Automatic Pump Shutdown Circuit

Abstract

In response to a sustained drop in the vacuum in a pneumatic line, a circuit automatically shuts down the vacuum pump (which is coupled to the line) for a short interval, and then restarts the pump.

Description

This invention relates to a relay circuit, and more particularly to a relay circuit useful for automatically shutting down a pump.

This invention is particularly applicable to shutdown of a vacuum pump (air pump, or blower) which is operating to provide a partial vacuum in a pneumatic tube system used for the transporting from one place to another of individual carrier units.

A typical pneumatic tube transporting system is described in the copending but now abandoned application, Ser. No. 276,625, filed July 31, 1972. The system so described may be utilized for transporting small samples of plant streams or tanks to a laboratory for analysis. The system operates as a vacuum system, a pump being used to draw air from the remote end of the tube to the end at the laboratory.

Longer systems, such as the one described in the above application, utilize several pumps, to provide a more even air flow in the tube and overcome the greater frictional effect of the long tube. Such multipump systems are divided into sections by normally closed valves, each pump having its own section of tubing. As disclosed in the above-identified application, these valves may be spring-loaded flapper valves, each valve being held shut (closed) by a combination of pressures from the spring and the vacuum in the tube.

Normally, the moving carrier (which contains the sample bottle, and is used to transport the sample through the tube) strikes the valve flap and kicks it open, being carried past the valve flap by its momentum. The valve then closes automatically. Occasionally, however, a carrier becomes lodged in a flapper valve, creating a blockage in the pneumatic tube. For minimizing maintenance, it is desirable to clear such blockages automatically.

An object of this invention is to provide an automatic valve-unblocking arrangement for pneumatic tubes.

Another object is to provide an automatic shutdown circuit for vacuum pumps.

A further object is to provide a shutdown circuit for vacuum pumps which operates in response to a pressure change.

An additional object is to provide an automatic pump shutdown circuit which functions to first shut down the pump for a short interval, and then to restart the pump.

A detailed description of the invention follows, taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a diagrammatic illustration of a portion of a pneumatic tube transporting system, with an automatic valve-unblocking arrangement according to this invention; and

FIG. 2 is a simplified circuit diagram of an automatic pump shutdown circuit.

Refer first to FIG. 1. A portion of a pneumatic tube 1 is illustrated, this tube being mounted mostly overhead but dipping down by means of a vertically extending leg 1' to near ground level, to provide, for example, for a sample drop indicated at 2. A carrier being transported moves through the line 1 as indicated by the solid-line arrows 3.

A spring-loaded flapper valve 4, which is mounted in the vertical leg 1' and which preferably has the construction described in the above-mentioned copending application, divides the tube 1 into an upstream section and a downstream section. Air is drawn from the remote end of the upstream section of tube 1 by means of the adjacent vacuum pump 5 (centrifugal blower), as indicated by the dotted-line arrows 6, and passes through an air take-off 7 (coupled to the main tube leg 1' just upstream of valve 4) to the intake of pump 5. The exhaust of pump 5 is to the atmosphere, as indicated at 8. Pump 5 is driven by an electric motor 9, to be described more in detail later.

In the downstream section of tube 1, air is drawn by a remote vacuum pump (not shown) through an atmospheric intake 10 (coupled to tube leg 1' just downstream of valve 4), and flows in the direction of the dotted-line arrows 11 to the remote pump (located at the downstream end of the downstream section of tube 1).

The pressure drop in the tube 1, and the flow of air (described) through the tube 1, propels the carriers in the direction 3. The moving carriers normally strike the valve flap 4 and kick it open, the valve closing automatically after the carriers have passed by the valve flap.

The valve 4 is spring-loaded, as described in the copending application above mentioned, and is held shut by a combination of spring pressure and the pressure differential (across its upper and lower faces) due to the air flows previously described.

When a carrier becomes lodged in a flapper valve such as 4 (that is, when the valve becomes blocked with a carrier), it can usually be removed (thus unblocking the valve) simply by shutting down the adjacent pump 5 (which is to say, the vacuum pump on that section of the line). The shutting down of the vacuum pump 5 relieves the differential pressure on the valve flap 4 (which pressure usually has theretofore been holding the carrier in the valve). Since all the flapper valves 4 are in a vertical position, once the pressure on the valve flap has been relieved or released the carrier drops through the valve with the aid of gravity, and proceeds down the tube 1. The valve 4 then closes, and the line is ready to be evacuated.

According to this invention, a relay circuit 12 (shown in detail in FIG. 2, to be described) is triggered by a sustained drop in line vacuum (which results when a carrier becomes lodged in the flapper valve 4), to automatically shut down the vacuum pump 5 for a short interval, and then restart the pump. It should be realized that when a carrier becomes lodged in a flapper valve such as 4, the valve is blocked open, causing the atmospheric pressure in intake 10 to be effective on the take-off 7. A vacuum switch 13 is coupled at 14 to the air take-off 7 to sense the pressure therein, this switch operating the relay circuit 12 (as will be described) to turn off the vacuum pump motor 9 (in response to a drop in the vacuum in line 7) for a short interval, and then to turn this motor back on.

Refer now to FIG. 2. The two buses 15 and 16 are connected across an alternating current source (115 volts) indicated at 17. When the manually-operated start switch 18 is depressed, an energization circuit is completed through the winding 19 of a relay 20, energizing this relay to close its normally open pair of contacts 21. When contacts 21 close, an energization circuit is completed through the winding 22 of a relay 23, by way of a normally closed, manually operated stop switch 24. When relay 23 is energized, its normally open contacts 25 close, to provide a holding circuit (around contacts 21) which keeps relay 23 energized after relay 20 is deenergized (when the start button 18 is released).

