US3593735A

US3593735A - Method and apparatus for maintaining a preselected partial pressure

Info

Publication number: US3593735A
Application number: US757317A
Authority: US
Inventors: Max A W Reiher
Original assignee: Dick Evans Inc
Current assignee: McDermott Inc; Dick Evans Inc
Priority date: 1968-09-04
Filing date: 1968-09-04
Publication date: 1971-07-20
Anticipated expiration: 1988-07-20

Abstract

Improving gas-mixing methods and apparatus for maintaining a preselected oxygen partial pressure in breathing gas supplied to a diver under an abnormal pressure. A mixing tank with separate gas inputs is provided to receive and blend together oxygen and filler gas according to a preselected ratio as breathing gas is withdrawn from the tank by the diver. More particularly, a pair of helical tubing lengths or strings are arranged about the inside surface of the tank to receive and dispense filler gas and oxygen uniformly along the length of the tank. A control circuit is also provided to continually measure the molecular oxygen content of the tank, and to admit oxygen whenever the molecular oxygen content drops below a preselected level.

Description

United States Patent [72] Inventor Max A. W. Reiher 2,915,059 12/1959 Le Masson 137/88 Gretna, La. 3,185,448 5/1965 Fraser et a1. 259/4 [21] AppLNo. 757,317 3,215,057 11/1965 Turek 98/115 ii :"f t d i i g Primary Examiner-Rober1 G. Nilson i c i E l Attarneys-Arnold, Roylance, Kruger and Durkee, Tom 1 1 i Arnold, Donald c. Roylance, Walter Kruger, Bill Durkee,

Frank S. Vaden, 111 and Edmund F. Bard [54] METHOD AND APPARATUS FOR MAINTAINING A PRESELEC'I'ED PAR-"AL PRESSURE ABSTRACT: improving gas-mixing methods and apparatus 10 Claims, 2 Drawing Figs for maintaining a preselected oxygen partial pressure 111 breathing gas supplied to a diver under an abnormal pressure. [52] US. Cl 137/88, A i i t nk with eparate gas inputs :is provided to receive 98/ 1.5, 128/142, 128/204, 137/604, 259/4 and blend together oxygen and filler gas according to a Int. preselected ratio as breathing gas is withdrawn from the tank 605d 1 1/035 by the diver. More particularly, a pair of helical tubing lengths of 88, or trings are arranged about the inside surface of the tank to 93, 604; 98/] .5; 128/142, 140, 142.3, 204; 2 receive and dispense filler gas and oxygen uniformly along the I length of the tank. A control circuit is also provided to con- [56] References cued tinually measure the molecular oxygen content of the tank, UNITED STATES PATENTS and to admit oxygen whenever the molecular oxygen content 2.830.583 4/1958 Finney, Jr 128/142 drops below a preselected level.

corvmor i UNIT HE L IUM SUPPL Y OXYGEN SUPPLY METHOD AND APPARATUS FOR MAINTAINING A PRESELECTEI) PARTIAL PRESSURE BACKGROUND OF INVENTION This invention relates to improved methods and apparatus for blending or mixing gases, and more particularly relates to methods and apparatus for mixing breathing gases according to a predetermined formulation during the supply of such gases to an artificial breathing atmosphere such as that provided for divers.

It is well known that the normal breathing atmosphere for humans and other nonaquatic animals is a mechanical blend or mixture of gases, and that this mixture is normally composed of about percent oxygen to 80 percent nonsustaining gas (mostly nitrogen). It is also well known that it is harmful for life which depends on gaseous oxygen to be subjected for any appreciable period to a breathing atmosphere which contains either too much or too little oxygen. However, what is not generally known is that it is not the percentage of oxygen in a breathing atmosphere which is important from the standpoint of life support. Instead, it is the molecular amount of free gaseous oxygen which must be present for life-sustaining purposes.

It is well known that divers, aviators, etc., are often required to operate for extended periods under extremely abnormal pressures, and in an ambient atmosphere which requires that they be continuously supplied with a flow of breathable gas. In the case of divers, for example, it is not uncommon for them to be subjected to ambient pressures which are many times greater than normal atmospheric pressure, and thus breathing gas must be supplied at the same abnormal pressure. In the case of aviators, the pressure is almost always only a fraction of normal atmospheric pressure. Nevertheless, in both instances the artificial atmosphere must be composed of the same molecular amount of oxygen as that normally required for life support purposes. Thus, the percentage of oxygen in the artificially supplied breathing gas must be varied according to the pressure of the breathing gas supplied.

