Hydraulics Flashcards
1
Q
The engineering science pertaining to the use of liquid pressure and flow to transmit power, multiply force, and modify motion
A
Hydraulics
2
Q
Pressure applied to a confined fluid is transmitted undiminished an all direction and acts with equal force on equal areas and at right angles to them
A
Pascal’s Law
3
Q
Three parts of the formula triangle for Pascal’s law
A
Force, Area, Pressure
4
Q
What is at the top of the formula triangle for Pascal’s law?
A
Force
5
Q
The measure of a bounded region or plane
A
Area
6
Q
Anything that tends to produce or modify motion
A
Force
7
Q
Force per unit area
A
Pressure
8
Q
Area is usually expressed in ___
A
Square inches
9
Q
Force is usually expressed in ___
A
Units of weight
10
Q
Pressure is measured in ___
A
PSI
11
Q
Two working surface areas inside a cylinder
A
Cap or blind end area
Net or rod end area
12
Q
Hydraulic pressure working on the cap end forces the piston rod to ___
A
Extend
13
Q
Hydraulic pressure working on the net area forces the piston rod to ___
A
Retract
14
Q
Cap end area =
A
D^2 x .7854
15
Q
The amount of weight a cylinder will push or pull
A
Working force
16
Q
Scientific unit of pressure roughly equal to the atmospheric pressure on earth at sea level
A
Bar
17
Q
psi =
A
bar x 14.5
18
Q
bar =
A
psi / 14.5
19
Q
The ability or capacity to do work
A
Energy
20
Q
Two types of energy
A
Potential
Kinetic
21
Q
Also known as stored energy
A
Potential energy
22
Q
This form of energy is present in a hydraulic system in the form of fluid pressure
A
Potential energy
23
Q
Also known as energy in motion
A
Kinetic energy
24
Q
This form of energy is present in a hydraulic system in the form of fluid flow
A
Kinetic energy
25
Energy can neither be created nor destroyed, but instead will simply be changed from one energy form to another
Law of conservation of energy
26
In hydraulics the ___ provides the mechanical advantage
Difference in piston areas
27
Hydraulic symbols are authorised and controlled by ____ under ___
International Standards Organisation (ISO)
| ISO Code 1219-2
28
Establishes principles for the use of symbols and specifies basic symbols and rules for devising functional symbols
ISO Code 1219-2
29
ANSI
American National Standards Institute
30
ISO
International Standards Organisation
31
NFPA
National Fluid Power Association
32
Provide a graphic depiction of hydraulic systems
Hydraulic symbols
33
Symbols shall be drawn to show the ___ position
At rest or neutral
34
The basic component for a rotating component
A circle
35
One triangle indicates
Unidirectional
36
Two triangles indicate
Bidirectional
37
Half circle indicates
A rotating component with a limited angle of rotation
38
The basic component for a control component
Square
39
The basic symbol of a conditioning apparatus
Diamond
40
Shown by a continuous solid line
Working line
41
Carries fill system flow, and includes suction line, pressure lines, and return lines
Working line
42
Shown by a dashed line
Pilot line
43
Used to send a signal or to control a valve or other component. These lines carry system pressures, but very little flow
Pilot line
44
Shown by a dashed line, small dashes
Drain line
45
Used to carry internal leakage fluid from a component to the reservoir. Very low pressure
Drain line
46
Shown by a short and long dashed line
Component enclosure line
47
Used to enclose two or more components to indicated close grouping
Component enclosure line
48
Shown by a double line
Mechanical connection line
49
Used to indicate mechanical connection
Mechanical connection line
50
Variable displacement for pump symbol
Arrow across the circle at a diagonal
51
Stores system fluid
Reservoir
52
Energy source for the pump
Prime mover
53
Provides fluid flow
Hydraulic pump
54
Protects system from over pressurisation
Pressure relief valve
55
Directs fluid flow
Directional control valve
56
Convert hydraulic energy to mechanical energy
Actuator
57
Removes contaminates from the fluid
Filtering device
58
Carry the fluid flow throughout the system
Conductors
59
Two types of hydraulic circuits
Open loop
| Closed loop
60
Most common type of hydraulic circuit
Open loop
61
The main characteristic of this hydraulic circuit is that atmospheric pressure forces fluid from the reservoir up the pump, and the pump creates flow for the circuit
Open loop
62
Hydraulic circuit where neither the inlet port nor outlet port of the pump or motor is connected to the reservoir
Closed loop
63
Fluid in a hydraulic system has four main requirements
Transmit power
Cool
Seal
Lubricate
64
Viscosity is measured in ___
