The present invention pertains to applicators for injection of anhydrous ammonia (NH3) into soil as a fertilizer.
In the application of anhydrous ammonia as a fertilizing agent, it is usual to utilize an applicator which includes a number of injection knives which are drawn on a tool bar with each knife making a small furrow in the soil. A conduit to carry anhydrous ammonia (NH3) is carried on each knife shank and terminates at the lower end of the knife, thereby permitting a stream of NH3 to be inserted in the furrow. The furrow is then closed, trapping the NH3 in the soil.
For purposes of supplying an anhydrous ammonia applicator, a portable tank containing liquid NH3 under pressure is drawn behind the applicator and NH3 from the tank is permitted to escape through a liquid conduit which couples to a control/distribution unit which distributes NH3 to the knives on the applicator. The NH3 is forced from the tank by vapor pressure within the tank in the vapor head above the liquid level of the tank. As the tank empties or as atmospheric temperatures decline, the head pressure declines and less pressure is available in the tank to urge liquid NH3 into the liquid conduit.
In addition to having a port for intake or discharge of liquid pressurized NH3, portable tanks for transport of liquid NH3 include a vapor port which communicates with the interior of the tank and is controlled by a shut off valve to prevent escape of NH3 gas from the tank. When liquid NH3 is being pumped into a portable tank, a vapor hose is connected to the vapor port on the tank and its shut off valve opened in order to allow movement of gaseous NH3 from the tank while liquid NH3 is being pumped into the tank. The vapor being allowed to exhaust from the tank is ported back to the main NH3 supply container.
When NH3 is being applied to a field, the head pressure of the NH3 vapor in the tank forces liquid NH3 from the tank. As the atmospheric temperature drops, the pressure of the gaseous NH3 in the pressure head of a portable NH3 tank drops, providing less pressure on the liquid NH3 in the tank resulting in the slowing movement of the liquid NH3 from the tank and into the ducts carried on the applicator knives. For example, at an outdoor temperature of 30° F., the pressure may only be forty pounds per square inch. This is a pronounced problem for application of NH3 fertilizer because application is preferably accomplished in the fall season, after harvest of grain crops from the field. Therefore, NH3 application on a cold day is slowed and may become erratic because insufficient pressure remains in the pressure head of the portable tank to supply a steady stream of liquid NH3. Additionally, as the NH3 portable tank is emptied, the pressure of the head declines and liquid NH3 is discharged more slowly even if atmospheric temperatures are summer like. To adjust for the problem of low head pressure, the operator of the fertilizer applicator must slow greatly to be sure adequate NH3 is being applied to the soil. This need substantially reduces productivity of the application equipment and the operator.
Previous efforts to overcome the problem of reduced flow of liquid NH3 when the atmospheric temperature is low include increasing the size of the liquid conduit from the tank, drawing from two or more tanks at the same time, and drawing liquid NH3 from a port in the bottom of the tank instead of from the standard dip tube provided on the top of the tank. These methods provide additional shortcomings or are ineffective. Drawing a second or third tank over the soil causes increased fuel consumption of the tractor or other power unit, as well as increasing compaction of the soil from additional wheels passing over the soil. Adding a bottom port to a standard dip tube equipped tank adds expense and increases the possibility for leakage from the tank, while doing little to solve the problem.
A method to maintain a preset pressure in the pressure head of the portable NH3 tank would be very desirable for use by operators of NH3 application equipment.