A-21
Model 199 Differential Pressure Unit (DPU)
Section 4
Torque Tube Rotation Check (Replacement Units)
Prior to installation as a replacement unit, a DPU should be checked for
proper torque tube rotation, per the following procedure:
1. Mount DPU on a stable base and connect to a standard pressure source.
2. Adapt a scale graduated in degrees to the torque tube housing.
3. Adapt a pointer to the exposed end of the torque tube shaft.
4. Apply 100% DP to the high pressure (HP) housing of the DPU. The
pointer should indicate 8 degrees of travel.
Range Change
Changing the range of the Model 199 DPU may require replacing the bellows
unit assembly with a unit of the desired range (see
Bellows Unit Assembly
(BUA) Replacement, page A-25
).
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
BEFORE
REMOVING DPU HOUSING BOLTS.
IMPORTANT: If accumulation of solids or semi-solids is extensive, remove the hous-
ings carefully to prevent damaging the bellows.
IMPORTANT: The calibration range of the DPU was carefully set at the factory. The
following procedure maintains the original factory bellows travel setting
while the range spring change is performed. This procedure must be
strictly followed while changing the range spring assembly or altering the
adjustment.
To replace the range spring assembly with either a new assembly of the same
range or one with a different range value, proceed as follows (this procedure
assumes that the DPU is either connected to an indicating instrument or fitted
with a scale and pointer to measure torque tube shaft movement):
2-1/8-inch Diameter Bellows
1. Remove the DPU from service.
2. Remove the pressure housing bolts and the low-pressure housing.
3. With the pointer at zero, remove the spring retainer screw, retainer
springs, and the range spring assembly.
IMPORTANT: The pointer will shift from zero. This is a normal action and the pointer
should not be readjusted at this point.