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ManualsBrandsSiemens Manuals658 Series Globe ValvesActuator Assembly, Normally Open, 10-14 psi
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Technical Instructions Powertop Two-Way Flared Valves Normally Open/Normally Closed
Document No. 155-310P25
May 16, 2005
Page 6 Siemens Industry, Inc.
Warning/Caution Notations
WARNING:
Personal injury/loss of life may occur if you do not perform a
procedure as specified.
CAUTION:
Equipment damage may occur if you do not follow procedure
as specified.
Operation
The actuator spring provides the necessary force to hold the stem in the raised or
normal position.
An increase in control pressure overcomes the spring pressure and moves the stem
downward. In a normally closed valve, this increases the flow of fluid through the valve.
In a normally open valve, an increase in pressure decreases the flow of fluid though the
valve.
With the loss of control pressure, the spring returns the valve to its normal position.
Sizing
The sizing of a valve is important for correct system operation. An undersized valve will
not have sufficient capacity at maximum load. An oversized valve can initiate cycling,
and the seat and throttling plug can be damaged because of the restricted opening.
Correct sizing of the control valve for actual expected conditions is essential for good
control.
Some variables that must be determined are:
• The medium to be controlled: water, etc.
• The maximum inlet temperature and pressure of the medium at the valve.
• The pressure differential that will exist across the valve under maximum load
demand.
• The maximum capacity the valve must deliver.
• The maximum line pressure differential the valve actuator must close against.
See Tables 3 through 6 for valve capacities.
Installation
NOTE: Install the valve in any position except upside down. The preferred installation
position is upright.
In concealed installations, allow three-inches (75 mm) from the top of the actuator to
remove the upper housing for valve servicing.
CAUTION:
Never use the valve housing as a lever arm to
tighten the body when taking up on a thread.
Install the valve so that the flow follows the direction arrow cast on the valve body.
Install hand valves on supply and return piping to allow for servicing.