1

Instrumentation Process

Control ValveLecture Nov 26, 2014

Dr Edi Munawar

Edi Munawar 1

Dr. Edi MunawarChemical Engineering Department

Syiah Kuala UniversityContact: edi.munawar@che.unsyiah.ac.id

Valve

2Edi Munawar

2

Control Valves

Control valves are used to provide a number offunctions and typically selected based on thefunctions and typically selected based on thefollowing basis: Application function Operating conditions Construction

3Edi Munawar

Sizing

Application Function

In general, the main function control valve is toperformperform. Isolation (ON-OFF valves) Flow control Directional control Protection (over pressure)

4Edi Munawar

3

Operating Conditions

As process equipment, the conditions of thesystem and the environment in which its to performsystem and the environment in which its to performsuch factors are need to be paid attention: Process pressures Process temperature Ambient conditions

5Edi Munawar

Process material and nature of fluid

Construction

A large range of valve designs are available andprovide differing performance both withprovide differing performance, both withadvantages and disadvantages. Generally, thecontrol valve characterized based on: Valve body type Plug and stem design St l

6Edi Munawar

Stem seals Materials of construction

4

Sizing

The size of a valve is dependent on the flow thatrequired through the valve The performance ofrequired through the valve. The performance ofvalves is well defined which simplifies the selectionprocess for a valve without need complicatedcalculations.

7Edi Munawar

Body Styles Valve

The basic style of control valve body are: Gl b Globe Cage Angle body Y pattern Split body

8Edi Munawar

Three way Butterfly valve Ball valve Rotary valve

5

Trim Configurations Valve

The trim configurations of control valve are: U b l d Unbalanced Balanced

Valve trim designs are provided by mostmanufacturers to give three different flowh t i ti

9Edi Munawar

characteristics: Equal percentage Linear Quick opening

The Guiding Configurations Valve

The guiding configurations of control valve are: C id d Cage guided Post guided Stem guided Skirt or Port guided

10Edi Munawar

6

ValveHandwheel

Stem

Plug

11Edi Munawar

Globe Valves

The globe is one of the most common types of body stylecommon types of body style for sliding-stem valves. The trim of a valve is essentially the internal parts that are in contact with the flow stream. Since the trim can absorbs the pressure of the flow, its

12Edi Munawar

design is an important consideration in determining the flow characteristics of the valve.

7

Globe Valves

Advantages Minimises disassembly for Minimises disassembly for

maintenance. Streamlined flow path with a

minimum of parts and no irregular cavities.

Disadvantages

13Edi Munawar

Leaking of the central joint due to thermal cycles or piping loads.

Valves cannot be welded in-line since the valve body is required to be split.

Cage Valves

Cage valves is valve where the plug travel inside thethe plug travel inside the cage. As the plug is aligned by the cage, the valve effectively self-aligns itself so that during assembly all the pieces fit together. Correct alignment reduces

14Edi Munawar

the problems of side loads.

8

Cage Valves

Advantages Suitable for many trim Suitable for many trim

types to be used. Easy to maintain. Top entry. No threaded joints to

corrode.

15Edi Munawar

Trouble-free when specified correctly

Disadvantages Not suitable for viscous

fluid.

Split Body Valves

Split body valves provide streamlined flow and reducestreamlined flow and reduce the number of bolted joints. These valves use one bolt to secure the valve with the seat ring clamped between the body halves. Their original design and

16Edi Munawar

subsequent operation was for difficult flows with high viscosity.

9

Split Body Valves

Advantages Streamlined flow Streamlined flow. Minimum number of parts. No irregular cavities.

Disadvantages Leakage problems with

central joint

17Edi Munawar

central joint. Inability to weld. Maintenance complications. Limitations on trim

modifications.

Angle Valves

These valves can be likened to mounting a globe valve into mounting a globe valve in an elbow. The Angle valve has little restriction on the out flow, so if flashing or cavitation occurs then it tends to do so further downstream from the valve.

18Edi Munawar

This saves not only on the maintenance of the valve, but also minimises any degradation in valve performance.

10

Angle Valves

Advantages The exiting flow is 90O to the The exiting flow is 90 to the

inlet flow. the elimination of an elbow

is required. Minimises any degradation

in valve performance.

19Edi Munawar

Disadvantages Requiring replaceable

inserts on the out-flow piping.

Y-Style Valves

This style of valve has the operating components tiltedoperating components tilted at a 45 degree angle to the flow path. In theory, the flow stream has fewer turns when fully open. In practice they are mainly used for drainage applications,

20Edi Munawar

operating at or near the closed position.

11

Y-Style Valves

Advantages Suitable used for drainage Suitable used for drainage

applications. Still can be operating at

near the closed position.

Disadvantages Maintenance is impaired

21Edi Munawar

with the added difficulty of aligning and handling the components.

Need more frequent maintenance.

Three-Way Valves

Three-Way Valves are a special type of doublespecial type of double ported valve designed for Mixing or Diverting.

