US3137174A - Fluid metering device - Google Patents

Description

J1me 1964 LE ROY R. HAWK ETAL 3,

FLUID METERING DEVICE Filed Nov. 9, 1962 2/ COMP/P619360 INVENTORS LEROY R HAWK V/RG/L E. SCRIBNER ATTORNEY United States Patent 3,137,174 FLUID METERING DEVICE Le Roy R. Hawk, Hayward, and Virgil E. Scribner, Pleasanton, Califi, assignors to the United States of America as represented by the United States Atomic Energy Commission 7 Filed Nov. 9, 1962, Ser. No. 236,752 1 Claim. (Cl. 73-423) This invention relates to fluid metering devices and, in particular, to a device for periodically injecting predeitermined volumes of fluid into a process stream.

It is often necessary to accurately meter small vol umes of a fluid into a process stream. This situation arises in the monitoring of radioactive eflluent streams, in

gas chromatography, and in certain phases of the pharmaceutical industry, e.g., controlled dilution of concentrated stock solutions. a

flows through the other. A pneumatically-actuated hypodermic syringe reciprocates between the two chambers through the septum, thereby transferring measured volumes of .the injection fluid into the process stream.

The invention will be described with reference to the accompanying drawing, of which;

FIGURE 1 is across sectional view of the metering device at the start of the operating cycle,

FIGURE 2 is a partial view showing the hypodermic syringe in the filled condition, y

FIGURE 3 is a cross-sectional view showing the syringe discharging into the process stream,

FIGURE 4 is a schematic diagram of means to ope ate the metering device in a predetermined motion cycle.

Referring now to FIGURE 1, there is shown an injection block 11 which slides in a groove 12 formed in a base 13. Upper, middle, and lower cylindrical bores 14, 16,- and 17, respectively, are formed into block 11. Upper bore 14 and lower bore 17 are constricted at their midpoints to form respective constrictions 18 and 19. A hypodermic syringe 21, having a piston 22 and a needle 23, is disposed within middle bore 16 so that one end of piston 22 projects beyond block 11, and needle 23 projects beyond the opposite side of the block. Doubleheaded pistons 24 and 26 are disposed within bores 14 and 17 respectively, and the piston shafts project beyond block 11 through airtight shaft seals 25 fixed thereto. Pistons 24 and 26 are disposed so that their shafts pass through constrictions 18 and 19 respectively. The space between the heads of pistons 24 and 26 is filled with a high-viscosity oil 27. Piston 24 is actuated by compressed air admitted into bore 14 via ports 28 and 29. Similarly, injection block 11 is actuated by compressed air admitted into bore 17 via ports 31 and 32. The admission of air into ports 28, 29, 31 and 32 can be controlled by various cyclic control means, e.g., solenoid valves in conjunction with a rotating electrical switch. FIGURE 4 is a schematic diagram of apparatus for operating the metering device in a predetermined motion cycle. Compressed air is admitted to a manifold 51' which, in turn, communicates with solenoid valves 52, 53, 54, and 56. The outlets of the solenoid valves are respectively connected to ports 28, 29, 31, and 32. An electrical timing mechanism 57 is connected to the electrical inputs of the solenoid valves so as to actuate the valves in a predetermined cycle. The electrical timer may comprise a rotating electrical switch, or other equivalent devices. Alternately, the admission of air into the 3,137,174 7 Patented June 16, 1964 ice linked together atone end so as to move as a single unit. The stroke of piston 24 (hence, piston 22 as well) is adjusted by means of a limiting screw 33. The shaft of piston 26 is fixed relative to base 13 by means of a link 34 and a lock screw 362 As will be described later, the position of piston 26 relative to base 13 determines the stroke of block 11;

A fluid 37 to be injected is contained within a well 38 bored into a first flow block 39. A process stream 41 flows through a channel 42 formed in a second flow block 43. Well 38 and channel 42 are connected by a transverse channel 44, but the process stream and the injection fluid are prevented from mixing by a self-sealing septum 46 disposed between flow blocks 39 and 43. Transverse channel 44 is sealed off at one end by a self-sealing partition 47. i The two flow blocks are fixed to base 13, and the entire block assembly is held together and made liquidtight by a pressure plate 48 which is forced against the block assembly by peripherally-spaced bolts 49. The pressure plate has a central cutout portion so that needle 23 can pass therethrough.

