US2821856A - Rapid gas-sampling valve - Google Patents

Description

Feb. 4, 1958 w. J. LEVEDAHL 2,821,856

- RAPID GAS-SAMPLING VALVE Filed Dec. 15, 1953 2 Shets-Sheet 1 INVENTOR Wz'U lkzm I Leueaahl BY W z m;

AGENT Feb. 4, 1958 w. J. LEVEDAHL RAPID GAS-SAMPLING VALVE 2 Sheets-Sheet 2 Filed Dec. 15, 1953 INVENTOR William lLeueda/zl M x m,

A6ENT United States Patent RAPID GAS-SAMPLING VALVE William J. Levedahl, Kensington, Mo., assignor to the United States of America as represented by the Secretary of Commerce The present invention relates to a valve for sampling gases and in particular to a valve for rapidly obtaining samples of gases under high pressures. An investigation of the reaction kinetics of any chemical process requires some knowledge of the proportions of reaction products present at various times during the progress of the re action. In those cases where the reaction occurs at a rapid rate, such as when investigating the combustion products of an internal combustion engine, the sampling rate must be extremely rapid if samples are to be obtained of products that are present only during the progress of the reaction. Therefore, the samples must be taken over extremely short time intervals, and the reaction must be stopped almost instantly upon removal of the sample from the combustion chamber. This latter requirement is necessary so that the products retained in the sampling chamber will be the same as those removed from the reaction mixture. In such an investigation there is the further limitation that the sample obtained must be large enough to permit analysis thereof, and the sample must be obtained during only one run, since the reaction may vary from run to run. The time of sampling will vary depending upon the type of reaction being investigated. However, if the valve is being used to sample com-bustion products of an internal combustion engine or other explosive reactions of the same rate, the time of sampling should be no more than 2X10 second. This is necessary so that the first and last portions removed will not be too different from the average. Further it is necessary that the length of time the valve is opened be accurately known so as to permit correlation between the gas investigated and other measured quantites.

It is therefore the primary object of the present invention to provide a valve for rapidly sampling gaseous mixtures.

it is another object of the present invention. to provide a valve for rapidly sampling gaseous mixtures in which the time of sampling is 2X second or less.

' it is another object of the present inventionto provide a valve in which the sampling operation starts almost instantly after receipt of the signal indicating the beginning of a run.

Another object of the present invention is to provide a valve in which the rate of sampling increases as the pressure of the gases increases.

Another object of the present invention is to provide a rapid gas-sampling valve in which the gaseous sample is rapidly expanded immediately after sampling, thereby stopping the reaction'almost instantly.

Another object of the present invention is to provide a gas-sampling valve which will obtain in one operation a sample large enough to allow analysis of the mixture.

Another object of the present invention is to provide a rapid gas-sampling valve in which the length of time the'valve is opened is easily and accurately determined.

Another object of the present invention is to provide a rapid gas-sampling valve which has very few moving parts.

2,821,856 l tened Feb. 4, 1958 Other uses and advantages of the invention will become apparent upon reference to the specification and drawings.

Figure 1 is a cross-sectional view of the valve of the present invention.

Figure 2 is a partial cross-sectional view of the valve of the present invention shown at right angles to the view of Figure 1.

Figure 3 is a cross-sectional view taken along line 3--3 of Figure 1.

Figure 4 is a cross-sectional view taken along line 4-4 of Figure 3.

Referring to Figure 1, the valve body 11 is adapted at its lower end to be inserted into the pressure chamber containing the gases to be sampled. The pressure of these gases is used as the force for actuating the valve. The valve body has a centrally disposed opening 12 which is separated from a second centrally disposed opening 13 by the bushing 14. The lower end of the valve housing is provided with a lower valve seat 16, which is removably mounted in the lower end of the housing. The internal periphery of the valve housing has an upward protrusion, or shoulder, 17, which provides for an upper valve seat. A piston 18, which is mounted on the valve stem 19, is constrained by the bushing 14 to travel along the axis of the centrally disposed opening 12 of the valve housing, or in the position in which the valve is shown, witha vertical motion. The flange 22 on the piston cooperates with the shoulder 23 on the lower valve seat 16 to provide a seal when the piston is in the lowest position. Also there is a very snug fit between the vertical sides of the piston and the lower seat which helps maintain a good seal. When the piston is in the raised position (it being shown in a partially raised position in Figure 4) the flange 22 of the piston cooperates with the shoulder 17 of the valve housing to again provide a seal between the piston and the housing. 2

