Hydraulic rate control system for sprayers

A hydraulic rate control system for maintaining a selected application rate at varying ground speeds. The application rate is selected through an operator control which permits the operator to dial in the spray tip size, the width of the spray pattern per tip and the desired spray rate in gallons per acre, and this application rate can be changed on the go. A ground-driven hydraulic oil pump directs its entire flow through a variable orifice, adjusted through manipulation of the operator control, and the oil pressure acts against a balance valve which maintains the pressure of the chemical to be sprayed equal to the oil pressure at the variable orifice. As the ground speed increases or decreases, the oil pressure and thus the chemical pressure increases or decreases accordingly to maintain the selected application rate.

BACKGROUND OF THE INVENTION 
The present invention relates generally to agricultural spraying implements 
and more specifically to a hydraulic rate control system for such 
implements. 
Agricultural chemicals such as herbicides, insecticides and fertilizers are 
often applied in liquid form to soil or crops. A solution of the chemical 
and a diluting liquid such as water are pumped from a tank through spray 
nozzles or the like to the soil or the crops being treated. For maximum 
effectiveness, economy and safety, the rate of application must be 
carefully controlled. As the speed at which the sprayer is propelled 
through the field is increased or decreased, the amount of chemical pumped 
must increase or decrease accordingly to maintain the desired gallons per 
acre coverage. 
At times during the spraying operation, the operator must change the 
application rate to best suit the particular soil, crop, weed, or insect 
conditions or the like encountered. Often the rate change cannot be made 
easily and accurately. 
The rate at which the chemical is applied is dependent on the nozzle or tip 
size and width of the spray pattern per tip, with the number of gallons 
per acre applied increasing as the tip size is increased or as the width 
per tip is decreased. A control is necessary which takes into account the 
tip size and the width per tip, and which utilizes a means for setting the 
desired gallons per acre coverage based on these factors and which is 
independent of the ground speed of the spraying implement. 
Typical of prior art rate control systems are those in which chemical 
concentrates from a separate supply tank are injected at a rate 
proportional to the vehicle's land speed into water which is dispensed at 
a constant rate. Such a system is shown for example in U.S. Pat. No. 
4,005,803 and requires separate tanks for storing the chemical and the 
dilutant. 
Other rate control systems, such as shown in U.S. Pat. Nos. 3,550,854 and 
3,670,962, utilize a centrifugal governor driven from a ground wheel to 
control the flow of liquid from the tank to the discharge nozzles so that 
the amount of solution applied per acre remains constant regardless of 
ground speed. Fairly complex and expensive drive, governor, and 
governor-controlled valve assemblies are required. 
Other types of systems have used ground-driven pumps for delivering the 
chemical to the nozzles at a pressure related to speed so that the gallons 
per acre sprayed remains essentially constant regardless of speed. 
However, the high pressure and high capacity requirements of present-day 
sprayers make such a system impractical since the output is limited, for 
example by wheel traction. Systems which use electronic regulating means 
have been devised for regulating sprayer output in proportion to rate of 
advance, such as that shown in U.S. Pat. No. 4,083,494. Such systems, 
however, often require variable displacement pumps or electrically 
operated valves which increase the cost and complexity of the system, and 
which require connecting the system to a source of electrical power. 
Another regulating system described in U.S. Pat. No. 3,784,100 utilizes a 
selector valve directly in the main flow line to the spray nozzles. The 
valve divides the flow between the nozzles and a bypass line leading to 
the inlet of the pump. A ground speed valve is adjusted to correspond to 
the vehicle ground speed. The device provides a predetermined application 
rate for a particular vehicle ground speed and crop row spacing, but 
requires the use of interchangeable valve cores with different sized 
orifices and the use of a chart for correlating ground speed, crop row 
spacing, application rate and pressure to determine the required operating 
pressure which is monitored with a meter. The control valve generally 
requires readjusting if the ground speed changes, and changing the spray 
rate requires more than simply dialing in the desired rate on the control. 
