1.What is the use of single seated valve?
The single seated valve is used on smaller sizes where an absolute shut off is required. The use of single seated valve is limited by pressure drop across the valve in the closed or almost closed position.

2.What is the use of double seated valve?
In double seated valves the upward and downward forces on the plug due to reduction of fluid pressure are nearly equalized. It is generally used on bigger size valves and high pressure systems. Actuator forces required are less.

3.What is the use of valve positioner?
Valve positioner can be used for following reasons:
1. Quick action
2. Valve hysterisis
3. Viscous liquids
4. Split range.
5. Line pressure changes on valve
6. Bench set not standard
7. Reverse valve operations

4.What are primary elements of measuring pressure? Which type of pressure can be measured by these elements?
Primary elements of measuring pressure are:
1. Bourdon Tube
2. Diaphragm
3. Capsule
4. Bellows
5. Pressure springs
These elements are known as elastic deformation pressure elements.

5.Name different types of bourdon tubes?
Types of bourdon tubes:
1. C type
2. Spiral
3. Helix

6.What are different types of control valves?
The commonly used control valves can be defined as follows:
a. Depending on Action:
Depending on action there are two types of control valves
1. Air to close
2. Air to close
b. Depending on body:
Depending on body there are 4 types of control valves
1. Globe valves single or double seated
2. Angle valves
3. Butterfly valves
4. Three way valves

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