Liquid level switch assembly

A liquid level switch assembly is provided which can be adjusted as to what liquid level will actuate the switch. A support bracket is mountable to the tank and a float arm is pivotally mounted to the support bracket inside the tank by way of a pivot axle. A magnet is mounted to the pivot axle such that the magnet rotates as the float arm pivots to follow the liquid level on the tank but such that the angular position of the poles of the magnet can be adjusted relative to the float arm when the float arm is retained as the magnet is rotated. A reed switch is mounted on the support bracket near the magnet such that when the float arm is in a predetermined range of angular position relative to the horizontal, the reed switch is actuated by the magnet.

TECHNICAL FIELD OF THE INVENTION 
The present invention relates to a liquid level switch assembly with a 
magnetic switch that is actuated when a float arm pivotally connected to a 
stationary arm pivots to a predetermined angular position relative to the 
stationary arm as a result of the liquid level in the tank. In one aspect, 
the present invention relates to such a switch assembly wherein the 
angular position of the float arm relative to the stationary arm at which 
the magnetic switch is actuated can be readily adjusted. 
BACKGROUND OF THE INVENTION 
Tanks are commonly equipped with a liquid level switch assembly having a 
float arm pivotally connected to a stationary arm which is mounted to the 
tank. The entire float arm can be buoyant or a float can be attached to 
the float arm at some point. The float arm pivots in response to 
fluctuations in the liquid level in the tank. Some switch assemblies of 
this type have a magnet fixed to one arm and a magnetically actuated 
switch fixed to the other such that when the float arm has pivoted to a 
predetermined angular position relative to the stationary arm, the magnet 
will actuate the magnetic switch. Such a switch assembly is shown in U.S. 
Pat. No. 4,513,185. 
A significant drawback of this type of switch assembly is that the angular 
position of the float arm relative to the stationary arm at which the 
magnet actuates the switch is not adjustable. Such non-adjustable switches 
are severely limited in their ability to be adapted to different 
applications such as different size tanks or different liquid levels at 
which it is desired for the switch to be actuated. For example, the design 
of a switch assembly developed to be actuated by a low liquid level of two 
inches in a two foot deep tank will minimally contain the following 
elements: 1) the length of the stationary arm; 2) the mounting position of 
the stationary arm on the tank; 3) the length of the float arm; and 4) the 
position of the float arm relative to the stationary arm at which the 
magnet will actuate the switch. However, if the liquid level at which the 
switch is desired to be actuated is changed from two inches to five 
inches, or if some of the tanks are two and a half feet deep instead of 
two feet, the design developed for the two inch, two foot application can 
not be readily adapted for these new applications. In order to provide a 
switch for the new applications, one or more of the four basic elements of 
the design will have to be changed. However, changing the lengths of the 
arms or the position of the switch assembly on the tank can involve 
repeated expensive design, component, manufacturing and/or installation 
changes for each new application that is encountered. 
Thus, a need exists for a switch assembly which can be readily adapted for 
a wide range of applications without having to change the size of its 
components or its position on the tank. The present invention provides for 
a switch assembly in which the angular position of the float arm relative 
to the stationary arm at which the magnetic switch is actuated is readily 
adjustable, thus allowing the present invention to be readily adapted to a 
wide range of applications without having to change its structure or its 
position on the tank. 
The advantages of the present invention include the ability to develop a 
switch assembly that can be easily adjusted for use in a wide range of 
applications instead of having to change the design, structure and/or 
installation of the switch assembly for each different application. 
Additionally, such an adjustable switch assembly greatly simplifies the 
manufacture of several assemblies in that the same components and 
manufacturing procedures will be used for each assembly and do not nave to 
be repeatedly altered to make a different switch assembly for each 
different application. 