Saybolt Seconds Universal (SSU)
65
Most commonly used hydraulic fluid
Navy standard hydraulic oil series 2 and 8
66
Numbering system used to measure a fluid's resistance to viscosity changes with changes in temperatures
Viscosity Index
67
A VI of ___ is preferred in most hydraulic systems
90 or above
68
Three general groups that hydraulic fluids can be placed in
Petroleum oils
Fire-resistant
Biodegradable
69
Most common group/category of hydraulic fluid
Petroleum oils
70
This hydraulic fluid can be blended with synthetic fluids
Petroleum oils
71
Three types of fire-resistant hydraulic fluids
Water in oil emulsion
Water-based
Synthetics
72
This hydraulic fluid is made of vegetable oil
Biodegradable
73
This fluid is comparable to petroleum based hydraulic fluids
Biodegradable
74
Any material foreign to a hydraulic fluid that has a harmful effect on system performance
Contamination
75
Approximately ___ of all hydraulic system failures result from contamination
80%
76
Filters may be made of many materials except ___
Wire screen
77
Filters are rated by __
Micron size
78
A micron is ___
1-millionth of a metre, or 39-millionths of an inch
79
The smallest particle visible to the naked eye is about ___
40 microns
80
A simple wire screen or wire strainer is rated for filtering fineness by ____
Mesh number or standard sieve number
81
The higher the mesh of sieve number ___
The finer the screen
82
When a filter is specified as so many microns, it usually refers to the filter's ____
Nominal rating
83
The size of the largest opening or pore in the filter
Absolute rating
84
Installed on the pump inlet side of the reservoir and may be located internally or externally
Strainer
85
Use a relatively coarse filtering element constructed of fine mesh wire
Inlet strainers
86
Should only be expected to prevent large particles from entering the pump and causing catastrophic failure
Inlet strainers
87
Two important requirements for any inlet strainer
- The strainer must be capable of passing the full pump volume within the permitted inlet pressure drop for that pump
- The strainer must provide bypass flow which is still within that limit if the strainer element is blocked
88
Remove contamination from hydraulic fluid, and is accomplished by forcing the fluid stream to pass through a porous filter element which traps the contaminants
Function of a filter
89
Filter elements are divided into two classifications
Surface-type elements
| Depth-type elements
90
The fluid stream has a straight flow path through the element, and contamination is trapped on the surface of the element
Surface-type elements
91
In this type of element, the fluid flow is forced to pass through a multiple layer element, and the multiple layers trap the contamination
Depth-type elements
92
The location of the filtering device is usually determined by the ___
Manufacturer
93
Two primary locations for filters
Pump discharge side
| Return side
94
Filters the fluid before is does the work
Pump discharge side
95
Filters the fluid before it returns to the reservoir
Return side
96
Used to measure the performance of filter elements
Filter ratings
97
Three types of filter ratings
Micron rating
Flow rate
Filter pressure rating
98
Filter's ability to effectively allow fill system flow to pass through the filter without causing undesired pressure increase
Flow rate
99
Filter's ability to remove contamination at a specified micron size
Micron rating
100
Filter's ability to function properly regardless of system pressure
Filter pressure rating
101
Provide a visual means of detecting filter condition while the system is operating
Filter condition indicators
102
Indicators with green, yellow, and red visuals react to the ____
Pressure differential
103
Reacts to the position of the bypass check valve
Mechanical indicator
104
Installed in a filter to ensure an uninterrupted flow of fluid
Bypass check valves
105
Symbol for filtering device
Conditioning component symbol with dashed line through the middle
106
Three general categories of contamination in a system
Built-in contamination
Ingress contamination
Internally generated contamination
107
Also referred to as environmental contamination
Ingress contamination
108
Occurs when there are solid particles present in the hydraulic fluid
Abrasion
109
Refers to repeated stressing of a surface
Fatigue
110
Caused by dynamic pressure reduction on hydraulic fluid, typically occurring in both the pump inlet and in an actuator
Cavitation
111
Indications of cavitation can be ___
Pump noise and fluid temperature rise
112
The presence of air or gas bubbles in the fluid
