US2756413A - Water flow alarm devices - Google Patents

Description

y 1956 A. J. LOEPSINGER ETAL 2,756,413

WATER FLOW ALARM DEVICES Filed March 2. 1953 4 Sheets-Sheet 1 FIG! INVENTORS ALBERT J. LOEPSINGER AMES A. DUNCAN ATTOR N EY WATER FLOW ALARM DEVICES 4 Sheets-Sheet 2 Filed March 2. 1953 INVENTORS R "a Y N m SN R PM 0 WM T LW 7% M J Q A .4 ms 6M MMB 2 G F y 1956 A. J. LOEPSINGER ETAL 2,756,413

WATER FLOW ALARM DEVICES Filed March 2, 1953 4 Sheets-Sheet 5 1N VEN TORS ALBERT J. LOEPSINGER 95155 A. DUNCAN V ATTORNEY July 24, 1956 Filed March 2. 1955 FIG. 5

A. J. LOEPSINGER ETAL 2,756,413

WATER FLOW ALARM DEVICES 4 She ets-Sheet' 4 1' Huimlil i H I'IHHhH JNVENTORS ALBERT J. LOEPSINGER JAMES A. DUNCAN BMQZM ATTORN EY United States Patent WATER FLOW ALARM DEVICES Albert J. Loepsinger, Providence, and James A. Duncan,

North Kingstown, R. I., assignors to Grmnell Corporation, Providence, R. I., a corporation of Delaware Application March 2, 1953, Serial No. 339,816

3 Claims. (Cl. 340-289) This invention relates to improvements in water flow alarm devices. More especially it has to do with water flow alarm devices particularly suitable for use in socalled wet-pipe fire protection systems.

When such a sprinkler system is installed in a building and connected to a city water main by a riser it is customary to provide a device which will given an alarm when one or more sprinkler heads open. Since the opening of sprinkler heads causes water to flow in the riser it is apparent that this flow could be employed to actuate such a device. However, because the pressure in city water mains is continually varying due to changes in the demands of nearby users and because some entrapped air is usually encountered in sprinkler systems, water flow may also occur in the risers toward the sprinkler system when no sprinkler heads have opened. Likewise, though a check valve is usually located in the riser to permit flow therein only in a direction toward the sprinkler system, foreign bodies or scale may prevent complete closing of this check valve and water flow may then occur in the riser away from the sprinkler system when no sprinkler heads have opened. Consequently, a satisfactory alarm device which is actuated by water flow in the riser must be capable of distinguishing water flow therein caused by the opening of sprinkler heads from water flow caused by mere variations in city water main pressure acting upon entrapped air in the sprinkler system and must respond only to the former.

I have discovered that when a by-pass which will be more particularly described hereinafter is provided around the check valve in the riser and a reservoir which will also be more particularly described is connected to the riser at a point on the sprinkler system side of the check valve, the opening of one or more sprinkler heads produces a combination of flow conditions through the bypass and the connection to the reservoir which is unlike those combinations which are produced by changes in city water main pressure.

Accordingly it is a general object of the present invention to provide a water flow alarm device for a water conductor which achieves an alarm-producing combination of flow conditions in its parts when the pressure drops on one side of a check valve in the conductor and does not achieve such a combination when the pressure on the opposite side of the check valve fluctuates.

A specific object of the invention is to provide for a water conductor a water flow alarm device having a plurality of indicating flow paths which are so associated with the Water conductor that a drop in pressure on one side of a check valve therein produces a combination of flow conditions in the indicating flow paths which is unlike all those combinations produced by changes in pressure on the opposite side of the check valve.

2,756,413 Patented July 24, 1956 Another object of the invention is to provide a device of the type described having for one of its indicating flow paths a by-pass around the check valve and having for another of its indicating flow paths an elongated connection between the water conductor and a water reservoir from which the water is resiliently urged.

