Variable Area Ratio Jet Pump

Abstract

A jet pump having a large ratio of the area of the mixing tubular member to the primary nozzle or nozzles area, is arranged for constriction of the mixing tube upon the application of fluid pressure on the exterior surface, resulting in a gradually decreasing mixing tube throat with a resulting considerable decrease in the area ratio.

Description

BACKGROUND OF THE INVENTION

Jet pumps, as now used to fill and pressurize inflatable equipment, are essentially rigid pieces of hardware. Being essentially rigid, the area ratio is fixed by the mixing tube dimensions and the primary nozzle or nozzles area. Depending on the physical dimensions incorporated into any one jet pump a fixed area ratio is obtained and consequently the performance of the unit is established.

During inflation and subsequent pressurization of inflatable equipment a large weight and volume of gas is required to unfold the unit and to distend it to its design shape. A smaller weight and volume of gas is then required to pressurize the inflatable to its operating pressure. While the unit is being unfolded and or distended, work is being performed by the gas discharged by the jet pump. This work is performed by pressurizing the inflatable to a value slightly higher than ambient pressure conditions with the actual pressurization requirements varying with temperatures. At the lower end of the inflatables operating temperature range the materials of construction frequently stiffen and require a much greater pressure to unfold and distend the unit.

A jet pump, as described above, must therefore be a compromise design to unfold and distend an inflatable under varying temperature conditions as well as to pressurize the inflatable to its operating condition.

SUMMARY OF THE INVENTION

The present invention pertains to a variable area ratio jet pump arranged to have an infinite number of possible area ratios between maximum and minimum, and which will adjust itself to the maximum pumping rate for the particular set of operating conditions it is pumping to at that particular instant. The structure conceived for the novel pump to be described provides a gain in pumping over compound or multiple stage pumps as well as a gain over the simplest single stage jet pump.

The variable area ratio pump of the present invention is designed for the maximum area ratio desired and consequently the maximum pumping rate required to fill the inflatable during its distention to design configuration. Mathematically determined slots are formed by the removal of material around the longitudinal circumference of the mixing tube. The remaining material around the circumference of the mixing tube then has the proper spring rate to deflect inwardly as a load is applied to the outside surfaces. As the walls deflect inwardly the cross-sectional area of the mixing tube decreases and consequently the area ratio decreases and the pressure to which the pump can pressurize the inflatable increases.

Any of the known methods of applying a load to the outside circumference of the mixing tube may be used as an illustration. One method is to incase it with a piece of coated fabric or similar non-permeable flexible material. In operation, slight pressurization of the inflatable would cause this fabric to press against the outside circumference of the mixing tube thereby exerting a force inwardly on the mixing tube. The material remaining (after the slots were cut) would then deflect inwardly reducing the cross-sectional flow area of the pump. This process would continue as pressure increased until the minimum predetermined cross-sectional area of the pump had been reached at the end of the inflation cycle.

The variable orifice pump will provide a weight savings as an end result of each installation by reducing the weight of primary gas required with its associated tankage weight. In addition, a reduction in inflation time will be obtained over a similar dimensioned single or compound jet pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the invention in use;

FIG. 2 is a curve plot of jet pump action, plotting ratio of mass flows against static pressure on the exterior of the mixing tube of the pump;

FIG. 3 is an enlarged elevation cross-section view taken on the line 3--3 of FIG. 1;

FIG. 4 is a longitudinal view partly in cross-section and partly in elevation with portions broken away, taken generally on the line 4--4 of FIG. 1; and

FIG. 5 is a view in cross-section, similar to FIG. 4 but showing the pump configuration obtained near the end of a fluid pumping operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 there is shown a jet pump 10 disposed in an inflatable device 12, which may be an elastic fluid distensible raft or an inflatable slide for emergency evacuation of people from an aircraft, for example. The normal situation of the inflatable device 12 is that in which it is folded, packed and stowed aboard an aircraft, for example; but ready for rapid deployment and inflation upon the occurrence of an emergency situation requiring immediate use of the fully inflated and pressurized apparatus 12. Inflation of such devices for aircraft is usually required to be substantially completed within 5 to 10 seconds.

