Final Flashcards
Advantages of Fluid Power
- Easy and accuary of control
- Control can be automated by PLC or microprocessor
- Multiplication of Force
- Very large forces can be generated and reversed quickly
Drawbacks of Fluid Power
- Hydraulic oil is messy and it will leak
- Conductors not as easy to route as “wires”
- Efficiency
- Hazards to Manage –> Fire, Noise, Hight pressure oil leak
Pressure Units
PSI
One pound of force applied to one square inch
Pressure Units
Pascal
The force of one Newton applied to the area of one square meter
Definition
Pascal’s Law
Pressure applied to a confined liquid is transmitted undiminished in all directions and acts with equal force on all equal areas and at right angles to those areas
Pascal’s Law the basis of Hydrostatics
The static part implies that the fluid is confined and at rest or nearly so
Definiton
Laminar Flow
A condition of flow in a passage that’s typified by slow movement of fluid in a relatively straight path along the cneterline of a passage
Definition
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
Definition
Meter In
To regulate the amount of fluid flow into an actuator or system
Definition
Meter Out
To regulate the flow of discharge fluid out of an actuator or system
Definition
Accumulator
A vessel, normally cylindrical, whihc is used to store fluid and gas for future release of the energy in the compressed fluid and gas
Schematic
Line
Working Main
Schematic
Pressure Compensated
Schematic
Reservoir
Schematic
Vented Reservoir
Schematic
Hydraulic Pump
Fixed Displacement
Schematic
Hydraulic Pump
Variable Displacement
Schematic
Hydraulic Motr
Fixed Displacement
Scehmatic
Hydraulic Motor
Variable Displacement
Schematic
Hydraulic Motor
Bi-directional
Schematic
Single Acting Cylinder
Schematic
Double Acting Cylinder
Schematic
Electric Motor
Schematic
Nonelectric Prime Mover
Scehmatic
Spring Load Accumulator
Schematic
Gas Charged Accumulator
Schematic
Heater
Schematic
Cooler
Schematic
Temperature Controller
Schematic
Filter, Strainer
Schematic
Pressure Gauge
Schematic
Flow Meter
Schematic
Temperature Indicator
Schematic
Direction of shaft rotation
(assume arrow on near side of shaft)
Schematic
Air Bleed
Schematic
Check Valve
Schematic
Pressure Relief
Schematic
Pressure Reducting
(No drain shown)
Schematic
Sequence Valve
Schematic
Counterbalance Valve
Schematic
Unloading Relief Valve
Schematic
Flow Control
Adjustable, Non-compensated
Schematic
2 Position/2 Way Directional Control Valve
Schematic
2 Position/3 Way Directional Control Valve
Schematic
2 Position/4 Way Directional Control Valve
Schematic
3 Position/4 Way Directional Control Valve
Schematic
3 Position/4 Way Directional Control Valve
Whats the purpose of an accumulator
- Energy source (supplement pump)
- Emergency Power
- Shock absorption (see on sprayer booms)
- Thermal expansion protection
- Leakage compensation
- Pulsation dampening
Types of Contamination
- Solid or Particle
- Heat or Thermal
- Air and Gas
- Water
- Chemical and Radiation
- Microbial Growth
- Built-in
- External
- Intermally Generated
- Maintenance Generated
Functions of an Reservoir
- Fluid container
- Cooling
- Allow air to separate out
- Allow debris to settle out
- Provide good inlet conditions to the pump
Why a resevoir may need to be pressurized
- High altitude operation
- Pump located above reservoir
- Cold weather start up
Benefits of utilizing Cartridge Valves
- Greater design flexibility
- Lower installed cost
- Smaller package size
- Alleviated external leakage
- Easier troubleshooting
- Easier maintenance
- Better organized plumbing
- Lower noise levels
Definition
Relief Valve
A valve that limits the pressure at its inlet port by exhausting flow present at its inlet port to another chamber of lower pressure potential its outlet port
Definition
Unloading Valve
A valve that’s normally closed and opens from a separte fluid source on rising pressure thats balanced against a precision spring
Definition
Simple Needle Valve
A two-way valve that may be opened or closed to block the flow of fluid in a passage
Definition
Pressure Reducing Valve
A valve that decreases the downstream pressure (at the valve outlet) to control the flow and therefore the outlet pressure to some present level
Definition
Sequence Valve
A valve that is normally closed or normally open and changes to the opposite state when pilot pressure is applied to its spring chamber at a present pressure level
Definition
Counterbalance Valve
A valve used to balance the weight of a machine or dead load by causing a back pressure in the system cylinders of sufficient magnitude to support the weight