Another object of the invention is to provide a device of the type described in which one end of the elongated connection joins the water conductor on the side of the check valve toward which water in the conductor is most readily permitted to flow by the normal operation of this check valve.

Another object of the invention is to provide a device of the type described in which elements are located in the indicating flow paths so as to be movable by the flow therein within restricted ranges, and in which an alarm is produced when these elements are in predetermined positions.

The best mode in which it has been contemplated applying the principles of my improvements is shown in the accompanying drawings but these are primarily illustrative because it is intended that the patent shall cover by suitable expression in the appended claims whatever features of patentable novelty reside in the invention disclosed.

In the drawings:

Figure 1 is a somewhat diagrammatic cross-sectional elevation view of my improved water flow alarm device,

showing an associated electronic circuit capable of actu ation to produce an alarm when each of the movable elements is in a particular predetermined position, and showing that no alarm is produced when the pressures on both sides of the check valve are the same because one of the movable elements is not then in its predetermined position;

Figure 2 is a plan view taken as on line 22 of Fig. 1, but with the electronic circuit omitted;

Figure 3 is an elevation view similar to that of Fig. 1, showing that no alarm is produced when the pressure on the lower side of the check valve is increasing, because one of the movable elements is not then in its predetermined position;

Figure 4 is an elevation view similar to that of Fig. 1, but showing that no alarm is produced when the check valve is held partially open and the pressure on the lower side thereof is decreasing, because again one of the movable elements is not then in its predetermined position; and

Figure 5 is an elevation view similar to that of Fig. l, but showing that an alarm is produced when the pressure on the upper side of the check valve is decreasing because each of the movable elements is then in its predetermined position.

Referring now more particularly to the drawings 'my improved device is shown installed on a riser 10 such as would connect a so-called wet-pipe fire protection sprinkler system to a city water main. It Will be understood, however, that my device is not limited in its use to sprinkler systems, but may be successfully applied wherever the system conditions which are to be detected and those which are to be ignored correspond to the sprinkler system conditions hereinafter described.

A check valve 12 is located in riser 10 and arranged to permit water flow upward therein toward the sprinkler system and to prevent water above it from flowing downward toward the city water mains. In normal operation that portion of the riser 10 which is shown in the drawings is completely filled with water above and below the check valve 12.

A by-pass 14 is provided around the check valve 12. This by-pass comprises two sections of tubing or pipe having an inside diameter considerably smaller than the inside diameter of the riser. The first section has one of its ends 14a-COI1Il66td to the riser. at apoint, thereon just above the check valve and has its other end 14b. connected to the bottom end of a vertically disposed gauge glass 16 containing a float 18. The second section of the by-pass 14 has one of its ends 140 connected to the top of the gauge glass 16 and has its other end 14d connectedto the riser at a point thereon just below the check valve.

Two additional sectionsof tubing or pipe, similar to those employed in the by-pass, serve to form a branch 20; leading from the riser to a. reservoir 22. The first section of this branch has one of its ends 20a connected tothe riser at a point thereon just above the check valve and has its other end-Zilbconnectedtoithe;topof a second vertically disposed gauge, glass 24 containing a float 26. The-second section ofv-the branch 20 has one of its endslflc connectedto the bottom of the gauge glass 24v disposed so that thisv airremains at the upper endthereof remote frornthe-point where the branch 29 is connected thereto. Anindicating glass 22a permits readyascertainment of the amount of entrapped air in the reservoir, and a plug 22b is provided at the top of the reservoir so thatadditional air may be introduced as required. The function of. the entrapped air 28'will be understood when the operation of-the device is described later herein.

