Flowserve Nordstrom Dynamic Balance Plug Valve and Double DB Plug Valve - Manual (Page 9)

Flow Control
Nordstrom Valves
FCD NVENIM2005-01 Dynamic Balance ® Plug Valve and Double DB ® Double Isolation Plug Valve 9
3.7 Testing and Adjustment
It is reasonable to assume that a valve that has been properly
inspected and installed will be in good condition and ready to oper-
ate. However, the actual operability of a valve can be proved only by
testing.
An initial inspection can be made by actuating the valve through an
open-close-open or close-open-close cycle. If no obvious problems
are observed, an actual test at pressure may then be applied while
tightness and operability are checked.
It is common practice after the installation of a piping system to
clean the system by blowing through the system with gas or steam,
or by flushing with a liquid to remove debris and/or internal protec-
tive films and coatings. Valve cavities may form a natural trap in
a piping system, and material not dissolved or carried out by the
flushing fluid may settle in such cavities and adversely affect valve
operation.
a CAUTION: If the system is being cleaned with a cleaning
material (gas or liquid) different from the line media, the
effect of the cleaning material upon the valve sealant must
be evaluated prior to use.
4 Operation And Maintenance
4.1 Introduction
An industrial valve, reasonably matched to a particular service appli-
cation and properly installed in a piping system, can be expected
to have a long service life when properly maintained. Unlike totally
passive components such as pipe fittings, vessels, etc., valves are a
special kind of machinery, with moving and wearing parts. The sat-
isfactory performance of these working parts depends on the long-
term preservation of various highly finished surfaces. Therefore, it is
important to practice proper operation and reasonable maintenance
of all valves throughout their service life.
4.2 Operation, Manual Valves
Most valves are actuated manually by causing rotational movement
of a handwheel, wrench, handle, etc. Care is required to assure that
such movement is in the correct direction, is not too fast or too slow,
and is applied through the proper distance. The terminal positions,
open and/or closed, have important functional significance.
Dynamic Balance Plug Valves do not rely on stem-actuating force
to provide tight shutoff. However, the correct position of the closure
element in these types of valves is very important. In some cases
the effort required to move the closure element might increase sub-
stantially during final approach to the closed position, giving a false
impression of having reached the required position.
a CAUTION: Failure to get to and stop at the full closed posi-
tion can result in leakage and consequent damage to the
sealing elements.
To seal properly, plug valves require correct positioning of the clo-
sure element. Closing travel should continue until a positive stop is
reached or until a position indicator reaches the closed position.
In order to minimize the effort required to operate a valve, some pur-
chasers specify oversized handwheels, longer wrenches or reduction
gearing. Operating personnel should be made aware that these “low
force” valves can be over torqued and thereby damaged.
4.3 Operation, Power-Actuated Valves
Functionally, closure performance characteristics are associated
with all valve types, regardless of the means of operation. Satisfac-
tory valve performance with power actuation requires appropriate
programming of the various requirements and constraints into the
actuator controls. Therefore, the actuator should be adjusted to
deliver an adequate opening, running, and closing force to suit the
anticipated service conditions. For position-sensitive valve types,
such as plug valves, the close control should be position-controlled
by external stops or limit switches. Be sure to contact the actuator
manufacturer’s operation manual for more detailed information.
Data required for selection and adjustment of power actuators
should be delineated clearly in purchase specifications for actuated
valves. This data includes but is not necessarily limited to:
a. Upstream pressure and differential pressure conditions at which
both opening and closing is required. Specify direction if appli-
cable. Additionally, specify if valve operation is required under
high-flow, “blow-down” conditions.
b. Speed of operation required or the maximum time for opening
and/or closing. Also, specify a minimum time if required due to
fluid dynamics.
c. Electrical power supply available (AC or DC voltage, phase,
frequency) for electrical power actuators or controls. Operating
conditions for reduced voltages should also be considered.
d. Pneumatic pressure available for pneumatic actuators (cylinders
or diaphragms). Also, specify fail-open, fail-closed, fail-as-is, or
any special requirements.
e. Requirements for position-indication signals.
Actuator selection and adjustments should normally be made by
Flowserve based on published literature and/or technical advice