US2856574A - Low water protector - Google Patents

Description

Oct. 14, 1958 Filed Sept. 7, 1955 WATTS A'Tzps 600 lov 50o E. J. SCHAEFER LOW WATER PROTECTOR 3 Sheets-Sheet 1 oct. 14, 195s E J' SCHAEFER 2,856,574

LOW WATER PROTECTOR Filed Sept. 7, 1955 3 Sheets-Sheet 2 INVENTOR.

Octf 14, 1958 E. J. scHAr-:FER 2,856,574

Low WATER PROTECTOR Filed Sept. 7, 1955 3 Sheets-Sheet .5

gwraf Y 19M M WIT LOW WATER PROTECTOR Edward J. Schaefer, Fort Wayne, 1rind. Application September 7, 1955, Serial No. 532,901

11 Claims. (Cl. S18- 455) This invention relates to a novel and improved electrical means for controlling the operation of a pump to prevent the pump from running when the normal supply of working uid in the liquid state is exhausted.

With the rapidly expanding use of submersible deep well pumps it is becoming increasingly apparent that low water conditions in wells occur more frequently than has been realized, the situation being particularly critical in certain regions of the contry. Low. water levels in wells have been found to account for a number of pump failures and consequently it has become particularly important in the case of submersible motor and pump units to provide effective protection against these conditions in order to prolong the life of both the motors and the pumps.

The schemes which have heretofore been proposed for protecting against low water conditions have been based for the most part on water flow or actual Water level in the well and have, therefore, been cumbersome, unreliable, and diihcult to apply. My invention, as hereinafter described, provides a simple and inexpensive scheme for obtaining the desired protection by means of a unique electrical circuit arrangement which does not depend directly on measurement of water ow or actual water level. Moreover, the present control scheme is eective in spite of normal voltage fluctuations of the supply line.

Accordingly, a primary object of my invention is to provide novel and improved control means for preventing a pump from operating without a normal supply of working fluid in the liquid state.

A further object of the invention is to provide novel and improved control means for protecting a submersible motor and pump unit against low water conditions in a well. i

Another object of the invention is to provide novel and improved electrical control means for obtaining low water protection in a submersible motor and pump unit without direct reliance on a measurement of actual water flow or water level.

An additional object of the invention is to provide novel and improved electrical control means for protecting a submersible motor and pump unit against low water conditions which is completely effective in spite of substantial uctuations in the voltage of the supply line.

Still another object of the invention is to provide an improved low water protection scheme for pumps including a novel combined low water cut out and cycle time delay switch.

A still further object of the invention is to provide a novel protective scheme for a motor-pump unit which protects against operation Without adequate working fluid but also permits normal stopping and immediate starting of the unit under manual control.

Other objects and advantages of the invention will become apparent from the subsequent detailed description taken in conjunction with the accompanying drawing, wherein:

Fig. l is a plot of certain experimental data to illustrate the underlying principle of the invention;

Figs. 2, 3, and 4 are schematic circuit diagrams showing a preferred embodiment of the invention in successive stages of operation; and

Figs. 5, 6, and 7 are additional circuit diagrams illustrating another embodiment of the invention in its successive operating stages.

My invention is based on the measurement of a change in power or Wattage atv the motor as an indication of whether or not the pump is actually pumping water or other working liquid. In a motor and pump combination for water wells or the like, it will be understood that if the normal supply of water is exhausted so that the pump loses suction, the load on the motor will drop far below normal with a corresponding change in the electrical operating characteristics of the motor such as the current flow to the motor and the voltage and wattage at the motor. By interposing in the motor supply line a circuit opening means including a watt sensitive relay which is responsive to a change in Wattage at the motor during underload operation, I am ableto obtain the desired low water protection in a simple inexpensive and completely reliable manner. The relay circuit may include a manual reset lockout arrangement when required or it may comprise a cycle time delay means in order to obtain relatively slow cycling and thereby avoid rapid off and on operation during low water periods.