In the preferred embodiment of my invention which is shown in the drawings, the gauge glasses 16 and 24 are identical andtheir respective floats" 18 and 26.are likewise identical. Accordingly, a description of one of these units will suflice for both. Thus considering gauge glass 16, it comprises a cylindrical tube 16a oftransparent material'having an inside diameter somewhat larger than the outside diameter of the tubing or pipe of the by-pass 14 in which it is located. Disposed across the lower and upper ends, respectively, of, this transparent tube and secured thereto are identical annular closure plates 16b and 16c.- The end 1412 of the first section of by-pass 14 fits nicely up into a central passage in-closure plate 16b and has a portion 14b which projects a short distance above the upper surface thereof. In the Walls of this projecting portion 14b small lateral holes 14b." are formed, substantially as shown.

Similarly, the end 140 of the second section of by-pass 14 fits nicely down into a central passage in closure plate 160 and has a portion 14c which projects a short dis-. tance below the lower surface thereof. In the'walls'of this projecting portion 140 small lateral holes 140." are formed, again substantially as shown.

Though thename I have chosen to give them would imply that the floats 18 and 26 have specific gravities less than the specific gravity of the liquid in the system, it will be understood that that name was selected merely forconvenienceof description, because in the preferred embodiment shown correct operation is possible only when the floats have specific gravities somewhat greater than the liquid. Accordingly, when there-isno movement of the liquid in the by-pass 14 or when the flow of liquid therein is downward through the gauge glass 16, the float 18 which is movable within the transparent tube 16a islocated at the lower end thereof and rests on the projecting portion 14b of the first by-pass section. Simi-. larly, when there is no movement of the liquid'in the branch 20 or when the flow of liquid therein is downward through the gauge glass 24, the float 26 -is located at the lower end of this gauge glass in a position which corresponds to the position just described of the float While the specific gravity of each of the floats 18 and 26 is greater than the specific gravity of the liquid in the system, as has been noted, it is not much greater, and consequently the tendency of each float to sink to the bottom of its gauge glass will be overcome and the float will remain at the top of its gauge glass when there is an appreciable flow of the liquid. upward therein.

The electronic circuit which is shown in Figs. 1, 3, 4' and 5 and whichwill be more particularly. described later hereinemploys two photo-electric tubes 30 and 32,having separate light sources 34 and 36, respectively. Tube 30' is arranged in, the circuit. so that. it will stopfiring and open a relay switch 38 when the light beam from its source 34 is prevented from falling upon it, and tube 32 is arranged so that it will stop firing and close another relay switch 40 when the light beam from its source 36 is prevented from falling upon it. An alarm is produced when relay switches 38 and 40 are both closed.

Tube 30 and its separatelight source 34; are disposed in such relation to the gauge, glass 16 that the light bearnfromthe source must pass laterally through the upper end of the transparent tube 16a-and the liquid therein before it falls onthis tube. When the float 18is located at the lower end of this gauge glass upon the occurrence of a downward flow of the liquid therein or no flow at all,

suflicient light passes therethrough to causethe tube 30' to fire, but. when the float 18 is held at the upper end of the gauge glass by an upwardflow therein, it serves to intercept the light beam and prevent it from fallingon the tube; whereupon the tube stops firing and switch 38- opens.

Tube 32 and; its separate light source 36 are likewise disposed in suchrelation to the gauge glass 24 that the lightbeam fronrthe source must pass laterally through,

the upper, end of a transparent tube 24a and the liquid therein before itfalls on the tube. When the float 26.

is locatedat the lower-end of this gauge glass upon the occurrence of a downward flow therein or no flow at all, suflicientlight passes therethrough to cause tube 32 to fire, but when float 26 is held at the upper end of this.

gauge glass. by an upward flow of the liquid therein it serves to-intercept the light beam and prevent it from falling on-the tube; whereupon this tube alsostops firing and switch 40 closes.

