US3500751A - Safety switch circuit - Google Patents

Description

March 17, 1970 I M. LQROBEYRTSON 3 ,500,751

mm swnca cmcun Filed my 27, 19s? INVENTOR KELBORNE L. ROERTSON United States Patent U.S. Cl. 10312 8 Claims ABSTRACT OF THE DISCLOSURE The invention comprises an arrangement of a latching relay and a time delay relay between a switch and a power line to a point of use, arranged so that power will not be fed through the power line until a predetermined time has passed to thereby prevent feeding power to the point of use prematurely in the event of malfunctions of the switch.

This invention relates to a circuit having means to assure that a first switch is closed before current is passed through a second switch to a point of use. More particularly, the invention is adapted for use with automatic oil well pumping equipment wherein a timing device causes a valve on the well to open, and upon said valve being opened, a pump is turned on to operate the well, but, of course, the invention is not limited to use in the oil industry.

In such automatic oil well pumping operations, one problem which arises is that the pump is sometimes turned on before the valve is opened. This problem most often arises due to malfunctions in a microswitch which is normally moved to the closed position by a portion of the valve when the valve is fully opened. If the microswitch should fail, or should stick in the closed position, the pump motor will be turned on and the pump will operate against a closed valve which results in damage or destruction of various other pieces of equipment, such as ruptured packings in the stufling box, ruptured flow lines, and the like. Such accidents can be very expensive since the released oil can damage crops, pastures, farmland, buildings, highways, and the like. The elimination of such property damages is an important advantage of the present invention. Another type of switch malfunction which can cause the pump to operate against a closed valve are breakdowns in the mechanical linkage of the microswitch, which has the same effect as a failure or sticking of the microswitch itself.

This invention provides a simple and relatively inexpensive circuit which can be incorporated into existing equipment, usually in the existing panel box housing the automatic equipment associated with the well, to solve the above problems.

The invention comprises a double throw latching relay and a time delay relay in combination with the existing time clock mechanism associated with the automatic well pumping equipment, which insures that current cannot be sent to the well pump motor until the valve is completely open.

In the accompanying drawing forming a part of this disclosure, the single is an electrical schematic of one em bodiment of the invention.

Referring now in detail to the drawing, 10 designates a circuit embodying the invention. Circuit 10 includes a pair of main power lines 12 and 14. Line 14 is controlled by a normally open switch 16 incorporated in a master time clock 18, and line 12 may be grounded. As is well known to those skilled in this art, oil wells are usually pumped for only intermediate periods because of technical considerations such as reservoir depletion, and because of legal considerations such as the various conservation laws. For example, it may be desired to pump oil from the well 3,500,751 Patented Mar. 17, 1970 controlled by circuit 10 for, for example, three hours out of each twelve hour period. In any case, the pumping time is built into the time clock 18 in well known manner and clock 18 will close normally open switch 16 and hold it closed for the preset periods. Thus, switch 16 closes in accordance with the preset schedule in time clock 18, and remains closed for periods of time equal to the time the oil well pump motor 15 is scheduled to work.

The oil well pump motor is fed current through a line 20 which is controlled by a pair of normally closed contacts 22 on a double throw latching type relay 24.

The mechanical portions of the system, which do not form a material part of the present invention, include a motor 15, which drives a pump 17, which pumps fluid in a pipe 19, which includes the mechanical portions of the motor valve 58, the electrical portions of which are de scribed below.

Relay 24 has two coils 26 and 28 and a second pair of normally closed contacts 30. One side of coil 26 is always connected to power from feed line 14, before clock 18, by line 32. The other side of coil 26 is connected by a line 34 to one side of a normally open, manually operated, push-button type reset switch 36, the other side of which is connected by line 38 to the other feed line 12. One side of normally closed contacts 30 is connected to feed line 14, after clock 18, by a line 40, and the other side of said contacts is connected to one end of a line 42. The other side of the pump controlling contacts 22 is connected by a line 44 to one side of coil 28, and the other side of said coil is connected to one end of a line 46. When both coils 26 and 28 are de-activated, the two contacts 22 and 30 are in their normally closed positions. If only coil 28 is activated, the contacts 22 and 30 will be open and relay 24 includes mechanical latching means which locks the contacts in the open position. Thus, activation of coil 28 will prevent any current from passing through line 20. To reset the circuit, manual reset 36 is momentarily depressed, thereby activating coil 26 which acts to unlock the mechanical latching means holding contacts 22 and 30 open. The cooperation of latching relay 24 with the rest of the circuit will be explained in the operation section below.

Circuit 10 includes a time delay relay 48, which comprises a single pair of normally closed contacts 50 and a coil 52. One side of contacts 50 is connected to the other end of line 46, running from coil 28 on relay 24, and the other side of said contacts is connected by a line 54 to feed line 12. One side of coil 52 is connected to the other end of line 42, and the other side of said coil is connected by a line 56 to feed line 12. The nature of time delay relay 48 is such that the coil 52 will take current for a predetermined length of time, 10 seconds in the embodiment of the invention being described, before opening the normally closed contacts 50.

