US3456871A

US3456871A - Method and apparatus for controlling a jet pump

Info

Publication number: US3456871A
Authority: US
Inventors: Rolf Gosling
Original assignee: Schutte and Koerting Co
Current assignee: Schutte and Koerting Co
Priority date: 1967-07-18
Filing date: 1967-07-18
Publication date: 1969-07-22
Anticipated expiration: 1986-07-22

Description

July 22, 1969 R. GsLlNG 3,456,871

METHOD ANI) APPARATUS FOR CONTROLLING A JET PUMP Filed July 18, 1967 2 Sheets-Sheet 1 :wc/WA Vf 0 fr v p FIG. la.:

Pff/h wm/Auf www? A FIG. 2.

l p/fa T ATTYS,

July 22, 1969 R. GsLlNG 3,456,871

METHOD AND APPARATUS FOR CONTROLLING A JT PUMP Filed July 1a, 1967 "2 sheets-sheet z n t L h m i# a@ .EQg Eg g t Q t q g s n i i rif I m mi i n l Q mi N Q *N Q 1 N N Q e u Ril i Q INVENTORI Ll. o ROLF GdsLaNG United States Patent O 3,456,871 METHOD AND APPARATUS FOR CONTROLLING A JET PUMP Rolf Gsling, Hannover, Germany, assignor to Schutte and Koerting Company, Cornwells Heights, Pa., a corporation of Pennsylvania Filed July 18, 1967, Ser. No. 654,190 Int. Cl. F04f 5/48; F02k 11/00 ABSTRACT F THE DISCLOSURE U.S. Cl. 230--111 4 Claims A control system for a jet pump, such as a stream jet vacuum pump wherein the thrust and suction streams initially flow at supersonic speed, in which the position of the shock zone or transition surface between the supersonic and s'ubsonic velocities -of the flow of thrust and suction streams 'in the diffuser is used to control the rate of flow of the thrust medium.

This invention relates to a method and apparatus to adjust or control a jet pump of the type having a compressible flow in the diffuser and a supercritical ratio of suction to discharge pressures.

In a jet pump of this type, the vmixture of the motive or thrust stream, which in most instances will be steam, and the suction stream flows initially at a supersonic velo-city. The change from supersonic to subsonic velocity of the thrust and suction stream Will `occur in a shock zone. This shock zone will 'be displaced in a direction toward the thrust nozzle when the reaction or back pressure increases or when the thrust pressure or thrust fiow decreases. Once this shock zone moves into the intake .Y

cone of the diffuser, the jet pump becomes unstable in operation and the pumping action can fail completely. In a similar manner when the reaction or back pressure decreases or thrust flow increases, the shock zone will be displaced into the exit cone of the diffuser. With the shock zone in the exit cone of the diffuser, the -rate of ow of the mixture of thrust and suction streams is accelerated increasing the pressure drop across the diffuser and decreasing the efficiency of the jet pump. The lowest ratio of flow of thrust fluid to flow of the suction field is attained when the jet pump is just about in stable operation which is when the shock zone is in the throat of the diffuser or just at the beginning of the diffuser outlet cone.

In daily actual operation of jet pumps of this type, variations in back pressureV as well as variations in the pressure of the thrust stream do occur. Prior to the present invention, to avoid such a jet pump from reaching an unstable operation the jet pump was operated with an excess amount of thrust stream flow to take care of the maximum back pressure which could occur and the minimum thrust stream pressure which could occur. VConsequently, it will be seen that prior to the present invention, jet pumps of this type operated most of the time with an excessive use of thrust fluid. l

With the foregoing in mind, a primary object of the present invention is to provide means for controlling or regulating a jet pump of this type to permit the shock zone to remain in the optimum performance position regardless of fluctuations of back pressure or thrust stream pressure. This is accomplished in the present invention by using a measurement of a condition of the stream of thrust and suction fluids within the throat of the diffuser as a means for regulating the -rate of flow of the thrust stream to maintain the shock zone in the throat of the diffuser. The condition of the stream of thrust and suction fluids in the diffuser used to control the rate of flow of the thrust stream fluid can be a measurement of the "ice static pressure gradient along the diffuser, the velocity gradient along the diffuser or a temperature gradient along the diffuser.