For example, each 100 molecules of gas in a normal breathing atmosphere may be assumed to include 20 molecules of free oxygen and 80 molecules of nitrogen and other free gases. If the diver is submerged to a depth such that his ambient pressure is doubled, the pressure under which his breathing gas is supplied must also be doubled. However, if the mixture which is proper at a pressure of I atmosphere is merely supplied at a pressure of 2 atmospheres, it will be apparent that the diver will receive a breathing mixture which is actually harmful because it contains twice as many oxygen molecules. Instead, what is required is that the 200 gas molecules present in a cubic unit of breathing gas supplied under a pressure of 2 atmospheres, must be composed of only the original 20 molecules of oxygen with the other 180 molecules being an inert or relatively inert gas such as nitrogen or helium.

It is rather difficult to mix oxygen and helium or nitrogen for breathing purposes according to precise percentages, and most of the mixing apparatus and methods of the prior art involve rather time-consuming techniques. Furthermore, no satisfactory technique has ever been developed whereby the breathing gas mixture may be selectively varied as it flows to the diver. These disadvantages of the prior art, however, are overcome with the present invention, and improved methods and apparatus are provided for selectively varying the partial pressure of the oxygen in a breathing gas supply during the use of such supply by a diver or other utilization system.

SUMMARY OF INVENTION In apreferred embodiment of the present invention, a cylindrical closed mixing tank is provided which includes an oxygen intake port at one end and a helium-(or nitrogen) intake port at the other opposite end. Oxygen enters the mixing tank through a helical length of tubing which is arranged along the length of tank and spirally about its inside surface. One end of the tubing is closed, and the other end is connected to the oxygen intake port. A plurality of spaced-apart ports are provided in the wall of the tubing facing always toward the longitudinal axis of the mixing tank. These ports may all be the same size. However, it is desirable that they be progressively larger as they approach the closed farthest end of the tubing, and the size and spacing of the ports should be such that the sum of the areas of all of the ports not be greater than the inside cross-sectional area of the tubing.

A second similar helical length of tubing is also similarly arranged about the inside surface of the mixing tank, with its open end connected to the helium intake port. Helium is received under pressure from a separate helium supply, and continually flows into the tank except when the pressure in the mixing tank is equal to or greater than the pressure of the helium supply. Accordingly, a check valve is preferably included to block backflow of gas from the mixing tank into the helium supply.

A separate supply of oxygen, preferably under a constant pressure substantially greater than the maximum expected pressure in the mixing tank, is connected to supply oxygen to the mixing tank by way of the first helical length of tubing. A suitable control system is also provided to continually measure the partial pressure of the oxygen in the mixing tank, and to generate a functionally related electrical signal whenever the partial pressure of the oxygen is less than a preselected partial pressure. A solenoid-controlled valve is preferably interconnected between the oxygen supply and the oxygen intake port, which opens in response to the electrical signal, and which snaps shut when the signal is discontinued. Thus, tiny jets of oxygen are momentarily injected into the mixing tank along its interior each time the partial pressure: of the oxygen drops below the preselected partial pressure sought to be maintained in the mixing tank and as the breathing :mixture is drawn from the mixing tank for the diver.

It is well known that helium cannot be effectively intermixed with oxygen if it is put in on top" of the oxygen, unless mechanical fans or stirring mechanisms are thereafter used to achieve intermixing of the gases. For this reason, it is common practice to vary the mixture by adding oxygen rather than by adding helium.

This disadvantage of the prior art has been eliminated by the methods and apparatus of the present invention, since the turbulence created by the jets of helium emitted from the helical tubing will intermix the input helium throughout the mixing tank. Accordingly, when it is desired to reduce the partial pressure of the oxygen in the breathing gas beingsupplied to a diver, the control system may simply be adjusted to call for a reduction of oxygen in the mixing tank, whereupon pure helium will be injected into the mixing tank to replace withdrawals of breathing gas by the diver. In this manner, the diver will simply breath off the excess oxygen until the proper ratio is achieved.