Aeration
113
Spongy actuator operation may be due to __
Aeration
114
Mechanical clearances within hydraulic components can be divided into two principle zones
- Up to 5 micrometers
| - 10 - 20 micrometers
115
Mechanical clearances are generally measured in ___
thousandths of an inch, ten thousandths of an inch, or fractions of a mm
116
Provides information on hydraulic systems that shall be tested and frequency of testing. Also provides information on sampling procedures
NEM, Chapter 262
117
Samples taken from a non operating system
Thief samples
118
Thief samples should only be taken when ___
The system cannot be operated
119
Sampling intervals on hydraulic systems that do not have a defined oil change interval shall be taken ____
Quarterly
120
Oil will be darker than original oil
Oxidation
121
Fluid will be cloudy or water droplets will be present
Water
122
Air will be visible when the sample is first drawn
Air
123
If you can see particles in the fluid, then is is very dirty
Contaminants
124
Store and supply hydraulic fluid for a system
Primary function of a reservoir
125
Transfer heat and allow for contamination settling and de-aeration of the system
Reservoirs
126
Sometimes referred to as a non pressurised reservoir
Vented reservoir
127
Most common type of reservoir used in the CG
Vented reservoir
128
In the event sea level atmospheric pressure is not available or the environment is extremely dirty, a ___ is used
Pressurised reservoir
129
Act as heat exchangers by allowing waste heat to dissipate through the walls
Reservoirs
130
Reservoirs are usually mounted in a location that is ___
2 to 6 inches above the deck
131
Constructed of welded steel plates with legs on all four corners to elevate it off the deck
Reservoir
132
Allows for easy fluid removal
Drain plug
133
Allows for air exchange
Breather assembly
134
In the case of pressurised reservoirs, a ___ replaces the air breather
Schrader-type
135
Used to check the fluid level to avoid exposing the system to contamination
Sight gauge
136
The filler opening is normally incorporated into the ___
Breather assembly
137
Separates the inlet line from the return line, forcing the fluid to slow down and allowing time for cooling, contamination settling, and air purging
Baffle plate
138
Removable plate normally installed on the ends of the reservoir, allowing access to the inside of the tank for maintenance and cleaning
Clean-out/access plate
139
Suction lines begin and return lines end ___ above the bottom of the reservoir
2 inches
140
Drain lines terminate just below ___
The low fluid level in the reservoir
141
A reservoirs capacity should be __
2 to 3 times pump flow
142
When fluid pressure increases, fluid temperature
Increases
143
Can be installed to supplement the cooling effects of the reservoir
Heat exchanger coolers
144
Type of heat exchanger used for hydraulic fluid
Shell and tube
145
May be installed in the reservoirs where the ambient temperatures are low
Heaters
146
The fluid temperature in the reservoir should be maintained above ___
110 degrees F
147
Component that absorbs hydraulic shock and stores fluid under system pressure as an auxilary energy source
Accumulator
148
Used in an accumulator to maintain pressure
Springs, weights, compressed gas
149
Absorbs a quantity of fluid above a preset pressure and releases it when the pressure reduces, thereby reducing pressure spikes or surges in some systems
Accumulator
150
Hydraulic shock absorber
Accumulator
151
Two types of accumulators commonly found in the CG
Spring loaded
| Gas charged
152
Two most common types of gas-charged accumulators
Piston-type
| Bladder or diaphragm-type
153
What kind of gas must not be used in a gas-charged accumulator
Oxygen or air
154
Most common accumulator in the CG
Gas-charged
155
Most common gas used for gas-charged accumulator
Nitrogen
156
Connect the hydraulic pump to the rest of the system
Hydraulic hoses
157
Conductor or passage used to transport fluid between components in a fluid power system
Flexible hose
158
Hydraulic hose construction
Multiple layers of rubber or other synthetic materials interlaced with wire mesh
159
Flexible rubber hose is identified by three things
Inside diametre
Service
Pressure class or working-pressure rating
160
The inside diametre of a hose is expressed in __
16ths of an inch
161
Three layers of hydraulic hose
Inner tube
Reinforcement layer
Outer cover
162
Hydraulic hoses with an overall length greater than ___ must be supported
30 inches
163
Support clamps should not be placed more than ___ apart
24 inches
164
