Powers 595 Series 11 Self-Operating Temperature Regulators - Type DB & DS Double Seat, Balanced User Manual

Page 3

Sizing and Selection

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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 plug and seat). For these reasons, the correct siz-
ing of the Regulator for actual expected conditions is considered
essential for good control.

NOTE: For best valve performance, select a bulb that contains
your process set point in the upper third of its temperature range
(see page 16).

Size the #11 Regulator for actual rather than maximum condi-
tions. Do Not size according to piping conditions; piping systems
are designed for different criteria than process controls. Refer
to Powers document AE-1—“Valve Selection and Sizing”—for
further recommendations.

Water Capacities

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Use a pressure drop of at least 25% of inlet pressure when sizing valves for water applications.

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.

Caution:

Do not exceed maximum 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.