Controlled multiple storage vessel gas trap

A gas trap having several independently controlled storage vessels (140,150). Access to each vessel is achieved via pneumatic valves (80,90), and these pneumatic valves are, in turn, controlled by solenoid valves (300, 380). The solenoid valves receive their electrical power from a relay system (520) which is controlled by a computer (550).

BACKGROUND 
1. Field of Invention 
This invention describes a computer controlled device, having several 
independently controlled storage vessels, for trapping various types of 
gases. 
2. Description of Prior Art 
There is a need for a computer controlled device which can collect multiple 
gas samples in sequence. There are many types of gas traps in the prior 
art, but none have these characteristics. Most prior art gas traps are 
intended for very specific tasks such as gas chromatography (Kunsman et 
al.; U.S. Pat. No. 3,731,466; 1973), crude oil detection (Ortega et al.; 
U.S. Pat. No. 5,408,868; 1995), distribution of corrosion inhibitors in 
gas (Johnson et al.; U.S. Pat. No. 4,615,387; 1986), or trapping gases 
released specifically from mud (Wright et al., U.S. Pat. No. 5,199,509; 
1993). Finally, the inventions of Benedict (U.S. Pat. No. 3,859,808; 1975) 
and Benedict et al (U.S. Pat. No. 5,859,807; 1975) describe a trap used in 
the processing of uranium hexafluoride. These devices have very specific 
structural features, different from those of the current invention, which 
make them unsuitable for general laboratory gas collection and analysis. 
Another class of traps is intended to capture certain gases for later 
disposal. Storage of samples is not the aim of these inventions. For 
example, the "automatic gas trap" of Lenfant (U.S. Pat. No. 3,677,279; 
1972) collects undesirable gas accumulations in liquid filled chambers. 
The patent by Gladon (U.S. Pat. No. 4,365,659; 1982) describes a trap 
intended to remove atmospheric pollutants by bubbling air through a 
chemically active solution, and the patent by Caton et al. (U.S. Pat. No. 
5,503,558; 1994) describes an invention relating to traps and filters for 
removing gaseous materials from exhaust gases of semiconductor 
manufacturing equipment. Finally, the patent by Boissin (U.S. Pat. No. 
3,712,074; 1973) describes a cryogenic trap for removal of gases from a 
chamber. None of these inventions is a gas sampling apparatus capable of 
storing a series of independent, individual, samples. 
Some industrial gas traps seek reuse of recovered gases. For example, the 
gas trap by Missimer (U.S. Pat. No. 5,261,250; 1993) describes a two stage 
apparatus capable of recapturing vapors lost during various industrial 
processes. Here, there is no interest in storing numerous samples, or in 
computer control, only bulk recovery of volatile substances. The invention 
by Worden et al. (U.S. Pat. No. 5,228,514; 1993) describes a gas trap 
which captures volatile gases by cooling and then releases them later by 
heating for later analysis. However, the Worden apparatus, which has a 
very different structure than the present apparatus, has no capacity for, 
storing multiple samples or computer control. 
SUMMARY OF THE INVENTION 
Accordingly, several objects and advantages of the present invention are: 
(a) to provide a trap capable of storing several samples of gas; 
(b) to provide a gas trap capable of computer control; 
(c) to provide a gas trap which will seal itself and preserve valuable 
samples in the event of a power failure; 
(d) to provide a gas trap made of ultra-clean, non-contaminating, valves 
and parts; 
(e) to provide a gas trap that requires little or no maintenance, except 
for occasional replacement of absorbent materials.

DETAILED DESCRIPTION OF INVENTION 
Referring to FIG. 1, a gas sample enters the apparatus through an inlet 
tube 10. Inlet tube 10 is connected to an initial pneumatic valve 20. When 
pneumatic valve 20 is open, the gas sample can pass through the pneumatic 
valve into an initial valve outlet tube 30. Tube 30 is connected by an 
inlet union 55 to a foretrap 40. The gas sample passes through union 35 
and goes into foretrap 40 for removal of unwanted impurities. 
