Control Valve
Actuators
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Basic Information
Valve Main components
Valve Body
Valve Bonnet
Valve stem
Valve closure member
Valve seat ring
Valve packing
Valve actuator (if it is controlled valve)
Valve Hand (if it is manual valve)
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Basic Information
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Actuators
Pneumatically operated control valve actuators are the most
popular type in use, but electric, hydraulic, and manual
actuators are also widely used. The spring-and-diaphragm
pneumatic actuator is most commonly specified due to its
dependability and simplicity of design. Pneumatically
operated piston actuators provide high stem force output for
demanding service conditions. Adaptations of both springand-diaphragm and pneumatic piston actuators are available
for direct installation on rotary-shaft control valves.
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Diaphragm Actuators
Pneumatically operated diaphragm actuators use air supply
from controller, positioner, or other source.
Various styles include: directacting (increasing air pressure
pushes down diaphragm and extends actuator stem, figure
3-31); reverse-acting (increasing air pressure pushes up
diaphragm and retracts actuator stem, figure 3-31);
reversible (actuators that can be assembled for either direct
or reverse action, figure 3-32); direct-acting unit for rotary
valves (increasing air pressure pushes down on diaphragm,
which may either open or close the valve, depending on
orientation of the actuator lever on the valve shaft, figure 3
33).
Net output thrust is the difference between diaphragm
force and opposing spring force.
Molded diaphragms provide linear performance and
increased travels.
Output thrust required and supply air pressure available
dictate size.
Diaphragm actuators are simple, dependable, and
economical.
1 February 2012
By Eng. Ahmed Ghreeb
Diaphragm Actuators
Control Valve
Piston Actuators
Various accessories can be incorporated to
position a double-acting piston in the event of
supply pressure failure. These include pneumatic
trip valves and lock-up systems.
Also available are hydraulic snubbers,
handwheels, and units without yokes, which can be
used to operate butterfly valves, louvers, and
similar industrial equipment.
Other versions for service on rotary-shaft control
valves include a sliding seal in the lower end of the
cylinder. This permits the actuator stem to move
laterally as well as up and down without leakage of
cylinder pressure. This feature permits direct
connection of the actuator stem to the actuator
lever mounted on the rotary valve shaft, thereby
eliminating one joint or source of lost motion.
Figure 3-34. Control Valve with
Double-Acting Piston Actuator
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Electrohydraulic Actuators
Electrohydraulic actuators require only electrical
power to the motor and an electrical input signal
from the controller (figure 3-35).
Electrohydraulic actuators are ideal for isolated
locations where pneumatic supply pressure is not
available but where precise control of valve plug
position is needed.
Units are normally reversible by making minor
adjustments and might be self-contained, including
motor, pump, and double-acting hydraulically
operated piston within a weatherproof or explosionproof casing.
Control Valve with Double-Acting
Electrohydraulic Actuator and Handwheel
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Manual Actuators
Manual actuators are useful where automatic control
is not required, but where ease of operation and good
manual control is still necessary . They are often used
to actuate the bypass valve in a three-valve bypass
loop around control valves for manual control of the
process during maintenance or shutdown of the
automatic system.
Manual actuators are available in various sizes for
both globe-style valves and rotary-shaft valves.
Dial-indicating devices are available for some models
to permit accurate repositioning of the valve plug or
disk.
Manual actuators are much less expensive than
automatic actuators.
Typical Manual Actuators
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Electric Actuators
Traditional electric actuator designs use an electric motor and
some form of gear reduction to move the valve. Through
adaptation, these mechanisms have been used for
continuous control with varying degrees of success. To date,
electric actuators have been much more expensive than
pneumatic for the same performance levels. This is an area
of rapid technological change, and future designs may cause
a shift towards greater use of electric actuators
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Terms and Definitions
ANSI rating class
numerical pressure design class defined in ASME B16.5 and used
for reference purposes
NOTE The ANSI rating class is designated by the word "Class"
followed by a number.
bi-directional valve
valve designed for blocking the fluid in both downstream and
upstream directions
bleed
drain or vent
block valve
gate, plug or ball valve that blocks flow into the downstream
conduit when in the closed position
NOTE Valves are either single- or double-seated, bi-directional or
uni-directional.
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Terms and Definitions
breakaway thrust
breakaway torque
thrust or torque required for opening a valve with maximum pressure differential
by agreement
agreed between manufacturer and purchaser
double- block-and- bleed (DBB) valve
valve with two seating surfaces which, in the closed position, blocks flow from
both valve ends when the cavity
between the seating surfaces is vented through a bleed connection provided on
the body cavity
drive train
all parts of a valve drive between the operator and the obturator, including the
obturator but excluding the operator
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Terms and Definitions
locking device
part or an arrangement of parts for securing a valve in the open
and/or closed position
manual actuator
manual operator
wrench (lever) or hand wheel with or without a gearbox
maximum pressure differential (MPD)
maximum difference between the upstream and downstream
pressure across the obturator at which the obturator
may be operated
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Terms and Definitions
flow coefficient
KV
volumetric flow rate, in cubic metres per hour, of water at a temperature
between 5C (40F) and 40C (104F) passing through a valve and resulting in a
pressure loss of 1 bar (14,7 psi)
NOTE follows:
Kv relates to the flow coefficient Cv in US gallons per minute at 15,6"C (60F)
resulting in a 1 psi pressure drop as
full-opening valve
valve with an unobstructed opening capable of allowing a sphere or other
internal device for the same nominal size as the valve to pass
Hand wheel
wheel consisting of a rim connected to a hub, for example, by spokes, and
used to operate manually a valve
requiring multiple turns
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Seat ring Retention Methods
1- Screw in Seat ring
Not suitable for high Temperature
application (Leakage)
Leakage could erode the seat ring and
valve body
Easy for installation and removal
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Seat ring Retention
Methods
2- Clamped Seat ring
Suitable for high Temperature
application (No Loose)
Suitable for high pressure drops
Attention to bonnet bolting torque is
important concern
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Plug Balancing
1- Unbalance valve Plug
Provide tight Shut off (only one
leakage path when the valve is
closed)
Instable operation
Required larger actuator specially
with larger sizes or high pressure
drop application
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Plug Balancing
Plug Balancing
2- Balance valve Plug
Introduce second leakage path
(Between the plug and the cage
Stable operation
Small stem forces so it could use
smaller actuator with larger sizes or
high pressure drop application
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Packing Options
The purpose of Packing is to create a tight seal between the
backing bore and the valve stem to prevent fluid leakage to the
atmosphere. Selection Criteria for packing include:
1-Low friction so that the actuator can stroke the valve
2- Compatibility of packing component with the process fluid.
3- Compatibility of packing parts with the service temperature.
The most used packing material are :
1- PTFE
2- Graphite
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Packing Options
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Packing Options
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Shut-Off Tightness
Control valve leakage is classified with
respect to how much the valve will leak
when fully closed. The leakage rate
across a standard double seat valve is
at best Class III
The following leakage rates are taken from the British Standard
BS 5793 Part 4 (IEC 60534-4).
1 February 2012
By Eng. Ahmed Ghreeb
Control Valve
Thank you.
Questions?
1 February 2012
By Eng. Ahmed Ghreeb