About ___ of the total length of the hydraulic hose must be allowed as slack to provide freedom of movement under pressure
5% to 8%
165
When a flexible hose is under pressure, it:
Contracts in length and expands in diametre
166
Selecting the correct connector or fitting depends upon three things
Type of circulatory system
Fluid medium
Maximum operating pressure of the system
167
Most commonly used hydraulic connector in CG applications
JIC 37* Flare
168
Permanent hose fitting are ___ when the hose is damaged or defective
Discarded
169
Reusable hoses installed for flexible connections typically utilise one of five methods for attachment of the fitting to the hose
- One-piece reusable socket
- Segmented, bolted socket
- Segmented socket, ring and band attached
- Segmented socket, ring and bolt attached
- Solid socket, permanently attached
170
The socket component is fabricated as a single piece. Screwed or rocked onto the hose OD, followed by insertion of the nipple component
One-piece reusable socket
171
Consists of two or more segments which are bolted together on the hose after insertion of the nipple component
Segmented, bolted socket
172
Consists of three or more segments. As with the bolt-together segments, the segments, ring and band are put on the hose after insertion of the nipple. A special tool is required to compress the segments
Segmented socket, ring and band attached
173
Consists of three or more segments. As with the other segmented socket type fittings, the segments ring, nuts, and bolts are put on the hose after insertion of the nipple
Segmented socket, ring and bolt attached
174
This type of socket is permanently attached to the hose by crimping or swaging
Solid socket, permanently attached
175
Do not use what to cap open hydraulic hoses
Rags or paper
176
Shelf life for all synthetic rubber flexible hoses and prefabricated assemblies shall not exceed ___
10 years
177
Bulk storage of hoses or hose assemblies should be in a ___
Cool dry area, never exceeding 100 degrees F
178
Never stack hoses ___
Too high
179
PMS for flexible rubber hose may be determined independently for each class of cutter, except for ___
Fleet system equipment
180
A second-level hose inspection should include a thorough examination of the hose for
Soft spots
Bulges
Accelerated deterioration
181
Long hoses should be inspected with the hoses __
Pressurised and under operating conditions
182
Inspections of long hoses should include
Alignment
Hose movement
Chafing
183
Replace any hoses past their __ year service life
8
184
It is recommended that ___ of all hoses be changed each quarter to eliminate the need to change all hoses at one time
5%
185
All hoses that are included in paper-based hose logs shall be identified with __
Individual hose tags
186
Hose tags for hoses identified in a hose log shall include three pieces of information
Hose log item number
Hydro test procedure and test date
Service life
187
Hose tags shall be attached using materials that ___
Will not damage the hose assembly
188
Apply what over the area of the hose to be cut
Electrical tape
189
Use what to cut hydraulic hose
Fine-tooth hacksaw or cut off wheel
190
Install fitting socket on end of hose by ___
Threading it counterclockwise with the appropriate open end wrench and slight downward pressure with thumb
191
Back the hose socket of ___ after it bottoms
1/4 turn
192
Install fitting into socket by applying light pressure in a downward direction while turning fitting in a ____ rotation
Clockwise
193
Leave ____ clearance between nut and socket to allow nut to swivel freely
1/32" to 1/16"
194
An assembly mandrel is required for all single-wire hoses in sizes ___
1/4" through 3/4"
195
Ensure the flexible hose has not backed out of the fitting more than __
1/16"
196
Flexible hose assemblies which are assembled shall be ___ before the hose assembly is installed
Hydrostatically tested
197
Hydrostatic testing procedures require a test pressure of ___, for approximately ___
Twice the rated working pressure of the hose
| Five minutes
198
Low pressure system
Less than 150 psi
199
Those hose assemblies identified as ___ do not have to be hydrostatically tested
Condition-Based Maintenance
200
Takes mechanical energy from a prime mover, and converts it into hydraulic energy
Pump
201
Heart of the hydraulic system
Pump
202
Any energy source used to drive any hydraulic pump
Prime mover
203
Symbol for prime mover, electric motor
Circle, M inside, mechanical connection line coming off
204
Symbol for prime mover, heat engine
Square within a square, mechanical connection line coming off