The various features and details of the present invention will be more fully described with reference to the accompanying drawings in which:

FIG. l is a schematic illustration of the thrust stream nozzle and diffuser of a jet pump with static pressure taps spaced along the diffuser in an area adjacent the throat of the diffuser;

FIG. la is a graph showing the static pressure along the diffuser axis with the shock zone at designated points in the diffuser;

FIG. 2 is a schematic illustration of the thrust stream nozzle and diffuser of a jet pump with a series of pitot tube pressure taps for measuring the velocity of flow at predetermined points along the diffuser;v

FIG. 2a is a chart showing the relationship of the pitot tube pressure along the diffuser axis with the shock zone at designated locations within the diffuser; and

FIG. 3 is a schematic diagram of a jet pump together with a control system for controlling the jet pump in accordance with the method lof the present invention.

The jet pump to which the present invention is applied comprises a conventional nozzle 10 including an adjustable spindle 11 to control theflow of the thrust medium and a diffuser 12 having an inlet cone 13, a throat portion 14 and an outlet cone .15. A reversible motor 16 is provided to move the spindle back and forth relative to the thrust nozzle 10 to c-ontrol the rate of flow of the thrust medium. Stream or other thrust medium will ibe supplied to the jet pump through an inlet pipe 17 leading to the nozzle 10. A conduit 18 leading into a chamber 19 surrounding the thrust nozzle 10 is connected to the source (not shown) of the suction stream. The exit of the outlet cone of the diffuser may be connected to the condensation and gas separating tank 20 in which the thrust fluid is separated from the suction fluid.

Referring specifically to FIGS. 1 and la, there is shown the static pressure along the diffuser when the shock wave or transition zone between supersonic and subsonic flow of the mixture of thrust and suction mediums is at points A through G, respectively. In addition, in FIG. 1 there are static pressure taps P1, P2, P3, and P4 as shown in the throat of the diffuser and the inlet end of the outlet cone.

It will be seen from FIG. la that the static pressure is substantially constant throughout the length of the throat of the diffuser to the shock wave at which point the static pressure increases abruptly. Also, as shown in FIG. la, the static pressure will decrease in the outlet cone of the diffuser from `the exit of the throat of the diffuser to the point where the shock wave exists at which time the static pressure will abruptly increase and thereafter increase substantially uniformly throughout the length of the outlet cone.

Thus, for example, if it is desired to maintain the shock wave at position C which is directly at the pressure static tap P2, the pressure at the pressure static tap will be as shown at P20 in FIG. la. If the back pressure irlcreases or the pressure of the thrust fluid decreases, Vthe shock wave will be moved to the left with respect to P2 and the pressure at P2 will abruptly increase. Similarly, if the back pressure would decrease or the thrust pressure increase, the shock wave will `be moved to the right with respect to P2 and the pressure at P2 will abruptly decrease. Accordingly, by maintaining the pressureat P2 constantjand maintaining this pressure as shown at P2C, the shock wave -Will be maintained at position C.

Similarly, the static pressure gradient at thev outlet of the throat and inlet end of the outlet cone of the diffuser may be used to control the position of the shock wave when it is desired to maintain the shock wave in an optimum position between two static pressure taps. It is evident, for example, if the shock waves were at position D, the pressure differential between P2 and P3 would be as shown at points P212 and P3D in the chart of FIG. la. Should the shock wave move forwardly in the outlet cone, for example, to E, the pressure differential between P2 and P3 would change to that as shown at P2E and P31.; in FIG. 1a. The following table shows the pressure gradient measured at three points-P1, P2, and P3 in FIG. 1 as the shock wave moves through positions A, B, D and G.

Shock zone position: Pressure gradient Should it be desired to maintain the shock wave at position D, it can be seen that the flow of thrust medium must be increased when P1 is greater than P2 but must be reduced when P2 is less than P3 until the condition in which P1 is greater than P2 which in turn less than P3 is obtained. If it is desired to use four measuring Points P1, P2, P3, land P1 the pressure gradients between these measuring points for shock wave positions at A, B, D, F, and G are as follows:

Again, a desired condition for regulating flow of thrust medium is when the shock wave is at point D utilizing these above points. When the shock wave is at position D, P1 is greater than P2 and P3 is less than P1. When P1 becomes less than P2 the ow of thrust medium must be increased and when P3 becomes greater than P1 the flow of thrust medium must be decreased.

