Powers 595 Series 11 Self-Operating Temperature Regulators - Type CD Composition Disc - Manual (Page 3)

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Caution: Do not exceed maxi-
mum pressure differentials for
given valve sizes. The maximum
differential is the pressure the
valve has against it at shutoff. Too
large a differential can cause valve
chatter and/or prevent shutoff.
Sizing and Selection
■
Proper sizing of the Regulator is essential for correct system
operation. An undersized regulator will not allow suffi cient fl ow
at maximum load. An oversized regulator may cycle and will not
utilize the full valve stroke for effi cient modulation of fl ow. This
results in poor control and shortened valve life (quicker deterio-
ration of valve disc and seat). For these resasons, the correct
sizing of the regulator for actual expected conditions is consid-
ered essential for good control.
NOTE: Select a bulb (see page 12) that has the desired set point
in the upper third of the temperature range for best valve perfor-
mance.
Size the #11 Regulator for actual rather than maximum condi-
tions. Do not size according to pipe size; piping systems are
designed for different criteria than process controls. Refer to
Powers Form #AE-1, Valve Selection and Sizing for further rec-
ommendations.
Maximum Operating Pressure Differential (differential for fl uid
fl ow): In order for the process medium to fl ow, a pressure drop
must exist across the valve. “Pressure differential” is the differ-
ence in valve pressure between the inlet and outlet under fl ow
conditions. The greater the differential, the greater the fl ow at
any given plug position.
Though the regulator should be sized for actual conditions, you
need to know the available differential at maximum fl ow. For
optimum control, take as much differential as possible across
the valve.
Water Capacities
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Use a pressure drop of at least 25% of inlet pressure when sizing valves for water applications.