Hygrostat and system

Details Hygrostat and system Hygrostat and system

1996-07-16

1998-08-18

Weldon, Kevin

Fluid sprinkling, spraying, and diffusing

With cutoff or flow varying means operated by means...

B05B 108

Patent

active

057948488

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to hygrostats of the type where the lengthwise expansion and contraction of an elongate hydroscopic element (with the uptake and release of moisture) is employed to operate a valve or position transducer (including electrical switches) that may be used to control the flow of water, to operate an alarm or indicate the level of moisture in the hydroscopic element. The invention is also concerned with hygrostat systems and methods.
The invention is particularly, but not exclusively, concerned with the automatic supply of water to pot-plants and to individual plants in open soil where the hygrostat is buried in the soil near the plant. However, some hygrostat units of this invention may also be mounted above ground and used to inhibit timer-based sprinkler systems during and shortly after rain.


BACKGROUND TO THE INVENTION

In attempting to develop a hygrostat unit and system suited to indoor and outdoor pot-plants, we have found many problems that have not been adequately addressed by the prior art. For such a unit needs to be small and cheap and must operate with great reliability for long periods of time. It must be capable regulating very low water flow-rates under a variety of abnormal conditions, including independent over-watering, soil dry-out (when the water supply is cut off) and negative water pressure or `suck-back` (which occurs when the water supply is lost and the system drains from the lowest opening).
We have found that most hydroscopic materials proposed in the art are quite unsuited to our purpose. Natural fibrous materials such as wood, paper, cork, leather or gut are highly variable, degenerate quickly in the soil and do not cycle in a repeatable manner. Most synthetic materials proposed in the art (e.g., polyacrylamide gels) also do not have good cyclic repeatability, they are so hydroscopic that they remain wet even when the soil is too dry for healthy plant growth, and they encourage root entanglement and fungal growth, which interfere with the operation of the hygrostat. We have also found that most prior art systems encase the hydroscopic element in such a manner as to create a micro-climate, which traps moisture. This problem may be further exacerbated by the release of water into the soil in the immediate vicinity of the hydrostat so that a column of mud forms around it. These factors result in poor and ineffectual regulation of the moisture content of the soil and, combined with the bulky nature of the devices, make such hygrostats wholly unsuited for use with pot-plants.
U.S. Pat. No. 3,204,872 to Whear discloses a hygrostat having a column of cork or wood mounted in a perforated metal container so that one end presses a diaphragm against an orifice to regulate the flow of water from an irrigation pipe into the ground immediately beneath the device, the container and pipe being buried in the soil. This device exhibits some of the problems mentioned above. That is, the wood or cork is bulky, has poor repeatability and quickly degrades in the soil. Also, the container creates a wet micro-climate not typical of the surrounding soil, the position at which the water is released tends to result in the `column of mud` problem. Suck-back draws this mud into the hygrostat and dry-out (caused by loss of water-supply) results in mud and sand setting between the wood and the diaphragm and/or between the wood and the container so as to prevent proper operation of the device when water supply is restored. The suck-back problem was addressed by U.S. Pat. No. 3,840,182 to Geffroy, which disclose the use of fine filters at the outlets. But these filters are subject to blockage.
Australian patent 523,482 to Beckmann discloses a hygrostat for use in regulating the flow of water through an above-ground hose, which passes through a transverse aperture in the top of a ground-spike that contains the hydroscopic element of wood or polyacrylamide gel. As the element absorbs moisture from the ground or from sprinklers, it expands to constrict the hose. However, thes

REFERENCES:
patent: 3204872 (1965-09-01), Whear
patent: 3512712 (1970-05-01), Benesch
patent: 3840182 (1974-10-01), Geffroy
patent: 3874590 (1975-04-01), Gibson
patent: 4095458 (1978-06-01), Wild
patent: 4182357 (1980-01-01), Ornstein
patent: 4214701 (1980-07-01), Beckmann
patent: 4648555 (1987-03-01), Gumbmann
patent: 4696319 (1987-09-01), Gant
patent: 4843758 (1989-07-01), Raczkowski
patent: 5329081 (1994-07-01), Jones
patent: 5368235 (1994-11-01), Dozdoff et al.

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