T2 Flashcards
What causes oil temperature to increase when it leaves the PRV’s?
Pressure decreases while temperature increases
Why should inside the surface of a control valve be smooth?
To reduce pressure drops inside the valve
List the 2 types of internal forces used to control the internal elements of a control valve.
Springs & pilot pressure
3 basic functions of springs in control valves
- Moving the spool in a DCV
- Setting maximum pressure in a PCV
- Serving as a biasing device in pressure compensated control valves
Are pressure reducing valves normally open or normally closed?
Normally open
What is an internally drained system
Oil is allowed to drain back to the return line
What is an externally drained system
Fluid is allowed to drain directly to the reservoir and seperate from the supply line
Two functions performed by pressure in control valves
- Control the force
2 Protect the system from damage
What is cracking pressure
The minimum required pressure to provide non zero volume flow rate
Define full flow pressure
The maximum pressure reached by the springs setting to allow maximum volume flow rate
What is override pressure
The difference between full flow and cracking pressure
Are pressure relief valves normally open or normally closed?
Normally closed
What are sequence valves
Valves that allow the operation of actuators in specified order
What are the two internal modes of operation for PCVs
- Direct operated valves
- Balancing piston valves
What is lubricity
A measure of friction reduction between moving parts
How does liquids and gases viscosity change with increasing temperatures
Liquids viscosity decreases
Gases viscosity increases
What is pour point of a fluid
Pour point is the temperature below which the fluid loses its flow characterisitics
How would fluids viscosity be an advantage in a hydraulic system
Viscosity contributes to pressure drop along piping and in different components.
Why should mechanical couplers be aligned between prime movers and the pump
To reduce noise and inefficiency in transmitting power
Why is a strainer installed in a hydraulic tank
To screen out large objects before the fluid enters the pump
Why do shafts in an unbalanced vane pump require radial bearings
The pressure difference between the higher and lower pressure chambers create radial force on the rotors shaft
What is foaming in oil
Air bubbles in oil
What causes foaming in oil
Too much movement in the tank and if the return line is above the fluid level
5 main functions of a reservoir in a hydraulic system
- Storage
- Filtration
- Removes excess thermal energy
- Releases air trapped in fluid
- Remove water from fluid