Located on top of the valve stem 19 is a butterfly 24- which has a relatively long thin rod 26 extending vertically from the top thereof. Positioned directly above the butterfly in the centrally disposed opening 13 is the boltlike member 27 which carries the valves latching and triggering mechanism. Located in a slot in this member and pivoted about the pin 30 is an arm 28 which carries at its lower end two prongs 29 which have cut-away portions which provide a horizontal shoulder 31. This horizontal shoulder rests on the top of the butterfly 24 and locks the piston in its lower position. The upper end of the arm 28 extends through the slot in the member 27 and a second slct'in the cutback portion of the housing 11 and is engaged by a notch 32 in the holding arm. 33, which is pivoted in the member 27 about the pin 35. The member 27 is mounted in the centrally disposed opening 13 of the valve housing 11 and is movable with respect to it. The member 27 is provided with a horizontal cylindrical hole 34 which is aligned with holes 36 in the valve housing. A cam 37 is inserted through the two holes and locked in place by the screw 38. A solenoid 39 is screwed into the top of the member 27, the bolt 41 extending into the hole 34 of the member 27 and seating against the eccentric portion 46 of the cam 37. The solenoid maintains the arm 33 in the extended position when the solenoid is not actuated, thereby holding the arm 28 in the position shown in Figure 1. When the solenoid is actuated the arm 33 is pulled towards the solenoid thereby releasing the arm 28. The pressure against the bottom of the piston is transmitted to the shoulder 31 of the arm 28. When the arm 28 is unlatched it rotates about the pin 30 and assumes the position shown in Figure 4, thereby allowing the piston to rise. It will be noted that as a result of this particular arrangement for releasing the piston, little energy is expended on accelerating thelatching mechanism. Thereice fore there-is littledelay between the actuation of the solenoid and start of the upward movement of the piston. This is essential to the proper operation of the system, since the solenoid will usually be triggered at the time the sample is to be taken and therefore little delay in operation can be tolerated.

When the piston is between the upper and lower valve seats, as shown in Figure 4, gases can flow around the piston and into the centrally disposed opening 12. When it is desired to reclose the valve after a run, the cam 37 is rotated to lift member 27, thereby bringing the shoulder 31 and prongs 29 to a position higher than the top of the butterfly 24. The arm 28 is then relatched by the arm 33 and the cam is again rotated to return the member 27 to the down position. During the downward movement of the member 27, the shoulder 31 engages the top of the butterfly and pushes the piston into its lower position.

The valve of the present invention was designed primarily for sampling gases under high pressures resulting from such phenomena as combustion or explosions. In order to obtain a very rapid sampling rate and to prevent contamination of the sampled gases, the areas through which the sampled gases are to pass must be evacuated. The centrally disposed opening 12 of the valve housing 11 is connected through a plurality of openings 42 with a groove 43 in the outer circumference of the valve housing and then through the opening 44 to a vacuum pump 46. The pump is used to evacuate all passages in the valve through which the sampled gas will pass. When a run is to be made the pump 46 is excluded from the system by means of the valve 47 and then the opening 44 connects only with the evacuated sample bottle 48. As previously stated, it is necessary when sampling combustion products which are still in the process of rapid change to provide for extremely rapid expansion of the products to reduce the pressure and stop the reaction very rapidly. This is provided in the present invention by means of the groove 43 and container 49. The groove, which is located a very short distance from the piston, opens into a large area for expansion of the gases close to the entrance area of the valve. The actual valve is smaller than the drawings, and it can be seen from this that the expansion area is very close to the entrance of the instrument.

Since the opening 12 is evacuated, air will tend to pass between the bushing 14 and valve stem 19 into the centrally disposed opening 12 and contaminate the sample. To prevent this, circumferential grooves 50 and 55 are provided on the inner and outer surfaces respectively of the bushing 14. The grooves are connected together and the outer groove 55 is connected through the passage 51 to a vacuum pump. Therefore the air is removed from the valve before it can reach the opening 12.

The rod 26, extending from the top of the butterfly, is used as a means for determining the starting and stopping times of valve operation. When the piston is in its lower position the top of the rod 26 is just at the edge of a beam of light which is produced by the bulb 52 and projected onto the phototube 53. When the valve is actuated, and the piston begins to rise, the rod 26 intercepts increasing amounts of light, and as the piston reaches its uppermost position, the rod 26 is blocking out most of the light. In this way the photocell sees at the start a beam of light of constant intensity. When the piston is moving, the photocell sees a beam of decreasing intensity, and when the piston has stopped, the photocell sees again a beam of constant, but lower, intensity. Therefore, if the output of the photocell is differentiated, two distinct voltage discontinuities will be obtained, one at the beginning of the movement of the piston and the second at the end of movement of the piston.

As previously pointed out, the movement of the piston depends upon the pressure differential across its front and back surfaces. Therefore the length of time that the piston is opened will depend'upon the pressure of the gas being examined. Also the amount of gas sampled will depend upon the pressure of the gas. It has been found that if the pressure of the gas is p. s. i., a sample of 1 milliliter will be obtained in two milliseconds. If the pressure is 500 p. s. i., the sample is approximately 4 milliliters and is obtained in about 1 millisecond. This decrease in sampling time with increase in pressure is extremely important, since the reactions occur more rapidly at the higher pressures, and therefore it is necessary to reduce the sampling time to obtain a more uniform sample.

