It is necessary to provide an indication of the level of fluid within many different types of tanks. For example, for holding tanks in sewage treatment systems on vehicles, it is necessary to know when the tank is full, or approaching full, so that it can be emptied. Typical conventional sensors for such tanks, such as those sold under the trademarks "SANX.RTM." and "TANKWATCH.RTM." by Sealand Technology, Inc. of Big Prairie, Ohio, indicate when the tank is full, or when the tank is three-quarters full and then full. Such sensors typically include one or more probes which extend into the tank. The probes comprise a hard plastic or brass probe shaft, and a sensor--such as a magnet slideable with respect to a reed switch--mounted at the bottom of the shaft. While conventional sensors are successful in sensing the full level of tanks, there are some circumstances when it is desirable to also sense the empty level of a tank.
The sensing of an empty level of a holding tank or the like--especially one that is mounted in a vehicle (such as a recreational vehicle, boat, or the like)--can be difficult to implement. If there is any substantial volume of fluid (which typically includes liquid, solids, and/or semi-solids in a holding tank) within the tank, as the vehicle moves along, rocks back and forth, brakes, accelerates, and the like, the dynamic forces applied by the fluid sloshing around inside the tank--which forces may be violent--can have adverse effects on the probes. Typically if the probe is long--and it may need to be up to about 22 inches long for conventional recreational vehicle or boat holding tanks--the moment applied to the probe can result in permanent bending or fracture of the hard plastic (rigid pvc) or metal (brass) probe shaft.
According to the present invention, a level indicating assembly for use in a tank, particularly for use in a tank in a vehicle such as an RV or a boat--is provided which is capable of sensing the tank empty condition, but will not prematurely fracture or deform as a result of violent slosh of fluid within the tank. According to the present invention this is accomplished by providing the probe shaft of a flexible material, such as flexible pvc tubing. Thus, the shaft may readily bend when subjected to forces within the tank as the tank moves, but will not break.
According to the present invention it has also been recognized that it is desirable to provide an "empty" indicator for holding tanks or the like, especially associated with vehicles. While a "full" indicator tells one when to empty the tank, when one is in the process of emptying the tank one is never sure when the tank is empty. Since emptying often is done utilizing a pump, if the emptying operation continues for a significant period of time after all the liquid, solids, and semi-solids have been removed from the tank and the pump sucks air, this may result in damage to the pump, particularly impeller type pumps. Alternatively, depending upon the tank construction, this may result in a vacuum being pulled in the tank, with subsequent damage to the interior of the tank or other tank components. These difficulties are avoided by providing an empty indicator in a holding tank or the like.
In order to provide an empty indicator for a holding tank that is commercially practical, there must be some adjustability in the probe length to accommodate different depths of tanks. For example commercial holding tanks may have depths ranging from about a foot to about two feet. Therefore it is desirable to provide a tank indicator assembly which has at least one probe shaft that is adjustable with respect to the tank fitting for the assembly. Therefore according to one aspect of the present invention there is provided a method of installing a tank level indicator in a tank using a fitting body having at least one probe associated therewith, the probe having a hollow shaft extending through a shaft fitting on the fitting body, and a sensor mounted at a first end of the shaft, and electrical wires extending from the sensor through the shaft, comprising the steps of: (a) Mounting the fitting body in the top of the tank. (b) Adjusting the position of the probe shaft with respect to the fitting body and shaft fitting so that the sensor on the probe shaft is at the desired position within the tank. (c) Cutting off any unneeded portion of the probe shaft extending above the shaft fitting. And, (d) connecting up the electrical wires associated with the probe to an indicator. Typically at least two probes having probe shafts are provided, and steps (b) through (d) are practiced for each. Step (b) is practiced for one of the probes so that the sensor is at or adjacent the bottom of the tank and thereby provides an "empty" indicator, while the other shaft is adjusted so that it senses a mid-level filling of the tank (e.g. one-half or three-quarters full). It is also desirable to provide a socket in the fitting body which has knock-out plug in it, and to knock out that plug if the socket is to serve as a vent, but to leave the plug in if the socket is not to vent the tank.
It is particularly desirable according to the present invention to provide "empty", mid-full, and "full" indications in a holding tank, particularly one associated with a vehicle. According to this aspect of the invention, a level indicating assembly for use in a tank adapted to be mounted in a vehicle is provided, the assembly comprising the following elements: A fitting body for fitting the assembly in operative association with a tank. First and second probes, each having a hollow probe shaft with electrical wires extending therethrough, and extending through the body, and a sensor element on the end of the shaft. And, a third probe sensor mounted directly to the fitting body. Shaft fittings for fitting the first and second probe shafts to the fitting body are provided which include means for allowing adjustment of the position of the probe shafts with respect to the fitting body. Typically the means for allowing adjustment of a probe shaft with respect to the fitting body comprise a collar of resilient material frictionally engaging the shaft, and locating means in the shaft fitting for receipt of the collar. The sensors are connected up by electrical wires to "empty", mid-level and "full" indicating means, such as indicator lights. Each of the sensors preferably includes an elongated central portion having a first vertical length and a condition responsive electrical element, such as a reed switch, therein near one vertical end thereof. Each sensor also includes an exterior float having a second vertical length less than the first, and movable with respect to the central portion, and having a condition generating element--such as the permanent magnet for use with the reed switch--for operating the reed switch when in substantial vertical alignment therewith. The condition responsive electrical elements are mounted near the top of the central portion for the second and third probes, and near the bottom of the central portion for the first probe, for maximum efficiency in sensing the various conditions sensed by the probes.
It is the primary object of the present invention to provide an effective level indication for a tank, particularly for a holding tank or the like adapted to be mounted in a vehicle, and a method of installation thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.