A-12
Appendix A
Model 224 Differential Pressure Unit
Startup
Observe the following practices when starting up a process monitoring instru-
ment:
1. Close the block valves.
2. Perform a zero check on the instrument as follows.
a. Open the bypass valve(s), then open one shutoff valve. This proce-
dure equalizes the pressure between both sides of the instrument.
The instrument should indicate zero.
b. If the instrument does not indicate zero, check for gas or liquid
entrapment in the DPU piping or in the DPU (depending on the
orientation of the piping layout and service).
c. If necessary, adjust the pen or pointer by turning the zero adjust knob
on the instrument until the pointer indicates zero.
IMPORTANT: For gas service, perform a zero check with both block valves closed. If
the gas fl ow is pulsating, a standing wave eff ect may occur in the pro-
cess line which can displace the indicator and appear as a zero error.
3. Check the manifold and piping for leaks as follows.
a. Open the bypass valve(s), then open one shutoff valve to pressurize
the instrument.
b. Close the shutoff valve and the bypass valve.
c. Observe the instrument for pen or pointer movement, up or down the
scale, which could indicate leakage.
IMPORTANT: Do not subject the DPU to unnecessary shock or overrange pressure
during operations.
DPU Maintenance
Periodically inspect the integrity of the DPU piping. Tighten all pipe joints as
necessary.
If the instrument is used in services where solids or semi-solids may accumu-
late inside the pressure housings, periodically inspect and clean the DPU. See
DPU Cleaning and Inspection below.
For calibration procedures for the Model 288A Diff erential Pressure Indicat-
ing Switch, see Section 3.
Required Tools
A screwdriver is needed for adjusting screws in the mounting bracket, and a
50-lb torque wrench is recommended for adjusting pressure housing bolts.
Summary of Contents for 288A
Page 56: ......
