Module 05: Industrial Valve

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Module 05 Industrial Valve
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1.0 Introduction

• Fluid Any substance that flow from one area to
  another area when it subjected to a normal and
  shear stress. Gases and liquids are both
  considered fluids
• Valve A mechanical device that is used in
  industrial piping to control the flow of fluids
• On-Off Service Valve that only operate in the
  fully open or fully closed positions are said to
  provide on-off service

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1.0 Introduction.

• Throttling Service Valves that control flow by
  partially restricting the passage of the fluids
  provide in what is called throttling service.
• Pressure Drop The loss of energy that occurs
  when a fluid encounters resistance passing
  through a valve. The greater resistance, the
  higher the pressure drop for a given flow rate. A
  higher pressure drop means that more energy in
  the form of pumping or compressing, must be used
  to move the fluid through the piping.

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2.0 Valve Functions And Applications

• Shut-off valves (block valves), whose purpose is
  to close off the flow
• Control valves, both manual and automatic, used
  to regulate flow

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Selecting a Valve Type

• When speaking of valves, it's easy to get lost in
  the terminology.  Valve types are used to
  describe the mechanical characteristics and
  geometry (Ex/ gate, ball, globe valves).  We'll
  use valve control to refer to how the valve
  travel or stroke (openness) relates to the flow
• Equal Percentage  equal increments of valve
  travel produce an equal percentage in flow
  change
• Linear  valve travel is directly proportional to
  the valve stroke
• Quick opening  large increase in flow with a
  small change in valve stroke

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Equal Percentage (most commonly used valve
control)

• Used in processes where large changes in pressure
  drop are expected
• Used in processes where a small percentage of the
  total pressure drop is permitted by the valve
• Used in temperature and pressure control loops

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Linear

• Used in liquid level or flow loops
• Used in systems where the pressure drop across
  the valve is expected to remain fairly constant
  (ie. steady state systems)

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Quick Opening

• Used for frequent on-off service
• Used for processes where "instantly" large flow
  is needed (ie. safety systems or cooling water
  systems)

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Typical Industrial Valve
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Gate Valve
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Gate Valve

• Best Suited Control  Quick Opening
• Recommended Uses1.  Fully open/closed,
  non-throttling2.  Infrequent operation3. 
  Minimal fluid trapping in line
• Applications  Oil, gas, air, slurries, heavy
  liquids, steam, noncondensing gases, and
  corrosive liquids

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Gate Valve

• Advantages
• High capacity
• Tight shutoff
• Low cost
• Little resistance to flow
• Disadvantages
• Poor control
• Cavitate at low pressure drops
• Cannot be used for throttling

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Globe Valve
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Globe Valve

• Best Suited Control  Linear and Equal percentage
• Recommended Uses1.  Throttling service/flow
  regulation2.  Frequent operation
• Applications  Liquids, vapors, gases, corrosive
  substances, slurries

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Globe Valve

• Advantages
• Efficient throttling
• Accurate flow control
• Available in multiple ports
• Disadvantages
• High pressure drop
• More expensive than other valves

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Ball Valve
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Ball Valve

• Best Suited Control Quick opening, linear
• Recommended Uses1.  Fully open/closed,
  limited-throttling2.  Higher temperature fluids
• Applications Most liquids, high temperatures,
  slurries

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Ball Valve

• Advantages
• Low cost
• High capacity
• Low leakage and maintenance
• Tight sealing with low torque 
• Disadvantages
• Poor throttling characteristics
• Prone to cavitation

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Butterfly Valve
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Butterfly Valve

• Best Suited Control  Linear, Equal percentage
• Recommended Uses  1.  Fully open/closed or
  throttling services2.  Frequent operation3. 
  Minimal fluid trapping in line
• Applications  Liquids, gases, slurries, liquids
  with suspended solids

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Butterfly Valve

• Advantages
• Low cost and maintenance
• High capacity
• Good flow control
• Low pressure drop
• Disadvantages
• High torque required for control
• Prone to cavitation at lower flows

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Plug Valve
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Plug Valve