FIG. 3 illustrates schematically a control system for carrying out the method of the present invention. `In the system of FIG. 3 there are three

static pressure taps

21, 22 and 23 which correspond to the pressure taps P1, P2 and P3 described above. Also in this system, it is desired to maintain the shock wave at position D which corresponds to the position D of FIG. 1.

In the control system of FIG. 3, the static pressure taps 21, 22 and 23 are connected to two similar pressureresponsive switches 24 and 25. The position of the switches 24 and 25 is controlled by spring biased

diaphragms

26 and 27, respectively. With equal pressure on both sides of the diaphragm, the switches 24 and 25 are in the position as shown in FIG. 3 with a circuit completed through the contacts 24a and 25a, respectively, of the switches. A conduit 28 connects the pressure tap 21 with one side of the diaphragm 26 of the switch 24 and a conduit 29 connects the pressure tap 23 with one side of the diaphragm 27 of the switch 25. A common conduit 30 connects the pressure tap 22 with the other sides of the

diaphragms

26 and 27.

In operation as the jet pump of the present invention is initially turned on, the spindle 11 will be in its fully retracted position permitting the maximum flow of motive stream through the nozzle 10. In any position of the shock wave within the inlet cone 13 or in the throat 14 of the diffuser upstream of the pressure tap 22, the pressure at the tap 21 will be less than the pressure .at the tap 22 which in turn will be less than the pressure at the tap 23. With this pressure relationship between the

taps

21, 22 and 23, the switch 24 will be in the position as shown in FIG. 3 with a circuit completed through the contact 24a and the switch 25 will be in a position with the circuit completed through the contact 25b. With the switches in this position, `a circuit is completed through the switch 24 to the contact R of the motor 16 causing the motor 16 to retract the spindle 11. As the shock wave moves past the pressure tap 22, for example, to the position shown in D in FIG. 3, the pressure at the tap 21 is greater than the pressure at the tap 22 which in turn is less than the pressure at tap 23. With this pressure relationship existing, the switch 24 will be in a position wherein the circuit is completed through contact 24b and the switch 25 will be in a position wherein the circuit is completed through contact 25b. With the switches in these positions, no circuit will be completed to the motor 16 and thus, the spindle will remain in the position it is in when the shock wave reaches position D. Should the shock wave move into the outlet cone 15 of the diffuser to a position downstream of the pressure tap 23, the pressure at the tap 21 will be greater than the pressure at tap 22 which in turn will be greater than the pressure at tap 23. With this pressure relationship existing, the switch 24 will be in a position in which circuit is completed through the Contact 24b and the switch 25 will be in a position wherein the circuit is completed through the contact 25a. With the switches 24 and 25 in this position, a circuit is completed through the switches 214 and 25 to the contact F of the motor 16 which causes the motor to drive the spindle 11 forward throttling the motive stream passing through the nozzle 10 'and decreasing the rate of flow of the motive stream. Decreasing the rate of flow of the motive stream will cause the shock wave to move in a direction upstream of the diffuser until the shock wave reaches the previously defined position D' between the pressure taps 22, and 23 at which time operation of the motor 16 will halt. Thus, it will be seen that this control system of FIG. 3 will cause the shock wave to assume a position at D and maintain the shock wave at this position. Should conditions within the system be such as to cause the shock wave to move away from this position, the control system will compensate for these conditions and move the shock wave back to the position D'.

Referring now to FIGS. 2 and 2a, there is shown the pitot tube pressure along the diffuser when the shock wave or transition zone between supersonic and subsonic ow of the mixture of thrust and suction mediums is at points A through G respectively. In addition, in FIG. 2 there are pitot tubes P11, P12, P13, and P11 as shown in the inlet end of the outlet cone of the diffuser.

It will be seen from FIG. 2a that the pitot tube pressure is substantially constant throughout the throat of the diffuser and is substantially constant downstream of the shock wave in the outlet cone. However, the pitot tube pressure drops uniformly from the inlet end of the outlet cone to the position of the shock wave. It is evident, for example, if the shock waves were at position B, the pressure at P11 would be greater than the pressure at P12 as shown at P1113 and P1213 in FIG. 2a and that the pressure at P13 and P11 rwill be the same as the pressure at P12. Also, if the shock wave were at position D, the pressure at P12 will be as shown in P1213 in FIG. 2a which will be less than the pressure at P11 but greater than the pressure at P13.

The following table shows the pressure gradient for three points of measurements Pn, P12, and P13 as the shock wave moves through positions A, B, D and G.