Foretrap 40 is composed of a standard vacuum trap 43 filled with an 
absorbent 47. Absorbent 47 may be any one of several chemical compounds. 
Calcium chloride (CaCl.sub.2) can be used to absorb water, lead nitrate 
[Pb(NO.sub.3).sub.2 ] absorbs H.sub.2 S, copper (Cu) and silver (Ag) metal 
absorbs SO.sub.2, Ascarite-brand carbon dioxide absorbent (Ascarite is a 
trademark of LECO Corporation, St. Joseph, Mich.) absorbs CO.sub.2, 
molecular sieve absorbs all gases except H and He, and silica gel can be 
used to absorb CO. Other absorbents are also possible for absorbing any of 
the compounds just described or other compounds. Furthermore, other 
absorbents may be used in combination with the absorbents above. 
After the gas sample has been cleaned in foretrap 40, it passes through a 
foretrap outlet union 50 which joins foretrap 40 to a tube 80. If unions 
35 and 50 are loosened, foretrap 40 may be removed for replacement of 
absorbent 47 when that service is required. Tube 60 is welded to the top 
of a canister 70. Other methods of joining tube 60 to canister 70 are also 
possible. Tube 60 conducts the gas sample into canister 70. The gas sample 
pressure can be monitored by a pressure sensor head 72 which is 
electrically connected by a pair of sensor wires 73 to a display unit 74. 
Sensor head 72 is usually a Penning gauge head, although other types of 
pressure gauge heads are possible. It is also possible to place the 
pressure sensor head in a different location on the system, or even, 
although inconvenient, to leave it out completely. 
There are several ways to build canister 70. A short piece of pipe can have 
top and bottom plates welded to it, as shown in FIG. 1, to form a hollow 
central region. Another possibility is to take two vacuum system blanks, 
place a copper vacuum seal between them and bolt the two blanks together. 
If the central region of one or both of the facing surfaces of the blanks 
is milled down, a hollow interior region is created. Still another way of 
building the canister 70 is to form a hollow torus out of pipe, tubing, or 
vacuum fittings such as elbows, short nipples, and "T-sections". Other 
construction techniques may be possible. 
The gas sample in canister 70 can now spread into canister outlet tubes 75 
which are welded onto canister 70. Other methods of attachment may be 
possible. The lower ends of tubes 75 are attached to left and right 
secondary pneumatic valves 80 and 90, respectively. The attachment of 
tubes 75 to valves 80 and 90 can be accomplished by pipe thread, or by 
means of a crushable ferrule, but it is much more usual to use a face 
seal. Of course, it is also possible to have more than just two secondary 
pneumatic valves hanging from the canister. Now, if pneumatic valve 80 is 
open and pneumatic valve 90 is closed, then the gas sample will pass 
through pneumatic valve 80 into a left secondary valve outlet tube 100, 
which is attached to pneumatic valve 80 by a face seal or another type of 
seal. The lower end of tube 100 is connected to a left outlet tube union 
120 which employs O-rings, or other devices, to make a vacuum tight seal 
to tube 100. The lower end of union 120 also employs an O-ring seal for 
vacuum tight attachment to the top of a left valved storage vessel 140. 
Union 120 is a standard commercial item, one supplier being the Cajon 
Company, Macedonia, Ohio. The union is sold under the unregistered name of 
"ultra-tort union". The vacuum tight union 120 allows a gas sample to pass 
from tube 100 into storage vessel 140. Naturally, if pneumatic valve 80 is 
closed and pneumatic valve 90 is open, a gas sample will pass through 
pneumatic valve 90, a right secondary valve outlet tube 110, a right 
outlet tube union 150, and into a right valved storage vessel 150. 