• Best Suited Control  Quick Opening
• The valve is positioned by turning a lever
• A quarter turn of the handle will completely open
  or close a plug valve
• Advantages When line of flow through a plug
  valve is straight, so when it is open there is
  very little turbulence and pressure drop

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Diaphragm Valve
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Diaphragm Valve

• The stem of the valve is used to push down a
  flexible diaphragm, which in turn blocks the path
  of the fluid. There are two different
  classifications of diaphragm valve based on the
  geometry of the valve body
• Weir type - A weir is cast into the body, and
  when closed, the diaphragm rests on the weir,
  restricting the flow
• Straight-through type - The bore runs laterally
  through the body and a wedge shaped diaphragm is
  used to make the closure

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Diaphragm Valve

• Application
• Suitable for handling aggressive fluids and for
  those containing suspended solids

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Check Valve
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Check Valve

• Non-return valve
• Application To avoid backflow

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Valve Actuator, Operation And Troubleshooting
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Valve Actuator, Operation And Troubleshooting

• Control Valve A valve used in automatic control
  situations that is positioned by a controller.
  Any manual valve can be adapted into a control
  valve by attaching an actuator to the valve body.
• Actuator A device that mechanically moves the
  stem of a control valve in response to a signal
  from a controller.
• Controller An instrument that automatically
  positions a control valve. A controller uses the
  energy of compressed air, hydraulic fluid
  pressure, or electricity to send signals to an
  actuator.
• Positioner A device that helps the actuator
  move the valve stem into the correct position.

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Control Valve
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Body Styles

• Control valves can be designed to have one or two
  openings for fluid to pass through.
• A valve that has one flow opening is called a
  single- ported valve.
• Single-ported valves are often used because they
  are inexpensive, require little maintenance, and
  are resistance to leakage once closed.
• The disadvantage of a single valve is that fluid
  pressure working against one side of the valve
  plug makes the valve difficult to position.

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Body Styles

• While in double-ported valve, there are two paths
  for fluid to flow through.
• Because of its design, a double-ported valve can
  handle higher flow rates than a single-ported
  valve of the same size.
• Since pressure is exerted somewhat evenly across
  the plugs, a double-ported valve is easier to
  position than a single-ported valve.
• The characteristics of double-ported valves makes
  them especially good for throttling service

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Pneumatic Actuator

• The actuator contains a diaphragm and a spring.
  It receives compressed air or pneumatic signals
  from the controller.
• A pneumatic actuator uses compressed air, or air
  pressure to move the stem of a control valve.
• The compressed air is introduced above the
  diaphragm. The air pressure tries to push the
  diaphragm down. The spring tries to keep the
  diaphragm up.
• When the air pressure against the top of the
  diaphragm exceeds the force of the spring, the
  valve stem is pushed downward and the valve
  closes.

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Pneumatic Actuator

• This type of valve is called an air-to-close
  valve. Increasing the air pressure above the
  diaphragm in an air-to-close valve causes the
  valve to close.
• Some valves are air-to-open which is increasing
  the air pressure to this actuator causes the
  valve to open. Air pressure in this actuator
  builds up below the diaphragm.
• The design of this valve makes it and air-to-open
  valve.
• Hence, what is important for an operator to know
  is whether increasing air pressure opens or
  closes a valve. An operator also needs to know
  whether a valve fails in the open or closed
  position.

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Electrical Actuator

• Some actuators use the energy of electricity to
  position a control valve. A solenoid is an
  example of this type of actuator.
• The solenoid consists of an iron core that slides
  in and out of wire coil.
• When electrical current is sent through the coil,
  a strong magnetic field is set up inside it. This
  magnetic field pulls the iron core up into the
  coil. When the current stops, the magnetic field
  collapses. And, the core is pushed out of the
  coil by a spring.

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Electrical Actuator

• The iron core of the solenoid is attached to a
  valve stem. An electrical signal from the
  controller magnetizes the coil. This pulls the
  core up, and the valve is closed.
• When the flow of current stops, the core is
  pushed out of the coil by the spring, and the
  valve opens.
• Because of the way a solenoid actuator positions
  a valve, it can only be used for on-off service.