From the foregoing description it is apparent that relay switches 38 and 4!) will both be. closed and an alarm thereby produced only when float 18 is in its down position in gauge glass 16 and sitmultaneously "fioat 26.

is in its.up position in gauge glass24. For any other combination of float positions one orthe other or both of-the relay- switches 38 and 48 will be open. As will be presently. understood when the operation of my improved device is particularly described, opening of one or more sprinkler. heads in asprinkler system above the check valve 12 will locate the floats so that an alarm is produced, and all other changes which may reasonably be expected to take place in the sprinkler'system, theriser and .the city water main will fail to so locate the floats with the result that no alarm is produced.

Operation that no water will flow in either direction in the by-pass 14; Consequently float 18 will be located in its down position.

Assume secondly that the water pressure at point P1 is at the same time equal to the water pressure at a point Since the point P1 is opposite the- Pa in the reservoir 22. Since the point P1 is also opposite the connection of the branch to the riser and the point P3 is at the same level a; point P1, the result of this second assumption is that no water will flow in either direction in the branch 20. Consequently, float 26 will also be located in its down position.

The two assumptions above suggested describe a condition of equilibrium. There being no pressure differentials which can produce flow no flow occurs in the riser, by-pass or branch. Such an equilibrium condition is relatively rare for the reason that the pressure in city water mains is normally fluctuating, but when it does occur it is apparent that no alarm will be produced because the float 26 is in its down position. See Fig. 1.

The fluctuations in city water main pressure above referred to take the form of slow increases or decreases with frequent surges superimposed thereon as a result of which the pressure in the riser below the check valve may change very suddenly and by a considerable amount either up or down. These surges are customarily described as positive and negative surges, respectively. As would be expected either a slow change in city water main pressure or a surge produces flow in the riser, bypass and branch.

Considering first a slow increase in city water main pressure or a positive surge, either of these will cause the pressure at P2 to increase, and if the sprinkler system were completely filled with water there would be a corresponding increase in pressure at P1 without any appreciable flow through the check valve 12 and through the by-pass. However, some air is almost invariably found to be entrapped in sprinkler systems when they are installed or have been reset after a fire or test. Accordingly, when the pressure at P2 increases an appreciable quantity of Water will flow through the check valve and by-pass before this entrapped air in the sprinkler system is sufliciently compressed to achieve a corresponding increase in the pressure at P1. The float 18 is located in its down position when this flow through the by-pass is taking place.

When the pressure at P1 begins to increase as a result of water flowing through the check valve and by-pass, it simultaneously begins to exceed the pressure at P3, and since the entrapped air 28 in the reservoir 22 is compressible water will flow through the branch to the reservoir until the compression of the air 28 is suflicient to cause the pressure at P3 to again equal the pressure at P1. The float 26 is located in its down position when this flow through the branch is taking place.

From the foregoing it will be clear that When there is a slow pressure increase or a positive surge in the city Water main no alarm will be produced because the float 26 is again in its down position. See Fig. 3.

Considering next a slow decrease in city water main pressure or a negative surge, either of these will cause the pressure at P2 to decrease. Thereupon the air entrapped and compressed in the sprinkler system tends to expand and cause a return flow of water in the riser toward the city water main. The check valve is provided for the purpose of preventing flow in this direction in the riser, but it is a matter of experience that these valves frequently are not completely tight and some return flow may take place through them. Accordingly, when the pressure at P2 decreases, flow occurs through the by-pass and also downward through the check valve, if the latter is not tight, until the pressure decrease at P1 corresponds to the pressure decrease at P2. This flow in the by-pass is in a direction to hold the float 18 in its up position.

When the pressure at P1 begins to decrease as a result of water flowing through the by-pass and possibly down through a leak in the check valve, it simultaneously becomes less than the pressure at P3, and since the entrapped air in the reservoir is compressed the drop in pressure at P1 will permit this air to expand and cause 6 flow in the branch toward the riser. This last-men tioned flow will continue until the pressures at P1 and P3 are again equal, and will be in a direction to hold the float 26 in its up position.

It is thus apparent that when there is a slow pressure decrease or a negative surge in the city water mains no alarm will be produced because this time the float 18 is in its up position. See Fig. 4.

