Siemens 599-01139 Instrukcje techniczne - Strona 5
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Powermite 599 Series MZ Zone Control Three-way Valves
Operation
Sizing
Siemens Industry, Inc.
Figure 2. Close-off Pressures.
As the valve stem moves downward, the flow through the
NO port decreases and the flow through the NC port
increases. As the valve stem moves upward, the flow
through the NO port increases and the flow through the
NC port decreases.
In the event of power failure, a fail-safe actuator returns
the valve to its normal position. Fail-in-place actuators will
hold the last commanded position. See the Technical
Instructions of the various actuators for additional
information.
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 considered essential
for good control.
The following variables must be determined:
•
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.
Technical Instructions
Document No. 155-199P25
October 24, 2005
Figure 3.
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