Chapter 2

Question 1

hydrostatic pressure

Answer 1

• atmospheric pressure is used to bring the fluid into the pump and accelerate the fluid inside the rotating mechanism
• pump deals with high pressure and negative pressure
• pump inside reservoir is easier if dont have enough Patm = “Flooded Suction”

Question 2

specific gravity

Answer 2

ratio of density of a material to the density of water at 4 degrees celsius and 1 atm

Question 3

function of a fluid

Answer 3

transmit power, lubrication, provide cooling, & seal clearances

Question 4

viscosity

Answer 4

• internal resistance of fluid molecules sliding past each other (resistance against shear)
• temperature dependent: if temp goes up, viscosity goes down

Question 5

three types of viscosity

Answer 5

• dynamic viscosity
• saybolt universal seconds
• kinematic viscosity

Question 6

saybolt universal seconds

Answer 6

• type of kinematic viscosity

- time it takes for oil to fill up a 60 mL flask = viscosity at that temperature

Question 7

problems associated with viscosity

Answer 7

too low of a viscosity or too high of viscosity

Question 8

too low of a viscosity (too thin)

Answer 8

• too much internal leakage (leads to pump wear and hydraulic motor/cylinder efficiency)
• not enough lubrication (component wear)
• spot welding of components (high temp.)

Question 9

too high of a viscosity (too thick)

Answer 9

• cavitation

- more pressure drops (waste of energy, less efficiency)

Question 10

flash point

Answer 10

vapors will rise, ignites in the presence of an open flame (wont sustain)

Question 11

fire point

Answer 11

vapors will rise, ignite in presence of an open flame, will sustain flame for about 5 sec (about 50 degrees F more than flash point)

Question 12

autogenous ignition temp.

Answer 12

burst into flames without ignition

Question 13

additives used in petroleum based fluids

Answer 13

• oxidation inhibiters
• rust inhibiters
• anti-corrosion
• anti-foam

Question 14

laminar vs turbulent

Answer 14

want laminar because if speed of molecules is too high, there are crazy pressure drops

Question 15

Darcy’s equation

Answer 15

• for pressure change in conductors

- considering a flowing system (bc of pressure drops)

Question 16

ways to minimize corrosion and rust

Answer 16

• limit introduction of air
• select a fluid with good oxidation/rust inhibiting additives
• provide filtration

Question 17

three factors that are important when discussing fire resistance

Answer 17

flash point, fire point, and autogenous ignition temperature

Question 18

flow control valves

Answer 18

• gate valve
• globe valve
• needle valve

Question 19

temperature compensated valve

Answer 19

• sharp edged orifice

- bi metallic rod

Question 20

pressure compensated flow control valve

Answer 20

contains compensated spool and bias spring

Question 21

corrosion

Answer 21

chemical reaction between fluid and a metal surface

Question 22

rust

Answer 22

oxidation of a ferrous metal

Question 23

laminar

Answer 23

layers of fluid particles remain parallel as the flow moves along the conductor

Question 24

turbulent

Answer 24

fluid layers break down as the flow moves along the conductor

Question 25

relief valve

Answer 25

used to limit pressure in an entire circuit, direct acting or pilot operated

Question 26

reduce in circuit efficiency occurs when:

Answer 26

there is a pressure drop across the valve and no mechanical output and heat is generated

Question 27

pilot operated relief valve

Answer 27

dart is held in place by the pilot spring, when the hydraulic force on dart becomes greater than the pilot spring force, the dart is unseated and fluid flows

Question 28

cavitation

Answer 28

condition when the pump is not completely filled with fluid