The foregoing technique is, of course, somewhat time consuming. If a more rapid reduction in oxygen partial pressure must be achieved, the control system may be adjusted to select the new ratio sought to be achieved, and the mixing tank may thereafter be vented until the molecular oxygen content of the tank drops below this new ratio. After this, the vent may be closed and the control system may then be permitted to inject helium and oxygen in the preferred manner until the proper balance and pressure is attained in the mixing tank.

Accordingly, it is an object of the present invention to provide novel methods and apparatus for supplying a preselected partial pressure of breathing oxygen to a life support system.

It is further an object of the present invention to provide improved methods and apparatus for selectively controlling the partial pressure of the oxygen in a subsea life support system and the like.

It is also an object of the present invention to provide improved methods and apparatus for varying the partial pressure of oxygen in a sealed atmosphere of breathing gas.

It is further an object of the present invention to provide methods and apparatus for maintaining a preselected partial pressure of the oxygen in a sealed breathing atmosphere under a varying pressure.

As hereinafter stated, it is well known that it is difficult and I time consuming to establish a uniform mixture of oxygen and helium or nitrogen without the use of mechanical whipping or stirring mechanisms. Thus the effectiveness of the present invention is dependent to a substantial degree on the use of the gas streams emanating from the ports in the helical tubing coils to achieve turbulence in the gas mixture within the mixing tank. Furthermore, it is a particular advantage that the mixing of the breathing atmosphere be performed during the withdrawal of breathing gas from the mixing tank by the diver or other utilization system. Accordingly, it will be apparent that it is desirable that the turbulence created in the mixing tank by the gas jets emanating from the ports in the helical tubing lengths, be established in a relatively uniform manner throughout substantially the entire length of the mixing tank, and that there be a uniform oxygen partial pressure throughout the mixing tank at all times.

Accordingly, it is a feature of the present invention that both helical tubing lengths be arranged in the mixing tank concentrically about the longitudinal axis of the tank, and that both such tubing lengths extend within the tank along substantially its entire length.

It is a further feature of the present invention that the ports in each helical tubing length face the longitudinal axis of the mixing tank, and that such ports be progressively larger in diameter, from the intake port to which the tubing is connected to the closed end of the tubing length, whereby each gas component will issue into the mixing tank at a uniform rate along the length of the tank.

It is further a feature of the present invention that the helium and oxygen intake ports be located at opposite ends of the mixing tank.

It is another feature of the present invention that the sum of the areas of the ports in each helical tubing length not exceed the total inside cross-sectional area of the tubing.

These and other objects, features and advantages of the present invention will be apparent from a consideration of the following detailed description, wherein reference is made to the figures in the accompanying drawing.

IN THE DRAWING FIG. 1 is a functional representation of an exemplary embodiment of a mixing system incorporating features of the present invention and suitable for use in supplying breathing gas to a deep sea diver or the like.

FIG. 2 is a pictorial representation, partly in cross section, of an exemplary mixing tank suitable for use with the mixing system illustrated in FIG. ll.

DETAILED DESCRIPTION Referring now to FIG. 1, there may be seen a functional representation of a helium supply 30, such as a conventional steel bottle or the like, and a functional representation of a similar oxygen supply 6. inasmuch as the depicted system is primarily intended to supply a breathing gas suitable for human life support, it will be apparent that the oxygen supply 6 contain relatively pure oxygen only. The helium supply 30 may contain either nitrogen or helium, depending on the pressure at which the breathing gas is expected to be utilized, but in either case, it is preferable that the filler gas be relatively pure.

As may further be seen, a mixing tank 2 is provided which includes a suitable drain pipe 3 and valve 4, and which further includes provision for receiving oxygen and helium (or nitrogen) at opposite ends. The helium flows from the helium supply 30 to the mixing tank 2, by way of a helium input circuit 41 including a helium supply shutoff valve 31, a variable helium pressure regulator 32 for reducing the pressure of the helium, a check valve as for preventing backflow from the mixing tank 2, and a helium intake shutoff valve 35. An emergency helium bypass valve 33 may also be provided in case of failure of the helium pressure regulator 32 to pass helium into the check valve 34L Oxygen may be seen to flow from the oxygen supply 6 to the mixing tank 2, by way of an oxygen input circuit 42 including an oxygen supply shutoff valve 8, a variable oxygen pressure regulator 10 for reducing the pressure of the oxygen, a normally closed valve 12 actuated by a solenoid 14, and an oxygen intake shutoff valve 16. A bypass valve 9 may be included to bypass oxygen around the oxygen pressure regulator 50, and a similar bypass valve 15 may be included to bypass oxygen around the solenoid-controlled valve 12.

