CA1153893A - Metering valve - Google Patents

Abstract

Abstract of the Disclosure A metering valve which is particularly advan-tageous for use in gas mixing devices such as patient ventilators, to accurately control the volume and fre-quency of gas flow for each gas and to provide a feed-back of the actual flow through the valve. A valve as-sembly which is infinitely openable within its operating range is connected to the core of a linear variable differential transformer. As the valve opens, the core of the transformer moves, causing a change in the output voltage from the transformer. The change in output voltage from the transformer can be interpreted by a microprocessor to discern the actual flow through the valve. Two or more of the metering valves can be used to accurately control the mixture ratios of two or more gases.

Description

METERI~G VALVE
Background Of The Invention Many types of gas supplying and gas utilizing devices require relatively precise metering of the gas flow volume. When the device is one which utilizes or supplies a mixture of two or more gases, the flow volume of each gas must be precisely measured. One example cf such a device is a medical respirator used to assist or control the breathing of a patient. ~t is a customary practice in respirators to mix various amounts of oxygen and ambient air and to discharge a predetermined volume of the mixture of gases into the patient at specific in-tervals. This is known as volume ventilating and is a procedure which has largely replaced ~he earlier patient ventilating technique known as pressure ventilating.
Since frequently the same respirato~ is used for many different patients having different breathing require-ments, the mixture of oxygen and air supplied thereby should be controllable within a range from 100~ oxygen to 100% ambient air. Likewise, the signal wave form for establishing a breathing pattern should be con-trollable.
A third patient ventilating technique known as high frequency positive pressure ventilation (H.F.P.P.V.) has gained increasingly favorable recog-nition for patient ventilating in various circumstances.
In the H.F.P.P.V. technique the patient's lungs are stopped, and low volume jets of air are intr~duced in rapid succession to the patient, simulating a panting type of breathing pattern. As many as 60 "breaths"
may be introduced in a one minute interval. It is believed by many people in the medical field that the 1.

H.F.P.P.V. technique can be tolerated more easily by the patient than volume ventilating is tolerated. An H.F.P.P.V. ventilator should also have means for con-trolling the gas mixture output within a range from 100% ambient air to 100% oxygen, and the signal wave form for the breathing pattern should also be control-lable to provide a variety of different breathing pat-terns.
in a device for performing any of the afore-mentioned patient ventilating techniques, three basic valving functions are required. First, mixing of the gases in predetermined proportions must be performed, usually by a mixing valve. Second, a flow rater is required to provide a signal for controlling the in-duced breathing pattern and the rate of breathing, and third, a throttle valve is required to control the volume of gas passed in each breath. These three functions have largely been performed by separate in-dividual valving apparatus which result in a relatively large device with numerous operating parts and many po-tential sources of malfunction. Further, because of the different volume and flow rate requirements for per-formance of the volume ventilating technique as com-pared with the requirements for the performance of the H.F.P.P.V. technique, and because of the limitations of the valving apparatus presently used therefor, separate ventilators are required for the preformance of each technique. Hence, substantial finan~ial investment by medical facilities is required for the different types of ventilators.
A further disadvantage of previous ventilators is that no precise feedback of the actual ventilator output is available for controlling the operation of 11538~3 the ventilator. Standard ventilators commonly have controls for selecting various gas mixture ratios and inspiration rates as well as for selecting one of several flow patterns; however, no precise feedback of the actual output is provided, and the flow pattern of the output is limited to only those few specific patterns which are made available on the ventilator.
Very little flexibility in flow pattern and rate is provided in most ventilators.
Summary of the Invention An object of the present invention is to provide a metering valve which is particularly advantageous for use in ventilating devices for medical patients, and which can be used for both volume ventllation and high frequency positive pressure ventilation of a patient.
A further object of the present invention is to provide a metering valve which provides a means for sensing and determining the actual valve output for reappraisal and adjustment of the output during the next successive output phase if necessary.
Still another object of the present invention is to provide a metering valve which can be used individually to control the volume and frequency of flow of a gas.
It is a preferred feature of the present invention to provide a metering valve which combines gas mixture ratio regulating, mixed gas output volume controlling, and output pattern determining functions in a single compact valve, and which is capable of producing a corresponding flow rate for any signal wave form.
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In another preferred embodiment it is desired to provide a metering valve which can be used in combination with another metering valve to control the flow frequency and volume and the mixing of two or more gases in a device.
These and other objects are accomplished in the present invention by providing a metering valve for dispensing a selected volume of gas at selected intervals, comprising a body having an inlet and an outlet opening therein, a passageway between the inlet and the outlet openings, valve element means for controlling the flow of agas through the passageway, a proportional solenoi~ assembly for moying the element means a selected distance for a selected period of time to open the passageway, and sensing means, such as a linear variable differential transformer, for determining the position of the element means and therefore the flow of gas through the valve.
In the preferred structure the valve has infinite operating positions within its operating range, and can be operatively connected to a micro-processor for controlling the frequency and the distance which the valve opens, thereby controlling the volume of gas passing through the valve and the frequency and pattern of gas output.
The frequency and volume of gas output are regulated by controlling the electric power input to the solenoid assembly and the electromagnetic field created thereby. The shaft may be connected to a linear variable differential transformer (L.V.D.T.) core and, in such case, moves the core in relation to movement of the element.
Core movement in the L.V.D.T. causes variations in the voltage output from the L.V.D.T. which can be analyzed :