Shock wave zone: Pressure progress The shock wave position at B is the optimum position and it can be seen that P11 is greater than P12 and that when P12 is equal to P13, the shock wave s at the point B. If P11 becomes equal to P12 the volume of the motive stream must be increased. Similarly, if P12 becomes greater than P13, the volume of the motive stream must be decreased. Thus, this pressure differential may be used to provide a control signal to control the flow of the motive stream. If it is desired to use four measuring points Pn, P12, P13, and PPPM the pressure gradients between these measuring points for shock wave positions A, B, D. F and G are as follows:

With four measuring points, it will be possible to maintain the shock wave positions between B and D. For example, when Pu becomes equal to Piz the flow of motive stream must be increased and when P13 becomes greater than P14 the flow of motive stream must be reduced.

Only one example has been given of a control system utilizing pressure differentials or pressure gradient throughout the diffuser to control the position of the shock wave. However, it can be Seen that when using static pressure taps or pitot tube taps, there are pressure gradients in the diffuser which can be used to provide a control signal to control the ow of motive stream which in turn will control the position of the shock zone within the diffuser.

While particular embdiments of the present invention have been illustrated and described herein, it is not intended to limit the invention to such a disclosure and changes and modifications may be incororated and embodied therein within the scope of the following claims.

I claim:

1. In a control system for a jet pump in which the stream of motive fluid and suction Huid initially flows at a supersonic velocity and is converted at a shock wave within said jet pump to sonic velocity; said jet pump having a diffuser including a central throat portion, an inlet cone converging inwardly toward the central throat, an outlet cone diverging outwardly away from the central throat, an inlet to said inlet cone in fluid communication with said suction medium, an adjustable nozzle adjacent the inlet to said inlet cone for supplying said thrust medium, and adjusting means for said nozzle to control the ow of said thrust medium; -a plurality of pressure taps spaced longitudinally of said diffuser to measure pressure at preselected points spaced longitudinally of said diffuser, one of said pressure taps positioned to measure pressure in said throat at one of said preselected points closely adjacent said outlet cone, and at least two of said pressure taps positioned in longitudinally spaced relation in said outlet cone with the first of said two pressure taps spaced a preselected distance from said throat to measure pressure at a first preselected point in said outlet cone and the second of said two pressure taps spaced from said throat further than said preselected distance to measure pressure at a second preselected point in said outlet cone; and control means operatively connected to said adjusting means for said nozzle, said control means responsive to the pressure measured `by said plurality of pressure taps to adjust said nozzle to maintain the transition shock wave between supersonic and sonic velocity of said stream of motive and suction fluids between said one preselected point in said throat and said second preselected point in said outlet cone.

2. A control system in accordance with claim 1 in which said control means operates to open said nozzle to increase the ow of thrust tluid when said shock wave is between said nozzle and said first preselected point in said outlet cone and operates to close said nozzle when said shock wave is beyond said second preselected point in said outlet cone in a direction away from said rst shock wave between said first and second preselected points in said outlet cone.

3. A control system for a jet pump in accordance with claim 2 wherein said pressure taps are static pressure taps.

4. A control system for a jet pump in accordance with claim 2 wherein said pressure taps are pitot tube pressure taps.

References Cited UNITED STATES PATENTS 2,140,306 12/ 1938 Beals 230-100 X 2,968,147 1/1961 Truly et al.

2,996,878 8/1961 Leeper 137-15.2

3,029,601 4/1962 Arnberg et al.

3,030,768 4/1962 Yahnke IS7-15.2

3,065,599 11/ 1962 Dew.

3,086,357 4/1963 Rubin et al. 137--15.2

3,102,387 9/1963 Caspar et al.

3,149,474 9/1964 Goodman 230-111 X 3,172,622 3/1965 Kalika et al. 137-152 X FOREIGN PATENTS 1,057,828 10/ 1959 Germany.

1,157,851 5/1964 Germany.

DONLEY I. STOCKING, Primary Examiner WARREN I. KRAUSS, Assistant Examiner U.S. Cl. X.R. 137-152, 271

P04050 (fu/69) Patent No.

lnventor(s) Dated Jul) 22, 1969 Rolf Gosling It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column l, line 14,

Column 5, line (SEAL) Attest:

Edward M. Fletcher, Ir.

Altestng Office-f 1, line 45,