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17 Park Drive, Franklin, New Jersey 07416 USA
Phone:1.973.209.4388    1.800.392.6310       Fax:1.973.209.6374        Email: info@naspco.com

(continued from page 1)

AIR REMOVAL

Deeper vacuums can complete air removal with fewer sequences. When dealing with a vacuum-resistant product, one vacuum from atmospheric (14.7 psia) to 2.0 psia, followed by a nitrogen backfill to 14.7 psia, will quickly reduce the %vol_air to 13.6% (Table I). Products that can withstand this rate and depth of vacuum will usually tolerate an equally rapid nitrogen injection. Fast ramp rates for nitrogen backfilling also minimize product-level moisture loss.

Process Phase	Cycle Segment	Set Point (in. HgA)	Set Point (psia)	Ramp Rate (psi/min)	Segment Time (min)	Cumulative Cycle Time (min)
Cycle start		29.9	14.7	N/A	N/A	0.0
Air removal	Evacuation 1	4.1	2.0	1.00	12.7	12.7
	Nitrogen purge 1	29.9	14.7	1.00	12.7	25.4
	Evacuation 2	4.1	2.0	1.00	12.7	38.1
Humidification	Steam injection	6.3	3.1	0.02	55.0	93.1
EtO inject	EtO injection	17.9	8.8	0.20	28.5	121.6
	Nitrogen overlay	29.5	14.5	0.20	28.5	150.1
	Gas contact	29.5	14.5	0.00	480.0	630.1
EtO removal	Postevacuation #1	4.1	2.0	1.00	12.5	642.6
	Nitrogen flush #1	29.9	14.7	1.00	12.7	655.3
	Postevacuation #2	4.1	2.0	1.00	12.7	668.0
	Nitrogen flush #2	29.9	14.7	1.00	12.7	680.7
	Postevacuation #3	4.1	2.0	1.00	12.7	693.4
	Final air inbleed	29.9	14.7	1.00	12.7	706.1
	Total cycle time (min)				706.1	706.1

Process Phase	Cycle Segment	Partial Pressure Air (psi)	Partial Pressure Inerts (psi) (nitrogen and steam)	Partial Pressure EtO (psi)	Total Partial Pressures (psia)
Cycle start		14.70	0.00	0.00	14.70
Air removal	Evacuation 1	2.00	0.00	0.00	2.00
	Nitrogen purge 1	2.00	12.70	0.00	14.70
	Evacuation 2	0.27	1.73	0.00	2.00
Humidification	Steam injection	0.27	2.83	0.00	3.10
EtO inject	EtO injection	0.27	2.83	5.70	8.80
	Nitrogen overlay	0.27	8.53	5.70	14.50
	Gas contact	0.27	8.53	5.70	14.50
EtO removal	Postevacuation #1	0.04	1.18	0.79	2.00
	Nitrogen flush #1	0.04	13.88	0.79	14.70
	Postevacuation #2	0.01	1.89	0.11	2.00
	Nitrogen flush #2	0.01	14.59	0.11	14.70
	Postevacuation #3	0.00	1.98	0.01	2.00
	Final air inbleed	12.70	1.98	0.01	14.70
	Total cycle time (min)

Process Phase	Cycle Segment	%Volume Air	%Volume Inerts (nitrogen and steam)	%Volume EtO	%Volume Total
Cycle start		100.00	0.00	0.00	100.00
Air removal	Evacuation 1	100.00	0.00	0.00	100.00
	Nitrogen purge 1	13.61	86.39	0.00	100.00
	Evacuation 2	13.61	86.39	0.00	100.00
Humidification	Steam injection	8.78	91.22	0.00	100.00
EtO inject	EtO injection	3.09	32.14	64.77	100.00
	Nitrogen overlay	1.88	58.81	39.31	100.00
	Gas contact	1.88	58.81	39.31	100.00
EtO removal	Postevacuation #1	1.88	58.81	39.31	100.00
	Nitrogen flush #1	0.26	94.40	5.35	100.00
	Postevacuation #2	0.26	94.40	5.35	100.00
	Nitrogen flush #2	0.03	99.24	0.73	100.00
	Postevacuation #3	0.03	99.24	0.73	100.00
	Final air inbleed	86.40	13.50	0.10	100.00
	Total cycle time (min)

Table I. Process calculations for cycle 1—deep-vacuum type.

In the case of a vacuum-sensitive product, such as a kit containing multiple devices, the air-removal phase could require multiple slow vacuums—down to 7.0 psia, for example. The first vacuum/nitrogen sequence will only bring the %vol_air from 100% down to 47.62% (Table II). In this case, the process engineer must consider that the desiccating effect inherent in this process is further amplified. Multiple vacuum/nitrogen injections coupled with slow ramp rates mean that there is more time for moisture to be driven out of the load by the induced pressure gradient. Water becomes more volatile as temperature is increased and pressure is decreased. In these circumstances, one must begin the steam-injection phase as soon as possible in order to replace some of the moisture lost during the multiple slow-vacuum phases.

