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What is hydraulics
the study of liquids
What is Pascal’s law?
Pressure applied on a confined fluid is transmitted undiminished in all directions, and acts with equal force on equal areas, and at right angles to them.
What are the advantages of hydraulic power?
- produces high power output with very small weight and size
- requires minimum day to day maintenance because the same hydraulic fluid used to drive the system is also used to lubricate the parts inside the hydraulic system.
- is simple to operate
- can be operated at varying speeds
- is reversible
- can be stalled without damage when overloaded and will start up immediately when the load is reduced
- Can be hooked up in a variety of configurations wherever they are needed to operate most efficiently.
Hydraulic systems are significantly less efficient than direct-drive systems.
True
What causes hydraulic system’s inefficiency to be more than that for direct-drive systems?
internal leakage called “slip” which is required to lubricate and cool the internal mechanical components of the hydraulic drive system.
Why is hydraulic power parasitic in nature?
it derives power from other sources
Horsepower
33,000 pounds lifted one foot in one minute.
Horsepower equation
multiply the pressure times the fluid rate.
gpm x psi
What are the major components of of the hydraulic system?
- Fluid
- Plumbing
- Pumps
- Actuators
- Reservior
- Heat Exchangers
Name a non-positive displacement pump.
C-pumps
What are non-positive displacement pumps typically used for?
fluid transfer in systems where the only resistance is created by the weight of the fluid and by friction
What force do most non-positive displacement pumps operate by?
centrifugal force
What defines a non positive displacement pump?
a pump with no positive seal between the inlet and outlet ports, and pressure capabilities are a function of drive speed.
For non positive displacement pumps, is the output reduced as the resistance is increased.
True* in fact, it is possible to completely block off the outlet while the pump is running
What is second only to contamination in the hydraulic fluid as a source of damage to hydraulic equipment?
cavitation
How is cavitaion is caused?
When you pull suction on the fluid, and the pressure at the pump drops below the vapor pressure of the fluid.
True or false, Collapsing cavitation bubbles can cause localized stress that literally explodes out small fragments of metal off the pump.
True
What is the localized damage due to cavitation called?
pitting damage
What is the best way to avoid cavitation?
by designing the equipment so there is adequate net positive suction head (NPSH). One way of doing this is placing the reservoir significantly higher than the pump and by always keeping the reservoir full.
What is the role of actuators?
actuators convert hydraulic energy back into mechanical energy.
What are the two types of hydraulic actuators?
cylinders and motors
True or False. Almost all actuators are reversible, including those used by Schlumberger
True
Motors are defined by their performance on four ratings. What are they?
- maximum pressure limitations
- displacement
- speed
- torque capacity
How can flow rate be determined?
multiplying the displacement by the rotations per minute of the device.
What is motor speed measured in?
rpm (revolutions per minute)
What is maximum motor speed rating defined as?
the highest number of revolutions per minute that the motor can maintain without sustaining damage at a given inlet pressure over a specified period of time.
What is torque defined as?
turning or twisting effort. It is the force component of the output of a motor and is expressed in inch-pounds, foot-pounds or newton-meters.
What is the mechanical efficiency of a motor?
the ratio of its actual torque delivered to its theoretical torque
True or False. Cylindrical or linear actuators output straight-line motion and force
True
True or False. Cylindrical or linear actuators have only one fluid chamber and exert force in only one direction
True
What is the role of the reservoir?
- hold the fluid
- dissipate heat
- allow entrained air to escape
- allow solids to settle
What type of reservoirs are typically used by Schlumberger?
atmospheric
Why are heat exchangers present on hydraulic circuits?
to provide more efficient temperature control of the hydraulic fluid than can be accomplished by the reservoir alone
What are a few sources of contamination in which filtering systems seek to remove?
- built in, such as debris left from the manufacturing process
- environmentally introduced, such as particles or moisture
- entering through a breather
- internally introduced, such as dirt in the fluid
Describe oil breathing in a hydraulic system.
When hot oil returns to the hydraulic reservoir and cools, it contracts
True or False, Most Schlumberger systems rely on both suction strainers and return filters
True
What are the 3 main types of valves?
- Directional control valves
- Pressure control valves
- Flow control valves
A check valve is a one-way directional valve
True
Define hydraulics
a means of transmitting power by pushing on a confined fluid. The input of the system is called the pump while the output is called an actuator.
