
2502 Series Controllers
Instruction Manual
Form 1446
November 2006
17
CJ4081-A
CU7387-B
C0311-2
PROPORTIONAL PRESSURE
SUPPLY PRESSURE
OUTPUT PRESSURE
NOZZLE PRESSURE
RESET PRESSURE
EXHAUST
PROPORTIONAL
BELLOWS
FIXED
PIVOT
MOVABLE ARM
PIVOTING
CROSS
SPRINGS
LEVEL SET
ADJUSTMENT
RESET
VALVE
PROPORTIONAL
VALVE
LARGE DIAPHRAGM
OF ASSEMBLY
RESET
BELLOWS
INNER CHAMBER
BEAM AND
FLAPPER
SMALL
DIAPHRAGM
OF ASSEMBLY
INLET END
OF RELAY VALVE
OUTER
CHAMBER
FIXED RESTRICTION
EXHAUST END
OF RELAY VALVE
DIAPHRAGM
ASSEMBLY
RESTRICTION
RELIEF
VALVE
DIFFERENTIAL
RELIEF VALVE
CAM
NOZZLE
RELIEF
DIAPHRAGM
Figure 11. Type 2502F Controller with Differential Relief Valve
produces smaller proportional responses, since part
of the output change is vented through the valve
exhaust and only the remainder is available to
reposition the bellows.
The reset valve can be adjusted to channel some or
all of the proportional pressure into a reset bellows
that opposes proportional bellows action. This
automatically dampens the effect of any proportional
overcorrection by a set amount per time interval, as
long as there is a deviation from the control point.
Figure 10 illustrates these principles at work in a
direct-acting right-hand-mounted construction
controlling liquid inflow to a vessel, by means of a
direct-acting diaphragm-actuated control valve.
Nozzle positions and bellows connections would be
reversed for direct action with left-hand mounting or
reverse action with right-hand mounting.
Type 2502F Controller with Differential
Relief Valve
This construction (figure 11) has a differential relief
valve used to prevent proportional pressure from
exceeding reset pressure by more than a set value,
a feature useful for intermittent control applications.
Proportional valve output registers in the outer
chamber of the relief valve as well as in the
proportional bellows.
A sudden increase in the output pressure will cause
a rapid pressure increase in the proportional bellows
and in the outer relief valve chamber. If the outer