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Hydraulics > Pressure Controls > Flashcards

Pressure Controls Flashcards

1
Q

Pressure control valves preform what 3 functions

A

Limit or otherwise regulate pressure
Create a pressure condition required for control
Cause actuators to operate in a particular order

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2
Q

What are the 2 classifications of pressure controls

A

Normally open

Normally closed

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3
Q

Spring constant

A

Expressed in pounds per inch of compression, indicates the stiffness of the spring

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4
Q

Pressure override

A

Is the difference in pressure between cracking pressure and full flow pressure. it is determined by the spring constant . the greater the spring constant the greater the pressure override

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5
Q

Direct acting valves

A

Force created by hydraulic pressure is directly opposed by spring force. Oil will only act against 1 spring to make a change. Can however use a pilot sense line

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6
Q

What are 3 names for pilot operated pressure control valves

A

Compound
Balanced
2 stage

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7
Q

Pilot poppet is designed to handle

A

High pressure and low flow

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8
Q

Main poppet spring is designed to handle

A

High flow and low presurre

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9
Q

What is the main advantage of a pilot operated valve over a direct acting valve

A

Pressure override is greatly reduced

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10
Q

What are the 5 basic pressure control valve applications

A 
Relief valves
Unloader valves
Pressure reducing valves
Sequence valves
Back pressure valves
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11
Q

What 4 common characteristics do a relief valves have

A

Always normally closed
Pilot pressure to open valve is connected in parallel directly upstream
Inlet port is connected in parallel to system is protects
Outlet port is connected to reservoir

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12
Q

What are 2 most common applications of relief valves

A

System

Circuit

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13
Q

Relief valves

A
  • Normally closed valve
  • Pilot pressure to open the valve is connected in parallel directly upstream of the valve
  • Inlet port is connected in parallel to the system or circuit that it protects
  • Outlet is connected to the reservoir
  • 1 turn of the adjusting screw is generally close to 1000 psi
  • A circuit relief will usually be set higher then the main system relief
  • Relief are generally mounted in the directional control valve
  • Main reliefs are set with engine at full throttle, dead head an actuator, and full flow going through relief
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14
Q

Circuit reliefs are usually set ______ then system relief valves

A

Higher

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15
Q

System relief pressure should be set how

A

Engine full throttle
Max flow through relief
Dead head a actuator

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16
Q

What is a second name for a back up ring

A

Anti excrussion ring

17
Q

What is the primary function of an accumulator

A

Stores hydraulic energy in the form of a volume of liquid under pressure

18
Q

What are the 3 types of hydraulic accumulators

A

Weighted
Spring Loaded
Gas charged

19
Q

Weighted accumulators

A

Has weights on top of a piston
Maintains a constant pressure regardless of the oil volume in the accumulator
more commonly used in industrial applications then mobile equipment

20
Q

Spring loaded accumulators

A

Use a coil spring acting on an accumulator piston to exert force on oil
The more oil that is forced in the higher the pressure will get at the compression force in the spring increases

21
Q

Gas charged accumulators use what gas

A

Nitrogen gas is used as it will not react with the hydrocarbons in the oil

22
Q

3 styles of gas accumulators

A

Piston
Bladder
Diaphragm

23
Q

What is the purpose of a accumulator located between the pump and DC valve

A

Stores energy

24
Q

Piston accumulators

A

One chamber with a piston in the middle that separates the gas from the oil
Piston is fitted is fitted with piston sealing rings to prevent internal leakage

25
Q

Pressure in a gas chamber

A

As more oil is forced into accumulator, the pressure rises due to compression of gas

26
Q

What happens if orifice in pilot operated pressure reducing gets plugged?

A

Valve stays open, over pressure results in outlet

27
Q

What are the 4 reasons accumulators are installed on equipment

A

Energy storage
Shock absorption
Gradual pressure build up
Constant pressure maintenance

28
Q

Unloader valve

A
  • Allows full pump flow to return to the reservoir while maintaining a minimum pressure at the pump outlet
  • Normally-closed valve
  • Inlet is connected in parallel with the system or the circuit it unloads
  • Outlet is connected to tank
  • Are always used in conjunction with a check valve
  • Pilot pressure to open the unloader is sensed from the high pressure side of the check valve
  • Are normally pilot operated valves – cannot afford excessive override
29
Q

Pressure reducing valve

A
  • A pressure control that allows one circuit of a hydraulic system to have a lower max operating pressure then the rest of system
  • Normally open valve
  • Pilot pressure to close the valve is sensed downstream of the valve
  • The inlet port is connected to system pressure
  • The outlet port is connected to the circuit to be operated at reduced pressure
  • A drain line from spring cavity is required
  • Will modulate
30
Q

What happens when the orifice gets plugged in a pressure reducing valve

A

The valve will stay open and not limit the maximum pressure

31
Q

Sequence valve

A
  • Causes actions to occur in a certain order
  • Maintain a predetermined minimum pressure in the primary hydraulic function
  • Normally closed valve
  • Pilot pressure to open the valve is sensed from upstream of the valve
  • Inlet port is connected in parallel to the function that must be completed first
  • Outlet is connected to the circuit to be operated second
  • Drain line required
  • A check valve is required to allow for rapid return of reversible actuators
32
Q

Counter balance valve

A
  • Control actuator movement by restricting return oil from the actuator
  • Normally closed valve
  • Connected in series with the actuator return line
  • A check valve is required to allow reversible actuators to return
  • Has 1 internal pilot line that senses directly upstream of the valve
  • Used on systems with a linear actuator
  • System always has a load against it
  • Do not work well with varying loads
33
Q

Pressure intensification - leaking seals

A

Pressure will be the same on both sides of piston. pressure to move load will have to be equal to the area of the rod

34
Q

Brake valve

A
  • Control actuator movement by restricting return oil from the actuator
  • Prevent load from over speeding motor
  • Provide a controlled deceleration of the load
  • Normally closed valve
  • Connected in series with the actuator return line
  • A check valve is required to allow reversible actuators to return
  • Has 1 internal pilot sensing upstream
  • Has a second pilot that has a remote pilot
  • Used on rotary actuators
35
Q

Line lock

A
  • Can be a single or double check
  • Hold a suspended load in the event that line ruptures
  • Prevent load from drifting if directional control valve leaks
  • Prevents the load from over speeding the actuator
  • Normally closed valve
  • Connected in series with the actuator
36
Q

Cross over relief

A

Also called cushing valve

Allow relief oil to go to other side of cylinder (low side closed loop)

Hydraulics (7 decks)

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