SUMMARY OF THE INVENTION 
The present invention provides a liquid level switch assembly adapted for 
attachment to a tank. In one aspect of the present invention, the switch 
assembly comprises a support bracket with one end adapted for attachment 
to the tank and another end for extending into the interior of the tank. A 
pivot axle is rotatably mounted to the support bracket inside the tank, 
and a float arm extends from the pivot axle in a direction nonparallel to 
the rotational axis of the pivot axle. At least part of the float arm is 
buoyant, and the float arm is pivotable about the rotational axis of the 
pivot axle. A magnet is mounted on the pivot axle so as to rotate about 
the rotational axis of the pivot axle as the float arm pivots. The magnet 
is also adjustable about the rotational axis of the pivot axle so that the 
angular position of the magnetic poles of the magnet with respect to the 
float arm can be adjusted. A magnetically actuated contact is attached to 
the support bracket and positioned relative to the magnet such that when 
the float arm is within a predetermined range of angular position relative 
to the support bracket, the magnet actuates the contact. 
A further aspect of the present invention provides a switch assembly as 
just described but further comprising a carrier ring that is snugly fit 
concentrically around part of the pivot axle such that rotation of the 
pivot axle rotates the carrier ring but such that the ring can be rotated 
relative to the pivot axle when the pivot axle is retained as the ring is 
rotated. Furthermore, the magnet is fixed to the ring such that adjustment 
of the ring relative to the pivot axle adjusts the angular position of the 
poles of the magnet relative to the float arm. 
Another aspect of the present invention provides a switch assembly where 
the angular position of the switch, instead of the magnet, is adjustable. 
Thus, the angular position of the float arm relative to the support 
bracket at which the switch is actuated is readily adjustable by adjusting 
the position of the switch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIGS. 1 and 2, the preferred embodiment of the switch 
assembly of the present invention is shown. Like numbers refer to 
corresponding parts in different figures. Switch assembly 10 is mounted to 
tank 12 to respond to a predetermined range of liquid level in tank 12. 
Switch assembly 10 comprises a support bracket 14 with a first end 16 
adapted for attachment to tank 12. First end 16 comprises a mounting plate 
18 with mounting holes 20 through which fasteners, for example screws or 
rivets, can be placed to attach mounting plate 18 to tank 12. It should be 
understood that first end 16 can be adapted for any tank and FIGS. 1 and 2 
show a preferred structure of first end 16 for a specific application. 
Support bracket 14 has second end 22 which communicates with the interior 
of the tank. 
With additional reference to FIG. 3, second end 22 comprises a portion of 
support bracket 14 and housing 24 mounted thereto with rivets 26. Housing 
24 has hub portion 28 defining a hole 30 opposite hole 32 in support 
bracket 14. Housing 24 has an open side 34 indicated on FIGS. 1 and 2. 
With additional reference to FIG. 4, pivot axle 40 is rotatably mounted in 
second end 22. Pivot axle 40 has a first end 41 disposed through hole 30 
and second end 42 disposed through hole 32. Pivot axle 40 has a block 
portion 46 that has passageway 48 extending therethrough. Block portion 46 
has outer periphery 50 in a hexagonal shape to provide flat surfaces 52 so 
that outer periphery 50 can be engaged by a wrench about two opposing flat 
surfaces 52 thus providing an adjustment means. Block portion 46 has a 
first lateral surface 54 facing towards first end 41 of pivot axle 40 and 
second lateral surface 56 facing towards second end 42 of pivot axle 40. 
Float arm 60 extends from pivot axle 50 in a direction non-parallel to the 
rotational axis of pivot axle 40. Preferably, float arm 60 is 
perpendicular to the rotational axis of pivot axle 40, but certain 
applications may dictate that float arm extend obliquely from the 
rotational axis. Float arm 60 has a proximal end 64 at pivot axle 40 and a 
distal end 68 with the float 72 attached thereto. Float arm 60 is 
pivotable about the rotational axis of pivot axle 40. Proximal end 64 is 
inserted into passageway 48 of block portion 46. Proximal end 64 can be 
retained in passageway 48 by any suitable means. In the preferred 
embodiment, block portion 46 is crimped around proximal end 64. A crimping 
device can be placed about two opposing flat surfaces 52 to crimp block 
portion 46 around proximal end 64. If desired, the float arm and pivot 
axle may be made of a single piece. 