Considering finally the eflects of opening one or more sprinkler heads in the sprinkler system, such an opening will cause the pressure at P1 to decrease. This has the same effect as an increase in pressure at P2, and consequently water will flow from the lower side of the check valve into the sprinkler system, most of this water pass ing upward through the check valve, and the remainder passing through the by-pass. The float 18 is located in its down position when this flow through the bypass is taking place.

The drop in pressure at P1, in addition to causing water flow in the by-pass and upward through the check valve, simultaneously becomes less than the pressure at P3 and causes the compressed air 28 to expand and produce flow in the branch toward the riser. Such flow in the branch holds the float 26 in its up position.

This time an alarm is given, as it should be when sprinkler heads open, because the floats 18 and 26 are now in their down and up positions, respectively. See Fig. 5.

It will be apparent from the foregoing description of operation that one desirable feature of my improved device is that false alarms due to fluctuations in city water main pressure are avoided by the use of two flow paths with flow indicating elements located therein and are not avoided by the use of time delay mechanisms located in the alarm circuit to suppress the alarm for a period of time calculated to exceed the time which elapses during the usual water main pressure fluctuation cycle. Later herein it will be seen that I find use for a time delay mechanism, but I need it only because of the inertia in the elements of my device. This inertia is very slight and accordingly the delay may be very short, for example, in the order of ten seconds. When time delay mechanisms alone are relied upon in water flow alarm devices to prevent false alarms by completely suppressing those alarms caused by water main pressure fluctuations, the delay necessary depends upon the duration of the cycle of these fluctuations and may in some instances be a matter of minutes. The duration of the fluctuations depends upon the hydraulic characteristics of each system.

One advantage in keeping time delays short will be appreciated when it is recognized that these time delays operate to suppress alarms which should be given as well as those which are false. Consequently, when an alarm should be given the water flow alarm device must be capable of remaining in an Marni-producing condition for a period in excess of the delay. In this connection, it will be recalled that float 26 in my device must be held in its up position by flow in the branch 20 to give an alarm. Such flow in the branch is the result of liquid driven from the reservoir 22 by the expansion of air 28. Obviously, there is a limit as to how long air 28 can continue to expand, and if the time delay period is long and the air stops expanding before this period elapses the float 26 will promptly settle to its down position and no alarm will be given.

Even if a water flow alarm device with an appreciable time delay therein can be made capable of remaining sufficiently long in an alarm-producing condition when an alarm should be given, nevertheless it will be understood to be another advantage of my device that the delay is short. The sooner an alarm which should be given is given the better.

Though I prefer to use floats in the by-pass and branch to indicate the directions of flow therein, it will be understood to be within the scope of my invention to use other well known means for indicating flow direction. Forexample flexible diaphragms may be employed inthe by-pass and branch, such diaphragrns being arranged to move in one direction or other in accordance with the flow.

It will also be understood that'when floats are used they need not have specific gravities greater than the specific gravity of the liquid in the system. A device within the scope of my invention and using floats is one in which the direction of flow in the by-pass is upward through the gauge glass therein when the pressure at P2 is. greater than the sum of the pressure at P1 and the head In and in which the direction of flow in the branchis upward and through the gauge glass therein when the pressure at P1 is greater than the pressure at P3. With such an arrangement correct operation would require the floats to have specific gravities somewhat less than the specific gravity of the liquid in the system.

For convenience of description the Water level in the reservoir 22 has been shown in the drawings to be above the point P1. This is not a requirement for successful operation of the device. However, if'this water level is below point P1, the amount by which it is below that point represents a head in the branch producing thatmuch more compression in the entrapped air 23. Such additional compression is not a disadvantage, but the lower the pressure in the reservoir the less strong it need be and the easier it is to replace any of the air 28 which may have leaked away.