The valve system used directly controls the solution to be sprayed which 
is common in many of the prior art examples, and therefore the chemical 
must be piped to the control at the operator's station, usually requiring 
more plumbing and increasing the danger of subjecting the operator to 
contact with the chemical if a leak occurs. 
In many of the prior art devices in which there is direct contact between 
the valve and the chemical to be applied corrosion of the control valve is 
a problem. In addition, the chemical often has a sticky base which will 
clog the valve and prevent accurate metering. Dirt or sediment in the 
solution to be sprayed can also cause clogging and result in 
malfunctioning of the metering system. 
SUMMARY OF THE INVENTION 
Therefore it is an object of the present invention to provide a rate 
control system for a sprayer which overcomes many of the disadvantages of 
the prior art devices. 
It is an object of the present invention to provide a rate control system 
for a sprayer which maintains the desired application rate regardless of 
speed and which provides a convenient operator control for selecting the 
desired rate taking into account the tip size and width of the spray 
pattern per tip. A further object is to provide such a system in which the 
spray rate can be changed on the go using a single operator control. 
It is a further object to provide a hydraulic rate control system for a 
sprayer in which the spray rate is easily adjusted by a single control 
without the need to consult a chart and is maintained constant regardless 
of the ground speed of the sprayer. Still another object is to provide 
such a system which is easily calibrated. 
It is yet another object of the present invention to provide a hydraulic 
rate control system for a sprayer which regulates sprayer output pressure 
in accordance with ground speed and which is relatively simple and 
inexpensive to manufacture, not requiring complex valve or pump structures 
or electrical controls. It is still another object to provide such a 
hydraulic system with an operator controlled regulator valve which is not 
directly in communication with the chemical solution being sprayed so the 
solution does not have to be pumped through the valve near the operator 
and so that problems of corrosion and clogging of the valve are reduced or 
eliminated. 
It is a further object of this invention to provide a hydraulic rate 
control system for a sprayer in which the output pressure is regulated by 
an operator-control valve which includes a scale for dialing in the 
desired application rate taking into account the tip size and width per 
tip and which allows the operator to accurately set the desired spray rate 
on the go to adjust for changing conditions. 
The hydraulic rate control system of the present invention is provided with 
a ground-driven hydraulic oil pump which directs its flow through a 
variable orifice, adjusted by an operator control which has a scale 
directly calibrated for tip size, width per tip and gallons per acre. A 
balance valve maintains the pressure of the chemical solution to be 
sprayed equal to the oil pressure at the variable orifice. As the ground 
speed increases or decreases, the pressure at the orifice changes 
accordingly and causes the pressure of the chemical solution to vary in 
like manner. 
For a given tip size and width per tip on the calibrated scale, the desired 
gallons per acre can be easily set and maintained without the use of a 
separate calculator and without further adjustments as the ground speed of 
the sprayer varies. The spray rate can be changed on the go by simply 
moving the control until it indicates the desired gallons per acre 
setting. No gear changes or multi-step adjusting procedures are required. 
The system eliminates the need to pump the chemical solution under 
pressure through the operator control. Problems of corrosion and clogging 
of the control are minimized. The ground wheel driven pump capacity only 
has to be sufficient to provide regulation since a separate pump delivers 
the solution to be sprayed to the nozzles or tips, reducing the size of 
the ground-driven pump and eliminating the problem of ground wheel 
slippage due to excessive pump loading. The desired spray rate is 
maintained without sophisticated controls, valves, or pumps, reducing cost 
and increasing the reliability and the life of the system. 
These and other objects, features, and advantages of the present invention 
will be apparent from the following description and the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The hydraulic rate control system for a sprayer diagrammatically 
represented in FIG. 1 includes separate hydraulic regulator and chemical 
solution spraying systems 10 and 12, respectively. The hydraulic regulator 
system 10 includes a fixed displacement pump 14, preferably of the gear 
type although other types could be used, driven by a ground wheel (not 
shown) in a conventional manner. The volumetric output of the pump 14 
varies with the ground speed of the sprayer. Connected to the pump 14 are 
an input line 16 and an output line 18. An operator control valve 
indicated generally at 20 and having a variable orifice 22 is connected 
between a line 23 and a return line 24 communicating with the output line 
18 so that the oil pump 14 directs its entire flow through the orifice 22. 
