Page 452 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

430 Major Process Equipment Maintenance and Repair

0 Verify that a suitable seal gas supply is properly connected. Pressure
and flow requirements should have been specified by the equipment
manufacturer.
Vera that the range of the nozzle actuator rod responds proportion-
ally to the specified air pressure signal. The range capability of the
air actuator is usually greater than the nozzle actuator travel, which
is set near the middle of the actuator range. The positioner on the
actuator is adjusted to make the nozzle position respond proportion-
ally to the air pressure signal.
Verify that the safety inlet trip system is functional. The solenoid
valve should be sized to close the trip valve in one-half second or
less.

Starting Procedure
Refer to the manufacturer’s data sheets and prepare a table for seal gas
data, correct lube oil operating temperatures and pressures, and all mom-
mended control settings. Use Table 8-10 for general guidance.

Caution: Verih that expander and compressor inlet valves are closed be-
fore proceeding. Veri& installation of an expander inlet screen
in the expander inlet process line with the screen side up-
stream. Likewise, in the compressor suction line.

Startup is as follows:
1. Admit seal gas to expander-compressor seals at the specified rate
of flow. Next, verify the existence of a free passage for the seal
gas leaking from the seals, especially for startup and shutdown
conditions. New seals sometimes require a brief “break-in” pe-
riod before reaching the specified flow rate. Meantime, hold the
seal gas supply at a pressure approximately 5 percent higher than
the pressure level to be sealed (e.g., expander rotor back pressure
or compressor impeller back pressure).
2. Open the pump bypass valve and the filter bleed valve. Then start
both lube oil pumps to sweep the lines free of gas. When the pres-
sure readings on the oil pressure gauges have stabilized, then
slowly close the pump bypass valve, close the filter bleeder valve,
and stop the auxiliary pump.
3. With manual control unit, regulate diaphragm actuator to set vari-
able nozzle at a low power position. Refer to manufacturer’s data
for nozzle positioner requirements.