Gas leak sensor system

A gas leak sensor system detects the presence of gas leaking into any one of a plurality of test spaces for example, refrigeration gas into a refrigeration case. A plurality of tubes extend from each of the test spaces to a sensor location whereat a selector valve is connected to each tube. A controller actuates the selector valves to select tubes in a particular order and a vacuum source draws air and any leaking gas through a selected tube and through a gas sensor to activate an alarm. The gas sensor is purged at least each time a leaking gas has been sensed.

BACKGROUND OF THE INVENTION 
Supermarkets and warehouses have many isolated refrigeration coils where 
potential leaks can occur. Individual sensing devices at each location 
would be cost prohibitive. U.S. Pat. No. 3,357,257 discloses the concept 
of a plurality of test spaces with tubing leading from the test spaces 
through valves to a single gas sensor, but no means for purging the system 
is disclosed. 
SUMMARY OF THE INVENTION 
A gas leak sensor system detects the presence of gas leaking into any one 
of a plurality of test spaces and includes a plurality of tubes extending 
f rom each of the test spaces to a sensor location. Selector valve means 
are connected to each tube and a gas sensor has an alarm. Control means is 
connected to actuate the selector valve means to select tubes in a 
particular order, means is connected to the selector valve means to draw 
air and any leaking gas through the selected tube and through the gas 
sensor, and means to purge said gas sensor at least when leaking gas has 
been sensed. Accordingly, a gas leak sensor system is disclosed which can 
sense a plurality of test spaces with a means to purge the gas sensor 
after the sensing of leaking gas. 
Another object of the invention is to provide a purging means which uses 
outside air from a location separate from the discharge from said gas 
sensor. 
Other objects and a fuller understanding of the invention may be had by 
referring to the following description and claims, taken in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a gas leak sensor system 10 embodying the invention. 
This sensor system detects the presence of any gas leaking from a 
plurality of test spaces 11-16, respectively. These may be confined spaces 
such as a refrigeration case with a refrigeration coil 17 therein and with 
some means to direct air over the coil 17 as shown in FIG. 1. A plurality 
of tubes 18 extend from each of the test spaces to a sensor location which 
is preferably at a central location. A leaking gas sensor 19 is at this 
sensor location and is designed to detect the presence of any leaking gas. 
In this particular embodiment this would be a refrigerant gas such as one 
of the freon gases. The gas sensor 19 has an alarm 20, which may be 
visible or audible or both. A controller 22 controls a group of selector 
valves 24. In this embodiment these may be solenoid actuated valves all 
connected to a manifold 25. One group of valves 26 is connected one each 
in each of the tubes 18 leading to the test spaces. These valves are 
preferably at the sensor location. Valves 27, 28, and 29 are connected 
between the manifold and a first gas source 31, a second gas source 32, 
and a gas tank 33, respectively. Each of these sources and the gas tank 
are sources of the same gas which the sensor 19 tests for leaks. A vacuum 
pump 30 is a means connected to draw air out of the sensor 19 and to eject 
it to outside air at a first location 34. A conduit 35 leads from the 
manifold 25 through a three-way valve 36 and a conduit 37 to the gas 
sensor 19. A vacuum gauge 38 is connected to the conduit 37. A conduit 39 
connects an input of the three-way valve 36 with another three-way valve 
40 to which a nitrogen tank 41 is connected as well as a purge air input 
from the outside air at 42 which is at a second location remote from the 
first location 34 so that there is no mixing of air outlet from the vacuum 
pump with the purge air input. 
FIG. 2 shows the construction of the tubes such as tube 18 as it terminates 
at one of the test spaces 11-16. The small diameter tube may be a flexible 
plastic tube, e.g. 1/4" diameter, but at the termination end shown in FIG. 
2 the tube is enlarged to perhaps 5/8" diameter for the terminal end 21. 
In operation, the circuit of FIG. 1 is controlled by the controller 22, 
which preferably is a central processing unit or CPU to control the 
various valves of the selector valve means 24. The vacuum pump 30 draws 
air from the test spaces 11-16 which in this example is a refrigerated 
coil environment which may be subject to leaks of the refrigerant gas. The 
vacuum pump draws air through the gas sensor 19 and exhausts this air to 
the outside at the first location 34. After the first test space 11 has 
been tested, then the controller controls the three-way valve 33 so that 
purge air is drawn in from the second outside location 42 to purge the 
sensor of any remaining gas therein. The next selected test space is 
chosen by opening the proper valve 26 and this might be the test space 12. 
