the present invention is directed to a fluid vacuum safety device 50 for use in a pump assisted fluid circulation system for the purposes of alleviating an intense vacuum that builds in the system when one or more of the suction intake ports of the circulation system become obstructed . referring to fig6 a typical fluid circulation system of the type commonly found in swimming pools and hot tubs is shown . a reservoir of water w is contained within a structure having side walls 2 and a bottom 4 . a main drain 6 having a drain cover grating is provided on the bottom 4 . at least one skimmer box 8 is provided along one or more of the side walls 2 at the water surface level sl . a drain suction intake line 10 leads from the main drain 6 to a main suction intake line 20 . a skimmer suction intake line 12 has an open end 13 in the skimmer box 8 which is maintained below the water surface level sl . the skimmer suction intake line 12 feeds into the main intake line 20 . the main intake line 20 is directed to a pump 24 which may have a screen trap 26 connected to the main intake line 20 , just prior to the intake of the pump 24 . a main output line 28 leads to a filter 30 . one or more return lines 32 extend from the filter 30 back to the water reservoir w to return water that is circulated through the system back to the reservoir w . fig6 shows the fluid vacuum safety device 50 properly installed in - line along the main suction intake line 20 of the circulation system , prior to the intake of the pump 24 and screen trap 26 . if an object or person is caused to be sucked onto one of the open ends of the suction intakes , such as the open end 13 of the skimmer suction intake 12 , the drain plate 7 or , if the drain plate is removed , the drain suction intake line 10 at the main drain 6 , a vacuum will instantly develop throughout the intake lines , including the main suction intake line 20 . the fluid vacuum safety device 50 is designed to react to this situation to immediately eliminate the vacuum in the system and , accordingly , the suction force at the open ends of each of the suction intake lines , including the skimmer suction intake 13 and the main drain intake 6 . upon reaching a predetermined vacuum level , which happens quite rapidly when one of the intakes becomes obstructed , the fluid vacuum safety device 50 causes air from atmosphere to be rapidly introduced into the main intake line 20 and throughout the other intake lines , thereby removing all suction force at the open suction intake ends 13 and 16 in the reservoir w . the air introduced into the system interrupts the prime of the pump 24 , thereby eliminating any further source of suction . referring to fig1 - 5 , a first preferred embodiment of the present invention is shown . the principal components of the fluid vacuum safety device 50 are shown in fig1 and include a sensor circuit 120 which senses the vacuum level in the fluid circulation system . the output of sensor circuit 120 is applied to an analyzer circuit 130 that allows the selective setting of a particular vacuum level ( a predetermined vacuum level ) by control circuit 140 that will define a trip point or emergency condition in the system . the analyzer circuit output is applied to the control circuit 140 for further processing and control of operational relays or contactors 150 . an isolated power supply 160 furnishes voltage for the circuitry . the sensor circuit 120 is depicted in fig2 and utilizes a strain gauge 122 ( sg1 ) to sense the vacuum in the pump return line 20 . the four internal elements , r1 , r2 , r3 , and r4 , in the strain gauge 122 form a bridge circuit . at 0 &# 34 ; of mercury vacuum pressure , the bridge circuit 122 is balanced and the output of the bridge is 0 , with the junction of r1 / r3 being equal to the junction r2 / r4 . the output of the junctions are applied to the inputs of ic1 , an operational amplifier 124 . when the bridge is balanced , the output of the operational amplifier 124 is approximately one - half the power supply voltage . as vacuum increases , the bridge becomes unbalanced and the r1 / r3 and r2 / r4 junctions change voltage levels in a direct relationship to vacuum pressure level in the system . this small change in voltage is amplified by the operational amplifier 124 and provides a useable level for the analyzer circuit 130 . resistor r5 sets the minimum gain of the operational amplifier , while the adjustable resistor r6 sets the maximum gain . the ability to control gain is necessary due to the wide variations of vacuum levels found in different systems . in a preferred embodiment , the operational amplifier 124 is a type 741 ic . the analyzer circuit 130 , as shown in fig3 contains a resistor ladder network 132 composed of resistors r1 - r9 . both r1 and r9 are variable