Information
-
Patent Grant
-
6684959
-
Patent Number
6,684,959
-
Date Filed
Friday, August 2, 200221 years ago
-
Date Issued
Tuesday, February 3, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Tapolcai; William E.
- Ali; Mohammad M.
Agents
- Ryan Kromholz & Manion, S.C.
-
CPC
-
US Classifications
Field of Search
US
- 169 13
- 169 14
- 169 15
- 169 24
- 169 44
- 239 68
- 239 73
- 239 69
- 239 303
- 239 304
- 239 305
-
International Classifications
-
Abstract
A system and method of maintaining a desired additive to water ration in a fire-fighting system including a water flow sensor configured to measure the water flow rate, a water pump, a hydraulic pump, a linear hydraulic cylinder driven by the hydraulic pump, an additive pump mechanically coupled to the linear hydraulic cylinder; and a pump displacement sensor configured to sense the position of the additive pump, the pump displacement sensor being in communication with the water flow sensor to maintain a pre-determined ratio of additive to water.
Description
FIELD OF THE INVENTION
This invention relates to systems for extinguishing fires, and in particular to a system for adding liquid foam concentrate into water lines in predetermined proportions.
BACKGROUND OF THE INVENTION
Conventional foam additive systems for fighting fires employ numerous mechanisms for supplying foam liquid concentrate via supply conduits to one or more of the discharge outlets of a water pump. The goal of such a system is to achieve “balanced flow” between the fluid line, typically a water line; and the additive line, typically a foam concentrate supply line. At balanced flow, the system responds to high fluid flow with a correlatively high additive flow, and corresponds to low fluid flow with a relatively low additive flow. Thus, at high water flow, foam is added at an equal flow calculated to maintain a predetermined ratio of water to foam. The same is true for low flow.
“Balanced flow” is particularly important in the fire-fighting field, because the water to foam ratio is critical to optimize fire fighting efficiency based on the type of fire fuel that that is present. Ranges between 0.2%-6% of foam have been reported as optimal, depending on the composition and fuel of the target fire. Further complicating the task of balancing flow is the extremely variable water flows and pressures. Thus, the volume and pressure of foam must meet the varying pressure and volume of water being used.
An exemplary embodiment of an additive pump system is a hydraulically powered demand system that varies additive pump output in response to different readings from a flow meter installed in the water pump discharge line that measures water flow rate. In a “flow rate” system, balanced pressure is achieved by control of water flow and additive flow rates.
One such flow rate system is disclosed in U.S. Pat. No. 5,174,383 (1992) to Haugen et al. The water flow meter signal is processed by a controller, e.g., microprocessor. The microprocessor sends a signal to the additive pump, e.g., a positive displacement piston pump, to regulate the flow rate of the additive line. Further, a measure of the additive pump output is fed back to the microprocessor, e.g., a speed signal is sent from a tachometer coupled to the drive shaft of the additive pump, to maintain the additive flow rate at the proper proportion to the water flow rate.
Another flow rate system is disclosed in U.S. Pat. No. 5,765,644 (1998) to Arvidson. To maintain the additive flow rate at the proper proportion to the water flow rate, the additive pump provides a feedback signal from a magnetic pickup associated with a notched wheel coupled to the drive shaft of the additive pump. Alternatively, a flow meter may be employed to measure the additive flow rate downstream of the additive pump.
While prior art systems are capable of accurately maintaining a pre-selected ratio of additive to water, these systems typically employ expensive pumps, e.g., gear pumps. Further, these are complicated systems, with the complex nature of the system negatively impacting the system reliability and cost.
The need remains for simple, accurate, and cost-effective control and monitoring of additive line flow. To overcome shortcomings of the prior art, an improved system to accurately maintain a pre-selected ratio of additive to water is disclosed. The system employs a novel pump and hydraulic cylinder arrangement, including a linear variable displacement transducer (LVDT) to measure the position, and thereby determine the speed, of the additive pump. The system provides an accurate, yet simple, cost-effective proportioning system for maintaining a desired foam to water ratio.
SUMMARY OF THE INVENTION
One aspect of the invention provides an additive proportioning system for a firefighting vehicle. The system comprises a source of pressurized water, a source of additive, and a hydraulic pump. A water flow sensor is provided that is responsive to the source of pressurized water and configured to measure a water flow rate.