In an alternative embodiment shown in FIGS. 5A and 5B, pivot axle 40' and 
proximal end 64' of float arm 60' are of a one piece T-shape construction. 
Second end 22' of support bracket 14' comprises a pin 36 fixed at one end 
to housing 24' and at the other end to support bracket 14'. Pivot axle 40' 
is generally annular and is rotatably mounted about pin 36. 
Float 72 rises and falls with the liquid level in tank 12 by swinging 
arcuately up and down about the rotational axis of pivot axle 40. The 
length and configuration of float arm 60 as well as the size and type of 
float 72 are a matter of the parameters of a specific application, for 
example, size of tank, placement of switch assembly, type of liquid, etc. 
Carrier ring 100 is snugly fit concentrically around part of pivot axle 40. 
Inside surface 112 of carrier ring 100 is frictionally engaged with 
outside surface 44 of pivot axle 40 such that carrier ring 100 moves with 
pivot axle 40 but such that carrier ring 100 can be rotated relative to 
pivot axle 40 if pivot axle 40 is restrained from rotation as carrier ring 
100 is rotated. Carrier ring 100 comprises sleeve 104 with flange 106. 
Flange 106 has outer periphery 108 in a hexagonal shape to provide flat 
surfaces 110 so that outer periphery 108 can be engaged by a wrench about 
two opposing flat surfaces 110. To rotationally adjust the carrier ring 
100 with respect to pivot axle 40, float arm 60 can be retained stationary 
while a wrench is engaged about outer periphery 108 of flange 106 and 
turned to overcome the frictional engagement between inside surface 112 of 
carrier ring 100 and outside surface 44 of pivot axle 40 to rotate carrier 
ring 100 about the rotational axis of pivot axle 40. Flange 106 has first 
lateral side 116 facing first end 41 of pivot axle 40 and second lateral 
side 118 facing first lateral side 54 of block portion 46 of pivot axle 
40. 
Carrier ring 100 is preferably brass and is pressed over first end 41 of 
pivot axle 40. First end 41 can then be deformed to raise a radial ridge 
58 and retaining washer 122 is placed between radial ridge 58 and the end 
of sleeve 104. 
Magnet 80 is fixed to carrier ring 100. Magnet 80 is preferably of a 
generally disc shape and has hole 82 through which sleeve 104 is inserted. 
Magnets of other shapes may be used. Hole 82 can be sized such that the 
inside of hole 82 frictionally engages with outside surface 114 of sleeve 
104. Magnet 80 has first side 84 which is abutted against first lateral 
side 116 of flange 106 and second side 86 facing away from flange 106. 
Adhesive material 120 can be placed between first side 84 and first 
lateral side 116 to contribute to the attachment of magnet 80 to carrier 
ring 100. As carrier ring 100 is rotated, whether it be with pivot axle 40 
or relative to the pivot axle 40 during adjustment, magnet 80 rotates with 
carrier ring 100. 
The present invention can be practiced without carrier ring 100. FIG. 6 
shows an alternative embodiment where magnet 80' has hole 82 sized so that 
pivot axle 40" fits snugly therethrough in frictional engagement such that 
magnet 80' moves with pivot axle 40" but such that magnet 80' can be 
rotated relative to pivot axle 40" if pivot axle 40" is retained as magnet 
80' is rotated. Magnet 80' could have a periphery including opposing flat 
surfaces so that a wrench could be used to adjust the angular position of 
magnet 80' relative to float arm 60". 