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Solenoid Valve
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Introduction to Control Valve
Control Valves Device that manipulates a
flowing fluids, such as gas, steam, water, or
chemical compound, to compensate for the load
disturbance and keep the regulate
process variables as close as possible to the
desired set point
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Control Valve Actuator Nomenclature

• Fail Open, FO or Air To Close, ATC
• A condition wherein the valve port remains open
  in the event of
• loss of actuator loading pressure to the
  diaphragm
• - No air/pneumatic, Valve in Open condition
• - 4 mA Fully Open, 20 mA Fully Closed
• Fail Closed, FC or Air To Open, ATO
• The condition wherein the valve port remains
  closed in the event
• of loss of actuator loading pressure to the
  diaphragm
• - No air/pneumatic, Valve in Closed condition
• - 4 mA Fully Closed, 20 mA Fully Open

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Control Valve Actuator Nomenclature
1.0 Valve Positioner / Pneumatic Positioner
- The primary function is to ensure that the
control valve stem position is directly
proportional to the respective value of
instrument o/p pressure, regardless of stuffing
box friction, spring hysteresis or off balance
forces on the valve plug - Positioners also
provide a convenient means of changing the
effective o/p pressure range of the controller
and also of changing the valve action 2.0
Actuator Spring - A spring, enclosed in the
yoke, to move the actuator stem in a direction
opposite to that created by diaphragm
pressure 3.0 Actuator Stem - A rod-like
extension of the diaphragm plate to permit
convenient connection to valve plug stem 4.0
Diaphragm - A flexible pressure responsive
element which transmits force to the diaphragm
plate and actuator stem 5.0 Direct Acting
Actuator (ATC) - An actuator in which the
actuators stems extends with increasing diaphragm
force 6.0 Dynamic Force - a force produced
by the fluid pressure on control valve components
while valve is throttling
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Control Valve Actuator Nomenclature
7.0 Fail Closed - A condition
wherein the valve port remains closed in the
event of loss of actuator loading pressure to
the diaphragm 8.0 Fail Open - A
condition wherein the valve port remains open in
the event of loss of actuator loading pressure to
the diaphragm 9.0 PDTC - Push Down
To Close, referring to the motion required to
seat the closure member of a control valve 10.0
PDTO - Push Down To Open, referring to the
motion required to fully open the closure member
of a control valve 11.0 Reverse Acting Actuator
(ATO) - An actuator construction in which
the actuator stem retracts with increasing
diaphragm pressure 12.0 Seat Load - The
total amount of system force, in pounds, that is
exerted against a fully closed control valve plug
or closure member 13.0 Spring Rate
(K) - The measurement of a spring to
determine its stiffness. Defined as the amount of
force in LBs. required to compress the
spring one inch 14.0 Stiffness - The
ability of the actuator to freeze the valve plug
in a desired position. A function of spring rate
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Troubleshooting

• Although an operator is not usually responsible
  for repairing valves, he should be able to
  identify problems so that the appropriate
  maintenance or instrument personnel can be called
  in.
• This requires troubleshooting skills on the part
  of the operator. The problems that occur in
  manually-operated valves are often easy to
  detect, such as a broken hand wheel or stripped
  screw threads.
• If the operating mechanism is working properly,
  but the valve still wont open or close, you can
  assume the problem is inside the valve.

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Troubleshooting

• Check valves do not have an external operating
  mechanism. So, when a check valve is not
  preventing a reversal of flow, you know the
  problem is inside the valve body.
• Control valves are usually more difficult to
  troubleshoot because more things can go wrong
  with them. If a control valve fails, your first
  action should be check the controllers signal to
  the actuator or valve.
• If the signal is incorrect, you know the failure
  is being caused by the controller.

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Troubleshooting

• Sometimes the signals from the controller to the
  actuator are disrupted by a leak, blockage, or
  short in the line that connects these two
  components. So, a control valve failure can also
  be caused by a problem in the signal transmission
  system. Most control valves are equipped with
  some type of valve position indicator.
• Another possibility is that the actuator is not
  working properly. If the diaphragm in a pneumatic
  actuator is torn or ruptured, it will not respond
  to changes in air pressure.
• A burned out coil or motor will cause an
  electrical actuator to malfunction.