Though I have found that flow in the branch 29 toward the riser 10 is very nicely accomplished by the expansion of air 28 which is entrapped in the reservoir and which is compressed by the pressure at P1, other arrangements in the reservoir for producing such flow will be obvious. For example, the reservoir could take the form of a collapsible bellows filled with the liquid and spring loaded for the expulsion of the liquid therefrom.

Turning now to consider the electronic circuit a pair ofleads 42 and 4-4 bring electric power from an alternating current power source (not shown) to one winding of an isolation transformer 46 the other winding of which has conductors 48 and Si connected to the opposite ends thereof. The isolation transformer 46 is used because it is desirable to ground a circuit of this kind, located, as it is, so close to water pipes, and withthis transformer the conductor i. may be thus grounded at point 52'without affecting the power source.

A voltage divider comprising a potentiometer 54 and a fixed resistor 56 is connected'across conductors 4-8 and 50. The photo-electric tube 30 has its cathode connected to the conductor 50 and its anode connected through a resistor 58 to the adjustable tap 54a of the potentiometer 54. In addition the anode of the photo-electric tube is connected directly to the grid 69a of a thyratron vacuum tube 60. This latter tube has its cathode 60b connected to the juncture of potentiometer 54 and resistor 56 and has its anode 6130 connected through a resistor 62 and the windings 38a of relay switch 38 to the con ductor 48. Power to heat the cathode 60b is drawn from atransformer 64 having one of its windings 64a connected across the conductors 43 and S0 and having'its other winding 6415 connected across a heating filament 60d within the tube. A second grid 6% is connected to the juncture of potentiometer 54 and resistor 56 and to a center tap on the transformer winding 64b. The relay switch 38 has a capacitor 33b connected across its winding 38a.

The portion of the electronic circuit thus far described operates as follows. Starting first at an instant in the alternating current power cycle when the conductor 43 has just gone positive and assuming that the float 18- is in its down position at this instant, the grid 6% of the thyratron 69. will be at the same potential as the cathode 6tib or less positive than this cathode because the light falling on phototube-30 from-source 34- fires this alarm bell 68.

phototubeandcauses it'to draw current through resistor: 58 anda portion ofthe potentiometer'54. The resistance of resistor 58-is chosenso that the voltage drop thereacross resulting from the current. drawn therethrough. by the phototube equals or exceeds the voltage drop: between the potentiometer tap 54a and the junctureof' the potentiometer 54 and resistor 56. H

Since the grid- 60a of thyratron 60 has a potential'less' positive than or equal to the potential of the cathode 6011 no current is drawn by the thyratron, the relay windings 33:: are deenergized and switch 38 is closed.

When the conductor 48begins to go negative later on in the alternating current cycle, phototube stops conducting because its anode is then negative'with respect to its a cathode, and though light from source 34 is still falling upon it, it will not conduct under these conditions. Ac-

cordingly, the grid 60a of the thyratron 60 then has'a potential equal to that at the potentiometer tap 54a; However, this potential is more negative than that of thecathode 60b and under these conditions thyratron 60 will not fire.

Assume now that the float 18 is moved to its up position where it prevents light from source 34 from falling on phototube 30. Tube 30 is then unable to conduct, and" consequently at an instant when the potential of conductor 48 has just begun to go positive the grid 60a of thyratron 60 will be positive with respect to the cathode 60b and the thyratron will begin to draw current through relay windings 38a, opening switch 38. Unlike the control grids of some other tubes the grid 60a of the thyratron, while capable of starting a flow of electrons from cathode to anode, has no control over this electron flow once it has started. Accordingly, as long as the potential on conductor 48 is passing through the positive portions of its cycles the thyratron is conducting. However, regardless of the fact that phototube 30 is not conducting, because. the float 18'is in its up position, the thyratron will not conduct when the potential on conductor 48 is passing I through the negative portions of its cycles. Therefore, during these portions relay windings 3811 are deenergized. Capacitor 38b is provided across these windings so that switch 38 will be held entirely open and will not chatter as a result of the alternate. energizing and deenergizing of the windings that occurs when phototube 30 is not conducting.-

The remainder of the circuit is a duplication of the portion just'described with the exception that the relay switch is closed when its windings are energized.