An actuator is fluidly connected to and driven by the hydraulic pump. An additive pump is mechanically coupled to the actuator and fluidly connected to the source of additive. The system further provides a pump displacement sensor configured to sense the position of the additive pump. The pump displacement sensor is in communication with the water flow sensor to maintain a pre-determined ration of additive to water.
In a preferred embodiment, the pump displacement sensor is a linear variable displacement transducer, the additive pump is a double acting piston pump, and the actuator is a hydraulic cylinder.
According to another aspect of the invention, the system further comprises a programmable logic controller.
According to another aspect of the invention, the system further comprises a proportioning valve in communication with a programmable logic computer.
According to another aspect of the invention, the additive is a thixotropic substance.
According to yet another aspect of the invention, the system provides multiple sources of additive.
According to another aspect of the invention, the system further comprises a means for mixing the additive with the water.
Another aspect of the invention provides an apparatus for mixing water and an additive in a firefighting vehicle. The apparatus comprises a programmable logic computer, a water flow sensor, and a hydraulic pump. The water flow sensor is responsive to a source of pressurized water and is electronically coupled to the controller. An actuator is fluidly connected to and driven by the hydraulic pump. An additive pump is mechanically coupled to the actuator and fluidly connected to a source of additive. An additive pump displacement sensor is configured to sense the position of the additive pump and is in communication with the controller.
In a preferred embodiment, the actuator is a hydraulic cylinder, the pump displacement sensor is a linear variable displacement transducer, and the additive pump is a double acting piston pump.
In a preferred embodiment, the controller provides communication between the water flow sensor, the proportioning valve, and the additive pump to maintain a pre-determined ratio of additive to water.
According to another aspect of the invention, the apparatus further comprises a proportioning valve fluidly connected to the hydraulic pump and the actuator. In a preferred embodiment, the proportioning valve is in communication with the controller.
According to another aspect of the invention, the apparatus further comprises a means for mixing the additive with the water.
According to another aspect of the invention, the controller adjusts the additive pump speed in response to the sensed direction of the additive pump.
Another aspect of the invention provides an additive proportioning apparatus comprising an actuator and an additive pump coupled to and driven by the actuator. The actuator is coupled to a linear variable displacement transducer that senses the position of the additive pump.
Another aspect of the invention provides a method of maintaining a desired additive to water ratio in a fire-fighting system. The method comprises the steps of inputting a pre-determined additive to water ratio into the controller; sensing the water flow rate; computing the additive flow rate by determining the position of a positive displacement piston pump at at least two defined intervals; computing the actual additive to water ratio based on the sensed water flow and additive flow rates; comparing the computed ratio with the input ratio; and adjusting the output of the positive displacement pump to substantially match the input ratio.
According to another aspect of the invention, the method further comprises the steps of re-sensing the water flow rate; re-sensing the additive flow rate; re-computing the actual additive to water ratio; re-comparing the computed ratio with the input ratio; and re-adjusting the output of the positive displacement pump.
DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic of a foam concentrate proportioning system for rescue and fire fighting vehicles embodying features of the invention.
FIG. 2
is a schematic of an alternative embodiment of the system shown in
FIG. 1
illustrating an alternative arrangement of the hydraulic cylinder and additive pump shown in FIG.
1
.
FIG. 3
is a partial sectional view of a hydraulic cylinder coupled to a linear variable displacement transducer.
FIG. 4
is an enlarged view of the additive pump shown in FIG.
1
and showing the path of additive through the pump and the resulting movement of the piston in a forward direction.
FIG. 5
is an enlarged view of the additive pump shown in FIG.
1
and showing the path of additive through the pump and the resulting movement of the piston in a reverse direction.
FIG. 6
is a software flow diagram useful in understanding the manner in which the microprocessor-based controller may be programmed.
DETAILED DESCRIPTION
Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention that may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
I. Additive Proportioning System
An additive proportioning system
10
suitable for use in fire-fighting and rescue vehicles is shown schematically in FIG.
1
. The system
10
desirably includes a series of conventional ball valves
12
and check valves
14
to control the flow of fluid through the system
10
. If desired, ball valves
12
can be motorized for ease of operation. It is to be understood that the arrangement of ball valves
12
and check valves
14
can vary. In addition, a greater or lesser number of ball valves
12
and check valves
14
than shown in the illustrated embodiment can be provided.
