Pressure switch having internal vent chamber

Layers of a thin, electrically insulating material are bonded together to form a switch. The bottom layer of the switch has electrically conductive areas aligned with openings through a second layer. A third layer has a pattern of spaced lines of an electrical conductor positioned over the openings in the second layer. Fluid pressure applied to the bottom layer causes flexing of the bottom layer toward the third layer to bring the electrically conductive areas into contact with the pattern of conductive lines on the third layer, thereby closing the switch. A vent chamber in the second layer is pneumatically coupled to the openings in the second layer so that when the switch is closed air in the openings in the second layer can be vented to the vent chamber. The switch can be used to sense changes in fluid pressure in a water system, for example.

BACKGROUND OF THE INVENTION 
This invention relates to flexible, pressure activated switches and, in 
particular, to such a switch which is especially suitable for use in water 
or other fluid systems where pressure of the fluid activates the switch. 
A pressure actuated switch is disclosed in commonly assigned U.S. patent 
application Ser. No. 176,538, filed Apr. 1, 1988 in the name of Henry L. 
West, and entitled "Fluid Pressure Switch Having Venting Means for 
Dispensing Back Pressure". The switch disclosed in such application 
comprises a plurality of layers bonded together to form a unitary switch. 
Two layers have electrically conductive elements thereon that are 
separated by another layer having openings aligned with the conductive 
elements so that pressure exerted against the switch surface deflects the 
layers to bring the electrically conductive elements into contact, thereby 
closing the switch. In order to avoid undesirable pressure increases in 
the openings when the switch is closed, the openings are vented through 
the top of the switch into large, closed chambers in a back-up plate so 
that closing the switch results in only nominal increase in the fluid 
pressure. In order to avoid leakage of water or other contaminants into 
the switch, the vent chamber in the back-up plate is surrounded by an 
O-ring which bears against the switch to seal the connection therebetween. 
The electrical conductors in the switch are either dome-shaped elements or 
comprise a strip of smooth stainless steel. 
While the switch disclosed in the aforementioned application has generally 
worked satisfactorily, it appears that improvements can enhance the long 
term performance of the switch. For example, when used with a water or 
other liquid system, the liquid sometimes enters the vent openings even 
though they are firmly sealed by O-rings in the back-up plate. When this 
occurs, the switch is shorted out and fails. Also, the O-ring used between 
the switch and back-up plate, together with an O-ring on the opposite side 
of the switch, may deform the switch over a period of time, thus degrading 
its performance. Also, in one embodiment disclosed in the prior switch, 
the circular domes used for the electrical contacts contain sharp edges 
that can cut into the adjacent plastic material of the switch. This 
problem is avoided in another embodiment of the switch which uses a smooth 
strip of steel or other conductive material in place of the domes. 
However, even the steel strips can deteriorate over a period of time under 
extended exposure to water at pressures of, for example, 100 psi, until 
the trip pressure changes significantly. This problem is believed to be 
caused by creep of the adhesive between the steel layer and the adjacent 
plastic layers. Also, failure of the adhesive bonding the various layers 
together can result in leakage of water or other fluids into the switch to 
cause shorting or other defects in the switch. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to eliminate the need 
to vent air outside the switch when the switch is actuated. 
Another object of the invention is to provide an improved thin, flexible 
switch which eliminates the need for O-rings on both sides of the switch, 
and thus avoid excessive deformation of the switch that O-rings can 
produce. 
A further object of the invention is to provide a thin, flexible switch 
which eliminates the need for electrical contacts in the form of domes, 
which are difficult to position and tend to cut into the adjacent plastic 
of the switch, or continuous sheets of metal which are difficult to bond 
to plastic layers due to creep in the adhesive used for bonding them. 
The present invention relates to a switch adapted to be closed in response 
to pressure exerted on the switch. The switch comprises a plurality of 
thin layers of an electrically insulating material. A first one of the 
layers has on one surface an area of an electrically conductive material. 
A second one of the layers is in contact with the surface of the first 
layer, and has an opening therethrough aligned with the area of conductive 
material on the first layer. A third one of the layers is in contact with 
the second layer. The third layer has on the surface facing the second 
layer an area of an electrically conductive material aligned with the 
opening in the second layer. The layers are sufficiently flexible to 
enable the areas of electrically conductive material to be brought into 
engagement by pressure exerted on the switch. Means communicating with the 
opening defines an internal vent chamber for reducing air pressure build 
up in the opening when the areas of electrically conductive material are 
brought into contact. The vent chamber is fully enclosed within the 
layers. 