dm:~ ~` - 4 -~lS313~3 by conventional micro-processors for determining the actual valve output. Diaphragms may be provided within the valve to balance the pressures on opposite sides of the valve element so that fluctuations in the inlet and/or outlet pressures will not cause the element to move. Two or more of the metering valves may be connected together for providing variable mixtures at any desirable volume and fre~uency within the operating ranges of the valves.
In another embodiment, there is provided a metering valve comprising a body having inlet and outlet openings therein and a passageway between the openings, a valve element for controlling fluid flow through the passageway, a proportional solenoid assembly for creating an electro-magnetic field, a shaft connected to the element and extending through the solenoid assembly, the electromagnetic field causing the shaft to move axially in the solenoid assembly for moving the element and opening the passageway, a linear variable differential transformer attached to the solenoid assembly and having a core connected to the shaft, the axial movement of the shaft causing axial movement of the core for varying the voltage output from the transformer to provide a feedback signal indicative of actual output from the metering valve.
In yet another embodiment, there is provided a metering valve assembly for dispensing a selected volume of gas at selected intervals, the volume and intervals being regulated in response to the actual flow through the valve previously, the assembly comprising a body having an inlet and an outlet opening therein, a passageway between the inlet and the outletopenings, valve element means for controlling the flow of a gas through the dm:\ ~' ~ S ~

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11538'~3 passageway between the inlet and the outlet openings, a proportional solenoid assembly for moving the element mear-s a selected distance for a selected period of time to open the passageway, and sensing means for determining the flow of gas through the valve and for providing a signal for controlling the means for moving the element means.
Additional objects and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.
Brief Description of the Drawings Figure 1 is a perspective view of a mixing and metering valve assembly for use in a ventilator;
Figure 2 is a perspective view of the mixing and metering valve assembly with the cover thereof removed, revealing the two mixing valve units therein;
Figure 3 is a top view of the mixing and metering valve assembly shown in Figure 1, with some of the con-cealed parts shown by broken lines;
Figure 4 is a side elevational view of the mixing and metering valve assembly shown in Figure 1, again with some of the concealed parts shown by broken lines; and Figure 5 is an enlarged cross sectional view of the mixing and metering valve assembly shown in Figure 3, taken on line 5 - 5 of the latter figure.
Detailed Description of the Preferred Embodiment Referring now more specifically to the drawings, and to Figure 1 in particular, numeral 10 designates a mixing and metering valve assembly suitable for use in a patient ventilator. The mixing and metering valve assembly includes a valve body 12 having an oxygen inlet 14, an air inlet 16, and a mixed gas outlet 18.