As can be seen from the above, the valve of the present invention provides rapid sampling, rapid expansion of the gases after sampling to stop the reaction, and an accurate measure of the opening and closing times of the valve, all of which is accomplished by a very simple mechanism.

Also, it will be noted that the delay in opening of the valve which results from the necessity for accelerating the trigger mechanism is very slight, since there is no delay in providing vertical acceleration of the triggering mechanism. Instead the mechanism is kicked to one side almost instantaneously, and therefore does not interfere with the accelerating system.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

What is claimed is:

1. A rapid gas-sampling valve comprising a valve housing having a cylindrical centrally disposed passage with an opening, a first circular flange protruding into the opening at a first end of said housing, a second circular flange protruding into the opening at a predetermined distance from said first flange, said opening having an enlarged portion intermediate said flanges and narrow portions adjacent said flanges the outer surface of said housing having a groove therein, said groove connected to the centrally disposed passage at a point between a second end of said housing and said second flange, means, cooperat ing with the outer surface of said housing, for providing a large enclosed space adjoining said groove, said housing having a second passage for connecting said groove with a large evacuated area, a piston including a third flange positioned in the opening between said first and second flange, of such diameter as to obstruct said narrow portions of said opening but of insutficient diameter to obstruct said enlarged portion, said third flange being seated against said first flange when the piston is in the extended position and being seated against said second flange when in the retracted position, a valve stem for said piston, a bushing located in the passage for constraining said valve stem to travel along the axis of the opening, means for preventing leakage of air from the area between the second end of said housing and said bushing into the area between said bushing and the first end of said housing. means for holding said piston in the extended position, electromechanical means, including a solenoid, for releasing the holding means, and means for determining the beginning and ending of motion of said piston.

2. The invention according to claim 1 in which the means for holding said piston in the first position comprises a first arm pivoted about an axis perpendicular to. and displaced from, the axis of the central opening, said arm contacting the top of said valve stem when said arm is in the holding position.

3. A gas-sampling valve comprising a. valve housing having a passage therethrough with an opening including narrow portions and an enlarged portion, a piston located in said opening, holding means for holding said piston in a first of said narrow portions of said opening, said piston being such size as to close said passage when said piston is in said first narrow portion of said opening, electromechanical means for rapidly releasing said holding means, said piston being free to move along said opening when said holding means is released, said pas;

sage being partially opened when said piston has traveled to said enlarged portion of said opening, said piston serving to close said passage when said piston has traveled to a second of said narrow portions of said opening, a peripherial groove on the outer surface of said housing, a second passage connecting said groove to said passage at a point just beyond said narrow portion of said opening and enclosing means, cooperating with the outer surface of said housing means, for providing a relatively large expansion chamber connecting with said groove.

4. The invention according to claim 3, including means for determining the start and finish of movement of said piston.

5. A valve for taking samples of gases under pressure, comprising a valve housing having a centrally disposed passage with an opening, a piston located in said opening and arranged for movement in said opening, said piston completely obstructing said opening when said piston is in a first position, said piston completely obstructing said opening when said piston is in a second position, said opening being only partially obstructed when said piston is intermediate said first and second positions, means for holding said piston in said first position, electromechanical means for rapidly releasing said holding means to allow said piston to travel from said first to said second position under the pressure of the gases to be sampled, said valve housing having a groove in-the outer surface thereof, said groove connected to said centrally disposed passage at a point near the second position of said piston, and enclosing means cooperating with said housing for providing a large enclosed expansion chamber connecting with said groove.

6. In a system for rapidly sampling and transmitting to a container gaseous mixtures under pressure, a valve having an outlet end adapted to be connected to said container and the other end connected to the source of gases to be sampled, a valve housing having a passage with an opening connecting the two ends of said valve, means for evacuating said passage in said valve, a piston positioned in said opening, means responsive to a first movement of said piston to isolate said outlet end from said source of gases, means for holding said piston in a first position, electromechanical means for rapidly releasing said holding means, permitting said piston to move longitudinally along said opening in said passage under the influence of the gases from said source to a second intermediate position of said piston coupling said outlet end to said source of gases, means responsive to a third position of said piston for again isolating said outlet end from said source of gases, and means connected to said passage and in juxtaposition to the junction of said valve and said source of gases for allowing rapid expansion of the gas sample.

References Cited in the file of this patent UNITED STATES PATENTS 1,266,389 Betz May 14, 1918 1,916,513 Jones July 4, 1933 1,958,664 Harmon May 15, 1934 2,408,799 Melichar Oct. 8, 1946 2,432,168 Morgan et a1. Dec. 9, 1947 2,645,940 Kohl et a1. July 21, 1953 2,660,052 Uhl Nov. 24, 1953 OTHER REFERENCES Article entitled, Rapid gas sampler, in Technical News Bulletin, vol. 36, No. 12 (December 1952), published by the National Bureau of Standards, pp. 189-190.

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