Breathing gas may be seen to be taken from the mixing tank 2 by way of a conventional pneumatic hose 17, or the like, which may be connected to a point of utilization such as a diver or a pressure bottle or tank sought to be charged, and which preferably includes a suitable outlet shutoff valve 18. Breathing gas pressure in the mixing tank 2 may also be reduced by means of a vent line 19 having a suitable vent shutoff valve 20.

In the depicted system, filler gas (helium or nitrogen or the like) is expected to flow into the mixing tank 2 each time the breathing gas pressure in the tank 2 drops below the preselected operating pressure in the tank 2. This operating pressure is necessarily always higher than the environmental or ambient pressure surrounding the diver, since it is necessary to drive breathing gas to the diver through a long pneumatic hose 17 or the like. For deeper dives, the operating pressure in the mixing tank 2 will usually be 50l00 p.s.i.g. higher than the environmental pressure, and often even higher.

In the system depicted in FlG. 1, the operating pressure for the mixing tank 2 is selected and established by means of the variable helium or filler gas pressure regulator 32. A suitable pressure gauge 23 with an associated shutoff valve 24 may be included to afford means for continuous observation of the pressure within the mixing tank 2.

Helium or nitrogen input is used primarily as a filler gas to maintain the desired pressure of the breathing gas in the mixing tank 2, and thus no input control is required for the filler gas other than the regulator 32. Oxygen input must be limited to that necessary to maintain the partial pressure of the oxygen in the mixing tank 2 according to life support requirements as hereinbefore explained. Accordingly, a suitable control system is preferably included, as hereinbefore stated, to open the solenoid-controlled valve 12 whenever the partial pressure of the oxygen in the mixing tank 2 drops below the level sought to be maintained, and to permit the valve 12 to close whenever the partial pressure of the oxygen rises above the level or valve sought to be maintained. More particularly, a sensor 36 such as that described in US. Pat. No. 3,071,530, may be disposed in the interior of the mixing tank 2, to continually generate an electrical signal functionally related in magnitude to the partial pressure of the oxygen in the mixing tank 2. The sensor 36 is connected by a lead 37 to a suitable control circuit 38, such as that presently manufactured by Teledyne, lnc. The control circuit 38 preferably receives the sensor output signal and continually compares such sensor signal with a selectively variable reference signal which is functionally related in magnitude to whatever partial pressure may be sought to be maintained in the mixing tank 2. If the sensor signal is equal to or greater than the selected reference signal, no control output signal will be generated and the solenoid-controlled valve 112 will remain closed, whereby helium or nitrogen will flow into the mixing tank 2 to replace breathing gas exiting through the hose 17 until the partial pressure of the oxygen in the mixing tank 2 is reduced to less than the partial pressure sought to be maintained. When this occurs, however, the sensor signal will be less than the selected reference signal, and the control unit 38 will respond to this unbalance by generating or passing a suitable control signal (such as 1 15 volts, 60 cycles AC) to the solenoid 14 by way of conductor 39. This will open the solenoid-controlled valve 12, and oxygen from the oxygen pressure regulator will be injected into the breathing gas in the mixing tank 2. Since it is desirable that this injected oxygen be fully blended and intermixed throughout the interior of the mixing tank 2 within the shortest possible time interval, it is desirable that this injection of oxygen create substantial atmospheric turbulence whereby such intermixing may be adequately achieved. Accordingly, it is desirable that the oxygen pressure regulator 10 be set to establish an oxygen input pressure substantially greater (suchas 50 p.s.i.g.), than the pressure setting of the helium pressure regulator 32.

