Measuring and testing – Liquid level or depth gauge – Hydrostatic pressure type
Reexamination Certificate
2000-06-08
2002-09-03
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Hydrostatic pressure type
C073S313000, C200S00100B, C200S081400, C200S0830SA
Reexamination Certificate
active
06443005
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to pressure-responsive systems and components and, more particularly, to apparatuses that sense fluid level or pressure and respond thereto by triggering a switching mechanism.
BACKGROUND OF THE INVENTION
It is often desirable to know information about fluid level in tanks. Determining fluid level and controlling fluid level in tanks, such as in sewage tanks, water cisterns or tanks, and other fluid system and storage vessels, whether enclosed or open and exposed to the environment, has been done in a number of ways. Where applicable and accessible, visual readings can be taken. In some systems, though, visual readings are not desirable, since a response to the level indication is typically desired, such as to pump more fluid into the vessel or to discharge fluid from the vessel. In other situations, visual readings are not available due to lack of access. In addition, control systems are typically employed to respond to a fluid level indication, such as to operate a pump or a valved member in a gravity inflow or discharge arrangement, or to illuminate a light on an indicator panel representing the fluid level, e.g. Having a human operator make a visual fluid level reading and manually initiate this desired function may not be desirable due to the repetitive nature of the function or due to the inefficiency of having a human operator in the system.
These control or indicator functions are typically handled by electronic control systems which are responsive to one or more switches that are triggered by fluid level or pressure input. In sewage tanks, for example, it is well known to use multiple tilt style float switches to control fluid level. These may be mercury switches or rolling ball style switches, where a ball triggers a microswitch within the mechanism, that are triggered when the whole switch mechanism tilts downward toward a tethered connection a sufficient amount. These tilt style float switches are each attached via an anchor tether either directly to the vessel interior wall, or to a bar, rail, or other vertically disposed structural member within the vessel, such that a plurality of these tilt style float switches are disposed vertically with each one representing a unique elevation of fluid level within the vessel. They operate on a one-to-one ratio, that is, at the point they are triggered they are meant to represent that specific fluid level within the vessel. Numerous problems, however, have been encountered with these mechanisms.
Turbulent conditions within a fluid-holding vessel can negatively impact performance of float switch systems. Within a sewage tank, e.g., turbulence can result from fluidized material inflow, but more typically from pump-discharged fluid material exiting the tank. This turbulence can create undesirable eddies and waves within the tank that can cause tethered tilt style float switches to become entangled, thus preventing them and the system from proper operation. In addition, the turbulence within the tank can cause inadvertent switching (i.e., a switch to trigger prematurely or later than desired) and what is often referred to as “contact chatter” of the switches within the tilt style float switch assemblies. Inadvertent switching can cause system inefficiency and degradation, such as from a false level reading or from a pump to turn on or off earlier or later than desired. Such contact chatter can cause the pump, which is responsive to the triggered switch, to cycle inadvertently on and off at a high rate, resulting in undue and undesirable system wear and operation.
Other problems that can result from tilt style float switches are due to the fact that they are disposed on the surface of the fluid material in the sewage tank, a highly corrosive and greasy environment. These tethered switches can become damaged from banging against each other and the tank wall during the turbulent system operation. In addition, the greasy outer surface of the tilt style float switches can cause them to intermittently adhere and even get stuck against the tank wall, thus affecting system performance and reliability. In addition, low pressure sewage system tanks in both residential and commercial use are often of corrugated side wall construction. These corrugations can serve as a series of mini ledges or shelves to the grease-covered tilt style float switches, thus facilitating their adherence and entrapment.
The tilt style float switches can also become corroded. Leaking mercury from some styles of these switches poses a serious environmental and health hazard. Non-mercury versions of the tilt style float switches can similarly be ruined by corrosion, such as of the contact or leads, thus rendering them inoperable.
Another type of known switching mechanism performs similarly to the typical ball float that operates the valve in a toilet, which floats with the fluid level and closes the valve when the tank is full after the toilet is flushed. In these switching mechanisms, the ball floats on the liquid and bumps switches on and off, but it can only act on a one-to-one ratio, that is, the ball float represents the actual liquid level when the switch is bumped and triggered, not some multiple thereof.
Electronic pressure transducers have been used to sense fluid pressure. These devices are disposed in the fluid and typically operate by direct pressure against a diaphragm area that changes its resistive value as the component strain changes. They require an electronic box to convert the circuit signals to analog relay outputs for use in controlling pumps, etc. Though reliable, these electronic pressure transducers and required electronics are expensive.
Another common problem with all of the aforementioned tilt style float switch, vertical ball float or electronic pressure transducer systems is in servicing these systems. Since they are disposed in sewage tanks or other fluid vessels, servicing them can be a messy, less than ideal, undertaking.
The present invention provides a new and unique pressure activated control apparatus and system that overcomes the above problems and others.
SUMMARY OF THE INVENTION
An improved pressure activated control apparatus is provided that includes a first resilient member having a first or outer surface exposed to the fluid and responsive to the fluid pressure to trigger one or more switches of a switching mechanism. It has a second or inner surface exposed to the inside of the apparatus that is sealed from the fluid. A force translation and switching mechanism is provided that responds to the force exerted by the pressure of the fluid on the outer surface of the first resilient member to trigger one or more switches within the apparatus. The pressure activated control includes a second resilient member that provides a biasing force against the force translation and switching mechanism in a direction opposite to the force exerted by the fluid pressure on the outer surface of the first resilient member. In this way, change in height of the fluid level within the vessel compared to movement of the force translation and switching mechanism is greater than one-to-one.
The apparatus of the present invention provides a reliable, affordable alternative to known tilt style float switches, vertical float switching assemblies and electronic pressure transducer-based systems used for, among other possibilities, determining fluid level or controlling fluid level in open or enclosed fluid holding vessels, such as fluid storage or septic tanks, cisterns, sump and sewage basins, and other fluid system and storage vessels. In one embodiment, the pressure activated control of the present invention is provided in an elongate, vertically disposed housing that can be connected to an interior side wall of a tank, cistern or other fluid-holding vessel, such that the first resilient member has an outer surface that is substantially always in contact with the fluid. The first resilient member can be a pliable rolling diaphragm made of durable nitrile rubber, or any other suitable material se
Chandler Systems, Inc.
Jocke Ralph E.
Walker & Jocke
Wasil Daniel D.
Williams Hezron
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