Instruction Manual
D200124X012
2500 and 2503 Controllers/Transmitters
June 2017
29
Figure 12. Direct‐Acting, Right‐Hand‐Mounted Fisher 2500‐249 Controller/Transmitter
CD2114-E
BO998-1
OUTER
BOURDON
TUBE CHANNEL
INNER BOURDON TUBE
CHANNEL
LEVEL SET
ADJUSTMENT
CAM
EXHAUST
MOVABLE ARM
FIXED PIVOT
NOZZLE
FLAPPER
FIXED
RESTRICTION
PROPORTIONAL VALVE
EXHAUST END
OF RELAY VALVE
INLET END OF
RELAY VALVE
SUPPLY
SOURCE
TO OTHER PNEUMATIC
INSTRUMENT, ON
TRANSMITTER
CONSTRUCTION
SMALL
DIAPHRAGM
OF ASSEMBLY
LARGE DIAPHRAGM
OF ASSEMBLY
DIRECT‐ACTING
DIAPHRAGM
CONTROL VALVE
VESSEL INFLOW
67CFR FILTER
REGULATOR
SUPPLY PRESSURE
OUTPUT PRESSURE
NOZZLE PRESSURE
PROPORTIONAL PRESSURE
EXHAUST
2503 Controller
This construction has the same flapper and sensor arrangement as the 2500 controller, but its Bourdon tube has a
three way valve operated by a plunger (see figure 13). Note that the switch point adjustment changes the position of
the moveable arm and attached Bourdon tube assembly; this in turn changes the switch point in relationship to the
process level. The differential gap of the 2503 either completely opens the relay valve for full output pressure or
completely closes the relay valve for full exhaust of the output pressure, allowing no in‐between throttling.
For a direct‐acting controller, as long as the process variable remains above the switch point, the flapper does not
depress the plunger of the Bourdon tube valve. In this condition, the Bourdon tube valve remains closed, providing full