Although in theory a control scheme of the foregoing general character can utilize any type of relay means responsive to an electrical operating characteristic of the motor, e. g. a current sensitive relay, I have found that as a practical matter the use of a watt sensitive relay means is necessary in order to obtain consistently reliable operation of the control circuit. The reason for this will become apparent by reference to Fig. `1 of the drawings in which are plotted the test results of a single phase l/z horsepower submersible motorpump unit when operating at various loads and at the indicated applied voltages. As is well known, the voltage of the usual supply line is subject to considerable lluctuation. For example, an ordinary 115 volt supply line may actually vary in voltage over a range of from volts to 126.5 volts. Such a variation of 25 or more volts is quite common, and frequently the extent of uctuation is even greater.

Referring to the lowermost group of curves in Fig. 1 wherein load is plotted against amperes, it will be seen that when the supply line is at 100 volts and the pump is imposing the lowest operating load, the current drawn by the motor is approximately 6.2 amperes as indicated by point a on the curve. However, at the opposite extreme set of operating conditions when the supply voltage is 126.5 volts and the pump loses suction as a result of a low water conditions, it will be seen that the current drawn by the motor is 6.6 amperes as shown at point a on the curve. Obviously, therefore, a low water cut-out control based on the principle of current reduction at the break suction point of the pump could be rendered totally inoperative by reason of a normal voltage fluctuation in the supply line. This is apparent because the current sensitive relay would necessarily have to be calibrated to hold in at the lowest operating load and lowest voltage condition of point a, but at the break suction point and the highest supply voltage situation of point a the current drawn by the motor under these conditions actually increases so that the relay would fail to drop out and disrupt the motor circuit. Moreover, even under the ideal conditions of a constant volt supply, it will be seen that the current drops only from about 6.4 amperes to about 5.4 amperes by point b. However, at the break suction point and' highest voltage condition, the watts are approximately 295 as represented by the point b on the curve. This is an excellent differential since it represents a drop of almost 40% in the power supplied to the motor even under the most unfavorable voltage fluctuation conditions. Moreover, with suchl a substantial operating differential, it is possible to utilize a very practical and inexpensive watt sensitive relay whilestill obtaining completely reliable operation of the control system.

Referring next to Figs. 2 to 4, the invention will be described further in connection with a circuit arrangement comprising a combined low water cut out and cycle time delay switch. In Fig. 2, the device is shown in completely inoperative condition when the pump is shut down. Fig. 3 illustrates the normal running condition of the control means. The condition existing just after the control means has operated to disrupt the motor circuit upon encountering a low water condition is illustrated in Fig. 4. A centrifugal pump 6 has an operating connection with an electric motor 7, and the motor 7 is connected to a source of electrical energy through a line comprising in this instance a pair of conductors 8 and 9. A main control switch such as a pressure switch 11 cooperates with a pair of contacts 12 interposed in the conductor 8 for placing the unit in operation or shutting it down.

The conductor 8 is connected to the series coil 13 of a watt sensitive relay which is in turn connected to a movable contact arm 14 having a fixed pivot 16 at one end and carrying a contact 17 at its other end. A spring 18 normally urges the arm 14 to its lowermost position shown in Figs. 2 and 4. The connection to the motor 7 is completed through a cooperating movable contact arm 19 which has a fixed pivot end 21 and carries a contact 22 at its opposite end. T he arm 19 is also provided with suitable means, such as a spring or the like, for normally urging it into engagement with the arm 14 at the contacts 17-22. ln the present instance, the arm 19 may be made of resilient spring metal so that its inherent resiliency tends to hold it in contact with the arm 14. A conductor 23 connects the arm 19 with the motor 7. The conductor 9 at the opposite side of the supply line is connected directl; to the motor 7, and the potential coil, designated at 24, of the watt sensitive relay is connected across the line by means of a conductor 26 extending between the conductors 8 and 9.

When the unit is shut down and the watt sensitive relay is not excited, as shown in Fig. 2, the contact arms -14 and 19 are in their lowermost positions with the contact elements 17 and 22 in engagement so that the system is ready for operation.