205
Symbol for prime mover, reduction gear
Circle, R/G inside, mechanical connection line coming off
206
Symbol for prime mover, manual
TT shape
207
Complete absence of pressure
Absolute vacuum
208
Unit of measure for vacuum
Inches of mercury (Hg)
209
Two basic classifications of pumps
Nonpositive displacement pump
| Positive displacement pump
210
The output from this pump is reduced as restriction to flow increases
Nonpositive displacement pump
211
Designed mainly for low pressure high volume systems, such as fluid transfer systems
Nonpositive displacement pump
212
Designed to deliver a set amount of hydraulic fluid with minimal delivery loss regardless of discharge pressure
Positive displacement pump
213
The amount of flow a pump produces in a given amount of time
Delivery
214
The amount of fluid that passes through a pump in one revolution, stroke, or cycle
Displacement
215
A positive displacement pump whose displacement cannot be changed
Fixed displacement pump
216
A positive displacement pump whose displacement can be changed
Variable displacement pump
217
The pump's suction and discharge ports can be shifted without changing the pump's direction of rotation
Bi-directional pump
218
Used to create fluid flow
Pumps
219
Resistance to flow creates ___
Pressure
220
Operate on the theory of increasing and decreasing volumes within the pump
Positive displacement pump
221
Three categories of positive displacement pump
Gear
Vane
Piston
222
A ___ is created when the teeth of a gear pump unmesh
Vacuum
223
Method through which the vanes are forced out of the rotor slots
Tracking
224
Tracking is accomplished in three ways
Springs
Centrifugal force
Hydraulic fluid
225
Almost all hydraulic vane pumps are __
Balanced vane pumps
226
Two designs of piston pumps
Radial
| Axial
227
Has the pistons arranged radially in a cylinder block
Radial piston pump
228
Has the pistons arranged parallel to each other and to the axis of the cylinder block
Axial piston pump
229
Axial piston pumps may be further divided into ___
Inline (swash plate)
| Bent axis types
230
The pistons are connected to a swash plate that has a reaction ring which rotates within itself
Inline (swash plate) axial piston pump
231
The pistons are fitted to bores in the cylinder block, and the piston shoes ride against an angled swash plate
Inline axial piston pump
232
The ___ creates the reciprocating motion in the pistons and controls the displacement of the pump by controlling the piston stroke length (Inline axial piston pump)
Angled swash plate
233
There are changes in velocity and pressure when pipe diametres change, as long as there is a constant flow rate
Bernoilli's principle
234
Two types of gear pumps
External gear pump
| Internal gear pump
235
Two types of vane pumps
Unbalanced vane pump
| Balanced vane pump
236
In a balanced vane pump, rotating the cam ring 180 degrees ___
Reverses the direction of rotation
237
Taking the swash plate back past 0 degrees will create ___
Fluid flow in the opposite direction
238
Created whenever fluid flow is resisted
Pressure
239
In hydraulic systems, resistance may come from ___
Load on an actuator
| Restrictions in the system piping
240
An important characteristic of fluid is that it will always take ___
The path of least resistance
241
The conductor and the components through which the fluid passes create two types of fluid flow
Laminar flow
| Turbulent flow
242
The most desirable type of flow; has minimal friction, low velocity, and occurs in straight piping
Laminar flow
243
Fluid particles do not move smoothly parallel to the flow direction
Turbulent flow
244
This flow is caused by a drastic change in direction of flow, reduced cross-section pipe size, or fluid velocity that is too high
Turbulent flow
245
This flow causes increased friction, increased operating pressure, wasted power, and increased heat generation
Turbulent flow
246
Limit system pressure, regulate system pressure, or control a load
Pressure control valves
247
Operate on the principle of a balance between pressure and spring force
Pressure control valves
248
Only open or close enough to maintain the required or set pressure
Infinite position
249
Pressure control valves are classified by four things
Pressure operating range
Size (flow rating)
Type of connections or mounting
Design
250
Pressure control valves are normally named for ___
Their primary function
251
In pressure control valves, there are three terms used in reference to pressure
Cracking pressure
Full flow pressure
Pressure override
252
The pressure at which the valve just begins to open