resistors . resistors r2 - r8 are all equal value resistors . in this manner , a high point and a low comparator point can be set via the r9 and r1 resistors , respectively , leaving six other equally valued comparator points between the high and low points . the voltages derived from this ladder network 132 are applied to the positive inputs of the comparator circuits 134 ( ic1 ) and 136 ( ic2 ). the output of the sensor circuit 120 is applied to the negative inputs of the comparators 134 , 136 . the normal output of the sensor circuit 120 is approximately one - half of the supply voltage . r9 is adjusted so that the positive input of comparator 136 is slightly above the steady state output of the sensor circuit 120 . under these conditions , the comparators are in the off state and their outputs are high . as vacuum is applied to the sensor circuit 120 , the output voltage will increase in a linear manner . the voltage increase is applied to the negative inputs of all eight comparator circuits of 134 and 136 . as the voltage increases , the first comparator at the junction of r8 and r9 will go into conduction . as the increase continues , each of the comparators will act in a like manner . if the voltage continues to increase to its design maximum , all eight comparator circuits will be conducting . any comparator that is conducting will have a low output . the comparators have an open collector output circuit and each is connected to the power supply 160 via an led 138 and series current limiting resistor 139 ( rp1 ). this condition will cause the led connected to each individual comparator to illuminate and indicate the level of vacuum reached . the output of each comparator is also connected to a spst switch contained in the switch bank 137 ( sw1 ). these switches each represent one of the eight comparator circuits . the switch that is connected to the comparator representing the preselected level of vacuum at which corrective action is desired is placed in the &# 34 ; on &# 34 ; position , and the output of the comparator is connected to the output line of the analyzer 130 . in this manner , an alarm condition will be achieved whenever the preset vacuum level is attained . the single switch that is selected as the trip level will always be illuminated since the led that corresponds to the selected level is connected to that switch and current will flow through the resistor contained in 139 , the led contained in 138 , the switch contained in 137 , and the input voltage clamp circuitry contained in the control circuitry 140 , described hereinafter . the sensor circuit 120 and the analyzer circuit 130 require a power supply voltage that is slightly higher than that required for the control circuitry 140 . this requires that the output of the analyzer circuit 130 be clamped at the maximum level of the input voltage allowed by the circuitry of the control circuit 140 . a clamp diode is utilized at the input of the control circuit 150 and completes the current path that allows the illumination of the selected switch on the switch bank 137 . referring to fig4 the control and relay circuitry 140 is shown , in accordance with the first preferred embodiment of the fluid vacuum safety device 50 . the input signal to the control circuitry 140 is the output of the analyzer circuit 130 and is applied to an inverter 141 to generate a true or high signal under an alarm or off - normal condition . the output of the inverter 141 is connected to a three input and gate 142 . the second input to this and gate 142 is the q &# 39 ; output of the service timer 143 . the service timer 143 is a 555 type timer and is set by the momentary activation of the service switch 144 . when this switch 144 is activated , the set input to timer 143 starts the timer cycle . this makes the q &# 39 ; output of the timer 143 false and applies a false to the and gate 142 . in this manner , any signal from the analyzer circuitry 130 is negated while in the service mode . when service is completed , the service person should momentarily activate the &# 34 ; service reset &# 34 ; switch 145 which will activate the timer 143 , reset circuitry , and restore normal conditions to the system . if the switch 145 is not pressed / activated , the timer 143 will time out and normal operation will be restored after a predetermined period of time . the third input to the and gate 142 is connected to another timer 146 which is also a 555 type timer . this particular timer 146 is started when power is turned on and applied to the device 50 . the q &# 39 ; output of this timer 146 holds off the and gate 142 for a short duration when the system initially starts in order to allow the pump of the fluid circulation system to reach prime . at the end of this duration , two of the and inputs are in