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Applied Fluid Power > Chapter 8 > Flashcards

Chapter 8 Flashcards

1
Q

four functions of a hydraulic fluid

A
  • transmit power
  • lubricate
  • seal clearances
  • provide cooling
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2
Q

effects of high temperature

A
  • oxidation of the oil
  • formation of insoluble gums, varnishes, and acids
  • deterioration of seals (they harden and leakage begins)
  • loss of lubricity
  • changes in viscosity
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3
Q

lubricity

A

the ability of the fluid to maintain a film between moving parts

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4
Q

indicator of high oil temperature

A
  • it will have a darker color and an odor of scorched oil

- heat-peeled paint on the surface of the components or reservoir

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5
Q

sources of heat generation

A
  • friction
  • undersized hoses/reservoir
  • fluid returning at high pressure over the relief unnecessarily
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6
Q

three types of heat exchangers are used to cool hydraulic oil

A
  • shell-and-tube
  • air cooled heat exchanger
  • plate and coil
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7
Q

three types of failure

A

degradation, intermittent, and catastrophic

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8
Q

degradation

A

the performance of the component degrades over time as surfaces wear, clearances increase, and leakage increases

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9
Q

intermittent

A

valves stick and then break loose such that operation is intermittent.

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10
Q

catastrophic

A

catastrophic failure occurs when a major component breaks apart. Often, debris causes the failure of other components, and a total replacement of the circuit is required

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11
Q

four sources of contamination in hydraulic fluid

A

built-in contamination, contaminated new oil, ingressed contamination, and internally generated contaminate

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12
Q

built-in contamination

A

this is contaminate that was left in the system when it was assembled

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13
Q

contaminated new oil

A

contaminate is introduced during the manufacture and subsequent handling of oil

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14
Q

ingressed contamination

A

this contaminate can enter with air flowing into the reservoir through the breather cap, or it can ride in on a cylinder rod

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15
Q

internally generated contaminate

A

particles removed from the interior surface of the components will circulate in the system until they are removed. Each impact of one of these particles with a surface causes more damage. This phenomenon is known as the wear regeneration cycle.

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16
Q

internally generated contamination causes damage in the following ways

A
  • abrasive wear: particles are hard, bridge across the clearance between two moving surfaces and abrade one or both surfaces
  • adhesive wear: moving parts adhere, or stick together, and damage results
  • fatigue: stress causes a crack which causes the surface to fall apart
  • erosive: particles erode the surface away
  • cavitation: shock waves from cavitation hits surface and cause damage over time
  • corrosive: chemical attack of material causes damage
17
Q

the current international standard for cleanliness of a hydraulic or lubricating fluid

A

ISO 4406: specifies a laboratory particle counting procedure to determine number and size (in microns) of solid particles in a milliliter of fluid

18
Q

solutions to heat generation

A
  • pump unloading (tandem center, selection of pressure, hi-lo system, pressure comp pump)
  • use less tees/crossings b/c of pressure drops
  • place values in system sized for max flow
19
Q

high temperature

A

temp higher than 160F causes a break down of fluid

-solution: heat exchangers

20
Q

clean fluid requires filtration. different ratings are

A
  • GPM rating: sized for max flow rate
  • psi rating: can undergo negative pressure
  • micron rating: cellulose (paper filter) and mesh (wire filter) [40 micron to 5 micron]
  • beta rating: ratio of particles
21
Q

silting

A

very small particles are forced into clearances by pressure and blocks the valve

22
Q

a number of factors are considered in setting a target cleanliness level

A
  • components in a system
  • fluid
  • start-up temperature
  • duty cycle
  • system design life
  • cost of production interruption
  • safety
23
Q

4 types of maintenance

A
  • none
  • preventive (set schedule)
  • corrective (fix as needed)
  • predictive
24
Q

where to place filters

A
  • before the pump (suction strainer/filter)

- after the pump to protect expensive components such as electric servo valves and proportional valves

25
Q

proportional valves

A

can control how much spool moves, it is a combination of a directional control valve and flow control valve, needs a high pressure filter to come before it

26
Q

servo valves

A

need very clean fluid b/c of small orifices, usually put a 2 or 2.5 micron filter before it

27
Q

three locations for placement of filter

A

pressure line, return line, and offline

28
Q

ISO 4406

A

data points at 2 um, 5 um, and 15 um

29
Q

fluids

A
  • petroleum based (have additives)
  • emulsions (fire resistant, oil and water)
  • synthetic (glycols, phosphate = fire resistant)

Applied Fluid Power (11 decks)

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