The output line is also connected to a control line 26 which in turn is 
connected to one section of a balance bypass valve 28, the operation of 
which is described in detail below. A reservoir 30 maintains a supply of 
oil or other suitable fluid which is circulated in the hydraulic regulator 
system 10. 
The chemical solution spraying system 12 includes supply hoses 32 and 34 
for directing the solution to the left- and right-hand booms of a 
conventional sprayer. The booms mount conventional nozzle tips 35 of 
various sizes which can be arranged in numerous spray patterns depending 
on the type of coverage desired. Spray valves 36 and 38 are provided for 
selectively opening and closing the fluid path to the supply hoses 32 and 
34 for right-hand or left-hand operation of the sprayer. 
A chemical supply pump 40 provides solution from a supply tank 41 to the 
supply hoses 32 and 34 via a high pressure output line 42. A bypass or 
return line 44 is connected to the output line 42 and directs the solution 
under pressure through the bypass valve 28 to a line 45 which empties into 
the tank 41. A low pressure input line 46 from the pump 40 communicates 
with the tank 41. The balance valve 28 maintains the pressure in the line 
44 and therefore in the line 42 feeding the booms equal to the pressure in 
the control line 26 in a manner described in detail below. The pump 40 is 
driven in a conventional manner preferably from the power take-off of the 
towing vehicle or from a pump drive if the sprayer is part of a 
self-propelled unit. 
The valve 28 includes a body 50 housing a piston assembly 52 and defining a 
control chamber 54 communicating with the control line 26. A chemical 
input port 56 cooperates with the lower end 58 of the piston assembly 52 
to provide a variable orifice indicated generally at 60, the size of which 
is dependent upon the position of the piston assembly 52 in the body, 
which in turn is dependent upon the pressures acting on the ends of the 
piston assembly. The control chamber 54 and the area of the balance valve 
28 surrounding the orifice 60 are separated by a pair of rolling diaphrams 
62 so that the fluid in the hydraulic regulator system 10 remains 
separated from the chemical solution in the spraying system 12. A manual 
control valve 64 is provided for static sprayer operation and includes a 
lower stem 66 which, when the valve is extended into the control chamber 
54, contacts the piston assembly 52 urging it downwardly to decrease the 
size of the opening 60. 
The function of the balance valve 28 when the manual control valve is in 
the upper position as shown in FIG. 1 is to regulate the chemical pressure 
in the line 44 so that it is equal to the oil pressure in the control line 
26. The oil pressure is dependent on the speed of the ground-wheel driven 
pump 14 and the setting of the variable orifice 22 of the operator control 
valve 20. The piston assembly 52 is free to move vertically depending upon 
the pressure of the oil in the line 26 and therefore in the control 
chamber 54, and the pressure of the chemical in line 44. The areas against 
which the fluid pressures act on either side of the piston assembly 52 are 
equal, and if the pressure in line 44 rises above the pressure in line 26, 
the piston will rise, increasing the size of the orifice 60 so that more 
of the chemical solution will flow through the bypass line 44 and the line 
45 into the tank 41 to reduce the output pressure of the supply pump 40. 
If the pressure at the input port 56 falls below the pressure in the line 
26, the piston will drop, decreasing the size of the orifice 60 to reduce 
the flow through the bypass line 44 and cause the output pressure of the 
pump to increase. 
