1. FIELD OF THE INVENTION
This invention relates to irrigation systems and more particularly to an irrigation ditch gate utilizing a lever actuated plate to pivot transversely across a passage in a water port and open and close the port. The invention further relates to an irrigation ditch gate which can be mounted in the sidewalls of an irrigation ditch and uses substantially uniform actuation force to activate a valve gate.
2. BACKGROUND
Several geographical regions such as the southwestern United States are suitable for crop production only with substantial amounts of irrigation. Therefore, many approaches to irrigating large sections of land have been used in such regions, including: canals, ditches, sloughs, dams and a variety of sprinkler systems. Sprinkler systems require pressurized water sources or pumping stations which are often unavailable or expensive, and use large numbers of mechanical parts which can fail. Therefore, one of the most widely used irrigation techniques is that of a distributed irrigation ditch system using gravity flow to transport water over large land areas.
Typical irrigation ditch systems employ one or more central ditches to transport the water across land and a series of drain or access pipes to further distribute the water into furrows or onto crop-bearing fields. As a part of this water distribution it is obviously necessary to control and monitor the flow of water out of irrigation ditches into irrigation pipes and smaller ditches to successfully produce crops by watering specific areas at specific times. Incorrect amounts of water, either too much or too little, can destroy growing crops, and water is too expensive to erroneously transfer to fallow areas. Therefore, several irrigation ditch gates have been designed in order to provide some control over the flow of water out of irrigation ditches.
Two widely used types of irrigation gates utilize square plates, that slide on two guide rails attached to the sides of an irrigation ditch to cover and uncover a port or opening for an exit pipe connected to the ditch. These gates rely on gravity to assist in lowering the gate into place. In one gate, a threaded rod actuator extends up over the side of the irrigation ditch where it attaches to a handle. The gate is raised or lowered by turning the handle which either rotates the rod through a threaded block fastened to the gate or is itself threaded.
The second, and very extensively used gate, employs a rod shaped actuator that terminates in a handle on one end and in a curve or cam on the other. The rod passes through a block or other bracket afixed to the gate. By turning the handle the cam of the rod is forced against the gate surface which levers against the gate and in turn presses it against the ditch sidewall to seal an opening. While this type of gate has served the agricultural community for years it does have several limitations and drawbacks.
The sliding plate type gates do not adequately seal. The cam type handle does not provide enough leverage advantage for a typical operator to be able to reliably seal the gate. Due to the force required, many farm workers do not even attempt to lock the gate cam in place leading to loss of water or crop damage.
On the other hand, when the gate is open there is a problem with the irrigation gate drifting closed. Depending upon water turbulence, flow rate, or debris, a gate using gravitational force for lowering or that travels in a vertical motion has a natural tendency to drift closed. Therefore, it is necessary to lock the gate in any open position. This requirement can be time consuming as well as unreliable. In fact for the cam type gate mechanisms, the locking force required often means that workers leave the gates unlocked, allowing them to drift closed. Gate drift thus makes repetitive patrols of irrigation ditches necessary to monitor and reset the gates. When combined with a lack of visual gate position indication, it is readily apparent that it is difficult to control irrigation rates with current state of the art designs.
A general problem with irrigation gate structures is the inability to provide visual indication of gate position. That is, one cannot tell if the gate is open, partially open, or closed, by visual inspection of the gate handle. Any change in the handle position occurs along one vertical direction and is small compared to the handle size. The ability to detect gate position visually is more than a mere "convenience". The economics of modern day agriculture have led to the development of farms with very large acreage. This translates to many miles of irrigation ditches, all of which must be controlled and monitored with a modicum of precision and reliability in order to produce the most efficient crop. Since a variety of crops may be cultivated, or raised in a predetermined rotational pattern, it is necessary to control the distribution of water across a farm in an uneven but predetermined pattern. Therefore, for the miles of irrigation ditch on a given farm, it is often necessary to set differing irrigation gates to close, partially open, or open positions. In a typical farming situation, an irrigation gate is placed at least every sixty feet along an irrigation ditch which can be on the order of 2-3 miles long. This requires the setting of 170-270 individual irrigation gates. It can be readily seen that controlling that many gates and knowing their precise position from day to day during a crop growing season, makes visual indication of the gate position very desirable.
Another problem with most irrigation ditch gate designs is the fact that they tend to seize when left unused. A typical irrigation system may be used for several months of crop production, and then left unused for many months. Generally the irrigation ditch will be drained of water, although this need not always be done, depending on the clarity of the water as well as its level during non-use. Current gate designs tend to capture or hold a small amount of water in the drain opening, exposing the metal parts to continued rusting. A sufficient amount of rust may form bridges between various metal parts that seize together, making it impossible to open when it is time to again activate the gate. In a typical farming situation, the workers trying to set such a gate may attempt to dislodge the gate by striking on it with some variety of heavy object. Sometimes this approach works, breaking loose the bridges formed by the rust and allowing the gate to move, however, two facts soon become apparent. One, there is no advantage offered by an actuator mechanism that operates by simply sliding a rod up or down. That is, it would be desirable to have some additional amount of force or leverage available to apply to the gate to try to dislodge it. Second, the gate may be damaged or destroyed in an attempt to dislodge it. In fact, there is a reasonably large business in selling replacement gates, since these gates are often damaged or simply rust out.
An additional problem related to the mechanisms used to actuate irrigation ditch gates is the non-uniformity of the actuation force or non-contiguous motions. These problems have hampered attempts to automate irrigation ditch systems for years. Present designs tend to require more force at some points of travel than at others. In addition, the force required for one gate is sometimes greatly different from the next. This stems from the fact that guide rails and associated parts for irrigation gates are custom installed in the irrigation ditch with the gates being inserted later. This leads to variations in the match between the gate dimensions and the guides.
While there have been attempts to provide a variety of rotating gate structures, they have suffered from similar drawbacks in terms of the force required to open and close, lack of visual indication for gate position, and rusting or seizing. Some of these designs require rotating and sliding motions which would make automation a complete task. In addition, current gates do not tend to be self cleaning and may even rely on special materials to form a water tight seal.
It would advance the art of water distribution and agricultural production if an irrigation ditch gate were provided that reduced problems with seizing, drifting and non-uniform actuation forces, and provided visual indication of the gate position. In addition, an irrigation ditch gate that could accommodate water debris and some abuse would prove beneficial.