30 November 1998
c. In piping circuits with three-way valves, the flow is constant. Therefore, friction losses are constant
and the pump pressure is constant. The three-way valve must close against the pressure difference
between the supply and return headers. Three-way valves should be sized for = 0.7 and the close-off
pressure rating should be specified to be twice the valve pressure drop.
Figure 2-18. Close-off pressure for three-way valves.
16. SURGE PROTECTION PROVISIONS FOR TRANSMITTER AND CONTROL WIRING. Because
HVAC control system transmitter signals and single-loop controller signals are interfaced with EMCS, the
appropriate surge protection will be provided in the HVAC control system design as described in TM 5-815-