The pump 10 is comprised of a nozzle member 14, as best seen in FIGS. 3, 4 and 5, coupled to a source 16 of pressurized primary inflation elastic fluid, through a conduit 18 having a valve 20 therein. The source 16 may be a bottle containing air or other compressible fluid under a pressure of 3,000 psi, for example, and may be provided with a pressure regulator (not shown) to drop the pressure in the conduit 18 down to a working pressure of about 150 psi. It is obvious, of course, that the invention is not limited to a bottle source of fluid but may be employed with inert gas generators or any other preferred source adapted to provide pressurized gaseous primary fluid to the nozzle 14 of the pump 10.

Referring to FIG. 4 the pump 10 is illustrated as provided with an inlet section 22, shown in cross-section, and a mixing section 24 shown partially in cross-section and partially in elevation with parts cut away. The inlet 22 comprises a tubular member 26, preferably formed as a frustum provided with a screen 28 disposed at the extreme upstream larger end of member 26. Adjacent the screen 28 and on the interior of the large end of the member 26 is secured a ring 30 defining a flat face seat surface 32 facing downstream into the member 26. The ring 30 comprises a pair of flapper valve elements 34 which normally seat against the seat surface 32 to prevent reverse flow of fluid from downstream back through the screen 28. As shown in FIG. 4 the elements 34 are illustrated as fully open as would be the case when ambient secondary air is drawn through the screen 28 into the tubular member 26 as induced by pressurized primary air admitted to the nozzle member 14 which is disposed at the downstream smaller end of the member 26.

As seen in FIG. 3, the nozzle 14 is provided with a fitting 36 adapted to connection with the primary fluid source 16 for the supply of pressurized fluid to the nozzle jets 38 in the nozzle 14. As shown, the nozzle jet arrangement comprises twenty-nine jet directed passageways disposed at spaced intervals along the downstream face of the nozzle 14. It will be understood that any desired pump jet arrangement may be employed to provide primary pressurized fluid to induce the secondary fluid flow through the tubular member 26 from the ambient atmosphere. The arrangement shown is merely preferred for the intended application. In the preferred embodiment shown the ratio of the area of the main flow passageway of the pump 10 to the total areas of the jets 38 is preferably about 800:1.

The mixing section 24 downstream of the inlet section 22 comprises an outer tubular supporting member 40 having an inner tubular mixing member 42 disposed therewithin. Disposed between the members 40 and 42 for a portion of this length is a sleeve 44 comprised preferably of a flaccid impermeable material adapted to yield readily without resistance to fluid pressure on the outer surface thereof. The upstream and downstream ends 45 and 46 of the sleeve 44 may be bonded to the member 42 by cementing to form a seal against fluid leakage from the exterior to interior of the member 42 through apertures described below.

The inner member 42 is provided with a plurality of narrow, elongate, longitudinally extending, circumferentially spaced slot-shaped apertures 48 which are preferably shaped substantially as shown for a purpose described hereinbelow. The outer member 40 is provided with a plurality of apertures 50 which provide communication from the exterior of the member 40 to the outer surface of the sleeve 44.

In the fabrication of the tubular members 40 and 42 it is preferred to form them initially as flat metal sheets readily adapted to a stamping operation which stamps or punches out the metal portions in forming the respective apertures 50 and 48. After the stamping operation the flat sheets may be rolled in known fashion with abutting or slightly overlapping edges to form the tubular members, whereafter the faying edges may be secured as by seam or spot welding at spaced intervals.

It will be observed that the stamping of member 42 results in narrow elongate strips 49 remaining intermediate the long slotted apertures 48. In the preferred embodiment the member 42 is formed of a thin-section resilient metal whereby the strips 49 have a springy quality which tends to retain the generally cylindrical form of the member 42 in its normal static condition as shown in FIG. 4. In the active condition of the pump 10 the strips are adapted to yield resiliently under the urging of the sleeve 44 when a pressure differential appears thereacross, resulting in constriction of the fluid flow passageway forming the throat of the pump, as described below.

