Response Response characteristic sufficient to control system
Failure Action Power
Stiffness
Others
Upon power failure, Action to safe side of control system
temp., buoyancy, etc..)
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Functions Power Source Sensor Setting and sensing of change Function of Actuator
Type of Actuators
Application
Features
2
3.2 Function of Valves
Power
Spring type : Medium
(*Hydraulic unit) Cylinder type : Large
Stiffness
Not large but practically enough
Construction
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Simple
Not required
Explosion Proof (Partially required for
Valve
open from an auxiliary energy such as air press., oil press., electric power etc..
Regulator
Receive necessary power to close or open from the object fluid to be controlled(press..
3. Outline of Valves阀概述
3.1 Definition and Classification of Valves定义和分类
Devices with movable mechanism that regulate the flow of
Valve fluids or gates by opening, closing or obstructing its passages.
3
3.4 Comparison of Actuators
Item / Type
Pneumatic
Hydraulic
Response
Dead time : Long Travel time : Fast
Power
Failure
Action
Easy / Sure (Spring or Volume
tank)
Manual
Manually open or
close
Automatically close or open by means
Automatic of pressure, buoyancy, centrifuge,
electricity, etc...
Control Receive necessary power to close or
Diaphragm
Pilot Bellows Float Direct Inner Valve Centrifuge, etc.
Differential Pressure Pressure
Safty Relief Float Valve Temp.Control Steam Trap, etc.
Fast Response
Manual Valves Manual Visual Human Eyes & Hands To set opening manually Handwheel Lever
Lower price
3.3 Function of Required for Actuators
Travel
Travel required for valve stroke
Control for pressure, level, temperature, viscosity, density, etc ON-OFF action
Precise control capability Applicable to high temp. fluid Wider setting range Cascade control capability
Regulators Fluid pressure Valve itself
Control Valves Air Pressure Oil Pressure Electric Power Instruments
Pressure, Spring, Weight
Controller
To set opening in proportion to fluid press.
accessories)
Tubing & Wiring
(*Hydraulic unit)
Normally simple
Maintenance/Price
4
Easy / Low
Dead time : Short Travel time : Fast Difficult (Accumulator req’d) *Built-in: small *Separate: large
Driving force to overcome unbalanced force, friction & seat surface pressure
Stiffness design to keep stable action for varying stem thrust
Environment (Explosion, Dust & Water proof etc..) Reliability, Durability,Maintainability
No External power source required Small in size
Simple Operation
To set opening in proportion to signal level Pneumatic (Diaphragm,Cylinderj Electric iMotor, Solenoidj Hydraulic Elect-Hydraulic Elect-Pneumatic