Midterm Flashcards
Advantages of Fluid Power
Ease and Accuracy of Control
Control can be Automated by PLC or Microporcessor
Multiplication of Force
Very large forces can be generated and reversed quickly
Disadvantages of Fluid Power
Hydraulic Oil is Messy and will leak
Conductors not as easy to route as “wire”
Efficiency -> Not always the most efficient
Hazards to manage
- Fire
- Noise
- High pressure oil weak
Pressure Units
PSI
This is fairly intuitive to US one pound of force applied to one square inch
Pressure Unit
Pascal
The force of one Newton applied to the area of one square meter
Pascal’s Law
Pressure applied to a confined liquid is transmitted undiminished in all directions and acts with equal forces on all equal areas and at right angles to those areas
How is the Pascal Law the Basis for Hydrostatics
Static part implies that the fluid is confined and at rest or nearly so
Most Common Source of Contamination
Solid or Particle
Heat or Thermal
Air and Gas
Water
Chemical and Radiation
Microbial Growth
Bulit-In
External
Internally Generated
Maintenance Generated
Benefits of Cartridge Valves
Greater Design Flexibility
Lower Installed Cost
Smaller Package Size
Alleviated External Leakage
Easier Troubleshooting
Easier Maintenance
Better Organized Plumbing
Lower Noise Level
Laminar Flow
A condition of flow in a passage that is typified by slow movement of fluid in a relatively straight path alon gthe cneterline of a passage
Turbulent Flow
A condition of flow in a passage that is typified by rapid movement of fluid in a passage where the fluid is churning and bouncing off the passage walls
“Meter-In” Flow Control
To regulate the amount of fluid flow into an actuator or system
“Meter-Out” Flow Control
To regulate the flow of discharge fluid out of an actuator or system
Cavitation
A localized gaseous condition within a liquid stream which occurs where the pressure is reduced to the vapor pressure
Torque Efficiency
A function of speed and fluid viscosity
Volumetric Efficiency
A function of clearance spaces, system pressure and pump speed
Pressure Intensification
Occurs on the Annular (rod end) side of the double acting cylinder when in “meter-out” control
What can cause Cavitation at a Pump
- Can occur in overrunning loads
- Can have same negative effects in both pumps and cylinders
- May need to protect the load from falling
- Typically use some type of “meter-out” control to manage
Schematic
Vented Reservoir
Schematic
Reservoir
- Fluid Container
- Allow air to separte out
Schematic
Relief Valve
- Provide protection to hydraulic system so components dont seize or burst
Schematic
Filter
- Removing solid contamination
Schematic
Fixed Displacement Pump
- Providing a constant flow
Schematic
Variable Displacement Pump
- Providing only what the system needs
Schematic
Directional Control Way
(3 positions,4 ways)
- Direct fluid to specific location
Schematic
Double Acting Cylinder
- Moves force in both directions
Schematic
Single Acting Cylinder
- Moves force in one direction and relying on gravity to retract
Schematic
Fixed Displacement Motor
- Provides constant torque
Schematic
Variable Displacement Motor
Reversible
Schematic
Working Line
Schematic
Pilot Line (Drain)
Schematic
Variable Displacement Motor
- Range of torque/speed wanted
Schematic
Adjustable Orifice
- Restricting flow (able to adjust)
Schematic
Check Valve
- Allowing flow in one direction & not in the other way
Schematic
Flow Meter
- Measures the volume of fluid moving through
Schmetic
Pressure Gauge
Breakout Torque*
How much torque is required to start a part’s rotation from a stationary position
- Ex. Grain Auger (stopped when fully loaded)
How does breakout torque relate to running torque?
Breakout torque can be considerably less than running torque
Cylinder Stop Tube
- Limit Extension
- Can also control buckling in long cylinders
Where would a cylinder stop tube be used?
Scissor Lift
Telehandler
Where can Accumulators be used?
On sprayer booms for shock absorption
Purpose of a Accumulator
Can store or temporarily absorb, hydraulic energy in the form of fluid under pressure
Most Common Types
Spring Loaded Accumulator
Spring provides the force on the pistion
- Combination of the force and pistion area determines the pressure on the fluid in the accumulator
Most Common Types
Gas Charged Accumulator
Fluid is forced into the accumulator, gas that occupies the space is compressed
Most Common Types
Piston Accumulator
A free piston separating the gas from the fluid in a cylinder
Pilot Operated Relief Valve
Design of relief valve have a significantly lower pressure override characteristics
- used in hydraulic systems where the amount of pressure overrides is critical to protecting circuit components and hydraulic lines
Direct Acting Relief Valve
Either a ball or a poppet is held in the closed postion by an adjustable spring
- Blocks the flow path to the tank
Possible Effects of Cavitation on a Hydraulic Pump
- Pump Performance Deterioriation
- Mechanical Damage
- Noise & Vibration
Pseudo-Cavitation
Air is entering the inlet side of a pump
Symptoms of Entrained Air
- Increased Heat-Load
- Increased Noise Levels
- Decreased Efficiency
Where to look for the source of air in Hydraulic Systems
- Pump Seals
- Pipe Fittings
- Low Reservoir Fluid Level
How to confirm entrained air in a circuit
Placing a small drop of oil or grease around the leak site area
Pressure Compensated Flow Valve
A constant output flow rate into a branch circuit regardless of system input pressure or load pressure
Schematic
Pressure Compensated Flow Valve
Directional Control Valve
2 Positions, 2 Ways
Directional Control Valve
2 Position, 3 Ways
Directional Control Valve
2 Position, 4 Ways
Directional Control Valve
3 Position, 4 Ways
Directional Control Valve
3 Position, 4 Ways