For the purpose of illustrating the operation of the invention, FIGURE 1 shows the apparatus at the start of the injection cycle. The syringe is empty, and the tip of needle 23 is immersed in the injection fluid 37. To start the cycle, compressed air is admitted to port 28, and port 29 is opened to the atmosphere. The admitted air forces piston 24 to the right and, since piston 24 is linked to piston 22, also forces piston 22 to the right which causes the syringe to fill with injection fluid 37. The stroke of piston 24, and hence the injection volume, is determined by the position of limiting screw 33. Constriction 18 operates in conjunction with viscous oil 27 as a frictional damper to prevent piston 24 from moving too rapidly under the compressed air pressure. FIG- URE 2 shows the syringe in the filled condition with piston 24 in contact with screw 33.

In the next phase of the injection cycle, compressed air is admitted to port 31, and port 32 is opened to the atmosphere. The admitted air exerts force to the right on piston 26, and to the left on the closed end of bore 17. Since piston 26 is fixed relative to base 13 by link 34 and lock screw 36, the resultant force is directed to the left. Therefore, block 11 slides in groove 13 towards the left. constriction 19 operates in conjunction with viscous oil 27 as a frictional damper to prevent block 11 from moving too rapidly under the compressed air pressure. The movement of the block pushes needle 23 through septum 46, and the tip of the needle is immersed in process stream 41. Compressed air is admitted to port 29, port 28 is opened to the atmosphere and, as a result, piston 22 is pushed home, thereby discharging the loaded syringe intothe process stream. FIGURE 3 shows the apparatus at this stage inthe injection cycle. The cycle is completed by admitting compressed air to port 32 and opening port 31 to the atmosphere. The resultant force directed to the right causes block 11 to slide towards the right in groove 13. Needle 23 is pulled back through septum 46, and the relative positions of the components are restored to those shown in FIGURE 1.

The invention has been described in terms of injecting a fluid of constant composition into a process stream.

'However, the apparatus can be modified to inject a fluid Septa 46, and 47 must be fabricated of a self-sealing material, otherwise the continuous penetration by needle 23 would result in leakage between the injection fluid and the process stream.- Several synthetic elastomers have excellent self-sealing properties. In particular, ,Silastic rubber (a silicone rubber) has been tested as a septum material, and has exhibited no detectable leakage after several hundred cycles of operation.

7 Various modifications may be made in the invention without departing'from the principle thereof, and the scope of the invention is intended to be limited only by the following claim.

What is claimed is: g A fluid metering device comprising, i (a) agrooved base, v v (b) an injection block sli eably mounted on said grooved base, said injection block having first, second, 7 and third cylindrical bores formed therein, (0) a hypodermic syringe disposed within said second cylindrical bore, said syringe comprising a barrel, piston, and needle, I (d) first and second double-action pistons disposed respectively within said first and third cylindrical bores,

said first double-action piston being linked to said syringe piston, and said second double-action piston being adjustably locked to said base,

(e) valve and control means for operating said doubleacition pistons in a predetermined motion cycle,

( first and second fiow blocks fixed to said grooved base, said first'and second fiow blocks having first and second fluid chambers formed therein and a channel communicating between said first and second fluid chambers, said channel being oriented so that its longitudinal axis is collinear with the longitudinal axis of said syringe needle,

(g) a first self-sealing elastomeric septum terminating one end of said communicating channel,

(h) and a second self-sealing elastomeric septum disposed between said first and'second fluidchambers and intersectingrsaid communicating channel so as to prevent fluids in said first and second chambers from mixing.

References Cited in the file of this patent UNITED TA ES PATENTS 3,096,653 Martin et a. July 9, 1963

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