When start switch 18 is depressed to energize relay 20, the normally open relay contacts 26 of the latter close, energizing the motor starter coil 27 (through closed switch 24) to turn the pump motor 9 (FIG. 1) on. When starter coil 27 is energized, the start-hold contacts 28 (illustrated as a switch) close, keeping the starter coil 27 energized through these (now closed) contacts 28 and the normally closed contacts 29 of a time delay relay 30 (the stop switch 24 being closed). Time delay relay 30 has a time delay of 30 seconds, which means that its contacts are operated 30 seconds after its winding 35 is energized. When the start button 18 is released, relay 20 is deenergized, opening its contacts 21 and 26.

Whenever it is desired to manually turn the pump motor 9 off, the starter coil 27 is deenergized by depressing the stop switch 24, which breaks the keep-on circuit previously established for coil 27. When coil 27 is deenergized, the start-hold contacts 28 open. When stop switch 24 is depressed, the holding circuit previously established (by way of contacts 25) for relay 23 is opened, deenergizing this latter relay; the deenergization of relay 23 returns its contacts 25 and 40 to the open position illustrated.

The vacuum switch 13 is a commercially-available pressure switch having a C contact 31 (connected to bus 15) and an NC contact 32 (which is connected through the normally closed contacts 33 of a time delay relay 34 and the winding 35 of relay 30 to bus 16), as well as another contact (not shown, and not used). Time delay relay 34 has a time delay of 60 seconds, which means that its contacts are operated 60 seconds after its winding 36 is energized.

When the pneumatic tube 1 is operating normally, there will be a vacuum of two to four inches of mercury in the air take-off 7. When the flapper valve 4 becomes blocked, as by a carrier becoming lodged therein, the vacuum will decrease drastically in the take-off 7, to which the vacuum switch 13 is pneumatically coupled, at 14. When this vacuum decreases below three-fourth inch of mercury, the vacuum switch contacts 31-32 will close, energizing the winding 35 of time delay relay 30 through the normally closed contacts 33. Thirty seconds thereafter, the contacts of relay 30 will operate. Contacts 29 of relay 30 open, removing power from the motor starter coil 27, which deenergizes blower motor 9 (FIG. 1) and shuts down the vacuum pump 5 which is adjacent the blocked valve 4.

The normally open contacts 37 of relay 30 are connected in series with a counter 38, between buses 15 and 16. Therefore, each time that relay 30 operates, counter 38 is energized, to add one count. Preventive maintenance of the pneumatic tube requires a weekly check of this counter, and the keeping of a log of counter readings. An excessive number of pump shutdowns may indicate: (1) insufficient suction (the pump setting and the pump intake screen should be checked); (2) badly worn flap in the valve such as 4 (the flap surface should be checked); (3) a dry tube (bulk oil should be added upstream); (4) a defective vacuum switch.

The winding 36 of relay 34 is energized when switch contacts 31-32 close, but this relay has a time delay of 60 seconds. Therefore, 30 seconds after the contacts of relay 30 operate, the contacts of relay 34 will operate. The contacts 33 of relay 34 open, breaking the circuit to winding 35 and causing relay 30 to release, closing its contacts 29. When relay 34 operates, its normally open contacts 39 close, and since relay 23 is always energized (locked in by its contacts 25) unless the stop switch 24 is depressed, thus maintaining its contacts 40 closed, the starter coil 27 is energized through relay contacts 39 and 40. This reenergizes the motor 9, turning the pump 5 back on.

When the pump 5 is thus restarted, the vacuum in the line should build up, thus opening the vacuum switch contacts 31-32 and removing all power from relays 34 and 30 (winding 35 of relay 30 having been previously deenergized by opening of contacts 33, as previously stated). The pump 5 will stay on because the start-hold contacts 28 are closed (by energization of starter coil 27) and the normally closed relay contacts 29 are now closed.

The pump 5 may be shut down for maintenance, repairs, etc. by depressing the stop button switch 24. This opens the holding circuit for the relay winding 22, deenergizing relay 23. In addition, since the normal energization circuit (including start-hold contacts 28 and the normally closed relay contacts 29) for the motor starter coil 27 is connected to power bus 15 through stop switch 24, opening of this latter switch deenergizes starter coil 27 and thus turns off the pump 5 (due to deenergization of blower motor 9). It may be here noted that the alternate or parallel energization circuits for motor starter coil 27 (these being, on the one hand, relay contacts 26, and, on the other hand, the series combination of relay contacts 40 and relay contacts 39) are both connected to power bus 15 through stop switch 24.

Claims

We claim:

1. In combination, a vacuum pump normally operating to produce a partial vacuum in a line, a vacuum switch operated to the closed position in response to a decrease in the vacuum in said line to below a preset value, a first time delay relay connected in series with said switch and operating its contacts at the end of a first time interval, said relay having a pair of contacts which when operated act to shut down said pump; and a second time delay relay connected in series with said switch and operating its contacts at the end of a second time interval, said second relay having a pair of contacts which when operated act to start said pump.

2. Combination of claim 1, wherein said second time interval exceeds said first time interval.

3. Combination of claim 1, wherein said second time interval is on the order of 60 seconds, and said first time interval is on the order of thirty seconds.

4. Combination set forth in claim 1, including also electrically energized counter means, said first relay having another pair of contacts which when operated cause energization of said counter means.