Circuit 10 includes a valve 58 which controls the fluid line 19 through which the fluid pumped by the pump 17 must pass. Such valves are known in the art as hydromotor valves, and include a microswitch having a moveable switching member or arm 60, a central contact 62, an inactive position contact 64 and an activated position contact 66. The valve 58 includes a motor, designated 68, which actually o erates the mechanical valve, shown diagrammatically in line 19, and which also moves an element 70 which cooperates with switch arm 60. It will be understood that element 70 and the left hand portion of arm 60 diagrammatically represent the mechanical linkage in the switch and valve and that this linkage could be more complicated, depending on the nature of the valve being used. The mechanical arrangements of the parts are such that under normal operating conditions, i.e., where there are no malfunctions, element 70 will move switch arm 60 off of contact 64 and onto contact 66 only when the valve is fully open. Valve 58 also includes a coil 72 which operates a check valve forming part of the so-called valve operation. This coil is a safety device forming a part of most conventional valves themselves, and since it is activated for the entire time contacts 16 in the clock 18 are closed, it need not be explained in further detail here.

Feed line 14 is connected to central contact 62 of the microswitch. A line 74 connects contact 66 to line 44 on one side of coil 28 in latching relay 24. A jumper line 76 connects the remaining contact 64 of the microswitch to one side of the motor 68. Another jumper line 78, which is in effect an extension of feed line 14, interconnects central contact 62 with one side of coil 72, the other side of which coil is directly connected to the other feed line 12 by a line 80. Feed line 12 is connected to the remaining contact on motor 68.

OPERATION In devices heretofore used, components like clock 18 and valve 58 only were used. The arrangement was such that the point of use, the oil well pump motor 15 in the example being described, was connected directly to contact 66 of the microswitch in valve 58. With this arrangement, malfunctions in the nature of the switch arm 60 sticking in the activated position, i.e., against contact 66, resulted in the oil well pump motor being turned on before the line valve was opened, resulting in damage to or destruction of other pieces of well equipment.

The circuit of the present invention avoids the above described undesirable conditions. The operation of the invention will first be described during a normal sequence of operation, and will then be described if there should be a malfunction.

In normal operation, master time clock contacts 16 close in response to the predetermined schedule set on the clock. Line current is fed through line 14 to microswitch contact 62. From this contact, the current is fed through line 78, to check valve coil 72, and to main line 12. Simultaneously, current is fed through switch arm 60, contact 64, jumper 76, and the motor 68 which immediately starts to open the line. valve. In the embodiment being described, motor 68 takes approximately 30 seconds to fully open the mechanical valve.

Simultaneously with initiation of operation of motor 68, current is fed through line 40, normally closed contacts 30 on latching relay 24, through line 42, through coil 52 of time delay relay 48, and to feed line 12 via line 56. After about 10 seconds, the coil heats sufficiently to operate its normally closed contacts 50 and these contacts 50 open.

At the end of the 30 seconds required for the valve to open, element 70 will move switch arm 60 into electrical contacting relation with contact 66. Current will then flow through line 14, switch arm 60, line 74, line 44, still normally closed contacts 22, and through line 20 to the oil well pump motor 15, or other point of use.

Thus, it can be seen that the time delay built into coil 52 must be less than the time required for motor 68 to open the mechanical valve, since contacts 50 control lines 46 and 54 running to coil 28 of latching relay 24, and once coil 28 is disabled by the opening of contacts 50, it is no longer possible for anything to stop current from being fed through line 20 to the point of use.

In the event of any malfunction resulting in switch arm 60 being in contact with contact 66 at the time the normally open contacts 16 in the clock close, line 20 will 'be disabled and prevention of the pump starting against a closed valve will have been accomplished. The flow path will be through line 14, malfunctioning switch arm 60 now in contact with contact 66, line 74, coil 28 of latching relay 24, line 46, still normally closed contacts 50 on the time delay relay 48, and to line 12 via line 54. Coil 52 on the time delay relay begins receiving current at the same time as the malfunctioning switch arm in valve 58, but the time delay feature of coil 52 assures that contacts 50 remain normally closed for a long enough time to disable line 20.

When the pump motor fails to start, various conventional warning systems, not shown, will automatically come into action to warn an operator at a central location, to sound a bell, or to otherwise make the fact of the malfunction known. Maintenance personnel are sent to the site and correct the malfunction. Upon correction of the malfunction, the reset switch 36 is operated to operate coil 26 via lines 32, 34 and 38, therebyreturning contacts 22 and 32 to their normally closed position, readying the circuit for future service.

