Evaluation of the Compression methods on theSealing Performance of Gland Packing
gland packing of different materials. In addition, the1. Introduction

operation time required for each compression method

The gland packing serves to seal the internal fluid by

was measured and evaluated from the viewpoint oftightening the packing gland with bolts andsealing performance and operating efficiency.

compressing the gland packing. For this reason, it has
been found that the sealing performance greatly
depends on the compression pressure. However, theWinter 2020
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2. Test method

effect of the compression method is unknown. The2-1）Test equipment and test method

compression method includes batch compression in

Figure1 shows a schematic diagram of the compression

which several rings are compressed at one time andequipment. Using this test apparatus, the sealing

divided compression in which compression isperformance by the compression method in the batch

performed several times for every two or three rings.

compression and the divided compression was

It is thought that the divided compression increasescompared. Furthermore, the sealing performance atthe density of the gland packing and improves thethe time of recompression, which has the same effectsealing performance, but the quantitative effect is not

as retightening after batch compression or divided

known. In addition, batch compression is generallycompression, was also measured. Three types of gland

used because it takes time for divided compression. In

packing were used: carbon fiber gland packing

this study, the effect of the compression method on（No. 6137）, PTFE gland packing（No. 7233）, andthe sealing performance was evaluated along with the

expanded graphite gland packing（No.VF-10T）.

mechanical behavior such as stress relaxation using2-2）Test conditionsCompressionequipment
N2

Compression pressure：19.6MPa
Leak-measurement

Stem

GlandFluid：Nitrogen gas
Fluid pressure：1, 5, 10 MPa
Gland packing ring number：6 pcs
2-3）Test method

Gland packing

Four compression methods were used: batchcompression, batch compression +recompression（hereinafter referred to as "batch +recompression"）,divided compression, divided compression+recompression（hereinafter referred to as "divided+recompression"）. After stress relaxation wasFigure1
11Compression equipment and test equipment

stabilized, sealing tests were conducted.

Technical Papers

Batch compression:①②

batch +recompression > divided +recompression. SinceSix gland packing rings are attached to the test

the leakage decreases with the compression method withequipment.

high residual stress, it can be concluded that there is aAfter compressing the gland packing withcorrelation between residual stress and leakage.

compression equipment at 19.6 MPa for 30
seconds, fix the head position of thecompression equipment.
③

Wait until stress relaxation stabilizes④

Nitrogen gas（1, 5, 10 MPa）was used into the test
equipment for leakage measurement⑤

Exhaust nitrogen gas⑥

Perform recompression（batch + recompression）
under the same conditions as step ②⑦

Carry out steps ③ to ④ .

Figure2

Residual stresses of carbon fiber（No.6137）

Divided compression:①

Two gland packing rings are attached to thetest equipment.
R elease the compression equipment after

Winter 2020②

compressing the gland packing with a compression
equipment at 19.6 MPa for 30 seconds③

① to ② are repeated twice, a total of 6 pieces
are mounted, and the head position of thecompression equipment is fixed④

Wait until stress relaxation stabilizes⑤

Nitrogen gas（1, 5, 10 MPa）was used into the test⑥

Leakage of carbon fiber（No.6137）

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equipment for leakage measurement

3-2）PTFE gland packing（No.7233）

Exhaust nitrogen gas

Figure4 shows the residual stress after stress⑦ Perform recompression（divided + recompression）⑧

Figure3

relaxation of PTFE gland packing（hereinafter, PTFE）

under the same conditions as step ②

and Figure5 shows the sealing test results after stress

Carry out steps ④ to ⑤

relaxation. The residual stresses of batch compression
and divided compression became almost the same, and3. Test Results and Discussion

batch +recompression and divided +recompressionalso became almost the same. However, the difference3-1）Carbon fiber gland packing（No.6137）

was found in each sealing performance.