The pressure in the line 26 which controls the pressure in the line 44 is 
determined by the speed of the ground wheel driven gear pump 14 and by the 
size of the variable orifice 22 which depends on the setting of the 
operator control valve or regulator 20. The valve 20 includes a dial 
assembly 70 with a knob 72 secured on a bolt 74 by a setscrew 76. The bolt 
74 is threaded through a body portion 78 of the valve assembly which in 
turn is secured to a valve frame 80 by a plurality of bolts 82. The bolt 
74 moves axially as it is turned by the knob 72. An arrow or indicator 84 
fixed to an annular plate 86 rotates with the knob. A gallons per acre 
(GPA) scale 88 is provided on a second annular ring 90 approximately 
concentric with ring 86. The ring 90 is mounted on an annular base 92 
which is secured to a third ring 94 which includes a width per tip scale 
(W/T) 96. The scales 88 and 96 are fixed with respect to each other, but 
are movable with respect to a tip size scale 98 on a fourth ring 100 fixed 
to the frame 80 by a series of sheet metal screws 102. A spring and washer 
assembly 104 is mounted coaxially with the bolt 74 between the knob 72 and 
the body 78 to provide a friction surface for the knob 72 to prevent 
unwanted setting changes. 
The inner end of the bolt 74 contacts a circular disk member 106 which is 
secured to the side of a shaft 108 by a bolt 110. The shaft 108 extends 
upwardly from a body portion 112 of the valve assembly 20. The lower 
portion of the bolt 108 extends into a chamber 114 located in the body 
portion 112. The chamber 114 communicates with the return line 24 through 
a connector and filter 116 and with the line 23 through a line connector 
118. An orifice disk 120 is retained on the end of the shaft 108 with a 
washer and nut assembly 122 and is maintained against an upper lip section 
124 of the body 112 in the chamber 114 by a spring 126 acting between the 
lower portion of the chamber and the lower portion of the disk. The shaft 
108 includes a portion with a square cross-section which receives a square 
aperture in the disk 120 to prevent relative rotation of the parts. A 
torsion spring 128 having one end secured through the orifice disk 120 and 
the other end fixed with respect to the body 112 biases the shaft 108 
about its axis so that the circular disk 106 remains abutted against the 
bolt 74. A small circular hole 130 is provided in the circular disk 120 
and remains aligned with a circular bore 132 which forms a passage between 
the connector 118 and the chamber 114. A second hole 134, essentially 
square, is provided in the circular disk 120 such that a corner of the 
hole lies approximately the same radial distance from the center of the 
disk 120 as the small hole 130. As the bolt 74 is unthreaded from the body 
78, the torsion spring 128 rotates the disk 120 and the square hole 134 
moves from the position shown in FIG. 3 to over the bore 132, increasing 
the size of the variable orifice 22. The small hole 130 also shifts 
towards the left from the position shown in FIG. 3 but remains in 
communication with the bore 132 even when the square hole 134 is in the 
maximum clockwise position. As the bolt 74 is threaded into the body 78, 
the size of the orifice 22 decreases until the square hole 134 is 
completely out of communication with the circular bore 132. The hole 130 
allows some oil to be pumped through the hydraulic regulator system 10 
even when the operator control valve is adjusted to the least flow 
position. 
As best seen in FIG. 4, the dial assembly 70 is arranged somewhat in the 
fashion of a circular slide rule with the three scales 88, 96 and 98 
graduated logarithmically. The arrow or indicator 84 which turns with the 
knob 72 as the bolt 74 is turned within the valve body 78 indicates the 
chemical application rate in gallons per acre on the scale 88. As noted 
previously, the gallons per acre scale 88 and the width per tip scale 96 
rotate in unison. The tip size scale 98 is stationary, and when setting up 
the dial assembly 70 the indication for the particular width per tip 
dimension used with the sprayer is moved to a position opposite the tip 
size on the scale 98. The GPA scale moves with the width per tip (W/T) 
scale. 
As the knob 72 is rotated in the counter-clockwise direction from the 
position shown in FIG. 4, the screw 74 moves outwardly with respect to the 
body 78. This allows the torsion spring to move the disk 106 and the shaft 
108 so that the square hole 134 in the circular disk 120 moves over the 
bore 132 to increase the size of the variable orifice 22, increasing the 
flow of oil through the bypass line 24 and therefore decreasing the 
pressure in the line 26. Rotating the knob 72 in the clockwise direction 
decreases the amount of the coincidence between the bore 132 and the 
square hole 134 to restrict flow in the line 24 and increase pressure in 
the line 26. 