Although a reliable control unit 38 is available from several commercial sources, and although a sensor 36 such as that depicted in U.S. Pat. No. 3,071,530 is generally quite dependable and accurate, it should be remembered that the system depicted in FIG. 1 is intended to provide life support under extremely dangerous conditions. Accordingly, it is desirable to continually monitor the actual oxygen molecular content of the breathing gas in the mixing tank 2, and this may conveniently be achieved by an analyzer 40 such as that depicted in US. Pat. No. 2,913,386. Such an analyzer 40 may be conveniently connected to sample the contents of the mixing tank 2 by means of a suitable pipe or pneumatic hose 2] connected to the mixing tank 2 by a suitable shutoffvalve 22.

Referring now to H6. 2, there may be seen a more detailed illustration of a mixing tank 102 suitable for use inthe system depicted functionally in FIG. I. As represented, the tank 102 may be a closed, generally cylindrical vessel having a drain pipe 103 and drain shutoff valve 104, a vent pipe 119 and vent shutoff valve 120, and a pressure gauge 123 with suitable shutoff valve 124, as hereinbefore explained. Breathing gas may be withdrawn by the diver by means of a conventional pneumatic hose 117 having a suitable shutoff valve 118 as depicted, and the breathing atmosphere in the tank 102 may be continually sampled by a suitable analyzer (not depicted) which may be connected to the tank 102 by a pneumatic hose 121 and suitable shutoff valve 122. A sensor 136, such as that depicted in US. Pat. No. 3,071,530, may be suitably disposed in the tank 102 to generate an electrical signal functionally indicative of the molecular content of free oxygen in the tank 102, and such signal may e transmitted by a suitable lead 137 to a control unit (not depicted).

As hereinbefore explained, is the function of the mixing tank 102 to provide a collection or blending region for oxygen and any suitable filler gas such as helium or nitrogen. Accordingly, helium may be received through a helical tubing length 141 arranged in the tank 102 in a spiral manner adjacent the inside wall of the tank 102 and about its longitudinal axis. The helical tubing length 1141 has a closed end, and thus the helium or other filler gas emanates into the tank 102 through parts 150 which are spaced along the tubing 141 inside the tank 102 and uniformly facing the longitudinal axis of the tank 102. These ports 150 may be any suitable size and spacing, but it is desirable that the ports 150 increase in size progressively along the length of the tubing 141 toward its closed end. Further, it is especially desirable that the sum of the areasof the ports 150 not exceed the inside cross-sectional area of the tubing Ml.

As may be see in FIG. 2, oxygen may be delivered into the tank 102 through another similar helical tubing length 142 having one closed end within the tank 102 and having its other open end connected to receive oxygen as hereinbefore explained. Accordingly, a series of ports 151 facing the longitudinal axis of the tank 102 may. be provided in a suitable spaced-apart arrangement along the length of the helical tubing 142, and these ports may progressively increase in areal size toward the closed end of the tubing 142. In addition, it is particularly desirable thatthe sum of the areas of these ports 151 not exceed the inside cross-sectional area of the tubing 142.

Although the use of the presentinvention for the purpose of subsea life support has been emphasized herein, it should be clearly understood that the invention may also be used to provide a properly oxygen-enriched breathing mixture for aviators and the like. When the invention is employed for this alternate purpose, the operating pressure inthe mixing tank 2.

must be kept at a level greater than 1 atmosphere notwithstanding that the environmental pressure of the aviator will be less than 1 That and that the oxygen ratio of the breathing gas is greater than the ratio which is normally life sustaining at a l atmosphere pressure.

Another feature of the present invention involves the size and shape of the mixing tank 2 depicted in FIG. ll. As hereinbefore stated, it is especially suitable that the tank 2 have a generally cylindrical share as illustrated by thy mixing tank 102 depicted in MG. 2. The tank 2 may also be spherical in shape, and other suitable configurations may suggest themselves from a consideration of the principles of the present invention. hat is more important is that the size of the mixing tank T02 is functionally related to the number and size of the ports 150 and ll5ll in the two helical tubings M1 and 142. As hereinbefore explained, the size and number of these ports 1150 and 151 determine the amount of turbulence which intermixes the helium with the other breathing gases in the tank 102. If the tank 102 is too large the turbulence may be inadequate, and thus the diameter of the tank 102 is directly functionally related to the number and size of the ports T50 and i.