a true state . this is a normal operation . if an alarm condition should be encountered , the alarm input to the and gate will go true . with all three inputs true , the output of the and gate 142 will go true and activate the set input to the latch 147 . the latch 147 remains in a set state until it is manually reset via the alarm reset switch 148 . when the latch 147 is set , the relay 149 is activated and the normally closed ( n / c ) contacts open . this drops the power to the contactor that allows the pump of the circulation system to run . at the same time , the normally open ( n / o ) contacts close and provide power to operate the vacuum breaker 170 ( see fig5 ) which will allow the release of any object held to the open ends of the intake lines ( return lines ) leading from the reservoir w to the pump 24 . once this happens , the pump 24 cannot be restarted until the alarm reset switch 148 is activated . it should be noted at this point that the device 50 can be configured with additional relay contacts to allow the use of various warning devices and indicators which are activated at the preset vacuum pressure level ( alarm condition ). referring to fig5 the device 50 , in accordance with the first preferred embodiment , is shown wired along with a vacuum breaker 170 to other components of a fluid circulation system . the diagram of fig5 is representative of a preferred configuration of components for use in the fluid circulation system of swimming pools and hot tubs . in fig5 the fluid vacuum safety device 50 is shown wired to the vacuum breaker 170 and other components . when the timer 180 of the system goes active , power is applied to the transformer 190 , which supplies low voltage ac to the safety device 50 . one side of the low voltage ac is also supplied to the contactor 200 and the vacuum breaker 170 . if conditions are normal , the low voltage ac circuit will be completed to the contactor 200 which will allow the motor 210 of the pump 24 to run . once the initial time period for pump start - up is complete , the safety device 50 monitors operating conditions . if an off - normal condition is encountered , the safety device 50 will break the circuit to the contactor 200 and complete the circuit to the vacuum breaker 170 , thereby introducing air from atmosphere into the suction intake lines ( return lines ) of the system and eliminating vacuum pressure between the pump 24 and open ends of the suction intake lines . this state will be maintained until the device 50 is manually reset after the off - normal condition has been cleared . with the incorporation of additional contacts , other indicators or warning devices can be added . referring now to the remaining drawing figures , the fluid vacuum safety device is shown in accordance with an alternative embodiment and is indicated as 50 &# 39 ;. the safety device 50 &# 39 ; includes a base unit 52 defined primarily by an inverted t - section formed of pvc having a main through passage 54 defined along the bottom of the inverted t and having opposite open ends 55 , 55 &# 39 ; which connect in - line to the main intake line 20 , as seen in fig6 . during normal operating conditions , water flow will travel in the direction of the arrow 56 in the through conduit 54 towards the pump 24 . the inverted t - section of the base unit 52 further includes an upwardly extending vent port 60 extending upwardly from the through passage 54 , in fluid communication therewith , to a top open end 62 . the top open end 62 is surrounded by an annular flange 64 having an o - ring seal 67 fitted to a top face 68 . a frangible membrane 70 rests on the o - ring 67 in covering relation to the open top 62 of the vent port 60 . the frangible membrane 70 may be provided with an increased thickness about its outer periphery , defining a surface engaging rim 72 . the central zone 74 within the surrounding rim 72 extends across and completely covers the open top 62 of the vent port 60 and is of a reduced thickness relative to the rim 72 . the frangible membrane 70 , and particularly the central zone 74 , may be formed of glass or other materials having shattering or disintegrating characteristics . the thickness of the central zone 74 of the frangible membrane 70 will vary depending upon both the desired predetermined negative pressure at which the frangible membrane is caused to implode and disintegrate , as well as the diameter of the opening 62 which the central zone 74 covers and the material characteristics of the membrane . nonetheless , the central zone 74 is thin ( in most instances less than 1 / 8 &# 34 ; thick ) and will implode and disintegrate in response to the suction force ( indicated by the arrow 76 ) as occurs when one or more suction intakes become obstructed . the ideal vacuum pressure at which