A primary fire fighting fluid, such as water is supplied via the water supply
16
, e.g., a fire hydrant. The water supply
16
is connected to a water pump
18
through intake conduit
19
as is common in fire-fighting apparatus. Arrows and double dot dash lines in
FIG. 1
depict the path of water flow. As
FIG. 1
shows, the water flow path is split as the water is discharged from the water pump
18
through branched conduit
20
. A portion of the water is directly discharged through conduit
20
. Thus, conduit
20
can serve as a waste line. Alternatively, conduit
20
can be used as an additional fire-fighting line should it be desirable to discharge water directly onto a fire without the addition of an additive.
A portion of the water discharged from the water pump
18
follows the path of branch
20
A into a mixing manifold
22
for mixing with an additive. A conventional flow meter
24
comprised of an electro-mechanical sensor monitors the water flow rate through conduit
20
A. In the preferred embodiment, the flow meter
24
is a Model 220B flow meter manufactured by Data Industrial of Mattapoisett, Mass. The sensed data is then input through signal line
26
to a programmable controller
28
, e.g., a conventional microprocessor, to calculate the water flow rate.
In the preferred embodiment, the controller
28
is a programmable digital controller, e.g., Pierce brand manufactured by HED of Hardford, Wis. A power source
30
, such as the power source from the rescue or firefighting vehicle, provides power to the controller
28
through electrical line
31
. A switch or switching means is also provided to turn the controller
28
“on” and “off” at the appropriate times (not shown).
In the preferred embodiment, a thixotropic material is the additive traditionally mixed with water and used to fight fires. More preferably, liquid foam concentrate is the additive to the water. However, additives other than a thixotropic material or liquid foam concentrate may be used based on fire fighting efficacy.
Liquid foam concentrate is supplied from dual additive tanks
32
, which may hold the same or different additives. The path of additive flow is depicted by arrows and dashed lines in FIG.
1
. Additive tanks
32
are connected to an additive pump
34
, which will be described in detail later. Branched conduit
36
connects the additive tanks
32
to the additive pump
34
. An inlet
38
can be provided to allow for the connection of an external additive source with conduit
36
. Conduit
36
can include a screen filter
40
that serves to remove undesired matter and debris from the additive solution.
As will be apparent, any number of additive tanks
32
or external additive sources can be employed. Conduit
42
connects the additive pump
34
with the mixing manifold
22
for mixing the additive with water and discharging the mixture through conduit
44
, e.g., via a hose and nozzle (not shown).
The system
10
includes a conventional hydraulic system
46
of the type well known in the art. Arrows and dot-dash lines in
FIG. 1
depict the flow path of hydraulic fluid through the hydraulic system
46
. The system
46
comprises a hydraulic fluid reservoir
48
, a hydraulic pump
50
, a heat exchanger
52
and a proportional directional control valve
54
. In the preferred embodiment, the pump
50
is a gear pump manufactured by Bosch Rexroth of Hoffman Estates, IL. The control valve
54
is a proportional control valve. In the preferred embodiment, the valve
54
is a Rexroth valve manufactured by Bosch Rexroth of Hoffman Estates, Ill. A portion of the water as it is discharged from the water pump
18
is diverted through branch
20
B and is circulated through a heat exchanger
52
to cool the hydraulic circuit. A return line
56
directs the water from the heat exchanger
52
back to the water pump
18
for recycling through the system
10
.
The hydraulic pump
50
may be driven by any of a number of power inputs. In the preferred embodiment, the pump
50
is driven by a water pump transmission
58
by drive shaft
60
. The same transmission also drives the water pump
18
by drive shaft
62
. In an alternative embodiment, the pump
18
may be driven by any conventional power take-off (not shown) on the vehicle to which the system
10
is installed. The pump
50
operates above a predetermined speed therefore assuring that a sufficient volume and pressure of hydraulic fluid is supplied to the proportional directional control valve
54
.
The hydraulic pump
50
drives a linear actuator, e.g., a conventional positive displacement, piston type hydraulic cylinder
64
having a piston/rod assembly
66
The assembly
66
includes a piston
65
coupled to a rod
67
and configured for fore and aft movement within a cylinder
69
(see also FIGS.
4
and
5
). In the preferred embodiment, the cylinder
64
has a piston diameter of 1.5 inches and a piston stroke of approximately eight inches.
