Ics3305 Unit 5 Control Valves

School of Technology, Energy and Apprenticeship
Instrumentation Control & Electrical Technology (ICET)
ICS3305 – F2013

Unit VI: Control Valves

- Control Valves As Final Control Element
- Control Valves Basic Elements
- Control Valves Actuators
- Valve Positioner
- Valve characteristics
- Valve Sizing
- Control Valve Flow coefficient Cv
- Critical Flow Conditions
- Control Valve Body Design

1

School of Technology, Energy and Apprenticeship
Instrumentation Control & Electrical Technology (ICET)
ICS3305 – F2013

Objectives
• Introduce different types of valves
• Explain the operation of valve main parts operation
• Explain the characteristics and signature of valves
• Describe the functions of a transducer, positioner, actuator, and regulator
30% stem position will yield 90% of the flow b- Linear: The flow rate varies linearly with the stem position.
It represents the ideal situation. The
Q
S

relationship can be expressed as follows: Q
S max max Where Qmax is maximum flow rate (m3/s or ft3/s), S is the stem position (m or ft) in which Smax is the maximum travel (m or ft) c- Equal Percentage: A given change in the stem position will result in equal change in the flow rate. This type of valves does not shut off the flow
Q max
R
 completely, there are Qmin. The rangeability R is defined for this of valves as
Q min
The relationship with the stem position and R is given by: Q  Q min R (S / S

max

)

School of Technology, Energy and Apprenticeship
Instrumentation Control & Electrical Technology (ICET)
ICS3305 – F2013

35

School of Technology, Energy and Apprenticeship
Instrumentation Control & Electrical Technology (ICET)
ICS3305 – F2013

36

Example 6.1
An equal percentage valve has a maximum flow of 50 cm3/s and a minimum of