Textiles: fluid treating apparatus – Machines – Single tub and automatic sequential operation mechanism
Reexamination Certificate
2000-07-19
2002-11-19
Stinson, Frankie L. (Department: 1746)
Textiles: fluid treating apparatus
Machines
Single tub and automatic sequential operation mechanism
C068S012020, C068S012210, C068S207000
Reexamination Certificate
active
06481246
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for controlling the liquid level in a washing machine.
A typical washing machine controls the water fill level of the tub by use of an air dome, including a pressure switch in communication with a sealed tube. The open end of the tube is in communication with the bottom of the wash tub and extends upward toward the pressure switch. As water enters the wash tub and the sump, water enters the opening of the air dome hose and, as the water level rises, the air pressure in the sealed tube increases and ultimately trips the pressure switch. When the pressure switch trips, the washing machine stops filling. One example of a typical air dome is disclosed in U.S. Pat. No. 3,397,716.
One major problem with prior art air domes occurs when water enters the air dome hose. When water does enter the air dome hose, the water does not always come out due to the vacuum caused by the sealed hose. When this happens, the fill level of the washing machine increases since a greater fill level is required to trip the pressure switch. The fill level required to trip the pressure sensor will increase by an amount equal to the length of the water column trapped in the air dome hose. In other words, if six inches of water are trapped in the air dome hose, the level at which the washing machine will quit filling is increased by six inches. It is possible that the increased fill level will cause the washing machine to overflow.
A common way that water becomes trapped in the air dome hose is when a small amount of water is left in the sump at the bottom of the wash tub. possible that the increased fill level will cause the washing machine to overflow.
A common way that water becomes trapped in the air dome hose is when a small amount of water is left in the sump at the bottom of the wash tub. When the washing machine is tipped, for moving or maintenance for example, water will flow into the hose and will not come out. When this happens, the next time the washing machine is filled, the water level required to trip the pressure switch will be greater by an amount equal to the amount of water trapped in the air dome hose.
Another problem associated with prior art air dome hoses, such as that disclosed in U.S. Pat. No. 5,964,001, is the formation of condensation in the small diameter tube extending between the air dome and the pressure switch. Such condensation forms as a result of changes in the water temperature from hot to cold. Such condensation is hard to drain from the small diameter tube due to surface tension. Eventually, the condensation can migrate upwardly along the tube to the switch, and cause failure of the switch.
Another problem can arise if the pressure switch is mounted above the tub, as in the '001 patent. If there is a leak in the air dome, there will be no change in air pressure within the dome in response to changing water levels. Therefore, the switch will not actuate, leading to overflow of the washing machine tub.
Accordingly, a primary objective of the present invention is the provision of a pressure switch for controlling the water level in a washing machine without the problems associated with the prior art.
Another objective of the present invention is the provision of an air dome pressure switch which is mounted to the drain pump of the washing machine.
Another objective of the present invention is the provision of a pressure switch which is mounted below the tub so as to be actuated by water pressure in the event of an air leak in the air dome.
A further objective of the present invention is the provision of a pressure switch which is mounted adjacent the air dome so as to minimize or preclude formation of condensation.
Another objective of the present invention is the provision of a sensor for controlling water level in a washing machine tub, which is mounted independently of the tub.
A further objective of the present invention is the provision of a sensor for controlling water level in a washing machine, which is economical to manufacture, and effective and durable in use.
These and other objectives will become apparent from the following description of the invention.
SUMMARY OF THE INVENTION
The water level control pressure switch of the present invention is mounted to the drain pump of a washing machine, independently of the washing machine tub. An air dome extends from the water inlet line of the pump, so as to be partially filled with water during the fill cycle of the washing machine. The pressure switch is mounted directly to the air dome. The switch is angularly disposed to allow condensation to drain away from the switch. Since the pressure switch is mounted to the drain pump below the tub of the washing machine, in the event of an air leak in the air dome, the switch will still be actuated by water pressure, thereby preventing overflow of the tub. The pump housing, pump inlet, pump outlet, and air dome are integrally formed.
REFERENCES:
patent: 1832906 (1931-11-01), Johnstone
patent: 2001661 (1935-05-01), Ball
patent: 2133708 (1938-10-01), Larson
patent: 2203828 (1940-06-01), Larson
patent: 3060713 (1962-10-01), Burkall
patent: 4203462 (1980-05-01), Beller
patent: 5345637 (1994-09-01), Pastryk et al.
patent: 5881578 (1999-03-01), Proppe et al.
patent: 5964001 (1999-10-01), Johnson
Hansen Ted L.
Johnson Troy A.
VandeHaar Evan R.
VanNorden Russell L.
Maytag Corporation
McKee Voorhees & Sease, P.L.C.
Stinson Frankie L.
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