Typically, storage vessels 140 and 150 are made of borosilicate glass, 
although other types of glass or metal storage vessels are possible. The 
manufacture of glass storage vessels involves starting with a commercially 
available valve body (denoted by left and right valve bodies 145 and 155, 
respectively, in FIG. 1). Valve bodies 145 and 155 have attached to them 
left and right valve body handles 145 and 155, respectively. The valve 
bodies are then straight sealed to the open end of left and right storage 
vessel bottoms 147 and 157, respectively. The bottoms 147 and 157 are 
formed by closing one end of a piece of borosilicate tubing with a torch. 
Storage vessels 140 and 150 dip into a refrigerant filled Dewar 160. The 
depth to which the storage vessels 140 and 150 penetrate below the surface 
of the refrigerant is governed by raising or lowering the apparatus by a 
support loop 165. If the apparatus will be unattended for a long period of 
time, it will be necessary to insert the storage vessels 140 and 150 
fairly deeply into the refrigerant. In fact, it may even be necessary to 
make storage vessels 140 and 150 with extra long bottoms 147 and 157 to 
provide extra penetration into the refrigerant. The refrigerant used in 
Dewar 160 may be isopropanol and dry ice, liquid nitrogen, a mixture of 
liquid and solid pentane, liquid neon, or other substances. The presence 
of the refrigerant eventually causes all, or some component, of the gas 
sample which was introduced into the apparatus to freeze in bottoms 147 
and 157. Once the gas sample is frozen in place, storage vessels 140 and 
150 may be manually closed by handles 145 and 155. Storage vessels 140 and 
150 may now be removed from the apparatus, provided that both valves 80 
and 90 are closed, by loosening the lower O-ring seal on unions 120 and 
130. Once separated from the apparatus, the gases trapped in storage 
vessels 140 and 150 may be studied in a mass spectrometer, or other 
instruments, or used for other purposes. 
Between introduction of gas samples it is necessary to evacuate all parts 
of the apparatus described up to this point. This is accomplished by 
pumping out any unwanted residual gases through a canister evacuation tube 
170, which is connected to a pneumatic evacuation valve 200. When 
pneumatic valve 200 is open, unwanted gas expands through pneumatic valve 
200, and an evacuation valve outlet tube 210, to be removed by a high 
vacuum pump 220. Pump 220 is an oil diffusion pump, turbomolecular pump, 
or another type of high vacuum pump. Pump 220 has a high vacuum pump 
outlet tube 230 which is connected to a roughing pump 240. Roughing pump 
240 is usually, but not necessarily, a mechanical type of pump. Unwanted 
gases passing through pump. 220, tube 250, and roughing pump 240 are 
finally expelled through a roughing pump outlet tube 250. 
The pneumatic valves 20, 80, 90, and 200 are standard gas controlled 
valves. Typically air, nitrogen, or some other gas at a pressure of about 
80 psi (other pressures are also possible) is used to open and close the 
pneumatic valves. This control gas is isolated from the sample gas and 
does not mix with, or contaminate, the sample gas in any way. The control 
gas is conducted to pneumatic valve 20 through an initial pneumatic 
control pressure line 260, which is usually made of copper, although lines 
made of stainless steel, plastic, and other materials are possible. This 
patent application uses a pneumatic valve 20 that is normally closed when 
the gauge pressure in line 260 is zero. This type of valve will prevent 
the escape of gases already in the apparatus, or the introduction of new 
gases into the apparatus, in the event of a power failure. However, it is 
possible, although not as advantageous, to use normally open valves as 
well. The pressure in line 260 is controlled by an initial solenoid valve 
270. Solenoid valve 270 is an electrically controlled three-way valve, and 
in the event of a power failure (zero voltage applied), vents to air so 
that zero gauge pressure remains in line 260. When a voltage is applied to 
solenoid valve 270, solenoid valve 270 connects line 260 to the gas 
pressure in an initial solenoid valve inlet tube 280. It should be noted 
that it may be possible to use other types of valves in place of the 
solenoid valve used in this preferred embodiment, so that the valve 
described above should not be considered a limitation on this application. 