dm~ - 5a -11538~3 Anodized aluminum alloys are suitable materials for body 12, although other suitable materials may also be used.
An oxygen metering valve 20 controls the flow of oxygen between oxygen inlet 14 and mixed gas outlet 18, and an air metering valve 22 controls the flow of air between air inlet 16 and mixed gas outlet 18. An oxygen pressure tap 24 and an air pressure tap 26 axe disposed in body 12, and a pressure tap outlet 28 is also provided. Oxygen meter-ing valve 20 and air metering valve 22 are similar in con-struction and perform similar functions in controlling the flow of the gases between the inlets thereof and the mixed gas outlet. It should be understood that one metering valve may be used individually for providing a predetermined flow o~ a gas in any selected wave form. Similarly, in an apparatus having more than two gas inlets, three or more metering valves may be used to provide a calculated volume flow of each gas at a predetermined frequency and in any wave form pattern for providing variable mixtures of the various gases. The two-metering-valve embodiment shown in the drawings is merely one example of an advantageous use of the present metering valve invention.
Metering valves 20 and 22 are connected by wire harnesses ~0 and 32, respectively, to electrical con-nectors 34, 3~, 3~ and 40 disposed on a bracket 42. The bracket may be stainless steel, aluminum, or the like, and is connected to body 12 by screws 44, 46, 48 and 50.
A housing cover 52 encloses the metering valves and bracket and includes holes 54, 56, 58 and 60 through which connectors 34, 36, 38 and 40 extend when the cover is in place on body 12. The cover can be made of an acrylic thermoplastic, such as methyl methacrylate, or other ~iS38~3 suitable material, and is held on body 12 by screws 62, 64, 66 and 68. It should be understood that the shapes of body 12 and cover 52, and the position and orientation of the various inlets and outlets, as well as the electri-cal connectors, can be varied, and the arrangement of parts shown in the drawings is merely one suitable arrangement.
As mentioned previously, oxygen metering valve 20 and air metering valve 22 are similar in construction, and the description of oxygen metering valve 20 to follow is similarly descriptive of air metering valve 22. The oxygen metering valve will be described more fully with reference particularly to Figure 5, and parts of air metering valve 22 which correspond to the parts described for oxygen metering valve 20 are designated with prime eference numerals similar to the oxygen metering valve reference numerals.
Oxygen metering valve 20 includes a valve as-sembly 80 driven by a proportional solenoid, which includes a valve element or seal assembly 82 operating between pass-ageways 84 and 86 to control the flow of oxygen between oxygen inlet 14 and mixed gas outlet 18, and a propor-tional solenoid assembly 88 for moving element 82 to open and close the passage. Valve assembly 80 is operatively connected to a linear variable differential transformer (L.V.D.T.) assembly 90 which provides a voltage output signal that can be interpreted by a microprocessor, for analyzing the position of element 82 and therefore the volume and frequency of oxygen transmittal between oxygen inlet 14 and mixed gas outlet 18.
Element 82 includes a sealing member 92 which engages a seat 94 in passageway 84 to prevent the flow of oxygen from passageway 84 to passageway 86. The mem-11S;3~1~3 ber 92 is disposed on a valve element body or retainer 96 connected to a shaft 98 which extends through sole-noid assembly 88 and is connected to L.V.D.T. assembly 90 as will be described more fully hereinafter. A
stem assembly 100 extends from element 82 in the op-posite directicn from shaft 98 and includes a stem 102 in an open area generally indicated by numeral 104 be-tween passageway 84 and passageway 86. The open area 104 in body 12 extends through the outer surface of the body, and a cap 106 for the opening, of material similar to that of the body, is connected to the body by bolts 108. A diaphragm 110 is disposed on the end of stem 102 and is held on the end of the stem by a washer 112 and a screw 114. Synthetic materials such as silicone cr dacron are suitable for the diaphragm. The diaphragm is disposed between cap 106 and a shoulder 116 in body 12 and seals the area between the cap and body and also the end of stem 102. The diaphragm is a rolling friction-less seal which provides pressure balancing of the valve element so that variations in outlet pressure will not affect operation of the element.
Proportional solenoid assembly 88 includes a housing 130 threadedly connected to body 12 at threads 132 and secured in the housing by a set screw 134. Dis-posed within housing 130 are a front ring assembly 136, a rear ring assembly 138 and a magnet 140 between the aforementioned ring assemblies. A coil assembly 142 is disposed axially in the solenoid assembly, and an armature assembly 144 is disposed axially in the coil assembly.
Shaft 98 extends through the armature assembly and has a 9~3 diaphragm 146 disposed thereon which is held against seal retainer 96 by a nut 148. The diaphragm is si-milar to diaphragm 110 and is held against a shoulder 150 in housing 130 by a retaining ring 152. The dia-phragm operates similarly to diaphragm llO in balancing inlet pressure forces. Thus, diaphragms 146 and llO
equalize the pressure forces on opposite sides of ele-ment 82 so that the seating and unseating of member 92 on seat 94 is not affected by differences in pressure forces on opposite sides of the element.
Front ring assembly 136 includes a ring 154 and a spring 156 disposed between nut 148 and a shoulder 157 of ring 154. Rear ring assembly 138 includes a ring 158 and a spring 160 disposed against a shoulder 161 of ring 158. The springs are flat tempered spring steel which bend when member 92 is moved away from seat 94, and which move the shaft axially to return the member to the seated position when the activating current to the proportional solenoid assembly is interrupted. The coil assembly 142 includes a bobbin 162 wrapped with magnet wire in the area indicated by numeral 164. Wires 166 and 168, which form a part of harness 30, extend from the coil assembly and can be connected to an electrical power source through the aforementioned electrical connectors. Armature assembly 144 includes an armature 170 and an armature plate 172 disposed on the armature and separated from spring 156 by a shim 174. Armature 170 is threadedly engaged on shaft 98 and causes axial movement of the shaft in response to the field created by the coil as-sembly and magnet when an electric current is applied to the coil assembly through wires 166 and 168. Hence, 115389~