Cracking pressure
253
Maximum pressure when the valve is fully open and full system flow is going through the valve
Full flow pressure
254
The difference between cracking pressure and full flow pressure
Pressure override
255
In high-pressure/high-volume systems, a high-pressure override can cause ___
A loss of power and efficiency
256
Most common types of pressure control valves
Pressure relief valves
257
Limits the maximum operating pressure for the entire system, thereby protecting the system from overpressurisation and overload
Pressure relief valves
258
Pressure relief valves are located __
Off the main line coming from the pump
259
Two types of pressure relief valves
Direct-acting
| Compound
260
Two advantages of a direct-acting pressure relief valve
Inexpensive
| Easy to maintain
261
Two disadvantages of a direct-acting pressure relief valve
Does not respond well to constant pressure changes
| Large pressure override
262
This type of pressure relief valve is used to alleviate high-pressure override
Compound
263
This pressure relief valve contains two stages: An upper stage, which contains a pilot valve, and a lower stage, which is the main valve
Compound
264
Contains ports connecting the valve to the system, a spool (also known as a balanced piston), and a 20-psi light spring that holds the balanced piston in position
Compound pressure relief valve
265
How large is the orifice in the piston in a compound pressure relief valve
.040-inch
266
The spring for the main spool is a light spring rated at ___ (Compound pressure relief valve)
20 psi
267
DCVs
Directional Control Valves
268
Direct the fluid flow in a system
Directional control valves
269
By opening and closing ports, these valves can bypass, start, and stop actuator movement
Directional control valves
270
Flow paths in DCVs known as ___
Ways
271
Allow fluid flow in one direction but will block flow in the opposite direction
One-way check valves
272
Two types of check valves
Ball type
| Poppet type
273
A ball is held against the seat by a light spring (usually 5 psi)
Ball-type check valve
274
Instead of a ball, it will have a poppet held against the seat by a light spring
Poppet-type check valve
275
Usual psi of spring in check valve
5 psi
276
Used to prevent hydraulic fluid in the pump from draining into the reservoir while the system is secured
One-way DCVs
277
Used to allow fluid to bypass the filter
Bypass check valve
278
Also known as load lock valves and are commonly used in steering systems
Pilot to open check valve
279
In a two-way DCV, the spool position in the valve determines whether ___
The valve is open or closed
280
The symbol for DCVs are broken down into several important parts
Positions
Ways
Center-type
Actuation
281
To determine the number of DCV positions ___
Count the number of boxes
282
Refers to the number of active porting connections
Ways
283
To determine the number of ways ___
Count the number of connections or lines attached to the valve
284
The ports on a DCV are labeled as ___
P - pressure
T - tank
A
B
285
Have three ports and maybe two or three position valves
Three way DCVs
286
This type of DCV will be used to reverse the direction of an actuator
Four-way DCVs
287
On most three position, four-way DCVs the end positions are ___
Parallel ported
| Cross-ported
288
With a three position valve, the center position may be one of the following
Closed
Open
Float
Tandem
289
Determines the center position of the DCV
Application of the system
290
All ports are blocked, stop the actuator at any position and hold it there
Closed center
291
When in the center position, system pressure before the valve will be at ___
Relief pressure
292
All ports are open to each other, will move the actuator, they do not have control of the load
Open center
293
Open centers are not used in systems with ___
More than one DCV
294
A, B, & T ports are open to each other
Floating center
295
Used mainly with linear actuators, used in systems with more than one DCV, will not have control of he load
Floating center
296
P & T ports are open to each other while A & B ports are blocked
Tandem center
297
Used to unload the pump in the center position, not used in systems with more than one DCV, stop the actuator at any position and hold it there, can be reversed for other operations
Tandem center
298
Two-way and three-way DCVs can have ___ on one or both ends of the spool to return it to the neutral position
Springs
299
On two-position DCVs, the spring is called ___
Spring-offset
300
On three-position DCVs, the spring is called ___
Spring-centred
301
