Exam 1 Key Points

Question 1

Pascal’s Law

Answer 1

Pressure applied on a confined fluid is transmitted undiminished in all directions, acts with equal force on equal areas and at right angles to them.

P=F/A

Question 2

Bernouilli’s Law of Conservation of Energy

Answer 2

More energy going into a pipeline than going out due to decrease in height.

Question 3

Hydraulics

Answer 3

A means of transmitting power by pushing on a confined liquid.

Input - pump
Output - actuator

Question 4

Pros of Fluid Power

Answer 4

Ease and Accuracy of Control
Multiplication of force
Constant force & torque
Simplicity, Safety and Economy

Question 5

Cons of Fluid Power

Answer 5

• Oily and messy
• Catastrophic failure –> bursting lines and -loss of control
• Noisy
• Combustibility of oils

Question 6

Advantages of Hydraulics

Answer 6

• Variable Speed
• Reversible
• Overload protection
• Small packages
• Can be stalled
• Pump output is constant regardless of pressure

Question 7

8 Components of a Fluid Power System

Answer 7

Hydraulic fluid
Pump
Tank/Reservoir
Piping
Valves
Actuator
Prime Mover
Filtering

Question 8

4 Primary Functions of a Fluid Power System

Answer 8

Transmit Power
Lubricate
Dissipate Heat
Seal Clearances

Question 9

Properties of Hydraulic Fluids

Answer 9

Good Lubricity
Idea Viscosity
Chemical Stability
Compatibility w/ System Materials
High Degree of Incompressibility
Fire Resistant
Good Heat Transfer Capability
Low Density
Foam Resistance
Non-toxicity
Low Volatility

Question 10

Viscosity

Answer 10

Resistance to flow at a given temperature

**Single most important property of a hydraulic fluid

Question 11

Too high of a viscosity causes:

Answer 11

• High resistance to flow
• Increased energy consumption due to increased friction
• Increased input torque requirement at the pump
• Slow or sluggish operation/actuation
• Insufficient separation of air from the oil in the reservoir
• Pump cavitation

Question 12

Too low of a viscosity causes:

Answer 12

• Increased internal leakage
• Excess wear
• Decreased pump efficiency (volumetric) due to increased leakage and possible cylinder blow-by (could cause increased cycle times/slower machine operation)
• Internal leaking causing an increase in operating temperature

Question 13

Absolute Viscosity

Answer 13

Resistance encountered when moving one layer of liquid over another.

Question 14

Kinematic Viscosity

Answer 14

The amount of time needed for a fixed volume of oil to flow through a capillary tube.

Question 15

Temperature adversely affects:

Answer 15

• Specific weight
• Specific gravity
• Viscosity

Question 16

Purpose of valves

Answer 16

• Regulates pressure
• Controls fluid rate
• Controls direction of fluid movement

Question 17

Why does a piston retract faster than it extends?

Answer 17

Due to less volume to fill up the same amount of horsepower.

Question 18

Pumps

Answer 18

• Convert mechanical energy into hydraulic energy
• Supply fluids at the correct flow rate and/or pressure to components downstream of the pump
• Pumps do not generate or manipulate operating pressure in a hydraulic system - they produce flow

Question 19

Pumping Theory

Answer 19

• Partial vacuum is created at inlet
• Atm. pressure pushes fluid out of the reservoir and into pump intake
• Mechanically, the pump pushes the fluid out of the discharge
• Pumps create flow and pressure as a result of the resistance to that flow

Question 20

Pump Classifications

Answer 20

Positive Displacement

Non-positive Displacement

Question 21

Positive Displacement

Answer 21

Delivers the same amt. of fluid per shaft revolution despite the outlet flow of pressure

Question 22

Non-positive Displacement

Answer 22

Flow rate varies greatly with changes in resistance flow