Switches 38 and 40 are in series with a battery 66 and As has been pointed out previously an alarm is produced when these switches are both closed.

There are modifications. of the general circuit hereinabove described which would be satisfactory. For example, float 18 could be arranged to darken phototube 30 when in its down position and switch 38 arrangedto close when windings 38a are energized. Likewise, a. similar reversal could be used with respect to float 26, phototube 32 and switch 40. However, I prefer the arrangement shown because floats 18 and 26 are normally in their down positions, with light falling on the phototubes. Consequently, when adjustments of the potentiometer tap 54a are made necessary by changes in the transparency of the gauge glasses and liquid which changes alter the amount of light falling on the phototubes and" hence the amount of current flowing therethrough, such potentiometer adjustments are more readily made.

Another. satisfactory modification would be one in which only one phototube is used, the light source thereforv being arranged to pass through both gauge glasses before falling onthe tube and only being unobstructed by both floats when the combination of fiow conditions in the bypass and branch indicates a sprinkler head opening.

It will be apparent to those skilled in the art that changes in the positions of the floats may be detected by circuits which do not employ phototubes. For eX- ample, the floats could be made of magnetized material with primary and secondary transformer coils disposed around each gauge glass, one-half of the secondary being wound in one direction at the upper end of the gauge glass and the other half wound in the opposite direction at the lower end of the gauge glass. Positioning of the magnetized float at the top of the gauge glass would then cause the induced current in the secondary coil to be 90 out of phase with the current which would be induced therein upon positioning of the float at the bottom of the gauge glass. This difference in polarity could be employed to give an alarm when both floats have moved into the positions which indicate that one or more sprinkler heads have opened.

Similarly, movements of the floats rather than the positions thereof could be employed to actuate an alarm device by inducing currents in coils wound around the gauge glasses. Thus, each float cannot reach its alarm position without moving thereto, and the current which could be induced by this movement could be employed to close a switch in the alarm circuit.

Because there is some inertia in the floats and liquid which must be overcome before they respond to a change of conditions, a complex pattern of slow pressure changes and surges in the city mains could conceivably cause the device shown to give a false alarm. Such a false alarm would be of very short duration because the inertia referred to is not great, but it would be troublesome, and, accordingly, I have provided, as previously noted, a timedelay 70 in the alarm circuit to withhold the alarm for a few seconds after switches 38 and 40 are both closed.

Without in any sense limiting the scope of this invention, I provide hereinafter certain specifications for the structure of the device shown in the drawings, which specifications are illustrative of those I have found satisfactory: The ratio of inside diameters of the riser 10 to the by-pass 14 and to the branch 20 may be 6:1. When the liquid in the system is water the floats may be made of aluminum, and the ratio of inside diameter of the transparent tube to the largest diameter of the float may be 1:0.96. liquid.

In the electronic circuit the transformer 46 may have a ratio of primary to secondary turns of 1:1. Resistors 54, 56, 58 and 62 may have resistances of 5000 ohms, 1000 ohms, l megohms and 1000 ohms, respectively. The relay windings 38:: may have a resistance of 2500 ohms. Capacitor 38b may have a capacitance of 4 microfarads. The phototubes may be 929s with tungsten filament lamp light sources.

The elements in the portion of the circuit not provided with designating numbers may have the same specifications as their equivalents in the portion particularly described.

The power from the source (not shown) may be 60 cycle, 110 volt power.