by controlling the electrical field created, member 92 can be moved any distance from seat 94 within the oper-ating range of the valve, and can be held in an opened or closed position for any duration of time. The valve can be opened quickly, slowly, or in varying stages, and can be held in any partially opened or fully opened po~i-tion for any desirable length of time. Hence, any wave form of gas flow through the valve can be created.
The linear variable differential transformer assembly 90 includes a holder 190 connected to the valve assembly and an L.V.D.T. 192 héld in the holder by a set screw 194. Voltage input and output leads indicated gen-erally by the numeral 196, which also form a part of har-ness 30, extend from the L.V.D.T. to the electrical con-nectors and can be attached to a microprocessor for com-parison of the voltage output to the voltage input for interpretation of the valve output. The holder has a flange portion 198 which extends from the cylindrically shaped main body of the holder to housing 130. The flange is disposed against the end of ring 158, and a wave washer 200 is disposed on the top of flange 198 and has a spacer 202 disposed on top thereof. The entire L.V.D.T. assembly is held by a retaining ring 204 disposed in a channel in the inner surface of housing 130.
The L.V.D.T. is a conventional structure from which the position of an axially moveable core 206 is detected by comparing the voltage input to the voltage output of the device. A suitable type is an electro-mechanical transformer having a ferro-magnetic core and a primary and two secondary windings on a bobbin. The core is axially moveable and causes a change in the 10 .