Definition
Pilot Operated Check Valve
A special check valve that may be opened against a check load by applying pilot pressure from a secondary source to open the check to free reverse flow
Definition
Flow Divider
A mechanical device used to divide the fluid in a passage into two or more separate fluid streams
Definition
Flow Meter
An analog device which indicates the volume of fluid passing through its interior passage
Definition
Pressure Gauge
A visual indicator of pressure that is set for “zero” psi at atmospheric pressure and includes a dial which will continue to indicate the level of pressure above atmospheric pressure
Definition
Pressure Compensated Flow Control Valve
A valve used to cause a variable pressure drop in a fluid passage, thus reducing the amount of fluid that may pass through the passage regardless of pressure level at the inlet of the valve
Definition
Directional Control Valve
A valve whose primary function is to direct or prevent flow through selected channels
Definition
Cavitation
A localized gaseous condition within a liquid stream which occurs where the pressure is reduced to the vapor pressure
Definition
Starting Torque
Friction is the resistance to relative motion between two materials in contact with each other
Ex. Grain auger, grain has static to it dont want to stop an auger full of grain
Definition
Entrained Air
Any air present in excess of the saturation level of the fluid at a given pressure
Closed Circuit Hydrostatic Transmission
A provision for sensing the motor speed and using this signal to adjust the pump displacement to increase or decrease the motor speed until it reaches the set point
Open Circuit Hydrostatic Transmission
No feedback of the motor speed
Open Center Circuit
Have a passage designed in the casting that allows all inlet flow when the spool is in the neutral or cenmter position to pass through a bypass area at the low pressure drop
What happens to pump system pressure when DCV is active
When all valve spools are in neutral position (no work is being performed) the power consumed by the hydraulic system is at its lowest
Closed Center Circuit
Do not have a bypass passage and block all flow through the valve when the spool is in the neutral or center position
Standby Condition Closed Center Circuit
Closed center valves are used with variable displacement pumps where system flow in the neutral position does not exist as the pump will be in its “cut off” or “standby” position
Regenerative Flow
- Pressure is equal on both ends of cylinder
- Cylinder is effectively reduced to rod size
- Speed is increased
- Force capability is reduced
- Only applies in extension
Draw the concept of pressure override in a pressure relief valve
Direct Operated Relief Valve
Where either a ball or a poppet is held in the closed position by an adjustable spring
- This blocks the flow path to the tank
Pilot Operated Relief Valve
Used in hydraulic systems where the amont of pressure override is critical to protecting components and the hydraulic lines
How to achieve Pressure Compensated Flow
Piston or Spool Type
- By using springs to maintain a constant pressure drop across the metering orifice
What limits the allowable pressure for pressure compensated flow
An input pressure increases, output flow is restricted as either the piston or spool is closed off. This prevents an increase in output flow as the increase of input system pressure tries to force more flow through the valve
Simple Orifice
Conveniently be inserted into a hydraulic line as a stand alone valve or more typically into a hydraulic fitting as a means of restricting the flow into a branch circuit
Pressure Override
The measure of pressure increase over the nominal setting of a device when additional fluid flow is passed over the device after it initially opens
Pressure Intensification
Occurs on the Annular (rod end) side of a double acting cylinder when in “meter out” control
When do you see Pressure Intensification
Piston seal failure in meter out control
Volumetric Efficiency
A function of clearance spaces, system pressure and pump speed
Torque Efficiency
A function of speed and fluid viscosity
Temperature Contamination Effects on Hydraulic Fluid
Hydraulic fluid running over 140F effectively doubles the oxidation rate of the hydraulic fluid cutting its useful life in half
Causes for Cavitation
- Restrictions in the flow of the hydraulic fluid to the inlet
- Excessively clogged inlet screens or flters
- Running pump too fast