We claim:

1. Apparatus for producing an alarm on egress of liquid from a piping system which is substantially filled with liquid and which is supplied by a riser, said apparatus comprising a check valve located in the riser and adapted to pass liquid into the system, a conduit connected at its ends above and below the valve and forming a by-pass therearound, a free moving float element in said conduit having a specific gravity only slightly diflerent than that of the liquid and movable in a limited range and retained in a predetermined position by flow of liquid in the conduit ,toward the system, a liquid reservoir, a branch conduit having one end in communication with the riser and having its other end connected with the reser vpir, said reservoir being partially filled through said branch with liquid from the riser, means in the reservoir tending to expel the liquid therefrom, a free moving float element in said branch conduit and movable in a limited range and retained in a predeter- The reservoir 22 may be 80% filled with the mined position by a flow of liquid in the branch conduit toward the system, alarm producing circuit means, and means responsive to the positioning of each of said float elements to afiect the flow of current in'said circuit means and operative'when both said free moving float elements are in their respective predetermined positions to cause the alarm circuit means to give an alarm.

2. Apparatus for producing an alarm on egress of liquid from a piping system which is substantially filled with liquid and which is supplied by a riser, said apparatus comprising a check valve located in the riser and adapted to pass liquid into the system, a conduit connected at its ends above and below the valve and forming a by-pass therearound, a free moving float element in said conduit having a specific gravity only slightly different that that of the liquid and movable in a limited range between end positions and retained in one predetermined end position by flow of liquid in the conduit toward the system and when in its other position permitting flow thereby at least away from said system, a liquid reservoir, a branch conduit having one end in communication with the riser and having its other end connected with the reservoir, said reservoir being partially filled through said branch with liquid from the riser, means in the reservoir tending to expel the liquid therefrom, a free moving float element in said branch conduit and movable in a limited range and retained in a predetermined position by a flow of liquid in the branch conduit toward the system and permitting flow of liquid thereby in both directions, alarm producing circuit means, and means responsive to the positioning of each of said float elements to affect the flow of current in said circuit means and operative when both said free moving float elements are in their respective predetermined positions to cause the alarm circuit means to give an alarm.

3. Apparatus adapted to produce an alarm on egress of liquid from a piping system which is substantially filled with liquid and which is supplied by a riser, comprising a check valve located in the riser and arranged to pass liquid into the system, a by-pass around the check valve and having a vertically disposed transparent section, a free moving flow indicating means located Within the transparent section of the by-pass and movable by the flow of liquid therein within a limited range, said free moving indicating means being held in a predetermined position by a flow of the liquid in the by-pass toward the system, a reservoir partially filled with the liquid, 21 quantity of gas entrapped in the reservoir, a branch connecting the liquid-filled portion of the reservoir to the system side of the check valve and having a vertically disposed transparent section, an additional free moving flow indicating means located within the transparent section of the branch and movable by the flow of liquid therein within a limited range, said additional free moving indicating means being held in a predetermined position by a flow of the liquid in the branch toward the system, first, second and third electric circuits independent of the piping system, first and second relay-operated switches located and connected in series in the first circuit and having their relay windings located in the second and third circuits, respectively, photo-electric vacuum tube means located in the second circuit and actuated to conduct current by light falling upon it, a light source directing light through the transparent section of the by-pass and onto the photo-electric tube when the by-pass free moving indicating means is in its predetermined position, intermediate vacuum tube means located in the second circuit and actuated to energize the relay windings of the first switch by the occurrence of no current in the photoelectric tube, a second photo-electric vacuum tube means located in the third circuit and actuated to conduct current by light falling upon it, a second light source directing light through the transparent section of the branch and onto the photo-electric tube, said light being prevented from falling on the photo-electric tube by the said free moving branch indicating means when the latter is in'its predetermined position, second intermediate vacuum tube means located in the third circuit and actuated to energize the relay windings of the second switch by the occurrence of no current in the second photo-electric tube, and alarm producing means located in the first circuit and actuated by the simultaneous deenergizing and energizing of the relay windings of the first and second switches, respectively. 9

References Cited in the file of this patent UNITED STATES PATENTS"

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