Type 2500
Instruction Manual
Form 1013
December 2005
23
Figure 13. Direct-Acting Left-Hand-Mounted Type 2503 Controller
BD4466
−
A
CD2114
−
E
A1890
−
1/IL
Proportional Valve
The three-way proportional valve is adjustable to
allow some or all of the output pressure change to
feed back to the Bourdon tube outer channel,
providing proportional band control (see figure 12).
The Bourdon tube moves to counteract the pressure
changes in the nozzle, equaling the relay diaphragm
pressure differential. The relay valve maintains a
new output pressure according to the change in the
process variable.
A wide-open proportional valve (fully
counterclockwise) permits feedback of the output
pressure signal change and produces 100 percent
proportional response. A closed (fully clockwise)
proportional valve produces smaller proportional
responses, because part of the output pressure
change vents through the proportional valve
exhaust.
Type 2500S Controller
This construction has the same flapper, relay, and
proportional valve as the Type 2500 controller.
However, the nozzle is connected (figure 12) in such
a way that output pressure feedback (from the
movement of the Bourdon tube) moves the nozzle in
the opposite direction of the flapper. This action
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.
Type 2503 Controller
This construction has the same flapper and sensor
arrangement as the Type 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