The pneumatic valve 80 operates the same way as pneumatic valve 20, except 
that it is controlled by pressure in a left secondary pneumatic valve 
control pressure line 290. The pressure in line 290 is, in turn, 
controlled by a left secondary solenoid valve 300, which vents to air for 
zero applied voltage, and is fed by gas in a left secondary solenoid valve 
inlet tube 510. Tube 280 and tube 310 are both joined by a left three-way 
union 320 which is pressurized by a left intermediate pressure line 550 
from the low pressure side of a left regulator 340. Regulator 340 is fed 
by gas from a left high pressure line 350 which is directly connected to a 
left gas tank 360. The control of pneumatic valves on the right side of 
the apparatus is similar to that on the left side. Pneumatic valve 90 is 
opened by gas pressure in a right secondary pneumatic valve control 
pressure line 570, which is, in turn, controlled by a right secondary 
solenoid valve 580. Solenoid valve 380 vents to air for zero applied 
voltage, and is fed pressurized gas by a right secondary solenoid valve 
inlet tube 590. Similarly, pneumatic valve 200 is controlled by the gas 
pressure in a pneumatic evacuation valve control pressure line 400, which 
is, in turn, controlled by an evacuation solenoid valve 410. Again, 
solenoid valve 410 vents to air when zero voltage is applied to it. This 
venting produces zero gauge pressure in line 400, which causes pneumatic 
valve 200 to close, thereby preventing accidental loss of a gas sample in 
the event of a power failure. Solenoid valve 410 is fed by an evacuation 
solenoid valve inlet tube 420. Tube 420 joins tube 390 at a right 
three-way union 430 which is fed gas from a right intermediate pressure 
line 440 that leads to a right regulator 450. Regulator 450 is connected 
to a right high pressure line 460, and line 460 is connected to a right 
gas tank 470. It should be noted that the left and right side of the 
apparatus can share a common intermediate pressure line, regulator, high 
pressure line, and gas tank. In this latter design variation, three-way 
unions would be replaced by a multi-port manifold and all the solenoid 
valve inlet tubes would feed into this manifold which would be pressurized 
by the single intermediate pressure line from a single regulator, high 
pressure lines and tank. Next, the electrical control of the solenoid 
valves will be discussed. 
Solenoid valves 270, 500, 380, and 410 are all electrically controlled 
three-way solenoid valves which pressurize lines 260, 290, 570, and 400 
respectively when they receive a voltage, as previously discussed. 
Solenoid valve 270 receives its voltage through a pair of initial solenoid 
valve electrical power lines 480, solenoid valve 300 receives voltage from 
a pair of left secondary solenoid valve electrical power lines 490, 
solenoid valve 580 receives voltage from a pair of right secondary 
solenoid valve electrical power lines 500, and finally, solenoid valve 410 
receives its voltage from a pair of evacuation solenoid valve electrical 
power lines 510. Power lines 480, 490, 500, and 510 are all connected to 
the output terminals of a relay system 520. Relay system 520 is a 
commercially available module which is manufactured and sold by Omega 
Engineering, Inc., Stamford, Conn. Relay systems from other companies may 
also be used, or custom made relay systems can be constructed from 
individual relays if desired. By turning different relays on or off 
electrical power can be sent to, or cut off from, various solenoid valves, 
thereby turning them on or off. The power used to perform this operation 
comes from a pair of relay system power lines 530. The signal used to turn 
different relays on or off in relay system 520 comes from relay control 
signal lines 540, which are, in turn, connected to a computer 550 powered 
by a pair of computer power lines 560. The computer 550 can, of course, 
also be powered by batteries. 
