KUMASI POLYTECHNIC
CHEMICAL ENGINEERING DEPT.
PROCESS DYNAMICS AND CONTROL
TYPES OF CONTROL VALVES AND THEIR INDUSTRIAL APPLICATIONS
BY GROUP 3
LECTURER: MR. ERIC DANSO-BOATENG D ANSO-BOATENG
6TH MAY, 2009
GROUP 3
NAMES
INDEX NO.
ABDU-SAMAD FAIZAH
CME 05081388
««««««
AGYEI EMMANUEL
CME05081395
...«««««
APPIAH-BONSU EUGENE
CME 05081412
.......................
KWABLAH BERNARD
CME 05081422
.....................
OKUTU MANESSEH
CME 05081432
....................
ANDERSON FREDERICK
CME 05081401
.....................
MUSAH SALIFU
CME05061081
.....................
SIGNATURE
PROCESS DYNAMICS AND CONTROL Control Valves Control valves are valves used mainly within industrial plants to control operating conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions. The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems. Positoners are used to control the opening or closing of actuator
based
on
Electric,
or
Pneumatic
the
Signals.
(www.cpcrefinery.blogspot.com/2009/03/control-valves-control-valves-are.html) A flow control valve regulates the flow or pressure of a fluid. Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges. (www.wikipedia.com/control_valves) A valve is a device that regulates the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure tolower pressure.The industries in which the majority of valves are used are oil and gas, power generation, mining, water reticulation, sewerage and chemical manufacturing. The most common valves used in chemical processing are ball valves, butterfly valves, diaphragm valves, and check valves. (Easily Select and Size Control Valves, Chemical Engineering Progress, March 1999, pages 45-50)
Valves are essential to the operation of any piping system that transports liquid. They range from the simple manual control valve with an on/off flow switch to the sophisticated actuated valve controlled by a computer-based programmable logic controller (PLC) that can proportion flow rate based on a variety of criteria. Choosing the right valve requires engineers to consider several factors. (Standard Handbook of Plant Engineering, McGraw-Hill, New York, 1995, pages 10-110 through 10-122)
Types of control valve
Control valves may be categorized as below:
o Conventional valve o Severe service valve o Pressure independent control valve Types of control valve bodies
The most common and versatile types of control valves are sliding-stem globe and angle valves. Their popularity derives from rugged construction and the many options available that make them suitable for a variety of process applications, including severe service. Control valve bodies may be categorized as below. Globe
control
valve
with
pneumatic
actuator
and
smart
positioner
(www.cpcrefinery.blogspot.com/2009/03/control-valves-control-valves-are.html)
Gate Valves Best Suited Control: Quick Opening
Recommended Uses: 1. Fully open/closed, non-throttling 2. Infrequent operation 3. Minimal fluid trapping in line
Applications: Oil, gas, air, slurries, heavy liquids, steam, non-condensing gases, and corrosive liquids. Advantages:
1. High capacity 2. Tight shutoff 3. Low cost 4. Little resistance to flow Disadvantages: 1. Poor control 2. 2. Cavitate at low pressure drops 3. 3. Cannot be used for throttling
Globe Valves Best Suited Control: Linear and Equal percentage
Recommended Uses: 1. Throttling service/flow regulation 2. Frequent operation Applications: Liquids, vapors, gases, corrosive substances, slurries Advantages: 1. Efficient throttling 2. Accurate flow control 3. Available in multiple ports Disadvantages: 1. High pressure drop 2.
More expensive than other valves
Ball Valves Best Suited Control: Quick opening, linear
Recommended Uses: 1. Fully open/closed, limited-throttling 2. Higher temperature fluids
Applications: Most liquids, high te mperatures, slurries Advantages: 1. Low cost 2. High capacity 3. Low leakage and maintenance 4. Tight sealing with low torque Disadvantages: 1. Poor throttling characteristics 2. Prone to cavitation
Butterfly Valves Best Suited Control: Linear, Equal percentage
Recommended Uses: 1. Fully open/closed or throttling services 2. Frequent operation 3. Minimal fluid trapping in line Applications: Liquids, gases, slurries, liquids with suspended solids Advantages: 1. Low cost and maintenance 2. High capacity 3. Good flow control 4. Low pressure drop
Disadvantages: 1. 2.
High torque required for control Prone to cavitations at lower flows
Piston Valves This type of valve has a hollow piston which is moved up and down by the actuator, covering and correspondingly uncovering the two-ports A and B. Port A and port B have the same overall fluid transit area and, at any time, the cumulative cross-sectional area of both is always equal. For instance, if port A is 30% open, port B is 70% open, and vice versa. This type of valve is inherently balanced and is powered by a self-acting control system.
Fig 6.1.12 Piston valve (shown as a diverting valve)
Slide Valves, Spindle Operated Slide valves tend to come in two different designs; wedge gate type and parallel slide type. Both types are well suited for isolating fluid flow, as t hey give a tight shut-off and, when o pen, the pressure drop across them is very small. Both types are used as manually operated valves, but if automatic actuation is required, the parallel slide valve is usually chosen, whether for isolation or control. Typical valves are shown in Figure 6.1.5.
Fig.
6.1.5
Wedge gate valve and parallel slide valve (manual operation) The parallel slide valve closes by means of two spring loaded sliding disks (springs not shown), which pass across the flow-path of the fluid, the fluid pressure ensuring a tight joint between the downstream disk and its seat. Large size parallel slide valves are used in main stream and feedlines in the power and process industries to isolate sections of the plant. Small-bore parallel slides are also used for the control of ancillary steam and water services although, mainly due to cost, these tasks are often carried out using actuated ball valves and piston type valves.
References
(www.cpcrefinery.blogspot.com/2009/03/control-valves-control-valves-are.html)
(Easily Select and Size Control Valves, Chemical Engineering Progress, March 1999, pages 45-50)
. (www.wikipedia.com/control_valves)
(Standard Handbook of Plant Engineering, McGraw-Hill, New York, 1995, pages 10-110 through 10-122)
Rosaler, Robert C., Standard Handbook of Plant Engineering, McGraw-Hill, New York, 1995, pages 10-110 through 10-122
Purcell, Michael K., "Easily Select and Size Control Valves", Chemical Engineering Pro gress, March 1999, pages 45-50