Figure2 shows residual stresses after stress relaxation ofThis is because, as shown in Figure6, In the case ofcarbon fiber gland packing（hereinafter, carbon fiber）.

one-time compression , the number of times theThe order of the lowest residual stress was as follows:

compression is pressed against the sealing surface isbatch compression < divided compression < batch

small, and the gap between the sealing surface and the+recompression < divided +recompression.

gland packing becomes large, so leakage increases but

Figure3 shows the sealing test results after stressfor divided compression, the gap between the glandrelaxation. The order of large amount of leakage was as

packing and the sealing surface was filled by the threefollows: batch compression > divided compression >times compression, and the leakage was reduced.
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Evaluation of the Compression methods on the Sealing Performance of Gland Packing

Figure8 shows the sealing test results after stressrelaxation. Carbon fiber and PTFE leaked less in batch+ recompression than divided compression, whereas
expanded graphite leaked less in divided compression
than batch + recompression. In the case of the divided
compression, the compression is released once to insert
the next gland packing. Since the expanded graphite is
obtained by pressing and solidifying the powder, it isdifficult to recover even if the compression is released
Figure4

Residual stress of PTFE（No.7233）

by divided compression, the leakage of divided
compression is less likely to occur because deteriorationof density and conformity of the sealing surface issmaller than batch +recompression.
Since the fibrous carbon fiber and PTFE are easily
restored, it is considered that the density of the glandpacking is reduced and the conformity to the sealing
surface is easily deteriorated, and the effect of the split
compression is considered to be smaller than that ofWinter 2020

the expanded graphite.
Figure5

Leakage of PTFE（No.7233）

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Figure7 Residual stresses of expanded graphite（No. VF-10T）

Figure6 Relationship between compression method and gap3-3）Expanded graphite gland packing（No.VF-10T）
Figure7 shows the residual stresses after stressrelaxation of the expanded graphite gland packing（hereinafter, expanded graphite）. Expanded graphite
originally had small voids and high density, so stressrelaxation was small and the residual stress is as highas 95% or more in all compression methods, thedifference between compression methods was also

Figure8

Leakage of expanded graphite（No. VF-10T）

small. There was almost no difference in the residual3-4） Effect of compression method for each packing type‌stress between the compression methods, but there

Figure9 shows a graph comparing the effects of thewas a difference in the sealing performance.

compression method for each packing material. The13Technical Papers

vertical axis of the graph represents the rate ofis recommended for applications requiring high sealingchange of the leakage of the other compression

performance.

methods when the leakage of the batch compression of
the blue bar is 100%. Divided+recompression was theleast leaking compression method for all types ofpacking.
Comparing batch +recompression and divided+recompression, the difference in carbon-fiber andPTFE leakage was 10-14% and the difference due tocompression methods was small. On the other hand,the difference in leakage of expanded graphite was43%, and the difference by the compression method
became large. As described in 3-3）, carbon fiber and
PTFE are fibrous and easily recovered, whereas

Figure10expanded graphite is hard to recover because it is

4. Conclusion

manufactured by solidifying powder. As a result, it isOperationaltime of compression methods

This study was able to evaluate the relationshipconformity to the sealing surface is not easily

between sealing performance and operation time due

deteriorated. Therefore, it is considered that the effectto differences in compression methods. Under theof the divided compression is remarkably obtained inpresent test conditions, in the case of carbon fiber andthe expanded graphite.

PTFE, since there was no significant difference in theleakage of batch + recompression and divided +recompression, it is recommended to perform

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unlikely that the density is reduced and theadditional tightening after batch tightening from theviewpoint of operational efficiency. In the case ofexpanded graphite, if the operational efficiency isprioritized, perform retightening after batchtightening, and if prioritizing sealing performance, use
retightening after divided tightening. It has been
Figure9 Differences in leakage amount due to compression methods

observed that the desired effect can be selected byusing an appropriate compression method.

3-5） Operation time for each compression method

It takes a lot of time to attach and detach the gland

Figure 10 shows the operation time for eachpacking and to tighten it in the plant site. We hopecompression method. The time required for thethat this study will help improve the tightening

divided + recompression was 3.6 times that of theefficiency of the gland packing.

batch + recompression. Performing divided +recompression with carbon fiber and PTFE with a 1014% difference in leakage is considered to beinefficient.
Divided + recompression with expanded graphite
showed 43% better sealing performance than batch +recompression. Division + recompression took 3.6
times operation time than batch + recompression, so it

Masato Hamade
Corporate Research andDevelopment GroupProduct Development
Division
14No.38