The system
10
desirably includes a proportioning valve
54
of the type known in the art to control the direction of hydraulic fluid flow through the hydraulic cylinder
64
. The proportioning valve
54
permits fluid flow in a first direction while preventing flow in the reverse direction to advance the assembly
66
of hydraulic cylinder
64
in a first direction while preventing flow in the reverse direction to advance the assembly
66
in a first direction. The valve
54
then permits flow in the reverse direction while preventing flow in the first direction thereby moving the assembly
66
in the reverse direction. The volume flow rate of hydraulic fluid is varied by the proportioning valve
54
based upon pulse width modulation input from the controller
28
through signal line
74
.
The hydraulic cylinder
64
is mechanically coupled to (e.g., by rod
76
) and serves to drive the additive pump
34
. In the embodiment illustrated in
FIG. 1
, the hydraulic cylinder
64
is positioned spaced from and parallel to the additive pump
34
. In an alternative embodiment, shown in
FIG. 2
, the hydraulic cylinder
64
is coupled to the additive pump
34
in a linear configuration. It is to be understood that the cylinder
64
and pump
34
may be variously positioned with respect to one another and such other arrangements will be apparent to those skilled in the art.
With reference to
FIG. 3
, the hydraulic cylinder
64
carries a linear variable displacement transducer (LVDT)
78
of the type known in the art. In a preferred embodiment, the LVDT
78
is a Model ICS 100 manufactured by Penny & Giles of Cwmfelinfach, Gwent, UK and Christchurch, Dorset, UK.
The LVDT
78
can be positioned within a bore
80
in rod
70
. The LVDT
78
is coupled to the cylinder
72
by threaded connector
82
. The LVDT
78
includes a slider
84
which permits the LVDT
78
to remain stationary with respect to rod
70
, while permitting fore and aft movement of rod
70
along the LVDT
78
. Movement of rod
70
alters the voltage output of the LVDT
78
. This arrangement thus permits the LVDT
78
to sense the position of the assembly
66
, and thereby the position of coupled additive pump
34
.
With reference to
FIGS. 4 and 5
, the additive pump
34
is a large bore conventional positive displacement, piston pump comprising a piston/rod assembly
86
sized and configured for fore and aft movement within a cylinder
88
. The assembly
86
includes a piston
90
coupled to a rod
92
In a preferred embodiment, the pump
34
is a FSC pump manufactured by Fluid System Components of DePere, Wis. Movement of the assembly
86
in a given direction draws a pre-determined amount additive into the pump
34
and contemporaneously expels a pre-determined amount of additive from the pump
34
. A pair of check valves
94
and
96
control flow of additive into the pump
34
from conduit
36
. Another pair of check valves
98
and
100
control flow of additive from the pump
34
through conduit
42
. This arrangement permits the pump
34
to serve as a double-acting pump, as illustrated in
FIGS. 4 and 5
.
As shown in
FIG. 4
when the assembly
86
advances in a forward direction (i.e., moves from right to left in direction of piston
90
, as shown in FIG.
3
), check valve
96
permits fluid flow into the pump
34
(as represented by arrow) and check valve
98
permits fluid flow out of the pump
34
(as represented by the arrow) while the remaining check valves
94
and
100
prevent flow in the reverse direction.
In this arrangement the pump displaces a given amount of fluid (F1) in front of the piston
90
(i.e., side of piston
90
away from rod
92
)
As shown in
FIG. 5
when the assembly
86
moves in the reverse direction (i.e., moves from left to right in direction of rod
92
, as shown in FIG.
4
), check valve
94
permits fluid flow into the pump
34
(as represented by the arrow) and check valve
100
permits fluid flow out of the pump (as represented by the arrow) while the remaining check valves
96
and
98
prevent flow in the reverse direction.
In this arrangement the pump
34
displaces a given amount of fluid (F2) behind the piston
90
(i.e., side of piston
90
coupled to rod
92
). As is apparent to one of skill in the art, because the rod
92
consumes space that would otherwise be available for fluid, the volume of fluid displaced is reduced, i.e., F2 is less than F1.
In a representative embodiment, F1 is 0.109 gallons of additive and F2 is 0.082 gallons of additive, providing a F1/F2 ratio of 1.33/1.