The invention, and its objects and advantages, will become more apparent in 
the detailed description of the preferred embodiment presented below.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIGS. 1 and 2, a switch of the present invention is 
generally designated 10 and comprises four layers 12, 14, 16 and 18. Each 
of the layers 12-18 preferably is made of an electrically insulating 
material that is relatively thin and flexible so that the individual 
layers and the switch when assembled is flexible and responsive to fluid 
under pressure to operate the switch. 
The layers have generally rectangular portions 12a, 14a, 16a and 18a of 
substantially the same size to provide a generally rectangular switch. 
Each layer also has a circular hole therethrough, as shown at 20a, 20b, 
20c, and 20d, to provide a through hole 20, FIG. 2. As explained layer, 
hole 20 is used for mounting the switch on a housing or other piece of an 
apparatus. 
Layer 12, shown at the bottom in FIGS. 1 and 2, comprises the side of the 
switch that receives the fluid pressure when the switch is used in a fluid 
system as explained later. Layer 12 has two spaced electrically conductive 
areas 22, 24 formed on the upper surface of the layer and generally 
equally spaced from the hole 20a. As illustrated in FIG. 1, the areas 22, 
24 are circular in configuration and can be applied to the layer 1 by a 
printing technique using a substance sometimes referred to as "silver 
ink". 
Layer 14 has a pair of circular openings 26, 28 that extend entirely 
through the layer. Openings 26, 28 comprise contact chambers and are 
aligned with the conductive areas 22, 24 on layer 12. Openings 26, 28 
preferably are slightly larger in diameter than the areas 22, 24. In 
addition, layer 14 has a third opening 30 that extends entirely through 
layer 14 and is offset to the side from openings 26, 28. A slot-like 
passage 32 connects openings 26 and 30, and a similar slot-like passage 34 
connects openings 26 and 28. Preferably these passages extend entirely 
through the layer 14. Opening 30 comprises an internal vent chamber and 
provides a space for air from openings 26, 28 when the conductive areas 
22, 24 are forced upwardly into openings 26, 28 as explained in more 
detail later. Passages 32, 34 provide pneumatic coupling between the vent 
chamber and the openings 26, 28. 
Layer 16 is positioned directly over layer 14. Layer 16 has on its surface 
facing layer 14 a pattern of an electrical conductor which, when engaged 
by conductive areas 22, 24 on layer 12 will complete electrical circuits. 
More specifically, the pattern of electrical conductor on layer 16 is 
illustrated as comprising three spaced conductive lines 36, 38 and 40. A 
portion of line 36 is positioned over the opening 28 in layer 14 and 
conductive area 24 of layer 12. A portion of line 40 is positioned over 
opening 26 in layer 14 and the conductive area 22 in layer 12. Line 38 is 
common to both openings 26, 28, i.e. a portion of line 38 is positioned 
over both opening 26 and conductive area 22, and over opening 28 and 
conductive area 24. Thus, when conductive area 22 is flexed upwardly in 
the switch it can contact a portion of both lines 38 and 40 to complete an 
electrical circuit therebetween. Similarly, when conductive area 24 is 
flexed upwardly, it can contact a portion of conductive lines 36, 38 to 
complete an electrical circuit therebetween. Lines 36, 38 and 40 extend 
into a leg or handle portion 42 of layer 16 and terminate at three rigid 
electrical pin connections 44, 46 and 48, respectively. The pins can be 
plugged into a suitable receptacle for connecting the switch in an 
electrical circuit. 
Layer 18 fits over layer 16. It has no conductive lines on it. Layer 18 
closes and protects the top portion of the switch when it is mounted in 
apparatus as described below. 
FIG. 3 of the drawings illustrates a typical installation of a switch 10 
between a housing 50 and a backup plate 52. Housing 50 has a generally 
flat surface 54 with a threaded opening 56. Backup plate 52 also has a 
cylindrical hole 58 therein that is substantially the same diameter as the 
hole 20 in the switch. The upper end of hole 58 is enlarged as shown at 60 
to form a shoulder 62. A mounting screw 64 has a threaded end that passes 
through the holes 58 and 20 in the plate 52 and switch 10, respectively, 
and is threaded into the hole 56 in the housing 50. Screw 64 also has a 
head 65 that is larger than hole 58 and engages the shoulder 62 to hold 
the backup plate and thus switch 10 firmly against the housing 50. 