Process Phase	Cycle Segment	Set Point (in.HgA)	Set Point (psia)	Ramp Rate (psi/min)	Segment Time (min)	Cumulative Cycle Time (min)
Cycle start		29.9	14.7	N/A	N/A	0.0
Air removal	Evacuation 1	14.3	7.0	0.25	30.8	30.8
	Nitrogen purge 1	29.9	14.7	0.25	30.8	61.6
	Evacuation 2	14.3	7.0	0.25	30.8	92.4
	Nitrogen purge 2	29.9	14.7	0.25	30.8	123.2
	Evacuation 3	14.3	7.0	0.25	30.8	154.0
	Nitrogen purge 3	29.9	14.7	0.25	30.8	184.8
	Evacuation 4	14.3	7.0	0.25	30.8	215.6
	Nitrogen purge 4	29.9	14.7	0.25	30.8	246.4
	Evacuation 5	14.3	7.0	0.25	30.8	277.2
Humidification	Steam injection	16.5	8.1	0.02	55.0	332.2
EtO inject	EtO injection	28.1	13.8	0.20	28.5	360.7
	Nitrogen overlay	29.5	14.5	0.20	3.5	364.2
	Gas contact	29.5	14.5	0.00	480.0	844.2
EtO removal	Postevacuation #1	14.3	7.0	0.25	30.0	874.2
	Nitrogen flush #1	29.9	14.7	0.25	30.8	905.0
	Postevacuation #2	14.3	7.0	0.25	30.8	935.8
	Nitrogen flush #2	29.9	14.7	0.25	30.8	966.6
	Postevacuation #3	14.3	7.0	0.25	30.8	997.4
	Nitrogen flush #3	29.9	14.7	0.25	30.8	1028.2
	Postevacuation #4	14.3	7.0	0.25	30.8	1059.0
	Nitrogen flush #4	29.9	14.7	0.25	30.8	1089.8
	Postevacuation #5	14.3	7.0	0.30	30.8	1120.6
	Final air inbleed	29.9	14.7	0.25	30.8	1151.4
	Total cycle time (min)				1151.4	1151.4

Process Phase	Cycle Segment	Partial Pressure Air (psi)	Partial Pressure Inerts (psi) (nitrogen and steam)	Partial Pressure EtO (psi)	Total Partial Pressures (psia)
Cycle start		14.70	0.00	0.00	14.70
Air removal	Evacuation 1	7.00	0.00	0.00	7.00
	Nitrogen purge 1	7.70	0.00	14.70	47.62
	Evacuation 2	3.33	3.67	0.00	7.00
	Nitrogen purge 2	3.33	11.37	0.00	14.70
	Evacuation 3	1.59	5.41	0.00	7.00
	Nitrogen purge 3	1.59	13.11	0.00	14.70
	Evacuation 4	0.76	6.24	0.00	7.00
	Nitrogen purge 4	0.76	13.94	0.00	14.70
	Evacuation 5	0.36	6.64	0.00	7.00
Humidification	Steam injection	0.36	7.74	0.00	8.10
EtO inject	EtO injection	0.36	7.74	5.70	13.80
	Nitrogen overlay	0.36	8.44	5.70	14.50
	Gas contact	0.36	8.44	5.70	14.50
EtO removal	Postevacuation #1	0.17	4.07	2.75	7.00
	Nitrogen flush #1	0.17	11.77	2.75	14.70
	Postevacuation #2	0.08	5.61	1.31	7.00
	Nitrogen flush #2	0.08	13.31	1.31	14.70
	Postevacuation #3	0.04	6.34	0.62	7.00
	Nitrogen flush #3	0.04	14.04	0.62	14.70
	Postevacuation #4	0.02	6.68	0.30	7.00
	Nitrogen flush #4	0.02	14.38	0.30	14.70
	Postevacuation #5	0.01	6.85	0.14	7.00
	Final air inbleed	7.71	6.85	0.14	14.70
	Total cycle time (min)

Process Phase	Cycle Segment	%Volume Air	%Volume Inerts (nitrogen and steam)	%Volume EtO	%Volume Total
Cycle start		100.00	0.00	0.00	100.00
Air removal	Evacuation 1	100.00	0.00	0.00	100.00
	Nitrogen purge 1	52.38	0.00	100.00	7.00
	Evacuation 2	47.62	52.38	0.00	100.00
	Nitrogen purge 2	22.68	77.32	0.00	100.00
	Evacuation 3	22.68	77.32	0.00	100.00
	Nitrogen purge 3	10.80	89.20	0.00	100.00
	Evacuation 4	10.80	89.20	0.00	100.00
	Nitrogen purge 4	5.14	94.86	0.00	100.00
	Evacuation 5	5.14	94.86	0.00	100.00
Humidification	Steam injection	4.44	95.56	0.00	100.00
EtO inject	EtO injection	2.61	56.09	41.30	100.00
	Nitrogen overlay	2.48	58.21	39.31	100.00
	Gas contact	2.48	58.21	39.31	100.00
EtO removal	Postevacuation #1	2.48	58.21	39.31	100.00
	Nitrogen flush #1	1.18	80.10	18.72	100.00
	Postevacuation #2	1.18	80.10	18.72	100.00
	Nitrogen flush #2	0.56	90.52	8.91	100.00
	Postevacuation #3	0.56	90.52	8.91	100.00
	Nitrogen flush #3	0.27	95.49	4.24	100.00
	Postevacuation #4	0.27	95.49	4.24	100.00
	Nitrogen flush #4	0.13	97.85	2.02	100.00
	Postevacuation #5	0.13	97.85	2.02	100.00
	Final air inbleed	52.44	46.60	0.96	100.00
	Total cycle time (min)

Table II. Process calculations for cycle 2—shallow-vacuum type.

A comparison of the two cycles illustrated in Tables I and II shows that the deep-vacuum cycle completes the air-elimination phase and arrives at the start of steam injection in 38.1 minutes, whereas the shallow-vacuum cycle requires 277.2 minutes.

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