Figure 4-6.-MRG LO unloading valve.
sensing point. The valve should modulate to
valve is the MRG LO unloader valve shown in figure
hold this pressure within 1 or 2 psi of the
setting. If the valve is out of adjustment,
adjust the pilot valve until the proper pressure
Normally, you will perform inspections of the
is achieved.
MRG LO pressure regulating valves while the MRG
LO system is in operation. Valve integrity (leaks) and
3. Lower the LO system pressure to below
proper pressure regulation will be your key concerns.
operating level. The hytrol valve should close
Engine-room personnel can use visual inspections to
tight, as indicated by the stem in the indicator
check for valve integrity. Pressure regulation can be
assembly going to the bottom of the sight tube.
monitored locally and at the operating console in the
central control station (CCS).
4. Return the LO system operating pressure to
the normal operating level. If the valve is
Self-contained pressure regulating valves have
functioning properly, proceed with manual
two modes of operation: (1) automatic and (2) manual.
operational testing. If the valve fails to operate
You can test both modes of operation locally. You
properly, perform a complete inspection of the
should perform these tests according to the PMS or
valve at the earliest possible time.
other authorized maintenance procedures. In the
following paragraphs, we will briefly describe the
Manual Operation. To test a self-contained
sequence of steps you should use for testing both
modes of operation. Please refer to figure 4-6 for
pressure regulating valve for manual operation, use
proper component identification and location.
the following steps in sequence:
Automatic Operation. To test a self-contained
1. Close globe valves A and B with the system
pressure regulating valve for automatic operation,
under pressure. The hytrol valve should stay
use the following steps in sequence:
closed regardless of fluctuations in the system
pressure.
1. Be sure globe valve A is closed and globe valve
2. Open globe valve A with the system under
B is open.
pressure. The hytrol valve should open
2. Vary the system pressure by any convenient
method and observe LO pressure at the remote
