Page 244 - Root Cause Failure Analysis

232 Root Cause Failure Analysis

Complete the equipment assembly, taking care when compressing the seal
into the stuffing box.
Seat the gland ring and gasket to the face of the stuffing box by tightening
the nuts and bolts evenly and firmly. Be sure the gland ring is not cocked.
Tighten the nuts and bolts only enough to form a seal at the gland ring gas-
ket, usually finger tight and one half to three quarters of a turn with a
wrench. Excessively tightening the gland ring nuts and bolts will cause dis-
tortion that will be transmitted to the running face, resulting in leaks.
If the seal’s assembly drawing is not available, the proper setting dimension
for inside seals can be determined as follows:
- Establish a reference mark on the shaft or sleeve flush with the face of the
stuffing box.
- Determine how far the face of the insert will extend into the stuffing-box
bore. Take this dimension from the face of the gasket.
- Determine the compressed length of the rotary unit by compressing it to
the proper spring gap.
- This dimension, added to the distance the insert extends into the stuffing
box, gives the seal-setting dimension from the reference mark on the
shaft or sleeve to the back of the seal collar.
- Outside seals are set with the spring gap equal to the dimension stamped
on the seal collar.
Cartridge seals are set at the factory and installed as complete assemblies.
These assemblies contain spacers that must be removed after being bolted
into position and the sleeve collar is in place.

Installation of Environmental Controls
Mechanical seals often are chosen and designed to operate with environmental con-
trols. If this is the case, check the seal’s assembly drawing or the equipment’s drawing
to ensure that all environmental-control piping is properly installed.

Seal Startup Procedures

Before equipment startup, all heating and cooling lines should be operating. These
lines also should remain in operation for a short period after equipment shutdown. On
double-seal installations, be sure the liquid lines are connected, the pressure-control
valves are properly adjusted, and the sealing-liquid system is operating before starting
the equipment.

Before startup, all systems should be properly vented. This is especially important on
vertical installations where the stuffing box is the uppermost portion of the pressure-
containing part of the equipment. The stuffing-box area must be properly vented to
avoid a vapor lock in the seal area that would cause it to run dry.

When starting equipment with mechanical seals, make sure the seal faces are
immersed in liquid from the beginning so they will not be damaged from dry opera-