The vacuum pump draws the air from this test space through the gas sensor 
to determine if there is any gas leaking in this test space 12. Next, 
again, the three-way valve 36 is actuated to draw purge air through the 
gas sensor. This purging occurs each time a different tube is selected and 
whenever the sensor detects refrigerant. If refrigerant gas is detected, 
then the gas sensor is purged with air and that same test space is again 
tested before the alarm 20 is activated. This helps eliminate false 
readings and to make sure that a leak is detected in the correct tube. 
When for some strange reason freon is sensed from the outside air source, 
a special alarm sounds and the system shuts down. In this case the system 
10 can shift to and sample an inert gas such as nitrogen from the tank 41 
by activating the three-way valve 40. An alarm will also sound when the 
tank pressure is too low to provide sufficient purging gas. 
When the system is first started, the vacuum pump 30 is activated and 
monitored for correct amount of the vacuum. If the vacuum is not correct, 
the system alarms and shuts down or an alternate vacuum source is 
selected. If vacuum is correct, the system samples the first outside gas 
source 31 and verifies correct operation. If not correct, the alternate 
second source 32 is sampled. If this is still not correct, the compressed 
tank source 33 is sampled and verified. If verification is o.k., the 
system continues in operation, but an alarm is registered that this source 
is being used as it is exhaustible. 
Next the port selection solenoid valves 26 are activated in a given order 
and each monitored port is selected and sampled for a period of time. If 
the port is free from contaminated gas, the next port is sequentially 
selected until all ports are selected in turn. After each port is sampled, 
or after each port is sampled which has a gas leak detected, the purge gas 
is selected to cleanse the sensor to insure that the new port selected 
starts out with a cleanly purged sensor to help eliminate spurious 
readings. Should a port indicate that it has contaminated gas present, 
then the control system stays at that particular port, shuts off that 
port, and then selects the purge port to cleanse the sensor. The system 
then tries the contaminated port again and if the level of gas is still 
above alarming conditions, the system then sends out its alarm to alert 
personnel of a gas leak. The system shuts off that port, purges the 
sensor, and then selects the next sequential port. It may be the case that 
several refrigeration coils or refrigeration cases could be connected in 
series together sharing the same environment so that several alarms could 
come from a single refrigerant leak. 
As shown in FIG. 2 the terminal end of each tube at the test space is 
enlarged and this prevents frost from plugging the end of the 1/4" tubing, 
without need for use of a heater. This enlarged terminal area collects the 
frost until the refrigerated coil goes through a defrost cycle. Should the 
end of the tube plug up for whatever reason, then the vacuum gauge 38 in 
the circuit registers too much of a vacuum and alarms the circuit of an 
indication that the tube is not sampling the monitored air. Also the gauge 
38 can be set for the opposite of that condition which would be an open or 
cut tube. By having the manifold at a central location, this can establish 
substantially equal vacuum amounts for each test space so that they all 
read approximately the same amount of vacuum. Then when a portion of the 
tube resistance is missing, the vacuum gauge notes the difference in 
resistance and alarms the circuit. 
The controller 22 has a timer so that once every 24 hours a calibrated leak 
from the first source 31 or gas tank 33 is sampled. If the systems 
responds properly to the calibrated leak, the normal sequence of operation 
continues. Should the sensor system 10 not respond to this leak, the 
system shuts down and alarms. 
FIG. 3 illustrates a type of gatling gun rotary valve 44 with a plurality 
of tubes 45 leading to the various test spaces 11-16. A purge air inlet 
manifold 46 is connected to alternate ones of the conduits around the 
periphery of the rotary valve 44. The center 48 of the gas valve leads to 
the gas sensor 19. This therefore becomes the selector valve means in 
place of the selector valve means 24 of FIG. 1. In use, the selector valve 
44 rotates in one direction to test each test space in sequence with the 
gas sensor 19 being purged of any contaminated gas in between each testing 
of a test space. 
FIG. 4 is a similar system with a rotary selector switch 50. A rotary arm 
54 can rotate among a plurality of contacts 51. Alternate ones of these 
contacts go to individual solenoid actuated valves 52 which select 
individual conduits going to the different test spaces 11-16. Alternate 
ones of these contacts 51 lead to a common conductor 55 which energizes a 
purge valve 53. Again the rotation of the selector arm 54 in a given 
direction will individually test the various test spaces 11-16 with 
purging between each testing of a test space. 
The present disclosure includes that contained in the appended claims, as 
well as that of the forgoing description. Although this invention has been 
described in its preferred form with a certain degree of particularity, it 
is understood that the present disclosure of the preferred form has been 
made only by way of example and that numerous changes in the details of 
construction and the combination and arrangement of parts may be resorted 
to without departing from the spirit and the scope of the invention as 
hereinafter claimed.