The LVDT
78
senses the position of the assembly
86
at given time intervals and inputs the sensed information into the controller
28
through signal line
102
for calculation of the position and speed of the assembly
86
. An input from the LVDT
78
of increased voltage corresponds to movement of the assembly
86
in the forward direction (i.e., in direction of piston
90
). An input from the LVDT
78
of reduced voltage corresponds to movement of the assembly
86
in the reverse direction (i.e., in direction of rod
92
). The controller
28
responds to the reduced volume of fluid displacement in the reverse direction by increasing the speed of movement of the assembly
86
.
Thus, the controller
28
provides communication between the LVDT
78
, the flow meter
24
, and the proportioning valve
54
. The rate of hydraulic fluid flow from the proportioning valve
54
is varied in response to output from the controller
28
(in response to signals received from the flow meter
24
and the LVDT
78
) to control the speed of the additive pump
34
so as to maintain a pre-determined ratio of additive to water.
II. System Use
The described system
10
thus maintains the predetermined ratio by monitoring water and additive flow rates at regular intervals and adjusting the speed of the additive pump
34
in response to sensed water flow rate and the speed, direction and position of piston
90
.
FIG. 6
provides a flow chart illustrating a portion of a program for maintaining a desired additive to water ratio. Other programs will be apparent to those skilled in the art.
The controller
28
receives input from the water flow meter
24
and compares the sensed flow to a desired flow rate (e.g., >10 GPM). A user interface desirably provides a display of the sensed flow rate and indicates whether the flow rate is within the desired range.
The controller
28
reads the desired setpoint, i.e., the desired additive to water ratio range entered previously into the controller
28
by firefighting personnel and determines whether the water flow rate is within the maximum of a pre-selected range for the desired setpoint. If the sensed flow rate is within the range, the controller
28
calculates the additive pump assembly
86
speed in both directions needed to maintain the desired setpoint. If the sensed flow rate is not within the pre-selected water flow range, the interface can be configured to display a pre-selected message at given intervals (e.g., flash message for 1 second every 3 seconds).
The controller
28
desirably reads the LVDT
78
at pre-defined time intervals to determine the position of the assembly
86
and thereby determines the rate of speed and the direction of the assembly
86
The controller
28
first determines if the assembly
86
is moving. In a preferred embodiment, if the controller
28
does not detect movement, the controller
28
determines whether the assembly
86
is at the end of a stroke. If the assembly
86
is not at the end of a stroke, such as in the initial start-up of the system
10
, the assembly
86
is advanced in a first direction (e.g., away from rod
92
) and the assembly
86
speed in that direction is read for input into the controller
28
. If the assembly
86
is at the end of a stroke, the assembly
86
is moved in the new direction and the controller
28
then reads the assembly
86
speed for the new direction.
When the controller
28
detects movement of the assembly
86
, the controller
28
then determines if the assembly
86
is moving at the correct speed to maintain the desired ratio. If the assembly
86
is moving at the desired speed, the controller
28
sends an output signal to the proportioning valve
54
to maintain the desired speed. However, if the assembly
86
is moving at too fast or too slow of speed, the controller
28
sends an output signal to the proportioning valve
54
to decrease or increase assembly
86
speed respectively. The system thereby maintains the desired additive to water ratio.
An inherent drawback of double-acting pump systems is that the volume of fluid ahead of the piston
90
is greater than the volume of fluid behind the piston
90
. As previously noted, the controller
28
compensates for this inherent drawback so that pump
34
output remains constant.
The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
Claims
- 1. An additive proportioning system for a firefighting vehicle comprising:a source of pressurized water; a source of additive; a water flow sensor responsive to the source of pressurized water and configured to measure a water flow rate; a hydraulic pump; an actuator fluidly connected to and driven by the hydraulic pump; an additive pump mechanically coupled to the actuator and fluidly connected to the source of additive; and a pump displacement sensor configured to sense the position of the additive pump, said pump displacement sensor being in communication with the water flow sensor to maintain a pre-determined ratio of additive to water.
- 2. A system as in claim 1wherein the hydraulic pump is driven by an auxiliary transmission.
- 3. A system as in claim 1wherein the hydraulic pump is driven by a power take-off of the vehicle.
- 4. A system as in claim 1 further comprising:a programmable logic controller.
- 5. A system as in claim 4wherein the water flow sensor sends an input signal to the controller.