An additional safety feature is that if reset button 36 should be operated before the malfunction is corrected, latching relay 24 will unlatch but then immediately relatch indicating that the malfunction has not been corrected. As shown, it is possible for an operator to circumvent the safety feature of the present invention by holding reset button 36 depressed for a time greater than the time delay built into coil 52 of time delay relay 48. To circumvent this possibility of human error, it is desirable to provide a reset switch 36 of a type that will permit only momentary contact, thereby preventing this kind of forced override of the safety feature of the present invention.

In the embodiment of the invention which has been built and is being successfully used; relay 24 is a Potter and Brumfield type No. KB17AG 4 pole, double throw latching relay; valve 58 is made by General Controls and is a hydromotor Model A, Cat. No. H l0A-320BICIFIFI- 13; and switch '60 is part of the hydromotor valve, one used is a Kalper Switch microswitch Model No. S4Al062.

I claim:

1. A circuit for feeding power to a point of use and to control means associated with said point of use, said control means comprising means to ready said point of use for the reception of power, said readying means requiring a period of time to ready said point of use for the reception of power, said control means comprising conditiona'ble switch means which are conditioned to permit the flow of power to said point of use when said point of use has been readied for the reception of power, and said circuit comprising means to prevent the flow of power to said point of use if said conditionable switch means are prematurely conditioned to permit the flow of power to said point of use.

2. The combination of claim 1, said control means comprising a motor valve, said conditionable switch means comprising a switch in said motor valve, said point of use comprising a pump adapted to pump fluid through a pipe, said readying means comprising a valve in said pipe operable by said motor valve, said motor valve comprising means to move said switch to a first position wherein power will flow to said pump after said pipe valve has been opened by said motor valve, said preventing means comprising time delay means adapted to prevent the flow of power through said switch to said pump for a period of time equal to the length of the time delay period in said time delay means, and the time delay period of said time delay means being a period of time less than the period of time required for said motor valve to open said pipe valve.

3. The combination of claim 2, said time delay means comprising a time delay relay, said circuit comprising a second relay, said circuit comprising means to feed power from a power source through said motor valve switch in said first position thereof through a pair of normally closed contacts on said second relay and to said pump, said time delay relay comprising a pair of normally closed contacts, said second relay comprising an operating coil, said circuit comprising connection means adapted to connect said normally closed contacts on said time delay relay with said operating coil of said second relay, said second relay comprising a second pair of normally closed contacts and said circuit comprising series connection means adapted to connect said second pair of normally closed contacts to the coil of said time delay relay and to a power source independent of said motor valve switch.

4. The combination of claim 3, said second relay comprising latching means adapted to latch said normally closed contactsin the open position when said contacts are moved to the open position by said operating coil, and said second relay comprising manually operated reset means adapted to unlatch said contacts.

5. A remote installation comprising motor valve means having a switch, said installation including pump means, timing means to control the motor valve means and the pump means; circuit means interconnecting the pump means, the motor valve means and the timing means; said circuit means comprising means to feed power to said pump means through said motor valve switch when said motor valve switch is moved to a first positionby said motor valve at the end of said motor valves valve opening operation, and said circuit means comprising means to prevent the flow of power to said pump means if said motor valve switch is in said first position 'before completion of said motor valves valve opening operation.

6. The combination of claim 5, said circuit means com prising time delay means having a time delay period shorter than the time required for said motor valves valve opening operation, and said preventing means being adapted to prevent the -flow of power to said pump means during the time delay period of said time delay means.

7. The combination of claim 6, said time delay means comprising a time delay relay, said circuit comprising a second relay, said circuit comprising means to feed power from a power source through said motor valve switch in said first position thereof through a pair of normally closed contacts on said second relay and to said pump means, said time delay relay comprising a pair of normally closed contacts, said second relay comprising an operating coil, said circuit comprising connection means adapted to connect said normally closed contacts on said time delay relay with said operating coil of said second relay, said second relay comprising a second pair of normally closed contacts, and said circuit comprising series connection means adapted to connect said second pair of normally closed contacts to the coil of said time delay relay and to a power source independent of said motor valve switch.

8. The combination of claim 7, said second relay comprising latching means adapted to latch said normally closed contacts in the open position when said contacts are moved. to the open position by said operating coil, and said second relay comprising manually operated reset means adapted to unlatch said contacts.

References Cited UNITED STATES PATENTS 2,219,359 10/1940 Goit et a1. 103-40 2,240,607 5/1941 Buck 10340 2,384,420 9/1945 Griswold 103-40 2,724,337 11/1955 Teeson 10325 3,012,510 12/1961 Kusner 10325 2,658,172 11/1953 Neubauer 3l7141 3,322,470 5/ 1967 MacDonald 317-135 WILLIAM L. FREEH, Primary Examiner US. Cl. X.R. 10325, 137-624.1l; 317-135, 141; 3l8103

Images