The downstream end of the inlet tubular member 26 is provided with an outstanding flange 52 by means of which the upstream end of the mixing section 24 may be secured to the inlet section 22 with a plurality of bolts 54 spaced around the flange 52 and threadably received in a ring 56 which bears against an outstanding flange 57 on the outer tubular member 40. Inner tubular member 42 has a flange 58 which is secured with a gasket 59 between the flanges 52 and 57, and the ring 56.

As noted above, the pump 10 extends into the inflatable 12. This is accomplished by providing the inflatable with an opening, the edge of the inflatable fabric adjacent the opening being secured between the ring 56 and an adjacent ring 60 by a plurality of bolts 62 disposed around the rings 56 and 60 intermediate the bolts 54. Thus in assembling the pump in the inflatable the rings 56 and 60 are assembled with the edge of the opening of the fabric of the inflatable therebetween and the bolts 62 are then secured. Thereafter the inlet and mixing sections 22 and 24 of the pump 10 are secured by the bolts 54.

In the storage condition the inflatable device 12 would normally be stowed with the pump 10 as mentioned above in a compact folded package constrained adjacent an aircraft exit door, for example. Upon the occurrence of a situation requiring inflation of the device 12, the constraint would be removed to deploy the device 12 outwardly from the door and simultaneously pressurizing primary fluid would be admitted through the nozzle jets into the cylindrical mixing tube 42 to pump secondary air into the inflatable. As the inflatable approaches full distention and pressure begins to build up in it, a pressure differential begins to be manifest across the tube 42 and sleeve 44. This pressure differential is resisted by the spring rate of the metal strips 49 of the tube 42. As the pressure differential increases the strips 49 gradually converge or retract inwardly toward the axis of the tube 42 under the pressure on the sleeve 44 until the tube assumes the configuration of the restricted throat substantially as shown in FIG. 5.

Thus the area ratio of the pump 10 gradually decreased from the maximum of 800:1, for example, down to a calculated minimum of 200:1, for example.

Jet pump action as aforesaid is illustrated in FIG. 2 where the curves 64 and 66 show the respective mass flow pumping action of a typical single stage jet pump with respective area ratios of 800:1 and 200:1. Thus in the case of curve 64 the mass flow ratio at the start of pumping is about nine and decreases to zero as the back pressure rises to about 0.8 psi, whereas in the case of curve 66 the initial mass flow ratio is only about 3.5 and drops off gradually to about 2.0 as the back pressure rises to about 2.0 psi. Intermediate curves between the curves 64 and 66 show that area ratios between 800:1 and 200:1 provide no solution to the stated problem.

In the case of a two stage pump the pumping action would follow the dashed discontinuous curve 68, but in the case of a pump according to the invention the pumping action would follow the dotted curve 70. It is readily seen that the relatively simple pump 10 according to the invention provides a decided gain over the action of even a complicated multiple stage jet pump.

Claims

I claim:

1. Apparatus for controlling a flow of fluid from a source into a fluid distensible chamber, comprising:

a. a substantially cylindrical conduit adapted for coupling between the source and the chamber,

a portion of the wall of said conduit being deflectable thereinto to vary the fluid flow therethrough, said deflectable conduit portion defined by relatively narrow and elongate alternating slot voids and slot strip material extending substantially parallel to the axis of said cylindrical conduit between the end portions thereof; and

b. means for applying a deflection force on said wall portion comprising a sleeve of impervious fluid distensible material overlying said deflectable conduit portion,

said means being adapted to being subjected to the fluid pressure in the chamber.

2. In combination:

a source of pressurized elastic fluid;

a fluid distensible chamber to be inflated with pressurized elastic fluid from said source; and

jet pump means operably disposed between said source and said chamber, said jet pump means including a substantially cylindrical rigid conduit extending into said chamber and a radially inwardly deflectable sleeve disposed in a portion of said conduit, said rigid conduit having openings therein in the portion of the conduit in which said deflectable sleeve is disposed to enable the fluid pressure in said chamber to be communicated to the exterior of said sleeve to radially inwardly deflect said sleeve, in response to chamber fluid pressure, into a variable area nozzle for the flow of pressurized fluid therethrough.