The spool is either spring-centred or ___
Detented
302
Means to lock the sliding spool valve in one position
Detent
303
Uses a spring and steel ball in a cylinder with the ball riding in a groove on the spool
Detenting
304
Shifts the spool or rotating element of a direct-acting directional valve
Operator or actuator
305
The means through which the valve is shifted from one position to another
Actuation
306
The five categories of actuators (operators)
```
Mechanical actuators
Pneumatic actuators
Manual actuators
Electrical actuators
Hydraulic actuators
```
307
Are either plunger or wheel type, device such as a cam or cylinder will move the spool into position
Mechanical actuators
308
Use air pressure from an external source to shift the spool
Pneumatic actuators
309
Are usually levers attached to the spools through some kind of linkage. Includes hand lever, foot pedal, push button, or other mechanical means
Manual actuators
310
Known as solenoid actuators, are on/off solenoids. Upon receiving an electrical signal, the solenoid is either fully shifted or off
Electrical actuators
311
Three-position DCVs will have a solenoid ___
One each end
312
Produce a limited amount of force and will only move short distances, so this type of actuation is used only on smaller, low-flow valves
Solenoids
313
Use pilot pressure and flow to shift the spool. An additional directional valve (pilot valve) normally controls this pilot pressure and flow
Hydraulic actuators
314
Often referred to as two-stage valves, and are normally electrically operated
Pilot valves
315
Causes and symptoms of valve failure include the following
Broken springs
Fluid contamination
Bound spool/piston
Fluid leakage
316
If the spring for the main spool is broken, the spool would not be able to ___. Fluid could then flow into the reservoir or actuator at the wrong time resulting in the system operating ___
Return to a neutral position
| At a slower than normal pace
317
Result of contamination wearing down sealing areas inside control valves
Fluid leakage
318
Malfunctioning valves cause a system to:
Operate at the wrong pressure
Operate at the wrong speed
Operate at the wrong time
Not operate at all
319
Pressure control valves use ___ to control their operation
System pressure
320
Flow control valves use ___ to control their operation
The rate of flow or, more specifically, the size of the path through which fluid flows into and out of the valve
321
Setting the size of the path controls the amount of flow exiting the valve
Flow control valve
322
By controlling the rate of flow within a hydraulic system, we can control the ___
Speed of an actuator
323
Disadvantage of the simple flow control valve is that when changing a load on the system to maintain the same actuator speed, you must ___
Adjust the valve
324
Three factors that affect flow rate through an orifice or restriction
Fluid temperature/viscosity
Orifice size
Pressure drop
325
The ___ the fluid, the faster the flow rate
Thinner
326
The __ the hole, the more fluid can pass through
Bigger
327
If a ___ exists in the system, the pressure preceding that orifice will rise
Restriction
328
The pressure downstream of the orifice will be ___
Lower
329
The ___ the pressure drop, the faster fluid will move through the restriction
Larger
330
Two types of flow control valves
Fixed orifice
| Variable orifice
331
Symbol for Flow control valve
Line, with two arcs on either side, apex facing the line
332
Simplest type of flow control
Fixed orifice flow control valve
333
Consists of a restriction, non adjustable
Fixed orifice flow control valve
334
Contains an orifice that can be adjusted
Variable orifice flow control valve
335
Major disadvantage of variable orifice flow control valve
Fluid pressure preceding the valve will be at or near the setting of the pressure relief valve
336
Over-running creates ___
Wasted power and heat
337
Most common flow control circuits
Metre-out
Metre-in
Bleed-off
338
Fluid leaving the actuator must pass through the flow control valve in order to return to the tank
Metre-out circuit
339
This arrangement will allow the system to control an over-running load
Metre-out circuit
340
Fluid entering the actuator will first go through the flow control valve
Metre-in circuit
341
This design is useful to control the speed but will not have any control over an over-running load
Metre-in circuit
342
Fluid is bled off to the reservoir prior to the actuators, thus controlling the speed on an actuator. This design is less accurate
Bleed-off circuit
343