Operation--FIG. 1 
Operation begins with initialization of the system. First fill Dewar 160 
with refrigerant if required. Then, turn on roughing pump 240. Valve 
bodies 143 and 153 should be in the open position. The interior of the 
system can now be evacuated so that a pressure of about 1 Torr (although 
other pressures are possible) exists in all parts through which a gas 
sample will pass. This pressure may be monitored on display 74. Next, turn 
on high vacuum pump 220 and wait until the pressure drops to about 
10.sup.-5 Torr (although other pressures are possible). The parts to be 
evacuated include all parts between pneumatic valves 20 and 200 down to, 
and including, storage vessels 140 and 150. This initial configuration is 
achieved when computer 550 sends a signal to relay system 520 and closes 
the electrical relay contacts which provide a voltage to solenoid valves 
500, 580, and 410 (but not solenoid valve 270). This action allows control 
gas pressure to open pneumatic valves 80, 90, and 200, so that the 
interior of the system can be evacuated. Once evacuation is accomplished 
as indicated by pressure gauge display 74, pneumatic valve 200 can be 
closed by removing the voltage to solenoid valve 410 and venting line 400 
to air. The system is now configured to receive gas samples. 
Suppose it is desired to fill left valved storage vessel 140 first. The 
required procedure involves closing pneumatic valve 90 by removing the 
voltage from solenoid valve 380. Closing pneumatic valve 90 will prevent 
the gas sample from entering right valved storage vessel 150. Now, 
pneumatic valve 20 can be opened by applying a voltage to solenoid valve 
270. This procedure will allow the gas sample to enter the interior of the 
system, including storage vessel 140. Once the gas sample fills the 
system, pneumatic valve 20 can be closed by removing the voltage from 
solenoid valve 270. If the gas sample is in a form ready for collection, 
and if the pressure of the gas sample is high enough to allow a sufficient 
amount of gas to fill storage vessel 140 for the intended purpose, then 
pneumatic valve 80 can be closed by removing the voltage from solenoid 
500. The gas sample is now safely stored. Any extra gas remaining in the 
system can now be removed by applying a voltage to solenoid valve 410. 
Solenoid valve 410 will then open pneumatic valve 200, thereby evacuating 
the system volume above the storage vessels. However, it is often the case 
that the gas sample filling the interior of the system is so precious that 
all of the gas sample must be condensed into storage vessel 140 for 
analysis. Or, the gas sample filling the system may be a mixture of gases, 
only one component of which a researcher is interested in. In order to 
collect all of the gas sample in the system, or a component of interest, 
freezing methods can be used. For example, suppose a researcher desires to 
collect a minute quantity of carbon dioxide to be used for carbon dating, 
or separate carbon dioxide from a mixture of carbon dioxide, oxygen, 
nitrogen, and argon (i.e. separate carbon dioxide from air). The procedure 
of choice is now to leave pneumatic valve 80 open while the left storage 
vessel bottom 147 is dipped into refrigerant filled Dewar 160. If liquid 
nitrogen is used as the refrigerant, then carbon dioxide will quickly form 
in bottom 147 as a layer of dry ice, but volatile substances like oxygen, 
nitrogen and argon will not condense if the sample pressure is much less 
than about one third of an atmosphere. During carbon dioxide condensation 
the pressure indicated on display 74 will drop. Once the pressure stops 
dropping and levels off, condensation of carbon dioxide is complete. 
Pneumatic valve 200 may now be opened by applying a voltage signal to 
solenoid 410. When this action is taken, the volatile gases oxygen, 
nitrogen, and argon will be pumped away (as indicated by the reading on 
display 74) leaving pure frozen carbon dioxide in storage vessel 140. 
Pneumatic valves 80 and 200 may now be closed by removing the voltage from 
solenoid valves 500 and 410 respectively. The example just given involving 
the trapping of carbon dioxide is only meant to be illustrative and should 
not be considered a limitation on this patent application. The system is 
now ready to receive its second gas sample. 
