User Guide

VP 658 S and VP 658 SC Powertop Sequence and Sequence Changeover Valves Technical Instructions
Document No. 155-092P25
November 20, 2008
Siemens Industry, Inc. Page 5
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 may initiate cycling
and the seat and disc may be damaged because of the restricted opening. Correct
sizing of the control valve for actual expected conditions is considered essential for good
control.
Some variables that must be determined are:
1. The maximum inlet temperature and pressure of medium at the valve.
2. The pressure differential that will exist across the valve under maximum load
demand.
3. The maximum capacity the valve must deliver.
4. The maximum medium pressure differential the valve actuator must close against.
5. See AB-1 “Valve Selection and Sizing” for further recommendations.
See TabIe 2 for valve capacity.
The Powertop sequence changeover valve does not require sizing in the same manner
as the sequence valve. The changeover valve does not control the quantity of water
flowing through the system but diverts the flow from one return to the other.
NOTE: Even though it is not necessary to "size" a changeover valve, the pressure
drop across the valve will add resistance to the flow of the medium.
Installation
• Leave plastic cover in place until after painting.
• In concealed installations, sufficient room should be allowed so that the actuator
assembly can be removed for valve servicing. A distance of three inches (76 mm)
from top of housing is sufficient.
• Install changeover valve so that flow is out of the ports marked "hot" and "cold". The
inlet is the common port.
• Install sequence valve so that flow is into the ports marked "hot" and "cold". The
outlet is the common port.
• The valve housing should never be used as a lever arm to tighten the body when
taking up on a thread.
• For best performance install the valve vertically in an upright position.
• Installation of hand valves on supply and return piping is recommended to allow
servicing.