Many other modifications and variations in the structures depicted and described herein will be readily apparent from a consideration of the concept of the present invention. Accordingly, it should be clearly understood that the methods and apparatus described herein and depicted in the accompanying drawing, are illustrative only and are not intended as limits to the scope of the invention.

What I claim is:

l. A mixing system for establishing and maintaining a gas mixture having a preselected oxygen partial pressure which comprises:

a first gas supply for providing a filler gas under a first preselected pressure;

an oxygen gas supply for providing oxygen under a second preselected pressure;

a mixing tank having a filler gas intake port connected to said first gas supply and an oxygen intake port connected to said oxygen gas supply;

first tubing means communicating with said filler gas intake port and spirally arranged proximate the inner surface of said mixing tank;

second tubing means communicating with said oxygen gas intake port and spirally arranged proximate the inner surface of said mixing tank;

said first and second tubing means having a plurality of sidewall openings therein generally directed toward the interior of said mixing tank; and

control means for sensing the oxygen partial pressure in said mixing tank and admitting oxygen to said mixing tank in amounts to establish said oxygen partial pressure in said mixing tank at said preselected oxygen partial pressure.

2. The system described in claim ll wherein said oxygen gas supply provides said oxygen at a second preselected pressure which is substantially greater than said first preselected pressure.

3. The system described in claim 2 including first selectively variable pressure-regulating means for establishing said first preselected pressure and to supply filler gas'to said mixing tank when the internal pressure of said tank is less than said first preselected pressure.

4. The system describe in claim 3 including a check valve interconnected between said first selectively variable pressure regulator and said mixing tank to prevent backflow of said gas from said mixing tank to said first gas supply.

5. The system described in claim ll including a normally closed control valve interconnected between said oxygen gas supply and said mixing tank, said valve being adapted to be opened by said control means.

6. The system described in claim wherein said oxygen gas supply includes a second selectively variable pressure regulator interconnected between said oxygen supply and said control valve for establishing said second pressure.

7. The system described in claim 1 wherein said mixing tank comprises a generally cylindrical vessel; and where said first and second tubing means are arranged proximate the inner cylindrical surface of said vessel along substantially the entire length of said vessel.

8. The system described in claim 7 wherein said first and second tubing means have said sidewall openings directed generally toward the longitudinal axis of said cylindrical ves-

Claims

1. A mixing system for establishing and maintaining a gas mixture having a preselected oxygen partial pressure which comprises: a first gas supply for providing a filler gas under a first preselected pressure; an oxygen gas supply for providing oxygen under a second preselected pressure; a mixing tank having a filler gas intake port connected to said first gas supply and an oxygen intake port connected to said oxygen gas supply; first tubing means communicating with said filler gas intake port and spirally arranged proximate the inner surface of said mixing tank; second tubing means communicating with said oxygen gas intake port and spirally arranged proximate the inner surface of said mixing tank; said first and second tubing means having a plurality of sidewall openings therein generally directed toward the interior of said mixing tank; and control means for sensing the oxygen partial pressure in said mixing tank and admitting oxygen to said mixing tank in amounts to establish said oxygen partial pressure in said mixing tank at said preselected oxygen partial pressure.

2. The system described in claim 1 wherein said oxygen gas supply provides said oxygen at a second preselected pressure which is substantially greater than said first preselected pressure.

3. The system described in claim 2 including first selectively variable pressure-regulating means for establishing said first preselected pressure and to supply filler gas to said mixing tank when the internal pressure of said tank is less than said first preselected pressure.

5. The system described in claim 1 including a normally closed control valve interconnected between said oxygen gas supply and said mixing tank, said valve being adapted to be opened by said control means.

6. The system described in claim 5 wherein said oxygen gas supply includes a second selectively variable pressure regulator interconnected between said oxygen supply and said control valve for establishing said second pressure.

8. The system described in claim 7 wherein said first and second tubing means have said sidewall openings directed generally toward the longitudinal axis of said cylindrical vessel.

9. The system described in claim 1 wherein the inside cross-sectional area of said first tubing means and of said second tubing means is in each case greater than the sum of the areas of the sidewall openings in each of said first and second tubing means respectively.

10. The system described in claim 1 wherein said sidewall openings in said first tubing means and said second tubing means increase in size with increasing distance of said openings from the intake port to which said tubing means is connected.