Product Overview

Technical Instructions Powermite 599 MT Series Terminal Unit 2-way Valves
Document Number 155-196P25
February 9, 2018
Page 8 Siemens Industry, Inc.
Figure 2. Close-off Pressures.
Operation
Figure 3 shows the normally open valve in the open or full flow position and the
normally closed valve in the closed or zero flow position. The valve spring provides the
necessary force to hold the stem in the raised or normal position.
In the event of power failure, a spring return actuator returns the valve to its normal
position. Non-spring return actuators will hold the last commanded position. See the
Technical Instructions of the various actuators for additional information.
Figure 3.
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
considered essential for good control.
See Tables 3 through 6 for valve capacities.