US2240119A - Adjustable venturi tube - Google Patents

Description

April 29, 1941.

J. M. MONTGOMERY EI'AL ADJUSTABLE VENTURI TUBE Filed Nov. 2, 1938 FIG. 2

JAME

INVENTORS MONTGOMERY lc PIC K ATTORNEY.

Patented Apr. 29, 1941 2,240,119 ADJUSTABLE VENTURI TUBE Columbus, 01110, and Eric James M. Montgomery,

Pick, East Rocka way, N. Y..

assignors to The Permutit Company, New York, N. Y., a corporation of Delaware Application November 2, 1938, Serial No. 238,402

6 Claims.

This invention relates to adjustable Venturi tubes and it comprises a Venturi tube having a throat, and a needle member axially movable within the tube so as to variously constrict the throat, the needle being so shaped that the rate of flow of fluid through the tube producing a given pressure diiferential bears a substantially straight line relationship to the axial movement of the needle.

In controlling or metering the flow of a fluid, or in proportioning one stream of fluid to another, the use of Venturi tubes, circular orifices or similar devices is well known. All these devices produce a pressure difl'erential or pressure loss which is used as the motive power for the work of controlling, metering or proportioning. The pressure diflerential changes substantially in proportion to the square of the rate of flow of the fluid. Consequently, a relatively small increase or decrease in the rate of flow produces a relatively large increase or decrease, respectively, of the pressure diflerential. A high pressure loss is, of course, objectionable in most cases because it constitutes a waste of pumping power or, with a given available pressure, reduces the rate of flow. A small pressure differential, on the other hand, does not permit high accuracy of metering, controlling or proportioning. Practical considerations thus place both upper and lower limitations on the pressure diflerential or loss and it follows that the rate of flow through a fixed Venturi tube or oriflce must be held within a narrow range. changes appreciably, be it permanently or temporarily, the Venturi tube or orifice must be replaced by a larger or smaller one, as the case may be. This is obviously both annoying and cumbersome.

One object of our invention is to provide a Venturi tube in which the rate of flow for a. given pressure difierential is readily wide range; another object is to provide manual adjusting means of such character that movement of the adjusting means produces a substantially proportional change of the rate of flow; and a third object is to provide a Venturi tube which produces a high pressure diflerential with relatively small pressure loss.

We attain these objects by the device illustrated in the accompanying drawing, in which- Figure 1 is a longitudinal section through a Venturi tube according to our invention with the Of Fig. 1;

- needle in an intermediate position;

Figure 2 is a section along lines 2-2 and adjustable over a Consequently, when the flow Figure 3 is a section along lines 3-3 of Fig. 1.

Similar numerals refer to similar parts throughout the several views.

Referring now to the drawing, the Venturi tube I0 is provided with flanges II for connecting it to a fluid carrying pipe (not shown). The tube has a cylindrical inlet l2, a converging inlet section l3, a cylindrical throat l4, a diverging outlet section I5, and a cylindrical outlet l6. Within the tube is a needle I! with a specially shaped tip IS, a cylindrical portion l9 having a diameter slightly smaller than the throat I4, and four flns 20 which slide in outlet l6 and thus guide the needle I! co-axially with the tube I0. One of the fins 20 is provided with gear teeth 2| meshing with a gear 22 keyed to shaft 23. The shaft 23 is rotatable in bearings 24 and 25 which, as shown in Fig. 3, guide the teeth 2| on either side thus keeping them in mesh with the gear 22 and preventing the needle II from, turning. The shaft 23 extends through stuiflng box 26 and carries a handle 21 which is provided with a pointer 28 indicating the position of the needle I! on a dial 29. A clamp 30 with thumb screw 3| serves to grip shaft 23, thus preventing any unwanted movement of the needle.

A pressure connection 32 communicates through openings 33 with the cylindrical inlet l2 and a second pressure connection 34 communicates through openings 35 with the throat H of the tube It, the center lines of openings 35 being located on line 2-2 on which the cylindrical throat l4 and the diverging outlet section l5 meet. The pressure connections 32 and 34 serve for connection of the Venturi tube to a meter, a

rate of flow controlling diaphragm valve, a proportioning device, or the like.

After loosening thumb screw 3| the handle 21 may be turned, thus shifting the needle. In the extreme left position of the needle the cylindrical portion I9 slides into the throat I4 and the free area for the passage of fluid is a narrow annulus. In the extreme right position of the needle the point of tip I8 is withdrawn from the throat I 4 so that the full area of the throat is opened for passage of fluid. Any desired degree of opening between these two extremes may be obtained by suitable adjustment of the needle.

