls pressure of 50-250psi. (BFD 200psi)

Question 10

main components of priming system ’08s

Answer 10

priming switch
priming pump- rotary vane positive displacement
priming valve

Question 11

briefly describe how priming pump works

Answer 11

As priming pump is activated, the vanes rotating create a seal, this results in a vacuum in the priming pump. Once the pumps vacuum is less than atmospheric pressure the pump is primed

Question 12

explain what components and parts make up the emergency hydraulic operation on T11, 12 if there’s pto failure

Answer 12

emergency hydraulic switch in cab
12 volt rotary vane positive displacement pump
40 gallon hydraulic reservoir

Question 13

Define cavitation

Answer 13

Increase in RPM without an increase in pressure. The pump is trying to put out more water than it’s getting in, this causes the pump to “run away”. This creates a vacuum and drops atmospheric pressure in the pump. When this happens water can boil as low a 50-60*F. Boiling water enters the pump they collapse or implode. Them imploding against the pump causes damage such as pitting

Question 14

Explain the compression brake or jake brake?

Answer 14

Uses the engine compression to slow the vehicle during the compression stroke. Near the end of the compression stroke the slave piston opens the exhaust valve and releases the air, this wastes the energy created during the stroke and slows the vehicle. Has 3 settings low, medium, high. This is how many cylinders it’s forcing air out of, low-2 cylinders, med-4, high-6

Question 15

Maintenance of discharge relief valve?

Answer 15

4 way valve off remove strainer and clean it
Throttle up to 150 psi
Turn 4 way valve off and on a few times
Replace strainer

With 4 way valve on turn pilot valve all the way counterclockwise to relieve spring pressure
Turn 4 way valve off and on several times

Question 16

Explain the fuel filter/water separator

Answer 16

Located between the fuel tank and the engine, it separates the water from the fuel and filters the fuel before it reaches the engine. Works in 3 separate stages- separating, coalescing, and filtering
Separating- uses a centrifugal action and separates liquid and solid contaminants down to 30 micron, the heavier contaminants fall to bottom of bowl.
Coalescing- some lighter contaminants are floating and eventually bead together and fall to the bottom of the bowl
Filtering- remaining minute contaminants are filtered out thru the replacement element
Because water is heavier than fuel it sinks to the bottom and will send electric signal to fuel water indicator in cab. Filter must be drained.

Question 17

Explain the auxiliary cooler?

Answer 17

Aux cooler is used to cool the water temp of the engine. Coolant flows thru small tubes in the exchanger or cooler. When aux knob is used cool water from the pump enters the cooler or exchanger and flows around the small tubes that the coolant is moving thru and exchanges heat thus cooling it down. The water than flows back thru another hose to the pump

Question 18

Explain turbocharger on ’08s

Answer 18

Exhaust gases goes to high pressure turbo (bottom) and spins turbine, it than moves up to low pressure turbo and spins that turbine, it than moves thru waste gate and out exhaust system.
During this time, new air has come in thru filter and goes to low pressure turbo and gains speed, than goes to high pressure turbo and gains more speed, than is pushed out to pre cooler where it’s cooled and than to after cooler and eventually cooler air is pushed into cylinders to ignite. The more air added the more fuel is injected creating more horsepower.

Question 19

Explain the retarder

Answer 19

Located at the output of the transmission and consists of vaned rotor which rotates in a vaned cavity. When retarder pedal is pressed trans fluid from the accumulator is released and directed into the retarder cavity. The interaction of the fluid with the vanes causes the vehicle to slow

Question 20

Explain Donaldson air restriction indicator?

Answer 20

Monitors the air filter to have sufficient air flow. When restriction limit is reached and filter service is needed a bright red shows thru the window. Once filter is replaced reset by pushing on top of indicator.
(It uses a water manometer, when pressure increases water rises, when 25” is reached red indicator shows)

Question 21

Main components of priming system old rigs?

Answer 21

Priming handle
Priming pump- positive displacement rotary vane
Priming valve
Priming tank

Question 22

Rotary screw compressor works how

Answer 22

Has 2 meshing screws (rotors) that move in a continuous sweeping motion to compress air. Lubricating oil bridges space between the screws which provides a hydraulic seal and transfers mechanical energy. (Very little pulsation with this type compared to piston type compressor)

Question 23

Variable demand pump does what

Answer 23

Pumps the amount of oil that the hydraulic system needs