115;~893 voltage induced in the secondary windings when power is applied to the primary winding. The voltage from the output terminals is proportional to the displacement of the axially moveable core. When used in the present metering valve, the axially moveable core of the L.V.D.T.
is connected by a stud 210 to shaft 98. Hence, axial movement of the shaft as the valve opens and closes moves the core of the L.V.D.T., thereby changing the output voltage from the L.V.D.T. The changes in output voltage can be interpreted by a microprocessor which con-trols the operation of the solenoid operated valve as-sembly, and feedback of the actual output of the valve is provided. The microprocessor will include knowledge of the pressure and gas flow characteristics, as well as knowledge of the position of valve element 82 in inter-preting the output from the valve. A nut 212 is disposed on shaft 98 on the opposite side of spring 160 from stud 210. The stud includes a shoulder 214 with a washer 216 disposed thereon. A spring retainer 218 is disposed on stud 210 and is connected to an inwardly extending portion 220 of holder 190. A spring 222 is disposed between re-tainer 218 and washer 216. The stud slides axially in retainer 218 when shaft 98 moves axially; hence, as the valve opens, with member 92 moving away from seat 94, stud 210 is moved into and toward the L.V.D.T., thereby moving the core of the L.V.D.T. axially and causing a change in the voltage output from the L.V.D.T.
Air metering valve 22 is similar to oxygen metering valve 20; hence, a detailed description thereof is not required and will not be given. For purposes of clarity, several of the parts of air metering valve 22 have been shown in Figure 5 and are designated with prime ~153~ 3 numerals similar to the numerals designating the cor-responding parts in oxygen metering valve 20. A pas-sageway 230 from the air metering valve intersects with passageway 86 at mixed gas outlet 18. Hence, the oxygen passing through oxygen metering valve 20 meets and mixes with the air passing through air metering valve 22 at mixed gas outlet 18. Legs 232, 234, 236 and 238 may be disposed under body 12, and if the legs are threadedly con-nected to the body, the legs may be adjusted to level the valve assembly.
In the use and operation of a mixing and metering valve embodying the present invention, oxygen inlet 14 and air inlet 16 are connected to supplies of the gases. Appropriate connections are made between con-nectors 34, 36, 38 and 40, a microprocessor, and an elec-tric supply source to provide an electrical input to the solenoid assembly 88 and voltage inpuL and output con-nections to L.V.D.T. 192. In the off, or at rest, po-sition, when no current is being provided to solenoid assembly 88, springs 156, 160 and 222 hold shaft 98 in a position such that member 92 is engaged on seat 94, and oxygen entering oxygen inlet 14 is prevented from passing through area 104 and passageway 86 to outlet 18.
When an electric current is provided to the solenoid assembly, causing the creation of an electromagnetic field, shaft 98 is moved axially as a resllt of the axial movement of armature 170 to which the shaft is connected.
Member 92 is moved away from seat 94, permitting the passage of oxygen from passageway 84 to passageway 86 through area 104. The strength of the field required to move the shaft is determined by the strength of springs 156, 160 and 222, and the distance which member 92 is moved from seat 94 is determined by the strength of the field created in the solenoid assembly. Thus, the volume of gas passæng through the valve is controlled in part by the degree to which the valve is opened, which is con-trolled by the strength of the electromagnetic field, and, in part, by the time which the valve is open.
The valve remains open until the current supplied to the coil assembly is interrupted, and the electromagnetic field is terminated. When the electromagnetic field is terminated, springs 156, 160 and 222 move shaft 98 axially until member 92 engages seat 94, effectively blocking the flow of gas through the valve. It is clear that any wave form of gas flow can be created in the pre-sent valve by simply controlling the characteristics of the electromagnetic field created in the solenoid assembly.
For example, a sudden high voltage input to the coil as-s embly will rapidly move the valve element to a fully opened position. Alternatively, the current supplied to the coil can be moderate at first and steadily increasing, thus resulting in the valve opening slowly, or the electro-magnetic field can be moderately established at first and held at that level, with a subsequent increase crea$ing a low volume gas flow followed by a higher volume gas flow.
Other variations in the characteristics and volume of gas flow can likewise be created. Hence, when used in a ven-tilator, the metering valve can be used to provide a gas for volume ventilating, as well as high frequency positive pressure ventilating, and one ventilator can be used for both techniques, creating virtually any desired inspiration wave form.
Axial movement of shaft 98 is directly trans-ferred to axial movement of core 206 in L.V.D.T. 192, in that stud 210 is connected to the shaft and to the core. Thus, as valve element 82 is moved away from seat llS38~33 94, core 206 is moved axially in L~V~D~T~ 192, and the voltage output from the L~V~D~T~ changes. The changes in voltage output from the L~VoD~T~ correspond to changes in the position of valve element 82. Thus, the exact characteristics of the valve output and the exact wave form of the valve output are mirrored by changes in the voltage output from the L~V~D~T~ The microprocessor means controlling the current to solenoid assembly 88 may also receive and interpret the voltage signals to and from the L~V~D~T~ to interpret the valve output and make adjustments in the current supplied to the solenoid assembly, if re-quired.
Air metering valve 22 operates similarly to oxygen metering valve 20, and the air passing therethrough enters passageway 230 and meets with the oxygen from passageway 86 at mixed gas outlet 18. Thus, by controlling the flow of gases tnrough each valve, precise ratios of mixtures at outlet 18 are created. One hundred percent oxygen or air can be provided simply by sending no electric current to the solenoid assembly of the valve for the gas which is not desired, so that the va]ve does not open and only gas from the other valve reaches outlet 18. Normally in a respirator the two valves will open for the same time duration when mixed gas is required. To vary the ratios of oxygen and air in the mixed gas, the distances which the valve elements are moved from the seats are controlled so that a greater volume of the gas desired in a higher percent will flow through the controlling valve thereof to outlet 18 than will the other gas.
One metering valve of the present invention can be used to control the flow of a gas in a device, and can provide any wave form of flow pattern for the gas in ad-dition to a feedback signal which can be used to analyze the exact output from the valve. In devices having more than two gases flowing therethrough, three or more of the metering valves can be used, one metering valve for each of the gases.
Although one embodiment of a mixing and metering valve has been shown and described in detail herein, vari-ous changes may be made without departing from the scope of the present invention.

