United States Patent Office
DIFFERENTIAL DENSITY MANOMETER Frederic Lissau, Forest Hills, N.Y., assignor to Liquidonics, Inc., Westbury, N.Y. Filed Mar. 27, 1970, Ser. No. 23,367 Int. CI. G01I 7/IS U.S. CI. 73—401 10 Claims
This invention concerns a differential density manometer capable of measuring extremely low pressures or pressure differentials.
Primary pressure measurements are made by converting gravimetric forces to pressure readings. Manometers usually measure pressure by displacement of a column of fluid in a vertical readout tube. The column height or head, depending on the density of fluid, is a direct measure of pressure sustaining the column. The conventional manometer is limited at the low end of the measurable pressure range by the minimum amount of fluid displacement which can practically be read on the readout tube.
The present invention provides a manometer adapted to measure very low pressures in the range of 0.00001 to 0.01 p.s.i. (pounds per square inch), in which range conventional manometers are generally inoperable. According to the invention, the present manometer employs an inverted vertical U-tube assembly having turned up end leg portions connected to identical cylindrical containers each containing a differently colored fluid. Pressure to be measured is applied at a pressure port in one container. The other container is open to atmospheric pressure. Any change in pressure applied at the pressure port is read on the U-shaped tube as a change in level of the meniscus where the two fluids meet in the tube. This change in level or pressure head depends on the difference between the densities of the two fluids. This difference ratio can be made quite small, so that the lowest readable differential pressure will be very small. Due to the gravimetric principle employed, primary, reliable, precise readings as low as 0.00001 p.s.i. are obtainable.
The construction and mode of operation of the differential density manometer will be explained in further detail in connection with the drawing, wherein:
FIG. 1 shows a differential density manometer in ver
tical elevational view, parts of the manometer are shown in vertical section.
FIG. 2 is a top plan view of the manometer of FIG. 1.
5 Referring to the drawing, the manometer 10 includes an inverted U-shaped transparent tube 12 having its bight at the top, and two spaced parallel vertical legs 14,16. One leg 14 is turned up to define a bottom bend 18 and vertical short lower leg portion 20. This end leg portion is se
10 cured to fitting 19 at the bottom 21 of an axially cylindrical container 22 of fluid 25. The container rests on horizontal platform 23 supported by legs 28 upon a base plate or platform 26. The upper end of the container has a cylindrical port 30 open to the atmosphere. An air filter
15 32 is fitted in port 30.
The other leg 16 of tube 12 is secured in a clamp 32 to crossbar 33 at the top of a rectangular frame 34. A manually operable valve 36 having a control knob or handle 38 is secured at the lower end of leg 16. A flexible
20 tube 40 is secured at one end to fitting 42 extending down from valve 36. Tube 40 is arranged in a U-shaped configuration like leg portion 20 and bottom bend 18. Tube 40 has a lower bend 44 and lateral vertical legs 46, 48. Leg 46 is attached to fitting 42. Leg 48 is secured to fit
25 ting 50 extending downwardly from a manually operable valve 52 having a control knob 53. Nipple 54 extends vertically downward from the bottom 56 of another cylindrical container 60. Tube 40 in effect constitutes a contiuation of leg 16. Tubes 12 and 40 are disposed in a
30 single vertical plane. This tube assembly has a uniform, fine narrow bore "a" which extends from end to end thereof.
Container 60 is axially vertical and is supported on a horizontal platform 62. The internal cross sectional areas
35 A of the two containers 22 and 60 are equal. At the top 66 of container 60 is a port 68 in which is a conduit 70. A gas under pressure to be measured is applied via conduit 70 to the top of fluid 75 in container 60. Platform 62 is adjustable in height with respect to platform 26 by means
40 of a sleeve 72 slidably disposed on a threaded post 74. The post is axially vertical and is secured in a boss 73. Nuts 76 and 78 below sleeve 72 and on top of platform 62 respectively lock the platform in place on the post. By this means the container 60 can be adjustably raised
45 and lowered. The two fluids 25 and 75 have different colors, fluid 25 being light colored and fluid 75 being dark colored, for example, or vice versa. The fluids have different densities so they are not mutually miscible, and meet at a meniscus M shown at level "0" on scale 85.
50 The scale 85 comprises graduated lines on a vertical plate 88. The plate is slidable vertically between vertical channel bars 90, 92 forming part of frame 34. The lower ends of the bars are secured to a base plate 93 mounted in a stationary position on platform 26.
55 Edge 94 of plate 88 is formed with rack teeth 95 engaged by a spur gear 96 supported on a shaft 98 and carried by lateral extension 99 of the frame. A nut 100 on shaft 98 locks the shaft and gear in a stationary nonrotatable position to hold the plate in a fixed position. A
60 knob 102 rotates the gear when nut 100 is loosened. By this arrangement the scale reading "0" can be set exactly at meniscus M in leg 16 of the tube.
The platform 26 can be leveled by means of leveling screws 104 provided with locknuts 106. Mutually perpen
65 dicular horizontal spirit levels 108 and 110 on the platform