A-25
Model 199 Differential Pressure Unit (DPU)
Section 4
Setting Bellows Travel
The travel of the DPU bellows must be adjusted if one of the following oc-
curs.
1. The range spring assembly is removed without following the procedure.
2. Broken range springs are replaced.
3. The indicator pointer has excessive overtravel.
4. The indicator pointer has excessive undertravel.
Setting the bellows travel requires that the DPU be attached to the actuated
instrument and connected to a test pressure source. The procedure for this
adjustment is presented in the manual for the actuated instrument.
Bellows Unit Assembly (BUA) Replacement
Before replacing the BUA, read the following warning messages and refer-
ence
Figure 2.1, page A-5,
to locate parts described in the following procedure.
WARNING: High-pressure gas hazard on disassembly of the DPU in
installations with pressures greater than 200 psig. To prevent possible
severe personal injury, death, or substantial property damage due to the
release of internal pressure, perform the pressure check procedure on
page A-18
before removing the DPU housing bolts.
IMPORTANT: If accumulation of solids or semi-solids is extensive, remove the hous-
ings carefully to prevent damaging the bellows.
IMPORTANT: Component Removal—See the manual for the actuated instrument for
particular components that must be removed to gain access to DPU case
mounting screws. Support DPU during disassembly. Do not loosen the
drive arm hold plug (located in the top of the BUA center plate) when
removing the mounting bracket. If the plug is loosened, bellows fill fluid
will be lost.
1. Disconnect the DPU piping and remove the instrument from service.
2. Loosen the actuated instrument drive arm and slide off of the torque tube
shaft. Do not disconnect the instrument linkage.
3. Remove the case-retaining screws and remove the case assembly.
4. Remove the indicator bracket screws and the indicator bracket.
5. Remove the pressure housings bolts and pressure housings.
6. Place the pressure housings on the replacement bellows unit assembly
and insert and start (only) the pressure housing bolts.