When the relay is energized by closing of the pressure switch 11 across the contacts 12, as shown in Fig. 3, the arm 14 is pivoted upwardly by the action of the relay and thereby mechanically pivoting the resilient arm 19 upwardly in unison therewith and the contacts 17 and 22 remaining in engagement so that the motor 7 is placed in running condition. As the arm 19 moves upwardly to its Fig. 3 position, it compresses a bellows 27 from the expanded condition thereof shown in Fig. 2 to the collapsed condition shown in Fig. 3. Air within the bellows 27 is discharged rapidly from the bellows 27 through a fast action check valve indicated schematically at 28. In other Words, there is no appreciable resistance to upward movement of the arm 19 and collapsing of the bellows condition drops to a value insufficient to maintain the` 27. As long as the watt sensitive relay 13-24 is energized at a predetermined wattage level, dependent upon the calibration of the relay, the contacts 17 and 22 are retained in engagement as shown in Fig. 3 so that the motor continues to run in the normal manner.

During normal operation when the pump 6 has an adequate supply of working liquid, the wattage at the motor 7 will be sufcient to maintain the watt sensitive relay in its energized Fig. 3 condition. However, the watt sensitive relay is calibrated to drop out when the wattage at the motor 7 falls below a predetermined Value. As pointed out in the previous discussion, this drop out value is one which will never be reached when the pump is pumping liquid, but as soon as the water level in the well falls to the point where the load on the motor undergoes a sharp decrease due to the fact that the pump loses suction, the watt sensitive relay will no longer be suiciently energized to overcome the force of the spring 18 with the result that thevcontact arm 14 is immediately retracted toits lowermost position as shown in Fig. 4 thereby-disrupting the motor circuit and stopping the pump. Although the resilient character of the spring arm 19 tends to cause the arm 19 to follow its companion arm 14 downwardly, therconnection of the arm 19 with the bellows 27 results in a time delayed return. Expansion lows so as to obtain the desired extent of time delay in the downward movement of the contact arm 19, the check valve 28, of course, being closed at this time.

When the arm 19 tinally reaches its lowermost position after a suitable time interval dependent upon the,

settingvof the regulating valve 29, the contact 22 reengages the contact 17 in the manner shown in Fig. 2 so,

as to reestablish the motor circuit. If by this time the supply of liquid in the well is back to normal the motor 7 will then operate atV normal load and the watts at the. motor will then be suiiicient to energize the watt sensitiverelay 13-24 and thereby return the control system to the normal running condition illustrated in Fig. 3. On the other hand, if the water level in the well is still too low, the underload condition will still prevail so that the wattage at the motor 7 will be inadequate to maintain the relay in energized condition. However, the starting input to the motor 7 when the circuit is first reestablished greatly overexcites the relay for an instant which isrsufcient to restore the arm 19 and the bellows 27 to their Fig. 3 condition. As heretofore pointed out, the bellows 27 is designed for practically instantaneous collapsing movement by reason ofthe check valve 28. As the motor 7 comes up to speed, the wattage input at the low water relay in energized condition and the arm 14 is thereupon returned to its Fig. 4 condition so that the motor circuit is again disrupted. Of course, the collapsedvbellows 27 again functions to delay reclosing of the contact 22 against the contact 17, and this sequence of operations is repeated on a time delayed automatic cycling basis until such time as the low water condition of the well corrects itself. Obviously, in the case of a prolonged lowl water condition in a well the cycle time delay action is necessary in order to prevent frequent starting and stopping of the motor.

In Figs. 5-7 another embodiment of the invention is illustrated which utilizes a manual reset lockout arrangement in place of the cycle time delay bellows device described above. With the previously described arrangement, there is no way of restarting the pump without the time delay. Obviously, there may be applications in which it is desirable to be able to start the pump immediately after it has been shut olf for any reason. For example, a submerged gasoline motor-pump unit requires protection against low liquid level conditions but at the same time must be capable of frequent manual stopping and immediate restarting without any appreciable time delay.

In Fig. 5 the circuit is shown with the unit completely shut down. Similar parts have lbeen given the same reference numerals as in Figs. 2-4. Thus, the manual control switch 11 in the line conductor 8 is shown in open position so that the motor 7 and the watt-sensitive relay 13-24 are deenergized. The arms 14 and 19 are biased to their lowermost positions by means of the springs 18 and 31, respectively, and the contacts 17 and 22 are engaged so that the system is readyfor operation.