It is to be noted that in any possible location of the needle the free cross-sectional area open for the passage of fluid decreases gradually from the inlet until it reaches a minimum in the throat at the section indicated by line 2-2 in Fig. 1 whereupon the free area again increases gradually toward the outlet. With this arrangemeat the maximum pressure differential created within the Venhn'i tube is always communicated to the pressure connections 32 and ll, yet a substantial portion of this pressure diiierential is recovered in the divergin outlet section II, making for the desired small overall pressure loss.

The shape of tip I! is such that the rate of flow with a given pressure difference between connections 32 and M bears a substantially straight line relationship to the movement of the needle. The change in discharge coemcient with changes of the needle position must be considered in determining the shape or contour of the tip. By way of example, the following table containsthe necessary dimensions for fabricating a suitable needle tip for a three inch diameter Venturi tube with a throat diameter of 2.050

The last diameter given in the foregoing table is also the diameter of the cylindrical portion ii.

For a Venturi' tube with a throat diameter other than 2.050 inches the diameters given above may be multiplied by a factor:

actual throat diameter The axial distances given above may be multiplied by a constant greater or somewhat smaller than unity, depending on the desired extent of axial movement. A needle tip thus dimensioned will give a relationship between axial movement and rate of flow at a given pressure differential very closely approximating a straight line function.

The tube as well as the needle are made of materials able to withstand any corrosive action of the fluid passing through the tube. In the case of water, brass or bronze may be employed.

Venturi tubes according to our invention permit adjustment over a wide range so that any desired pressure diflerential is obtainable with any given rate of flow. Yet, due to the pressure recovery in the diverging section of the tube the overall pressure loss is relatively small. The dial in conjunction with the straight line relationship between needle movement and rate of flow makes it possible to re-adjust the needle position quickly and without guesswork to take care of changed flow conditions.

What we claim is:

1. An adjustable Venturl tube having a converging inlet section, a throat, a diverging outlet section, an axially movable needle within the tube, means for moving the needle, and a tip on the needle adapted to be moved into and out of the throat, the tip of the needle being of torpedo shape and such as to provide a substantially straight line relationship between the extent of needle movement and the rate of flow through the tube with a constant difference between the pressure in the throat and the pressure in the tube ahead of the throat.

2. An adlustableventuri tube having in the order named a converging inlet section, a cylindrical'throat, and a diverging outlet section, an "axially movable needle within the tube, means for moving the needle, a tip on the needle adapted to be moved into and out of the throat in a direction from and to the diverging outlet section, and a pressure connection -communi-- eating with the inside of the tube at a point where the cylindrical throat and the diverging outlet section meet.

3.'An adjustable Venturi tube having in the order nameda converging inlet section, a throat, a diverging outlet section and a cylindrical section. an axially movable needle within the tube, a tip on the needle adapted to be moved into and out of the throat, the shape of said tip being such as to provide a substantially straight line relationship between the extent of needle movement and the rate of flow through the tube with a constant difference between the pressure in the throat and the pressure in the tube ahead of the throat, a plurality of fins on the needle adapted to slide in the cylindrical section, gear teeth formed on one of said fins, a gear meshing with said gear teeth, means for turning said gear, and a pressure connection communicating with the inside of the tube at a point where the throat meets the diverging section.

4. An adjustable Venturi tube having in the order named a converging inlet section, a throat, a diverging outlet section and a cylindrical section, an axially movable needle within the tube, a tip on the needle adapted to be moved into and out of the throat, a plurality of fins on the needle adapted to slide in the cylindrical section, gear teeth formed on one of said fins, a gear meshing with said gear teeth, a shaft for said gear, a pair of bearings for the shaft, the bearings forming lateral guides for the gear teeth, and means on the outside of the tube for turning the shaft.

5. An adjustable Venturi tube having a converging inlet section, a throat. a diverging outlet section, an axially movable needle within the tube, a tip on the needle adapted to be moved into and out of the throat, and means for axially moving the needle, the tip having substantially the following diameters at equal distances apart from each other, said diameters being in inches and all being multipliable by a factor: 0.511;

1.731; 1.821; 1.895; and 1.964.

6. An adjustable Venturi tube having a converging inlet section, a throat, a diverging outlet section, an axially movable needle within the tube, a tip on the needle adapted to be moved into and out of the throat, and means for axial- 1y moving the needle, the tip having a plurality of diflerent diameters at equal distances apart from each other, said diameters being substantially equal to a substantial portion of the followin diameters given in inches and all being multipliable by a factor: 0.511; 0.733; 0.933; 1.110; 1.268; 1.410; 1.533; 1.638; 1.731; 1.821; 1.895; and 1.964.

JAMES M. MONTGOMERY. ERIC PICK.

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