15.

Claims (24)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A metering valve for dispensing a selected volume of gas at selected intervals, comprising a body having an inlet and an outlet opening therein, a passageway between said inlet and said outlet openings, valve element means for controlling the flow of a gas through said passageway, a proportional solenoid assembly for moving said element means a selected distance for a selected period of time to open said passageway, and sensing means for determining the position of said element means and.
therefore the flow of gas through said valve.

2. A metering valve as defined in Claim 1 in which a shaft is connected to said element means, and said solenoid assembly for creating a magnetic field causes axial movement of said shaft.

3. A metering valve as defined in Claim 2 in which said sensing means includes a linear variable differ-ential transformer having an axially moveable core, the axial movement of which causes variations in an output signal from said transformer, and said shaft is connected to said core.

4. A metering valve as defined in Claim 1 in which said sensing means includes a linear variable differ-ential transformer having an axially moveable core, the axial movement of which causes variations in an output signal from said transformer, and said element means is connected to said core.

5. A metering valve as defined in Claim 1 in which said body has a second inlet therein, a passageway from said second inlet intersects with said passageway from said first mentioned inlet, a valve element means is provided for controlling the flow of a gas through said second passageway, a proportional solenoid assembly is provided for moving said second mentioned valve element means a selected distance for a selected period of time to open said second passageway, and a second sensing means is provided for calculating the position of said second element means and therefore the flow of gas through said valve.

6. A metering valve as defined in Claim 5 in which said assemblies for moving said valve element means to open said passageways include shafts connected to said element means and said solenoid assemblies create electro-magnetic fields causing axial movement of said shafts.

7. A metering valve as defined in Claim 6 in which said sensing means include linear variable differ-ential transformers having axially moveable cores, and said shafts are connected one to each of said transformer cores.

8. A metering valve as defined in Claim 5 in which said sensing means include linear variable differ-ential transformers having axially moveable cores, and said element means are connected one to each of said transformer cores.

9. A metering valve comprising a body having inlet and outlet openings therein and a passageway between said openings, a valve element for controlling fluid flow through said passageway, a proportional solenoid assembly for creating an electromagnetic field, a shaft connected to said element and extending through said solenoid assembly, said electromagnetic field causing the shaft to move axially in said solenoid assembly for moving said element and opening said passageway, a linear variable differential transformer attached to said solenoid assembly and having a core connected to said shaft, said axial movement of said shaft causing axial movement of said core for varying the voltage output from said transformer to provide a feedback signal indicative of actual output from the metering valve.