A passageway 66 in the housing 50 terminates at its upper end in an 
enlarged opening 68 at the surface 54 of the housing. An O-ring 70 is 
seated in the enlarged opening 68 around the passageway 60 and bears 
against the lower surface of switch 10 to seal the connection between the 
housing 50 and the switch 10. The opening 68 lies directly beneath the 
portion of layer 12 that contains the electrically conductive area 22. 
Similarly, another passageway 72 in housing 50 terminates at its upper end 
in an enlarged opening 74 that is at the surface 54 of the housing. An 
O-ring 76 is seated in the opening 74 and bears against the lower surface 
of layer 12 of the switch to seal the connection therebetween. Opening 74 
is located directly below the portion of layer 12 that contains the 
electrically conductive area 24. 
In operation, passageways 66 and 72 are connected to two sources of fluid 
under pressure, such as water, in a drinking water system. Fluid can pass 
through passageways 66, 72 and enter the respective openings 68, 74 and 
into contact with the lower surface of layer 12 of the switch. Water will 
not damage the switch because the switch is made of a plastic material 
that is not adversely effected by exposure to water, and because there is 
nothing on the lower surface of the switch which would produce an 
electrical short or otherwise deteriorate operation of the switch. When 
the fluid in passageways 66, 72 reaches a predetermined high value, the 
fluid pressure acting on the lower surface of switch 10 moves the 
electrically conductive areas 22 or 24 on layer 12 upwardly into contact 
with the conductive lines 36, 38, 42 on layer 16, thereby closing the 
switch. More specifically, pressure in passageway 66 can effect closing of 
the switch to establish flow of electric current between conductive lines 
38, 40, while pressure in passageway 72 can close an electric circuit 
between lines 36, 38. 
Layers 12-18 are very thin. Thus there is very little space in openings 26, 
28. When conductive areas 22, 24 are forced upwardly into the openings 26, 
28, air within such openings would ordinarily be highly compressed since 
the conductive areas substantially fill the openings 26, 28. However, by 
virtue of the vent chamber 30 and its connection to openings 26, 28 by 
means of the slot-like passages 32, 34, the air forced out of openings 26, 
28 by the conductive areas 22, 24 is allowed to vent into chamber 30. 
Moreover, if only conductive area 22 is moved into opening 26 while area 
24 remains in its normal undeflected position as shown in FIG. 2, air in 
opening 26 also can be forced into opening 28 to thereby further provide 
venting and undesirable pressure build up in layer 14. 
The vent chamber is completely within the switch. This internal venting is 
quite desirable and avoids the possibility of water or other fluids 
entering the switch through a vent hole extending outside the switch, such 
as disclosed in the beforementioned copending patent application. If no 
vent chamber is provided, it is possible that air under pressure in 
openings 26, 28 caused by closing of the switch could leak out of the 
switch, especially under sustained high pressure in passageways 66 and 72. 
This could produce a partial vacuum in openings 26, 28 when the pressure 
in passageways 66, 72 is relieved. Any such partial vacuum would create a 
condition which could hold the contacts closed after pressure was relieved 
in passageways 66 and 72. 
The switch as described herein is responsive to pressure in two passageways 
66, 72. However, by changing the electrically conductive patterns on the 
layers and the number of openings therebetween, one or more pair of switch 
contacts can be provided and used with one or more sources of fluid under 
pressure. 
The various layers of the switch are bonded together with an adhesive. 
Preferably the adhesive used is a water system adhesive when the switch is 
to be used in a water-proof environment as described herein. The material 
used for forming the layers can be any suitable type, a polyester plastic 
having been found desirable for this use. 
As mentioned earlier, the switch disclosed in the copening application can 
become distorted due to two O-rings of different sizes being on opposite 
sides of the switch. With the present design, only O-rings 70 and 76 on 
the lower side of the switch are needed in order to effect a satisfacfory 
seal. Thus the present invention eliminates the distortion problem which 
may occur with the earlier design. In addition, the backup plate for the 
switch disclosed in the beforementioned copending application requires 
grooves and other formations in it in order to accommodate O-rings. The 
backup plate 52 of the present invention is preferably flat, having a 
planar lower surface in contact with switch 10, thus reducing the cost and 
simplifying the manufacture of the backup plate. The present invention 
also eliminates domes and stainless steel strips disclosed in the prior 
application, and thus avoids potential problems associated therewith. 
While the invention has been described in connection with a preferred 
embodiment thereof, it will understood that various modifications and 
changes can be effected within the spirit and scope of the appended claims 
.