T3 Flashcards
What is sludge?
A thick gel-like two-phase substance composed of liquid and solid particles
Two situations where fluid temperature increases
-Increases during operation due to pressurization of the oil
-Increases when the fluid expands as it leaves the pressure relief valve
State the main difference between absorbent and adsorbent depth-type filters.
-Absorbent filters mechanically trap contaminants in oil
-Adsorbent filters mechanically trap contaminants and chemically remove them
Why are absorbent filters not used in hydraulic systems?
They may remove important additives from oil
What are filter condition indicators?
They sense the pressure difference between the filter inlet and outlet.
Where are filters placed in a hydraulic circuit?
-Pump inlet
-Working lines between pump and actuator
-On the return line before entering the reservoir
What is the main difference between sump strainers and suction filters in terms of their location?
-Sump strainers are installed at the pump inlet
-Suction filters are installed above the fluid level in the tank.
Why should suction filters be carefully inspected and replaced once clogged?
The clogged filter causes more reduction to the vacuum pressure at the pump inlet.
List 3 types of heat exchangers used in a hydraulic system.
-Radiators and finned conductors
-Shell and tube
-Immersion heat exchangers
How is the housing of working line filters different from return line filters?
The housing of working line filters are designed to stand the high working fluid pressure.
What is the purpose of fins on some types of heat exchangers?
The fins increase the exposed surface area for more heat transfer.
Which is more efficient in transferring heat: Liquid to liquid or air to liquid heat exchangers?
Liquid to liquid
Why are immersed electric heaters equipped with thermostats?
To limit the amount of heat delivered to the fluid. This helps avoid overheating.
What are two ways by which contaminants enter the system during operation?
- Dust may enter the system during rod retraction
- Dust and moisture could enter through the tank breather
What should be done to the system to ensure an adiabatic process?
The system should be perfectly insulated so no heat transfer is allowed.
What are the four main processes required for conditioning air?
-Removing entrapped dirt
-Removing water vapour
-Removing thermal energy
-Adding oil for component lubrication
Which carries less humidity; warmer or cooler air
Cooler air
What happens to excess amounts of water if the humidity is at 100%?
The excess amount of water condenses as water droplets
Should the lubricating oil be introduced between the compressor and the receiver?
No, it should be introduced before entering the working station
What is an isothermal process?
If heat is removed during the compression, temperature stays constant
What is an adiabatic process?
The process in which heat is not exchanged with the system.
5 main layers of the atmosphere
-Exosphere
-Thermosphere
-Mesosphere
-Stratosphere
-Troposphere
What is the approximate percentage of nitrogen and oxygen by volume at the sea level in the atmosphere?
78% Nitrogen
21% Oxygen
What is the main difference between a pressure relief valve and a sequence valve in terms of drain?
Sequence valves always have an external drain line.
