Gear Pumps and Hydraulic Systems
Gear Pumps
Two gears running together create flow.
Typically less expensive.
Less susceptible to contamination due to larger gears.
Fixed displacement: RPM directly relates to pump output.
Basic operating principle: convert mechanical energy into hydraulic energy (flow).
Pump Displacement
Fixed Displacement: Output is directly proportional to RPM. More basic.
Variable Displacement: Output can be adjusted, sometimes pressure compensated, reacting to load. More advanced.
Energy Conversion
Pumps convert mechanical energy to hydraulic energy (flow).
Pumps create oil FLOW, not pressure.
Pressure arises from resistance to flow.
Types of Pumps
Non-Positive Displacement: Inlet and outlet are hydraulically connected (e.g., water pump in a pickup truck).
Outlet restriction decreases flow.
Positive Displacement: No intentional hydraulic connection between inlet and outlet.
Requires a pressure relief valve for protection because it will continue to pump. If you don't release the pressure, something in the system could fail.
Displacement Defined
Displacement: Amount of oil flow a pump delivers per revolution of the input shaft.
Units: inches cubed per revolution or centimeters cubed per revolution.
Calculating Pump Flow Rate
Flow rate is the amount of oil flow a pump delivers in a given period of time.
Units: US gallons per minute (imperial) or liters per minute (metric).
Canada typically uses metric (liters).
Formula (Imperial)
231 is a constant (inches cubed per gallon).
Example
Pump displacement = 8 inches cubed per revolution
RPM = 1000
Understanding the importance of pump drive speed to determine the pump flow rate.
Formula (Metric): Same formula, different units.
Hydraulic System Components
Internal combustion engine drives the pump, could be an electric motor.
Reservoir: Vented type
Filter: Strainer (typically 100 mesh in the tank)
System Flow
Increasing pump speed (RPM) increases system flow.
More flow increases the speed of actuators (e.g., hydraulic cylinders lifting a dump body).
Flow makes it go; speed is not a result of pressure.
Pump Efficiency
How well the pump utilizes the power supply.
Two types: mechanical and volumetric.
Mechanical Efficiency
Amount of energy out of a pump compared to the energy put in.
Losses occur due to friction (e.g., 5% loss due to friction, resulting in heat).
As a pump wears, efficiency decreases.
Volumetric Efficiency
Comparison of theoretical flow (what it should deliver) and actual flow.
Example: A 90% volumetrically efficient pump with a theoretical delivery of 291.6 liters per minute may have 29 liters slipping back from the pump outlet to the inlet. 262.44 liters per minute is actually delivered to the system.
As the pump wears, volumetric efficiency decreases.
Pressure Ratings
The amount of pressure the pump can safely handle.
Depends on pump construction and application.
Gear Type Hydraulic Pumps
Unbalanced: Cannot handle high pressures like balanced pumps can.
Limit maximum pressure typically between 1,500-2,500 psi.
Refer to the manual for specific pressure ratings.
End plate may be used to limit internal leakage.
Approximately 80-85% efficient.
Rugged, durable, simple design.
Most popular type.
Not capable of variable displacement.
Output is determined by RPM.
Fluid Storage
Accumulators used to store energy.
Open triangle facing down: Gas-charged accumulator.
Liquid typically colored in symbols; gas typically open.
Heater space in, cooler space out.
Hydraulic Animations
Animations available to visualize pump and valve operation.
Pressure control valve example: Increase/decrease pressure to see valve movement.
The system's happy at normal flow/pressure. We haven't increased the pressure to a point where is needs to be relieved.
If, all of a sudden, the pressure is too high, the valve opens up and relieves the rest of the oil back to the tank.
Gear Pump Operation (Animation)
Gears rotate to generate flow.
Oil is pulled in as the gears come out of mesh, creating a vacuum.
Oil is carried around the housing in chambers between the teeth.
Oil is forced out of the pressure port as teeth go back into mesh.
Hydraulic Systems - Dump Truck Example
Gear pump driven by the PTO (Power Take-Off).
Valve positions: Raise, Hold, Lower.
Cylinder: Telescopic type.
Oil flows from the pump, extending the cylinder (raising the dump body).
In the hold position, the valve spool blocks pressure in the ram to hold it in place.
In the Lower position the spool shifts over, allowing the dump body to go down.
Additional Gear Pump Details
Both gears are turning creating the vacuum, which allows oil to get sucked into the gears there.
We know the oil from the reservoir or from the tank we are pointing out the outlet on our pump
We talked about pressure plates and other things that are incorporated in gear pumps to prevent more damage than it already does.
So even if they are hunting or non-hunting, people like to put gears back where they came from. Even if they're hunting or non hunting. It's a good idea to put those gears back from where they came from. Because when they first fired up, gears start to wear in the area wear into each other and create their own pattern. If you change the wear pattern, you're gonna be creating extra wear extra material. Extra material because because they have already cut themselves in. A big space here could lose efficiency.
Gear Pump Considerations
The outlet pressure against teeth causes heavy side loading on the shafts.
Pressure plates absorb impacts to prevent damage.
Mark gears before disassembly to maintain their wear patterns.
Matching gears and gears is critical. Gear shop does it for many many years already, right?
Pump Direction and Cavitation
Internal type gear pump, unidirectional pumps, have an inlet port that is larger on outlet port.
Counter clockwise rotation gear the gears come out of mesh on the inlet side.
Caused by sterile spunk restricted oil for cause cavitation. We we've been restricted oil flow because you can see they had it there, that it's being restricted oil.
Make sure we know it's cause from a restricted inlet oil flow when we talk about cavitation.
Cavitation Damage
Pressure spikes in the pump. This is the term that the implosion of what's happening due to cavitation, that it could be up to a million pounds per square inch in the pump when we operating the pump. What happens is the vapor's compressed by high pressure oil, and we continual starve in the pump, this is a kind of stuff that's going to be formed. You can get up to they said about a million pounds per square inch inside the pump, so and the sound is what you are hearing during all of that operation.
Cavitation vs. Aeration
Similar noise, but air is compressed, reducing lubrication and causing erratic jerky movement with the cylinders or pump due to air system. Leads to potential damage.
Leaks in oil hydraulic pump inlet line cause the air to draw into pump and machine it could draw into the system if you find an inlet leak, you will probably find it during what running. What do the what do they called there? A puddle there?
Hydraulic Pressure Relief
Protects the systems from excessive pressure type damage.
Directional Control Terminology
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Directional Control Valves
Three Common directional control valves:
Puppet valve
Rotary valve
Spool Valve. Which are we got for.