Chapter 3

Question 1

pressure control valves

Answer 1

• relief valve
• sequence valve
• pressure reducing valve
• direct operated counter balancing valve
• remotely operated counter balancing valve
• brake valve
• unloading valve

Question 2

relief valve

Answer 2

• simple relief valve
• pilot operated relief valve
• used to limit pressure

Question 3

unloading valve

Answer 3

• extension: clamp work piece and then form the work piece

- retraction: form retracts first and then unclamp

Question 4

gravity hydraulic presses

Answer 4

• relief valve=counter balancing valve
• directly or remotely operated
• normally non passing

Question 5

vertical press

Answer 5

• relief valve=counter balancing valve
• remotely operated, has a drain that comes from somewhere else
• direct always gives back pressure but remote sometimes doesnt

Question 6

accumulators

Answer 6

storage devices of hydraulic energy

Question 7

types of accumulators

Answer 7

• weight loaded
• spring loaded
• N2 gas type (inert gas)

Question 8

N2 gas type accumulators

Answer 8

• diaphram
• pistontype
• bladder

Question 9

precharge

Answer 9

-gas pressure of N2 inside of an accumulator when there is no fluid inside of it

Question 10

use of accumulators

Answer 10

• develop system flow
• absorb shock
• maintain pressure

Question 11

accumulator to develop system flow

Answer 11

• machine cycle (per min): 5 sec of work, 30 sec of charging accumulator, 25 sec of extra time
• working pressure: 500 to 1000 psi
• uses accumulator to get more speed
• accumulator will never charge with tandem center, must be block or flow center
• check valve makes sure fluid cant flow back
• if replace relief valve with unloading valve: saves horsepower/efficiency, will go back to tank at lower pressure
• always set accumulator to 100 psi below lowest working pressure

Question 12

water hammer

Answer 12

high shock

Question 13

inertia

Answer 13

reluctance of a body to start moving or stop moving once it is moving

Question 14

accumulator to absorb shock

Answer 14

• set precharge of accumulators to 100 psi higher than relief valve
• if suddenly stop energizing, load wants to keep going and this can cause pressure spikes in lines

Question 15

pilot operated valve

Answer 15

opens completely over a narrow pressure range, can operate over a wider pressure range without loss of fluid over the relief valve

Question 16

resistive load

Answer 16

load that acts in opposite direction to actuator motion

Question 17

overrunning load

Answer 17

load that acts in same direction to actuator motion

Question 18

full flow pressure

Answer 18

what you set the relief valve to

Question 19

direct acting relief valve

Answer 19

• only one poppet and one spring

- can withstand a higher pressure difference than pilot operated

Question 20

pilot operated relief valve

Answer 20

• 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
• used for overpressure protection
• opens completely over narrow pressure range

Question 21

cracking pressure

Answer 21

minimum upstream pressure at which the valve will operate

Question 22

unloading valve

Answer 22

used to dump excess fluid into the tank at little to no pressure

Question 23

unventing

Answer 23

piston moves enough to allow the dart to reseat

Question 24

sequence valve

Answer 24

used to ensure that a certain pressure level is achieved in one branch of the circuit before a second branch is activated

Question 25

pressure reducing valve

Answer 25

does not allow pressure downstream of the valve to exceed the set point

Question 26

counter balance valve

Answer 26

also called a holding valve, is used to prevent a weight from falling uncontrollably