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Ch76-I044963.fm Page 379 Tuesday, August 1, 2006 8:30 PM
8:30 PM
Page 379
1, 2006
Ch76-I044963.fm
Tuesday, August
379
379
MEASUREMENT OF THE RADIAL PRESSURE DISTRIBUTION IN THE SYSTEM
The distribution of the radial pressure of the piled-up packings in the system was measured under the
conditions described in previous section. The experimental system is shown in Figures 4 and 5. The
packings are placed firmly in a stuffing box and the stem can be operated by a control device. The hole
for the placement of the sensors was made at the side portion of the stuffing box, and radial pressure
was measured by the measuring method described earlier. Axial pressures on both sides were measured
using the load cell.
The result is shown in Figure 6 and 7. Ten graphite packings whose inside radius, outside radius, and
height are 5mm, 11,5mm, and 6.5mm, respectively, were piled up. The radial pressures are referred A,
B, C, D, and E sequentially from the undersurface side. Axial pressure on the side for tightly binding
the packings is referred to as the upper pressure and the pressure on the fixed end is referred to as the
bottom pressure. The stem was rotated at 0.2Hz.

1600 1602 1604 1606 1608 1610 1612 1614
3CG 600 900 1209 1 SCO 1SOO
Time(s)
TimeCsJ
Fig.6 Measurement of Distribution of Radial Pressure Fig.7 Measurement of Distribution of Radial
Pressure (on large scale)
The upper and bottom pressures and the radial pressures change cyclically in accordance with the
cycle of the stem operation. The values decrease and the fluctuation ranges increase with time. It is
considered that these changes are caused by the influence of stress relaxation and wear of the packings.
Moreover, it was confirmed that the phase of the pressure change is reversed in the upper and bottom
sides (Fig 7).

CONCLUSIONS

This study evaluated a method for measuring the radial pressure of gland packing of an automatic
control valve for the purpose of diagnosing failure, and the distribution of the radial pressure in the
system was measured using the newly developed method.

The following results were obtained:
(1) Compressibility of grease does not influence the measurement of radial pressure through grease.
(2) The radial pressure measured through grease is in general agreement with the value calculated
based on the circumferential strain outside the stainless ring stuffed with two pieces of packing
(3) The hydrostatic thrust bearing model can be applied to the outflow of grease, and this outflow's
influence on the measurement can be disregarded by providing a margin of about one piece of
packing on both sides of the sensor hole.