With pneumatic valve 80 closed, pneumatic valve 90 is opened by applying a 
voltage to solenoid valve 380. The next gas sample Tan now be allowed to 
enter the system by opening pneumatic valve 20. After gas sample 
introduction is complete, pneumatic valve 20 can be closed. If it is 
desired to only trap some gas in storage vessel 150, then pneumatic valve 
90 can be closed as well. However, if freezing the gas sample into bottom 
157 is required, then it is necessary to wait a predetermined time before 
closing pneumatic valve 90. Or, the decision as to when to close valve 90 
can be made by feeding the pressure from display 74 to the analogue to 
digital conversion board of computer 550 via a jack that is often provided 
on the back of commercially available pressure displays. When the pressure 
drops to some predetermined level computer 550 makes the decision to open 
the appropriate relay in relay system 520, thereby removing the voltage to 
solenoid valve 380 and closing pneumatic valve 90. Unwanted residual gas 
above storage vessel 150 can now be pumped away by opening pneumatic valve 
200 until display 74 indicates that a suitable vacuum exists within the 
apparatus. Pneumatic valve 200 can now be closed. If the system has more 
than two storage vessels, the procedure described in this paragraph can be 
repeated in a similar way until all storage vessels are filled. Naturally, 
the storage vessels can be filled in any order desired. Next, removal of 
filled storage vessels will be discussed. 
Once storage vessels 140 and 150 are filled, valve bodies 145 and 155 
should be closed manually by turning handles 145 and 155. Next, the 
apparatus might have to be raised by support loop 165 to pull the left and 
right storage vessel bottoms out of the refrigerant filled Dewar 160. The 
same thing can be accomplished by lowering Dewar 160. Now, the lower end 
of unions 120 and 150 can be loosened and storage vessels 140 and 150 
pulled down and removed from the unions. This procedure is safe since 
pneumatic valves 80, 90, and 200 are all closed, thereby preventing air 
from entering the system and burning the pump oil in high vacuum pump 220. 
The storage vessels can now be attached to a mass spectrometer, or any 
other instrument for analysis of storage vessel contents. Finally, the 
system shutdown procedure will be discussed. 
After gas sample filled storage vessels are removed, empty (except for air) 
storage vessels should be attached. The valve bodies of these storage 
vessels should be in the open position. Next, pneumatic valves 80, 90, and 
200 should be opened so that high vacuum pump 220 and roughing pump 240 
can remove the small amount of air that was originally trapped in the 
replacement storage vessels. Pneumatic valves 80, 90, and 200 can now be 
closed and the apparatus returned to its original position in Dewar 160 by 
means of support loop 165. Of course, during shutdown it doesn't mater if 
refrigerant evaporates from Dewar 160. Finally, high vacuum pump 220 
should be shut off to prevent any pump oil from burning. However, roughing 
pump 240 should always be left on. The system pressure will be about i 
Tort between times when the apparatus is in use. Of course, long term 
storage will require both high vacuum pump 220 and roughing pump 240 to be 
turned off. During long term storage close both the inlet tube 10 and 
roughing pump outlet tube 250 with some type of air tight plug. 
Summary, Ramifications, and Scope 
Accordingly, the reader will see that the gas trap described in this patent 
application is capable of being computer controlled and can store several 
gas samples. Several minor variations on the gas trap described in this 
application are described below. 
First, when absorbent 47 is replaced by glass beads, or other types of 
beads, having many possible shapes or sizes that fit into vacuum trap 43, 
and the outside wall of vacuum trap 43 is cooled with a refrigerant like 
isopropanol and dry ice, liquid nitrogen, liquid and solid pentane, or 
liquid neon, foretrap 40 becomes a cryogenic trap capable of capturing a 
variety of gases, and passing others, depending on the refrigerant chosen. 