10. A metering valve as defined in Claim 9 in which said solenoid assembly includes a housing, front and back rings disposed in said housing, a magnet disposed in said housing between said front and back rings, a coil assembly axially disposed in said magnet and said front and back rings, and an armature assembly axially moveable in said coil assembly and connected to said shaft.

11. A metering valve as defined in Claim 9 in which a spring is connected to said shaft for moving said shaft axially to seat said valve element in said passageway when said electromagnetic field is interrupted.

12. A metering valve as defined in Claim 9 in which a stud is connected to said core of said transformer and extends outwardly therefrom, and said shaft is connected to said stud.

13. A metering valve as defined in Claim 10 in which a holder is attached to said housing, and said trans-former is disposed in said holder.

14. A mixing and metering valve comprising a body having first and second gas inlets, a mixed gas outlet, and passageways from said first and second inlets to said outlet, valve elements operating in said passage-ways to control the flow of gas through said passageways, proportional solenoid assemblies for moving said elements independently preselected distances for preselected times, and sensing means connected to each of said elements for sensing the positions of said elements to determine the actual valve output.

15. A mixing and metering valve as defined in Claim 14 in which each of said solenoid assemblies includes a coil and an axially moveable armature, said coil creating an electromagnetic field for causing axial movement of said armature, and a shaft connected to said armature and to one of said elements and said sensing means is connected to said shaft.

16. A mixing and metering valve as defined in Claim 15 in which each of said sensing means includes a linear variable differential transformer having an axially moveable core, the axial movement of which causes changes in the voltage output from said transformer for determining the actual valve output, and said shafts are connected one to each of said cores.

17. A mixing and metering valve as defined in Claim 16 in which diaphragms are disposed on opposite sides of each of said elements for balancing the inlet and outlet pressure forces.

18. A mixing and metering valve as defined in Claim 16 in which housings are connected to said body, said solenoid assemblies are disposed in said housings, holders are connected to said housings, and said transformers are disposed in said holders.

19. A mixing and metering valve as defined in Claim 16 in which springs are connected to said shafts for moving said shafts axially to close said passageways when said electromagnetic fields are interrupted.

20. A metering valve assembly for dispensing a selected volume of gas at selected intervals, the volume and intervals being regulated in response to the actual flow through the valve previously, said assembly comprising a body having an inlet and an outlet opening therein, a passageway between said inlet and said outlet openings, valve element means for controlling the flow of a gas through said passageway between said inlet and said outlet openings, a proportional solenoid assembly for moving said element means a selected distance for a selected period of time to open said passageway, and sensing means for determining the flow of gas through said valve and for providing a signal for controlling the means for moving said element means.

21. A metering valve assembly as defined in Claim 20 in which a shaft is connected to said element means, said solenoid assembly axially moves said shaft in response to a signal input to said solenoid assembly, and said signal from said sensing means influences the signal to said solenoid assembly and the movement of said element means.

22. A metering valve assembly as defined in Claim 20 in which said body has a second inlet therein, a passageway from said second inlet intersects said passage-way from said first mentioned inlet, a valve element means is disposed in said second passageway for controlling the flow of a gas through said second passageway, a proportional solenoid assembly is connected to said second mentioned element means for moving said second mentioned element means a selected distance for a selected period of time to open said second passageway, and a second sensing means is provided for determining the flow of gas through said second passageway and for providing a signal for controlling the means for moving said second mentioned element means.

23. A mixing and metering valve comprising a body having first and second gas inlets, a mixed gas outlet and passageways from said first and second inlets to said outlet, valve elements operating in said passageways to control the flow of gas through said passageways, proportional solenoid assemblies for moving said elements independently preselected distances for preselected times, and sensing means for determining the gas flow through each of said passageways and for providing signals for regulating said solenoid assemblies in response to the actual valve output.

24. A mixing and metering valve as defined in Claim 23 in which each of said solenoid assemblies includes a coil and an axially moveable armature, said coil creating an electromagnetic field for causing axial movement of said armature, and a shaft connected to said armature and to one of said elements.