8
regulator knob in steps of ½ turns to reach 1475 Pa (5.9 in
wg) between the chamber and entry (P2-P1) and –1525
Pa (6.1 in wg) between the chamber and the gob (P3-P2),
respectively. At this time, nitrogen started leaking into the
entry more through the chamber’s hairline fissures (rib &
back) rather than the Kennedy stopping. When the regula-
tor was completely turned off, the chamber depressurized
within 72 seconds.
Figure 8 shows the differential pressures between the
chamber and entry (P2-P1) and between the gob and
chamber (P3-P2) as nitrogen is injected into the cham-
ber. Notice a slight decline when the differential pressure
between chamber-entry and gob-chamber reached 1575 Pa
(6.07 in wg) and 1560 Pa (6.241 in wg), respectively.
During this period, the barometric underground pressure
in front of the chamber “Pb(u)” remained fairly constant
at 78.67 kPa (23.24 in Hg). Table 2 shows the differen-
tial pressures between chamber -entry (P2-P1) and gob -
chamber (P3-P2).
Figure 7. Pressure differentials across the chamber stopping and seal -Test 1
Table 1. Pressure differentials across the chamber stopping
and seal -Test 1
Delta P
(Chamber)
Average P P2-
P1, Pa
Delta P
(Seal)
Average P
P3-P2, Pa
Δ1 42 Δ6 –51‑
Δ2 241 Δ7 –229
Δ3 471 Δ8 –467
Δ4 628 Δ9 –624
Δ5 804 Δ10 –805
Figure 8. Pressure differentials across the stopping (P2-P1)
and seal (P3-P2)
Table 2. Pressure differentials across the stopping (P2- P1)
and seal (P3-P2)
Delta P
(Chamber)
Average P P2-
P1, Pa
Delta P
(Seal)
Average P P3-
P2, Pa
Δ1 224 Δ7 –272
Δ2 676 Δ8 –895
Δ3 902 Δ9 –951
Δ4 1,165 Δ10 –1,185
Δ5 1,371 Δ11 –1,412
Δ6 1,506 Δ12 –1,553