The orifice formed by the holes 130 and 134 in alignment with the bore 132 
is controlled in such a manner by the knob 72 that the position of the 
control knob is approximated by the following equation: 
EQU N=K.sub.1 Log P (1) 
where N is the position of the control knob, P is the desired pump output 
pressure, and K.sub.1 is a constant. By having the position of the control 
knob a function of the log of the pressure, the dial assembly 70 can be 
used as a slide rule for setting tip size and width per tip since at a 
given speed: 
##EQU1## 
By adjusting the width per tip scale 96 by moving the third ring 94 with 
respect to the outer ring 100, the division function is achieved. The 
multiplication function is achieved by moving the knob 72 with the pointer 
84 which at the same time changes the size of the orifice 22. Therefore if 
the tip size is increased, the width per tip scale 96 would have to be 
rotated in the counterclockwise direction (FIG. 4) until the appropriate 
width per tip indication is aligned with the new tip size. The gallons per 
acre scale 88, which is connected to the width per tip scale 96 also is 
rotated in the counterclockwise direction. Therefore the indicator 84 will 
not have to be rotated as far in the clockwise direction to achieve the 
same gallons per acre rate as with the smaller tip size. Consequently the 
orifice 22 is larger and therefore the pressure at the line 26 is lower 
for a given GPA setting when a larger tip size is used. 
During operation of the sprayer as the ground speed is increased, the oil 
pressure out of the ground wheel driven pump 14 increases as follows: 
EQU P=K.sub.3 S.sup.2 (3) 
where P is the pump output pressure, S is the ground speed of the sprayer 
and K.sub.3 is a constant. The spray nozzles at the boom provides flow as 
follows: 
EQU Q=K.sub.4 .sqroot.P (4) 
where Q is the flow and P is the pressure at the spray nozzle, which in 
this case is equal to the pressure at the output of the pump 14 because of 
the action of the balance valve 28. Consequently, as the ground speed 
increases, flow increases proportionately according to the equation: 
EQU Q=KS. (5) 
In operation, the appropriate width per tip indication on the scale 96 is 
moved adjacent to the tip size on the scale 98. The knob 72 is turned so 
that the indicator 84 is aligned with the desired chemical application 
rate in gallons per acre on the scale 88. The booms are extended and the 
valves 36 and 38 are opened. The pump 40 is operated to supply fluid under 
pressure to the line 42 in the spraying system 12. As the sprayer moves 
across the field the pump 14 is driven at a speed proportional to the 
ground speed and supplies oil under pressure through line 26 to the 
balance valve 28 which maintains the pressure in the return line 44 and 
thus in the supply hoses 32 and 34 to the booms equal to the pressure in 
the line 26. If the ground speed increases or decreases, the pressure in 
line 26 varies accordingly, and the valve 28 acts to maintain the pressure 
in the line 44 at the same level so that the application rate remains 
essentially constant. If, for some reason, the operator wishes to change 
the application rate, he simply moves the indicator 84 opposite the 
desired gallons per acre coverage on the scale 88 thereby increasing or 
decreasing the size of the orifice 22 in the operator control valve 20. As 
the indicator 84 is moved in the clockwise direction, and the size of the 
orifice is decreased, the oil flow is restricted through the valve 20 and 
the output increases. The orifice 22 increases in size if the indicator 84 
is turned toward a smaller gallons per acre setting on the scale 88, and 
therefore more oil flows through the line 24 to decrease the pressure 
output of the pump 14 which, in turn, decreases the pressure of the 
chemical solution in the line 42. The output of pump 14 varies in 
accordance with the equation (3) above. 
Having described a preferred embodiment of the invention, various 
modifications within the spirit and scope of the invention will become 
apparent to those skilled in the art and can be made without departing 
from the underlying principle of the invention. Therefore, the invention 
should not be limited to the specific embodiment described and 
illustrated, but should be commensurate with the proper scope of the 
following claims.