Relief Valve - Emerson Fisher Level-Trol 2502 Series Instruction Manual

Instruction Manual
Form 1446
November 2006
FIXED
PIVOT
PIVOTING
CROSS
SPRINGS
NOZZLE
RESET
BELLOWS
CJ4081-A
CU7387-B
C0311-2
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
MOVABLE ARM
PROPORTIONAL
BELLOWS
BEAM AND
FLAPPER
FIXED RESTRICTION
INLET END
OF RELAY VALVE
Figure 11. Type 2502F Controller with Differential Relief Valve
2502 Series Controllers
LEVEL SET
ADJUSTMENT
INNER CHAMBER
EXHAUST END
LARGE DIAPHRAGM
OF RELAY VALVE
OF ASSEMBLY
SMALL
DIAPHRAGM
OF ASSEMBLY
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
RELIEF
VALVE
DIFFERENTIAL
RELIEF VALVE
CAM
RELIEF
RESET
DIAPHRAGM
VALVE
OUTER
CHAMBER
PROPORTIONAL
VALVE
SUPPLY PRESSURE
OUTPUT PRESSURE
NOZZLE PRESSURE
EXHAUST
PROPORTIONAL PRESSURE
RESET PRESSURE
DIAPHRAGM
ASSEMBLY
RESTRICTION
17