In Fig. 6 the normal running condition is shown wherein the control switch 11 is closed thereby energizing the motor 7 and the relay coils 13 and 24. As before, the arms 14 and 19 are thereby raised to their uppermost positions by the action of the relay While the contacts 17 and 22 remain in engagement. In place of the bellows device heretofore described, a small electromagnetic holding device is provided for retaining the arm 19 in its uppermost position. The electromagnet has a horseshoe core 32 and a high impedance coil 33 connected across the line by leads 34 and 36 extending to the conductor 26 at opposite sides of the relay coil 24. Interposed in the lead 36 is a spring pressed normally closed reset switch 37.

If during running the power drawn by the motor decreases below a predetermined value as determined by the relay calibration, the watt-sensitive relay then drops out so that the arm 14 is returned to its lowermost position by the action of the spring 18, as seen in Fig. 7. However, since the main control switch 11'is still closed, the magnet coil 33 remains excited and the arm 19Y is held in its uppermost positionso that the motor circuit is disrupted by disengagement of the contacts 17 and 22 and the pump is shut down. To restore the unit to running condition, the manual reset switch 37 is depressed thereby momentarily deenergizing the coil 33 so as to release the arm 19 and permit it to return tothe Fig. 5 position under ythe influence of the spring 31. Of course, the same resultcan be obtainedfby momentarily opening and then reclosing the main switch 11. When contact between the elements 17 and 22 is thus restored, the motor will then be started and will continue to run if the low liquid level or other decreased load condition has been corrected. If the low level condition still prevails, the relay will again drop out to its Fig. 7 position.

On the other hand, if during normal running of the unit as in Fig. 6 it is desired to shut o the unit temporarily, the main switch 11 may be opened whereupon the motor 7, the relay, and the magnet coil 33 are all deenergized so that the device is restored to its Fig. 5 position but contact between the elements 17 and 22 is maintained. Thus, although the holding circuit is disrupted, the main contacts 17 and 22 are never opened during a manual shut-down and the unit can be restarted immediately. without any time delay merely by reclosing the switch 11.

Although the invention has been described with particular reference to certain specific embodiments thereof, it will be understood that various modifications and equivalent arrangements may be resorted to without departing from the scope of the invention as derined in the appended claims.

I claim:

l. In a pumping system of the type wherein the pump load decreases when the supply of working iluid for the pump is exhausted, the combination of a pump, an electric motor having a driving connection with the pump and requiring a reduced wattage input when the load of the pump decreases, a motor circuit, and a relay including a series coil and a potential coil connected in the motor circuit to be responsive to reduction in wattage at th.n mdc during opertirn of the "fh an i"- adequ Le Iy of working fluid for ogen ng sad ci cuit, whereby to stopthe motor when thesupply of. working fluid for the` pump is exhausted.`

2. In a pumping system of the type wherein the pump load decreases when the supply of. working iluidfor the pump is exhausted, the combinationof an. electric motor, a pumpv having a driving connection with the motor, a line for connecting said motor across asource, circuit-opening means interposed in the line for interrupting the motor circuit, andtime delay means operatively associated with said circuit-opening means for providing time-delayed cyclic operation thereof, said circuitopening means including a watt-sensitive relay responsive to a reduction in wattage at the motor during underload operation for stopping the motor when the liquid supply of working uid for thepump is exhausted.

3. In a pumping system of the type wherein the pump load decreases when the supply of working uid for the pump is exhausted, the combination of 'an electric motor, a pump having a driving connection with the motor, a line for connecting said motor across a source, watt-sensitive relay means interposed inthe line and movable between running and stop positions for interrupting the motor circuit in response to a reduction in wattage atl the motor during underload operation whereby'to stop the motor when the liquidsupply of working uid for the pump is exhausted, and time delay means including anA expansible bellows operatively associated with said relay means for retarding movement thereof from stop position to running position whereby toprovide timedelayed cyclic operation of said relay means.

4. In a pumping system of the type wherein the pump load decreases when the supply of working uid'for the pump is exhausted, the combination of fan electric motor, a pump having a driving connection with the motor, a line for connecting said motor across a source, wattsensitive relay means interposedin the line and comprising a pair of movable contact arms` engageable for completing the motor circuit during normalload operation and adapted to be disengaged in response touareduction in wattage l at thel motor duringunderload; operation whereby to interrupt the motor circuit and stop the motor when the liquid supply of working fluid for the pump is exhausted, and time delay means operatively associated with one of said arms for retarding movement thereof from disengaged to engaged position with respect to the other arm whereby to provide time-delayed cyclic operation of said relay means.