Similar in design to pumps, the main difference is that it converts hydraulic energy, created by the pump to mechanical energy/force
Actuators
344
Two categories of actuators
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Linear actuators (hydraulic cylinders)
Rotary actuators
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345
Deliver their force in a straight line
Linear actuator
346
Deliver their force in a rotary motion
Rotary actuator
347
Convert the hydraulic energy created by the pump back into mechanical energy
Rotary and linear actuators
348
Where the work is completed
Actuator
349
The force that is created by a hydraulic motor
Torque
350
The turning effort of the output shaft
Torque
351
If torque is sufficient enough to overcome the resistance, ___ will occur
Rotary motion
352
Force x radius =
Torque
353
Hydraulic motors are rated by ___
Maximum pressure
Displacement
Torque
354
Three basic types of hydraulic motor designs
Gear (internal & external)
Vane (balanced & unbalanced)
Piston (inline and radial)
355
The angle of the swash plate determines ___
The speed and the amount of torque created by the motor
356
At a given pressure, a greater swash plate angle will provide ___ torque and a ___ shaft rpm
Higher
| Lower
357
A lower swash plate angle will provide a ___ torque, but a ___ shaft rpm
Lower output
| Higher
358
Difference in symbol of motor from pump
The triangle points inward on the motor symbol
359
Two basic types of linear actuators
Single-acting linear actuator
| Double-acting linear actuator
360
Retraction of a single-acting linear actuator is accomplished by ___
Gravity
The weight of the abject being moved
Manually
361
Retraction of a double acting linear actuator is accomplished with ___
Hydraulic fluid pressure
362
Similar to hydraulic rams
Single-acting linear actuator
363
Apply force in one direction only and rely on gravity or a counterforce to retract
Single-acting linear actuator
364
The main difference between a single-acting cylinder and a ram is that the ___
Cylinders use pistons
365
Most common type of actuator used in industrial hydraulics. Hydraulic pressure and flow are used to extend and retract the cylinder rod
Double-acting linear actuator
366
Two types of double-acting linear actuators
Double-acting differential linear actuator
| Double-acting nondifferential linear actuator
367
Refers to the different piston areas (net and cap) within the actuator
Differential
368
A double rod cylinder is an example of a ___
Nondifferential linear actuator
369
This design makes the speed and force equal in both directions
Nondifferential linear actuator
370
A device that converts fluid power into linear mechanical force and motion
Hydraulic linear actuator
371
Houses the piston and rod
Body (cylinder tube)
372
The body is connected to the head and end caps by ___
Tie rods and nuts
373
Prevent leakage between the cylinder body and head ends
Static seals
374
The ___ contain the fluid ports
Ends
375
The rod head end contains a ___ which prevents external leakage along the rod
Rod seal
376
The main body of the cylinder and is used with the cylinder end cap and cylinder head to create the cylinder chamber
Cylinder tube
377
Cylinder tube construction
Brass, steel, or aluminium
378
Determines the construction of the cylinder tube
Intended working pressure and use
379
The inside of the cylinder tube may be ___ to improve wear characteristics and to reduce corrosion
Plated or anodised
380
Used to create a sealed chamber on each side of the piston and are usually constructed from rolled steel or cast iron
Cylinder heads and end caps
381
Two types of seals found in hydraulic linear actuators
Static seal
| Dynamic seal
382
Primarily used to join two mating parts that remain stationary. Used in a linear actuator to prevent fluid leakage between the cylinder tube and cylinder head/end cap
Static seal
383
Used to prevent fluid leakage between a stationary and a nonstationary part
Dynamic seal
384
Two dynamic seals in a linear actuator
Rod seals
| Piston seal
385
Prevent fluid leakage between the cylinder head and the cylinder rod
Rod seals
386
Used to separate the cap end fluid from the rod end fluid
Piston seal
387
Usually constructed of cast iron and are the primary components that allow for the conversion of hydraulic energy to mechanical energy
Cylinder pistons
388
Installed to prevent hydraulic fluid from leaking past the piston. Used to separate one side of the piston from the other; usually cast iron or steel. Create two different chambers within the cylinder, and are designed to fir into slots around the circumference of the piston
Piston rings