Refrigerants other than those listed above may also be used. Furthermore, 
cooling may also be used in combination with chemical absorbents such as, 
but not limited to, those listed above in the section entitled "Detailed 
Description of Invention". Sometimes several identical foretrap 40 units 
must be connected together in series or parallel in order to completely 
remove certain impurities from the gas sample that one ultimately wishes 
to store. Or, several different types of foretrap 40 units must be 
connected together to remove several different types of undesirable 
species. In situations where a sufficiently complex combination of 
foretraps is involved it may even be necessary to supply the combination 
with its own system of vacuum pumps in order to properly evacuate the 
combination between introduction of different gas samples. Finally, it 
should be noted that in cases where the incoming gas sample is already 
clean there is no need for foretrap 40, and in that case the gas sample 
may be injected directly into tube 60 fop conveyance to canister 70. 
Second, all parts of the apparatus are preferably made of stainless steel, 
except for the vacuum trap 45 and the left and right valved storage 
vessels 140 and 150, respectively, which are usually made of borosilicate 
glass. Such a system is very clean and does not adsorb species from one 
sample and later release them to contaminate another sample. However, it 
is entirely possible to use other metals, glasses and plastics for the 
construction of the apparatus. These building materials include, but are 
not limited toy copper, brassy aluminum, and carbon steel for the metal 
parts. Fused silica, Vycor-brand high silica glass (Vycor is a trademark 
of Corning Glass Works, Corning N.Y.), and soda lime glass may be used for 
the vacuum trap and the storage vessels, although other glasses and even 
metals and plastics are possible. Teflon-brand PTFE (Teflon is a Trademark 
of E.I. dupont de Numours & Co., Wilmington, Del.), neoprene, synthetic 
rubber, or fluorocarbon elastomer, may be used for the seals in the unions 
and valve bodies 143 and 153. Other elastomers may also be possible for 
seals, and other parts of the apparatus as well. A variety of plastics, 
metals and other substances may be used for handles such as 145 and 155. 
Another variation on the basic theme of this invention involves the 
pneumatic valves. There are two basic types. There are directionless 
valves whose inlet and outlet ends are functionally identical so that they 
can be used in either of two orientations, and there are valves which only 
seal well when the flow is in one direction. Either type will work well in 
the invention described in this application. However, when valves with a 
direction are used care must be taken to insure that the direction of flow 
of pneumatic valve 20 points into the system since the pressure outside 
the system will generally be higher than the gas sample pressure inside 
the system. Pneumatic valves 80 and 90 should have a flow direction 
pointing toward the storage vessels if only frozen samples having a very 
low vapor pressure are stored. For gaseous samples it is often best to 
rotate the valves so that the flow direction points away from the storage 
vessel. Finally, the flow direction of pneumatic valve 200 should point 
toward the vacuum pumps. 
The valve bodies 145 and 155 may also have a specified flow direction, or 
they may be directionless. For directional valves the flow direction 
should usually point away from the storage vessel bottoms 147 and 157. 
In the case where the researchers intention is only to collect gaseous 
samples it is possible to omit Dewar 160. 
In cases where manual control is desired, the pneumatic valves can have a 
manual override or by-pass. 
The configuration of the vacuum pumps offers other possible variations in 
the design of the apparatus. For example, it is common in vacuum system 
design to use a high vacuum pump by pass so that roughing pump 240 can be 
applied directly to the system without having to work through high vacuum 
pump 220. 
Standard commercial parts, such as the three-way union "T"), may be joined 
to other parts by any vacuum tight method, including pipe threads, 
crushable ferrules, face seals, weld seals, or other methods of 
connection. 
Finally, support loop 165 may be replaced by other types of support 
devices. These devices can be attached to the top of canister 70 by 
welding, or, if the top of canister 70 is thick enough, screws may be used 
provided they do not cause an air leak by penetrating into canister 70. 
It should be noted that although this application contains many 
specificities, these should not be construed as limiting the scope of this 
invention but merely providing illustrations of some of the presently 
preferred embodiments of this invention.