5. In a pumping system of the type wherein the pump load decreases when the .supply of working uid for the pump is exhausted, the combination of an electric motor, a pump having a driving connection with the motor, a line for connecting the motor across a source, a pair of contacts interposed in the line, and watt-sensitive relay means connected to the line and the motor and including a movable element carrying one of said contacts, said relay means being energized under normal load operation of the pump for holding said contacts in engagement and said relay means also being responsive to a reduction in wattage at the motor during underload operation for interrupting said line by separation of said contacts thereby stopping the motor when the liquid supply of working Huid for the pump is exhausted.

6. In a pumping system of the type wherein the pump load decreases when the supply of working luid for the pump is exhausted, the combination of an electric motor, a pump having a driving connection with the motor, a line for connecting the motor across a source, wattsensitive relay means connected in circuit with the line and the motor and including movable contact means adapted to be moved in one direction upon energization of the relay means, biasing means normally urging the movable contact means in the opposite direction, and cooperating contact means engageable by said movable c^nact means during energization of said relay means, said relay means being responsive to a reduction in wattage at the motor during underload operation for releasing said movable contact means whereby the latter is disengaged from said cooperating contact means by the action of said biasing means thereby disrupting the motor circuit and stopping the motor when the liquid supply of working uid for the pump is exhausted.

7. In a pumping system of the type wherein the pump load decreases when the supply of working iluid for the pump is exhausted, the combination of an electric motor, a pump having a driving connection with the motor, a line for connecting the motor across a source, a pair of elongated movable contact arms interposed in the line, and watt-sensitive relay means connected to the line and arranged to move one of said arms in one direction when the relay means is energized, the other of said arms being normally retained in engagement with said one arm for completing the circuit and being movable in said one direction simultaneously with said one arm, spring means urging said one arm in the opposite direction when the relay means is deenergized, said relay means being deenergized in response to a predetermined reduction in wattage at the motor during underl-oad operation whereby to release said one arm for disengagement thereof from the other arm under the action of said spring means thereby disrupting the motor circuit and stopping the motor when the liquid supply of working Huid for the pump is exhausted, and means coacting with said other arm for retarding movement thereof in said opposite direction after said disengagement whereby to provide a time delay in reengagement ot said arms and reestablishment of the motor circuit.

8. The combination of claim 7 further characterized in that said last-named means comprises a bellows having a connection with said other arm, a one-way valve for rapidly discharging air from the bellows in response to movement of said other arm in said one direction,` and an adjustable valve for controllably admitting air to the bellows during movement of said other arm in the opposite direction.

9. In a pumping system of the type wherein the pump load decreases when the supply of working fluid for the pump is exhausted, the combination of an electric motor, a pump having a driving connection with the motor, a line for connecting the motor across a source, wattsensitive relay means connected in circuit with the line and the motor and responsive to a reduction' in wattage at the motor during underload operation for interrupting the motor circuit when the liquid supply of working fluid for the pump is exhausted, and releasable holding means for holding the motor circuit in interrupted condition until it is desired to restart the motor.

10. In a pumping system of the type wherein the pump load decreases when the supply of working uid for the pump is exhausted, the combination of an electric motor, a pump having a driving connection with the motor, a line for connecting the motor across a source, a pair of movable spring biased contacts in the line movable between engaged and disengaged positions for completing and disrupting the motor circuit, watt-sensitive relay means connected in the line and including one of said movable contacts, said relay means being responsive to a reduction in wattage at the motor during underload operation for releasing said one contact for movement thereof away from the other contact, and electromagnetic holding means cooperable with the other of said contacts for holding the same when said relay means is deenergized whereby said contacts are disengaged.

11. The combination of claim 10 further characterized in that said electromagnetic holding means includes an excitation coil connected across the line and a reset switch in series therewith for deenergizing said coil and releasing said other contact for restarting the motor.

References Cited in the le of this patent UNITED STATES PATENTS 1,731,373 Dauler Oct. 15, 1929 2,399,059 Pell Apr. 23, 1946 2,647,232 Ransom et al. July 28, 1953 2,722,648 Dunigan Nov. 1, 1955

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