22Edi Munawar

12

Three-Way Valves

MixingThe mixing valve has twoThe mixing valve has two inlets and one outlet. This type of valve would be used for blending of two fluids with the associated ratio control of the mix.

23Edi Munawar

Three-Way Valves

DivertingThe diverting application ofThe diverting application of 3-way valve can be used for switching or for bypass operations such as used in chilled water systems to prevent freezing in the pipes.

24Edi Munawar

pipes.

13

Butterfly Valves

The butterfly valves are equipped with discs whichequipped with discs which rotate to regulate the flow rate. The disc is very thin and occupies small space in the pipeline. The stem is centred on the axis of the pipeline. The disc pulls

25Edi Munawar

away from the seal upon opening. This minimises seal wear and reduces friction.

Butterfly Valves

26Edi Munawar

14

Butterfly Valves

Advantages Low cost and weight Low cost and weight. High flow capacity. Fire safe design. Low stem leakage.

Disadvantages

27Edi Munawar

g Over sizing.

Ball Valves

The Ball valve is one of the most common types ofmost common types of Rotary valves available. The valve is named from the valve plug segment being a ball or sphere that rotates on an axis perpendicular to the flow stream. Fully open

28Edi Munawar

to fully closed is performed by a 90 degree rotation of the plug segment.

15

Ball Valves

Advantages Lower cost and weight Lower cost and weight. Higher flow capacity (2-3

times of the globe valve). Tight shutoff. Fire safe. Low stem leakage.

29Edi Munawar

Disadvantages Over sizing.

Single Seated Valves

Single seated valves areone form of globe valve thatone form of globe valve thatare very common and quitesimple in design. Thesevalves have few internalparts. They are also smallerthan double seated valvesand provide good shut off

30Edi Munawar

capability

16

Single Seated Valves

Advantages Si l d i Simple design. Simplified maintenance. Smaller and lighter. Good shutoff.

31Edi Munawar

Disadvantages More complex designs required for balancing.

Double Seated Valves

Another globe valve bodydesign is double seated. Indesign is double seated. Inthis approach, there are twoplugs and two seats thatoperate within the valvebody

32Edi Munawar

17

Double Seated Valves

Advantages Reduced actuator force due to balancing Reduced actuator force due to balancing. Action easily changed (Direct/Reverse). High flow capacity.

Disadvantages Poor shutoff.

33Edi Munawar

Heavy and bulky.

Balanced Valves

Balancing is term used when the resultant force on the plug is neutral That means the plug is neitherthe plug is neutral. That means the plug is neither forced up or down by the pressure of the flow stream.The advantage of valve have neutral force on the plug is the actuator force required for controlled movement is greatly reduced The balancing is

34Edi Munawar

movement is greatly reduced. The balancing is applied to single-seated and double-seated valves in different ways.

18

Single-Seated Balancing

In a single seated valve, the forces resulted of the flowforces resulted of the flow stream can push against the plug, therefore greater actuator force is required to operate the valve movement. To balance a single-seated valve,

35Edi Munawar

balancing holes are added to equalise the pressure on the plug. However, this could reduce the valve shut off capability.

Double-Seated Balancing

Double-seated valves were originally designed fororiginally designed for balancing. These valves use opposing forces from the two plugs to minimise the actuator force required for control movement. The force on the upper plug is in

36Edi Munawar

the opposite direction to that on the lower plug and as such the result should be zero.

19

Guiding

The guiding term mean is to support position the valve plug over the travel route. Any forces that can causing vibrationover the travel route. Any forces that can causing vibration on the plug are resisted by the guide.Types of guiding designs: Cage Stem Post

37Edi Munawar

Port

Cage Guided

Cage guided is the most common type of guidingcommon type of guiding system. The plug moves in the cage with little tolerance. This design enables the plug to loading on supported by the cage with a large bearing area. Maintenance

38Edi Munawar

is decreased as the assembly is simplified with the components self aligning.

20

Cage Guided

39Edi Munawar

Stem Guided

Stem guided is a simple design where the stem itselfdesign where the stem itself is responsible for supporting and controlling the plug. Limitations occur due to the stem strength as the support of the stem is far away from the load on the

40Edi Munawar

plug. Guiding performance is impaired, but this type of valve is cheaper to manufacture and maintain

21

Post Guided

Post guided is mostly used if there is fouling risk. Theif there is fouling risk. The post guiding is a section of the stem from the plug that extends into the valve body. The diameter of post guiding is smaller than the plug but larger than the

41Edi Munawar

stem.

Port Guided

The port guided is very seldom used, but still inseldom used, but still in existence. This type guiding is used to align and guide the plug. The port design also has a relatively small bearing surface and has the same problems with fouling

42Edi Munawar

as with the cage guided valves.

22

Next Lecture

Control ValveControl Valve Selection

Thank you for your attention

43Edi Munawar

y y