the frangible membrane 70 disintegrates is approximately 20 in . hg . when the frangible membrane 70 is caused to disintegrate , as a result of the suction force of the vacuum condition in the through passage 54 and vent port 60 , air from atmosphere is able to quickly enter through the open top 72 to fill the intake lines of the fluid circulation system , thereby eliminating the vacuum . the frangible membrane 70 is maintained in place , in covering relation to the open end 62 , by a fitting 80 having a lower annular face 82 which opposes the flange 64 , sandwiching the rim 72 of the frangible membrane 70 therebetween , as seen in fig7 . the o - ring 67 absorbs pressure to prevent the frangible membrane 70 from cracking as the fitting 80 is advanced towards the flange 64 and against the rim 72 of the frangible membrane 70 . a female coupling 84 is provided to facilitate attachment of the fitting 80 to the base unit 52 , enabling threaded advancement and withdrawal of the fitting 80 relative to the flange 64 and frangible membrane 70 . threads 85 about the outer periphery of the fitting 80 intermesh with corresponding threads 86 on the inner face of the female coupling 84 . an inwardly directed flange 87 on the lower open end of the female coupling 84 engages the underside of the flange 64 of the vent port . the fitting 80 further includes a flat ledge 88 which proceeds inward to a reduced diameter extension 89 . the fitting 80 is open at both the opposite ends and has a larger diameter between the annular face 82 compared to a top open end 90 . the ledge 88 on the fitting 80 is provided with a plurality of air inlet holes 94 which extend from the top ledge 88 through the thickness of the fitting 80 to provide air flow communication between the exterior atmosphere and an inner chamber 96 above the frangible membrane 70 . once the frangible membrane 70 disintegrates , air from atmosphere enters through the air inlet holes 94 and through the top opening 62 of the vent port 60 and throughout the suction intake lines of the system to eliminate the vacuum . an electrical switching device 100 can be fitted to the fluid vacuum safety coupling 50 , as shown in fig7 and 9 . to facilitate attachment of the electrical switching device 100 , a female coupling 102 can be fitted to the device 100 for threaded engagement with an exterior threaded surface 91 on the reduced diameter extension 89 of the fitting 80 . the bottom portion of the electrical switching device 100 has a sensing assembly 104 which extends through the open end 90 of the fitting 80 . the sensor assembly 104 may be provided with a plunger or rod 106 which extends downwardly so that a distal end thereof engages a top surface of the frangible membrane 70 . a biasing element within the device 100 may be used to urge the plunger 106 downwardly against the frangible membrane 70 . this plunger 106 serves as an indicator to the electrical switching device 100 , indicating the status of the frangible membrane 70 . disintegration of the frangible membrane 70 results in further downward extension of the plunger 106 , thereby activating the electrical switching device 100 . the electrical switching device 100 may trigger an audible alarm housed within the device 100 and / or at a remote location via a hard wired or wireless connection . the electrical switching device 100 can further be used to shut off the pump 24 . still further , the electrical switching device 100 can be used to activate virtually any electronic component to perform a desired function once the frangible membrane 70 is shattered . while the instant invention has been shown and described in accordance with preferred embodiments thereof , representing a best mode of the invention at the time of filing of the application for patent , it is recognized that variations , modifications and changes may be made to the instant disclosure without departing from the spirit and scope of the invention , as set forth in the following claims and within the doctrine of equivalents .
a safety device for use in a fluid transfer system for a swimming pool or similiar application , having a pump which draws water from a reservoir through one or more intake lines each extending from an open end at the reservoir to the pump intake . the device analyzes negative pressure levels in the system and , upon detecting a negative pressure level being outside of a selected operational range , the device deactivates the pump and triggers a vacuum breaker device to eliminate negative pressure in the system , by introducing air from atmosphere into the intake lines thereby removing suction at the open ends of the intake lines . the safety device may further activate warning devices including audible and visible alarms to indicate that the system has been deactivated .