Fluid handling – Processes – Involving pressure control
Reexamination Certificate
2001-02-28
2003-05-27
Buiz, Michael Powell (Department: 3753)
Fluid handling
Processes
Involving pressure control
C137S486000, C137S487500, C137S557000, C251S005000, C700S284000
Reexamination Certificate
active
06568416
ABSTRACT:
TECHNICAL FIELD
The invention pertains to fluid delivery systems. More particularly, this invention relates to fluid flow and pressure regulation systems including valves, valve control systems, irrigation flush systems, pressure relief systems, and controlled fluid delivery nozzles.
BACKGROUND OF THE INVENTION
Significant advances have recently been developed in the field of agricultural irrigation. More particularly, increases in water and energy costs coupled with an improved understanding of crop-water relations has led to an increase in demand for precision irrigation management techniques. Because of this demand for precision irrigation management techniques, there has been a movement to develop low volume-high frequency irrigation systems. For example, a drip irrigation system, also referred to as trickle irrigation, is one example of a low volume-high frequency irrigation system.
A drip irrigation system provides several advantages over other types of irrigation systems, such as flood irrigation systems, furrow irrigation systems, and many sprinkler-based irrigation systems. A well designed and properly maintained drip irrigation system can realize a very uniform fluid application over a field, with variations on the order of less than ten percent across the field. Accordingly, a grower can achieve greater control over the quantity of water delivered to a crop in the field in order to more precisely meet known water requirements for the crop, and to maintain a proper balance between soil moisture and aeration. Additionally, water-soluble fertilizers can be carefully metered, or “spoon-fed” to the crop using a drip irrigation system because the drip irrigation system can deliver fluids (and fertilizer) at precisely the rate and location required by the crop which corresponds to a growth stage of the crop. Even furthermore, careful metering of fluid including water, fertilizer, and pesticide can decrease disease and weed pressure on crops, as well as lower energy requirements and reduce environmental impact.
One form of drip irrigation system uses drip-tape. Drip tape is a thin-walled, polyethylene product that is usually buried at a nominal depth within a crop bed, for the case of row crops. Alternatively, the drip tape can be buried adjacent to a tree or vine row in orchards and vineyards. One distinguishing feature of drip tape is that drip tape employs a turbulent flow path between a main flow channel, or supply tube, and an emitter, or outlet. Such feature results in a consistent, definable relationship between discharge and pressure. However, drip tape is not pressure compensating. Therefore, great care and precision should be exercised in the design phase of an irrigation project in order to ensure that pressure variations do not exceed certain defined criteria.
As a result, to ensure such precision, fields are typically mapped using a survey grade global positioning system (GPS) in order to develop accurate topographic maps from which an irrigation system is then designed. As an example of the importance in developing an accurate topographic map, a design error of 1 psi will result from having an elevation error of 2.3 feet, which could lead to a 10% error in flow. Such errors may become compounded when integrated over large areas of a field. The operating pressure within drip tape is limited to a narrow range, which rarely exceeds 12 psi, and is seldom lower than 4 psi. It follows that the lower the operating pressure the more important the accuracy of design calculations. Accordingly, such a design error will have a significant effect on the operating pressure within a drip tape.
For most regions where crops are grown and irrigated, crops are rotated from field to field in order to break cycles of plant diseases, and to maintain soil tilth and fertility. Because of the need to rotate crops, many growers who wish to use drip irrigation systems need to implement portable or “temporary” drip irrigation systems that can be moved from field to field. Typically, these systems consist of above-ground components that can be re-used each year, as well as adapted to changes in irrigation system design. However, drip tape from such systems is discarded each year. Furthermore, design changes are usually necessary to accommodate changes in topography, water supply and field size. In contrast to the disposable drip tape, portable and reusable components from such systems include sand media filters for water treatment, PVC fittings, control valves, control wire and “lay-flat” tubing.
Pressure control is principally achieved within a field using control valves. As a control element, control valves regulate pressure by controlling the flow rate into or out of a portion of the delivery system where regulation is required. A “main” control valve is typically located near the water supply and regulates downstream pressure of the flow to the main line. The main control valve also serves the purpose of sustaining a minimum pressure on the upstream side to properly operate the filtration equipment. A “zone” control valve provides secondary control and allows for the precise regulation of pressure at a “zone”. A “zone ” is understood to refer to an irrigated block within the field, and thereby being supplied by a single distribution line or sub-main line within a multiple zone irrigation system. Operation of the irrigation system is typically automatic and is accomplished through a centralized programmable controller for zone valve operation. Zone control valves, in this application, regulate pressure from a range of 17 to 30 psi, on the supply side, down to a zone pressure of approximately 11.5 to 13.0 psi, depending on the design requirements.
One exemplary control valve is the Nelson 800 Series control valve sold by Nelson Irrigation Corporation, of Walla Walla, Wash. Such control valve employs a control volume and an expandable and retractable “sleeve” or “boot” diaphragm, positioned and seated within the valve body about the main flow path. The sleeve acts as a throttling element as the control volume is allowed to expand or retract, modulating flow through the valve. Such control valves are known as self-directing control valves, where the force necessary to position the throttling element is derived from the fluid being regulated. The Nelson 800 Series control valve is unique in its design in that it employs internal struts to maintain the sleeve in good throttling position, even at low flows. This is known as proportional throttling. The flow path through the valve keeps streamlines relatively uniform and parallel, minimizing friction loss due to turbulence. Due to the low overall operating pressures of drip irrigation systems, minimizing friction loss is important. Competitive valves, employing alternative throttling methods, create greater turbulence and friction loss and do not provide the same flow control. The loss coefficient depends primarily on the shape of the valve, which determines the degree of flow separation and generation of additional turbulence. Filling and draining of the control volume is governed by a mechanical pressure regulating pilot.
Mechanical pilots are typical to self-directing pressure regulating valves in agricultural irrigation. In order to reduce flow through the valve and therefore lower downstream pressure, pressurized water from upstream of the valve is allowed to pass to the control volume through the pilot. Conversely, in order to increase the downstream flow and raise downstream pressure, water from the control volume is allowed to vent to atmosphere back through the pilot. A set point, or regulated downstream pressure, is determined by a reference load. A spring within the mechanical pilot provides the reference load, and fluid pressure, both upstream and downstream, is in hydraulic communication with the mechanical pilot in a scheme known as “three-way logic”. The sensitivity of the pilot is determined largely by the spring constant and by the size of the orifice regulating fluid flow into the pilot body. In operation, the balance of fo
Andersen Brian L.
Mittelstadt Robert
Tucker Jeffrey C.
Andersen Brian L.
Buiz Michael Powell
Krishnamurthy Ramesh
Wells St. John P.S.
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