Pumps – Condition responsive control of pump drive motor – Responsive to accumulation of pumped liquid in receiver
Reexamination Certificate
2000-01-25
2001-07-03
Thorpe, Timothy S. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
Responsive to accumulation of pumped liquid in receiver
C200S08400B, C200S08400B
Reexamination Certificate
active
06254351
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to float assemblies for sensing fluid levels and, more particularly, to a float assembly for actuating a switch.
2. Background Art
Conventional float assemblies for actuating a switch based on a fluid level typically include a pushrod that extends upwardly from a float and which moves vertically with the float in response to changes in the fluid level. The pushrod may actuate the switch directly or, alternatively, may actuate the switch via an intermediate lever.
In applications where the float assembly controls the operation of a pump, it is desirable to provide switching hysteresis or a control deadband that allows the pump motor to cycle between on and off operational states at an acceptable frequency and duty cycle. As is commonly known, without switching hysteresis, electrical noise or high flow rates into the pumped container may cause the pump motor to cycle rapidly between on and off states when the fluid level is near the switching point. Such rapid cycling of the pump motor can substantially increase power consumption and shorten the life expectancy of the pump motor. It is further desirable to provide a positive (i.e., substantially bounceless) switching action because mechanical bouncing of the switch contacts may cause the pump motor to be turned on and off rapidly despite any switching hysteresis or control deadband and may cause premature wear and failure of the switch contacts.
Some conventional float assemblies provide a control deadband by coupling the float pushrod to the switch via a lost motion connection, which allows the vertical displacement of the float to change over a predetermined range of fluid levels without causing any actuation of the switch. Additionally, many of these conventional float assemblies also incorporate an electrical switch having a snap-acting or detent mechanism to provide a positive switching action that eliminates or minimizes contact bounce.
In one known configuration illustrated in
FIG. 1
, a conventional float
10
follows the level of a fluid within a tank
12
. A pushrod
14
extends coaxially from the float
10
and is coupled to the float
10
so that the pushrod
14
follows the vertical displacement of the float
10
. The pushrod
14
passes freely through an opening (not shown) in a lever arm
16
which is coupled to a detent switch
18
. The pushrod
14
includes an upper pushnut
20
and a lower pushnut
22
that define a control deadband therebetween. This control deadband allows the pushrod
14
to move vertically through the lever arm
16
a predetermined distance without actuating the lever arm
16
or the detent switch
18
.
At a low fluid level
24
, the pushrod
14
is retracted into the tank
12
so that the upper pushnut
20
pulls the lever arm
16
downward to cause the detent switch
18
to be in one of two switching states. Similarly, at a high fluid level
26
, the pushrod extends out of the tank
12
so that the lower pushnut
22
pushes the lever arm
16
upward to cause the detent switch
18
to be in the other one of the two switching states.
While the float assembly shown in
FIG. 1
establishes a control deadband so that a pump motor controlled by the detent switch
18
is turned on at one fluid level and turned off at another fluid level, the structure of
FIG. 1
is relatively expensive to manufacture because it requires the use of an expensive detent switch. Further, placement of the pushnuts
20
and
22
on the pushrod
14
is labor intensive and tends to be imprecise, leading to a wide variation in the minimum and maximum controlled fluid levels.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a float assembly includes a carrier rotatable about a pivot axis. The carrier includes an actuation surface which is disposed at an actuating position when the carrier is disposed at a first rotational position and which is moved away from the actuating position when the carrier is rotated away from the first rotational position toward a second rotatable position.
The float assembly may further include a pair of spaced floats coupled to the carrier. The floats may be disposed on a certain side of a vertical line extending through the pivot axis when the carrier is disposed at the first rotational position and the floats may be disposed on opposite sides of the vertical line extending through the pivot axis when the carrier is disposed at the second rotational position.
The float assembly may be used in combination with a switch having an actuation arm which is moved to a switch actuation position by the actuation surface as the carrier is rotated to the first rotational position and the actuation arm may be biased by a spring to a switch deactuation position as the carrier is rotated toward the second rotational position.
In accordance with another aspect of the present invention, a float assembly for actuating a switch based on a level of a fluid includes a pivot member having a pivot axis and a switching surface and first and second floats coupled to the pivot member. At a first fluid level, the first and second floats lie on different sides of a vertical line extending through the pivot axis and the switching surface causes the switch to assume a first switching state and, at a second fluid level, the first and second floats lie on the same side of the vertical line extending through the pivot axis and the switching surface causes the switch to assume a second switching state.
In accordance with yet another aspect of the present invention, a float assembly includes a pivot member having a pivot axis and a float coupled to the pivot member. The float provides a first torque to the pivot member in a first direction when the float lies substantially to one side of a vertical line extending through the pivot axis and a second torque in a second direction to the pivot member when the float lies substantially on another side of the vertical line extending through the pivot axis. The float assembly may further include a means for applying a third torque in the second direction to the pivot member to cause the float to move from substantially the one side to substantially the other side of the vertical line through the pivot axis.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings.
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Gray Michael K.
Milton Roy Company
Thorpe Timothy S.
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