The preferred embodiment comprises carrier ring 100 so that the angular 
position of magnet 80 relative to float arm 60 can be adjusted without 
having to contact magnet 80 with a wrench which could potentially break or 
damage magnet 80. Magnet 80 has an outer diameter 88 and with reference 
back to FIG. 1, magnet 80 is preferably bipolar with its north pole 90 and 
south pole 92 positioned opposite each other on outside diameter 88 to 
define a polar axis 93. Thus, rotation of magnet 80 necessarily means 
rotation of the magnet's polar axis. 
Magnetically actuated switch 130 is attached to second end 22 of support 
bracket 14. In the preferred embodiment, the magnetically actuated switch 
is a reed switch. Switch 130 is a normally open reed switch having a first 
end 132 and second end 134. Housing 24 has bore 136 through which switch 
130 is disposed radially beyond the radial extent of magnet 80 and 
generally in the plane of rotation of magnet 80. Pivoting of float arm 60 
rotates magnet 80 and thus changes the position of the north-south axis of 
magnet 80 relative to switch 130. Magnet 80 is such that a certain range 
of angular position of magnet 80 relative to switch 130 causes the reed 
switch to close or be actuated. If magnet 80 is in an angular position 
relative to switch 30 outside this range, the reed switch remains open, or 
unactuated. Because the angular position of the dipole axis of magnet 80 
relative to float arm 60 can be adjusted, the position of the float, and 
thus the level of the liquid in the tank, at which switch 130 is actuated 
is correspondingly adjustable. 
The adjustability of magnet 80 is advantageous in that the switch of the 
present invention can be used in a variety of different sized tanks and 
applications. For example, if it is desired to respond to a low liquid 
level in a tank, the vertical distance from the top of the low liquid 
level to the pivot axle can be determined. From this distance, it can be 
determined what angle that float arm 60 will have with respect to the 
horizontal. The float arm can be retained at this position while the 
angular position of the magnet is adjusted until the magnet just opens the 
reed switch. If the next tank is shallower, the magnet on another of the 
same type switch can be adjusted accordingly to account for the changed 
low liquid level relative to the pivot axle. 
In an alternative embodiment shown in FIGS. 7A and 7B, the position of 
switch 140 is adjustable instead of magnet 142. Magnet 142 is attached to 
pivot axle 144. Switch 140 is mounted on member 146 which is frictionally 
engaged on pin 148. As float arm 150 pivots, magnet rotates relative to 
member 146. The angular position of member 146 can be adjusted by rotating 
member 146 about pin 148. Thus, the angular position of float arm 150 at 
which switch 140 is actuated can be readily adjusted. 
Switch 10 can be used to respond in a number of ways to a low liquid level. 
When reed switch closes, a circuit can be completed which powers an 
annunciator, for example. a light or audible alarm. Alternatively, closing 
of the reed switch can turn on a refill pump to replenish the tank. Switch 
10 can be used to respond to a high liquid level as well as a low liquid 
level. Switch 10 can open a drain valve or shut off a refill pump when a 
high liquid level is reached. 
In a further embodiment, more than one switch can be positioned around the 
rotational axis such that the magnet will successively actuate the 
switches as the float arm pivots. Each switch can provide for a different 
response. For example, one switch can indicate a low liquid level while 
the other switch can indicate a high liquid level. 
FIG. 8 shows another embodiment with the magnet and switch assembly used in 
combination with an arcuate variable resistor 160. Variable resistor 160 
is mounted in housing 24. Contact 164 is mounted to pivot axle 40 and has 
tongue 166 extend radially outward and in contact with variable resistor 
160. Thus, as the float arm pivots, the extent of arc of the variable 
resistor that the current travels through changes thus providing signal 
proportional to the liquid level in the tank. Using the variable resistor 
in combination with the magnet and switch allows both a continuous display 
of the liquid level and a switch that automatically reacts to a 
predetermined liquid level in the tank. 
Although a single embodiment of the invention has been illustrated in the 
accompany drawings and described in the foregoing Detailed Description, it 
will be understood that the invention is not limited to the embodiment 
disclosed, but is capable of numerous rearrangements, modifications and 
substitutions of parts and elements without departing from the spirit of 
the invention.