- 6. A system as in claim 4wherein the pump displacement sensor sends an input signal to the controller.
- 7. A system as in claim 4wherein the water flow sensor and the pump displacement sensor send an input signal to the controller.
- 8. A system as in claim 1 further comprising:a proportioning valve fluidly coupled to a source of hydraulic fluid and configured to drive the actuator.
- 9. A system as in claim 8wherein the proportioning valve is in communication with a programmable logic controller.
- 10. A system as in claim 9wherein the controller sends an output signal to the proportioning valve.
- 11. A system as in claim 1wherein the additive is a thixotropic substance.
- 12. A system as in claim 1 further comprising:multiple sources of additive.
- 13. A system as in claim 1, further comprising:a means for mixing the additive with the water.
- 14. A system as in claim 13wherein the means for mixing the additive with the water is a manifold.
- 15. A system as in claim 1wherein the actuator is a hydraulic cylinder.
- 16. A system as in claim 1wherein the pump displacement sensor is a linear variable displacement transducer.
- 17. A system as in claim 1wherein the additive pump is a piston pump.
- 18. A system as in claim 17wherein the additive pump is a double-acting piston pump.
- 19. An apparatus for mixing water and an additive in a firefighting vehicle, the apparatus comprising:a programmable logic controller; a water flow sensor responsive to a source of pressurized water and electronically coupled to the controller; a hydraulic pump; an actuator fluidly connected to and driven by the hydraulic pump; an additive pump mechanically coupled to the actuator and fluidly connected to a source of additive; and an additive pump displacement sensor configured to sense the position of the additive pump, the pump displacement sensor being in communication with the controller.
- 20. An apparatus as in claim 19wherein the hydraulic pump is driven by a hydraulic pump motor.
- 21. An apparatus as in claim 19 further comprising:a proportioning valve fluidly connected to the hydraulic pump and the actuator.
- 22. A system as in claim 21wherein the proportioning valve is in communication with the controller.
- 23. An apparatus as in claim 22wherein the controller provides communication between the water flow sensor, the proportioning valve, and the additive pump to maintain a pre-determined ratio of additive to water.
- 24. An apparatus as in claim 19, further comprising:a means for mixing the additive with the water.
- 25. An apparatus as in claim 24wherein the means for mixing the additive with the water is a manifold.
- 26. An apparatus as in claim 19wherein the actuator is a hydraulic cylinder.
- 27. An apparatus as in claim 19wherein the pump displacement sensor is a linear variable displacement transducer.
- 28. An apparatus as in claim 19wherein the additive pump is a piston pump.
- 29. An apparatus as in claim 28wherein the additive pump is a double acting piston pump.
- 30. An apparatus as in claim 19 whereinwherein the programmable logic controller adjusts the additive pump speed in response to the sensed direction of the additive pump.
- 31. An additive proportioning apparatus comprising:an actuator; an additive pump coupled to and driven by the actuator; wherein the actuator is coupled to a linear variable displacement transducer that senses the position of the additive pump.
- 32. An apparatus as in claim 31wherein the additive pump is a positive displacement piston pump.
- 33. An apparatus as in claim 32wherein the additive pump is a double acting pump.
- 34. An apparatus as in claim 31wherein the actuator is a positive displacement piston pump.
- 35. An apparatus as in claim 31wherein the additive is a thixotropic substance.
- 36. A method of maintaining a desired additive to water ratio in a fire-fighting system comprising the steps of:inputting into a controller a pre-determined additive to water ratio; sensing the water flow rate; computing the additive flow rate by determining the position of a positive displacement piston pump at at least two defined intervals; computing the actual additive to water ratio based on the sensed water flow and additive flow rates; comparing the computed ratio with the input ratio; and adjusting the output of the positive displacement pump to substantially match the input ratio.
- 37. A method as in claim 36, further comprising the steps of:re-sensing the water flow rate; re-sensing the additive flow rate; re-computing the actual additive to water ratio; re-comparing the computed ratio with the input ratio; and re-adjusting the output of the positive displacement pump.
- 38. A method as in claim 36wherein the additive is a thixotropic substance.
US Referenced Citations (46)
Foreign Referenced Citations (2)
Number |
Date |
Country |
3038-334 |
Oct 1982 |
DE |
000040595 |
Nov 1981 |
EP |