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Ch76-I044963.fm Page 378 Tuesday, August 1, 2006 8:30 PM
Ch76-I044963.fm
378
378 Page 378 Tuesday, August 1, 2006 8:30 PM
So far, the behavior of gland packing has been considered theoretically, and the measurement of its
[1] [3]
radial pressure has been performed using pressure measuring film, strain gages, etc. ~ . However,
these methods have had problems involving their inability to measure the pressure changes over time
and the distribution of radial pressure.

(Inside)
(Outside)
BEBri Axial Compression (Inside) (Outside)
Micro Washer
Gland
Gland Stem Radial Micro Washer
Pressure Pressure Sensor
Packing — Pressure Sensor
Packing
Gland
Gland
Packing
Packing
Grease
Grease
Radial Pressure
Radial Pressure
Fig.2 Method of measuring radial pressure of gland
Fig.l Composition of a control valve packing through grease

0 900 1809 2500 39D0 -4
limeb)
Fig.3 Comparison of measured value Fig.4 Structure of Measuring Device Fig.5 Photo of Measuring Device

METHOD OF MEASURING RADIAL PRESSURE THROUGH GREASE AND EVALUATION
OF THIS METHOD

The proposed measuring method is shown in Figure 2. A hole for sensors is made on the bonnet and
the radial pressure of the packing is measured through grease. The sensor is a Miniature Threaded
Pressure Sensor made by ENTORAN.

The packing's exact radial pressure value may not be measured if the packing is deformed by the hole
for the grease. Thus the accuracy of the measurement of the radial pressure through grease was
confirmed experimentally. A stainless ring of 14.5mm in height and 13mm in thickness that can be
stuffed with two pieces of packing was produced. Using this ring, the packing's radial pressures as
measured by the pressure sensor through grease and by a strain gauge were compared.
The pressure inside the ring, i.e., the average value of the packing's radial pressure P r is expressed
using the circumferential strain outside the ring e e [i]
The change of radial pressure when pressed by 2, 3, and 4 N-m using a torque wrench every 15
minutes is shown in Figure 3. From the graph, it is seen that the value of radial pressures measured
through grease and calculated from the strain outside the ring are mostly in agreement. Therefore, the
radial pressure value measured through grease can be stated accurately not only qualitatively but
quantitatively.