US20150233184A1

US20150233184A1 - System for regulation and control of water pressure and flow rate in a high pressure water application

Info

Publication number: US20150233184A1
Application number: US14/621,797
Authority: US
Inventors: Michael K. Pettay
Original assignee: Alamo Group Inc
Current assignee: Alamo Group Inc
Priority date: 2014-02-20
Filing date: 2015-02-13
Publication date: 2015-08-20

Abstract

A water bypass valve and system for regulation and control of water pressure and water flow rate in high pressure water applications having a water pressure safety relief valve. An operator may select a desired water pressure setting in an operator interface. The water system may be controlled by a computer processor that receives pressure data from a transducer in a high pressure discharge line and a speed sensor at a water pump drive shaft. The water bypass valve, controlled by the computer processor, may regulate water flowing back to the water supply tank, allowing the safety relief valve to remain closed over a wide range of water pump operating speeds.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/942,424 filed Feb. 20, 2014, the disclosure of which is incorporated herein by reference.

BACKGROUND

High pressure water applications include, but are not limited to, operations such as high pressure power washing and excavation. In the soil excavation process, high pressure water is used to loosen and excavate soil and other components while industrial strength vacuum is used to evacuate the debris. This process is favored when excavating around existing buried pipes, cables, and the like. However, it is also utilized in potholing, slot trenching, and other non-destructive excavations.
Because of the numerous variations of high pressure water applications, wide ranges of operating parameters (such as water pressure and flow rates) are required. Operators need to have the ability to adjust water pressure and flow rate as dictated by the job type and job conditions. However, water pumps currently utilized in most high pressure water applications have lubrication systems that require a minimum speed (e.g., rpm) to properly lubricate the internal components of the high pressure water pump. Further, water flow is proportional to the speed of the water pump.
With previous systems, if only a portion of the water flow resulting from a particular pump speed is utilized, a back pressure may be created and excess flow may be returned to the water supply tank, as necessary, via a standard safety pressure relief valve if the back pressure exceeds the design pressure of the safety relief valve. Thus, for a given water pump, this operating feature of previous systems may prevent an operator from operating over a wide range of flow rates at a pressure less than the system relief setting, regardless of what a particular job or application may require.

SUMMARY

Some embodiments of a system as described herein may provide a control system that senses the required flow needed (at a given pressure) for a particular job and regulates excess water to flow back to the water supply tank without going through the standard system relief valve. Some embodiments of the present invention may allow an operator to select the water flow and water pressure required for a given situation over a much wider range than has previously been possible.
As described herein, an operator may regulate water flow from about 25 gpm (gallons per minute) to 0 gpm, for example, at a selected pressure with one size water pump. In the past, the maximum/minimum flows possible were completely dependent on the particular size water pump utilized. For example, a 25 gpm water pump, due to minimum speed requirements, may have a minimum flow rate of approximately 10 gpm, for instance. In order to get flows down to a lower amount, such as 3-5 gpm, for instance, at the same pressure, a smaller water pump (e.g., a 10 gpm pump) may have been required. Thus, in situations where the high pressure water system is mounted on a mobile chassis or trailer, for example, the operator would have to change out the water pump. Embodiments of the present inventive system and apparatus may allow an operator with a given water pump to operate in multiple job conditions, because one pump can provide a wider range of flow rates.
In some embodiments of the present inventive system, the operator may select an appropriate operational pressure setting and the water system may be controlled by a computer processor (e.g., a microprocessor) that receives pressure data from a pressure transducer in the high pressure water discharge line and a speed sensor at the water pump drive motor. A unique electro-hydraulic water (EHW) bypass valve controlled by the microprocessor may regulate excess water flowing back to the water supply tank, allowing the standard safety relief valve to remain closed during a wider range of operating conditions.
In some embodiments, a system for regulation and control of water pressure and flow rate in high pressure water applications may include: a variable speed water pump configured for receiving water from a water reservoir; a discharge conduit configured for passing water from the water pump to a nozzle; a relief valve in fluid communication with the discharge conduit, the relief valve having a pressure limit, wherein the relief valve is configured to divert water from the discharge conduit to the water reservoir if a water pressure in the discharge conduit exceeds the pressure limit; a variable flow bypass valve in fluid communication with the discharge conduit, the bypass valve being controllable between a closed position and a fully open position, the bypass valve being configured to divert water from the discharge conduit to the water reservoir when the bypass valve is in an open position; a speed sensor configured for sensing a speed of the water pump; a pressure transducer configured for sensing a pressure in the discharge conduit; and a computer configured for setting a preselected water pressure via an operator interface, the preselected water pressure being less than the pressure limit; receiving a speed input signal from the speed sensor; receiving a pressure input signal from the pressure transducer; and in response to the input signals, controlling the speed of the water pump within a range of speeds and controlling the bypass valve in a manner that tends to maintain the pressure in the discharge conduit at the preselected water pressure.
In some embodiments, the system may further include a hydraulic control system having: a hydraulic drive pump configured for engagement with a power takeoff of a vehicle; a hydraulic drive motor operatively connected to the hydraulic drive pump, the hydraulic drive motor being operatively engaged with the water pump; a hydraulic controller configured for receiving a first output signal from the computer, the hydraulic controller being operatively engaged with the hydraulic drive pump; and a proportional hydraulic pressure control valve configured for receiving a second output signal from the computer, the proportional hydraulic pressure control valve being operatively engaged with the bypass valve; wherein the hydraulic controller is configured for controlling the speed of the water pump via the hydraulic drive pump and the hydraulic drive motor in response to the first output signal; and wherein the proportional hydraulic pressure control valve is configured for controlling the bypass valve in response to the second output signal. The hydraulic control system may further include a hydraulic charge pump operatively engaged with the hydraulic drive pump and in fluid communication with the hydraulic controller and the proportional hydraulic pressure control valve.
In some embodiments, the water pump may have a minimum speed, and the computer may be further configured to reduce the speed of the water pump if the pressure in the discharge conduit is greater than the preselected water pressure and the speed of the water pump is greater than the minimum speed.
In some embodiments, the computer may be further configured to divert water from the discharge conduit through the bypass valve if the pressure in the discharge conduit is greater than the preselected water pressure and the speed of the water pump is less than or equal to the minimum speed.
In some embodiments, an electro-hydraulic water bypass valve may be provided for use in a system having a water pressure safety relief valve for regulation and control of water pressure applications. The system may include an operator interface for setting a preselected water pressure, a computer receiving input from a water pump speed sensor and a water pressure transducer, wherein output from the computer regulates a variable displacement hydraulic drive pump and a proportional pressure control valve. A hydrostatic drive motor may be operatively connected to the variable displacement hydraulic drive pump and a high pressure water pump, the high pressure water pump being in fluid communication with a water intake conduit extending from a water supply tank. A discharge conduit may extend from an output side of the high pressure water pump to a discharge nozzle, the discharge conduit being in fluid communication with the water pressure safety relief valve. A fixed displacement charge pump may be engaged with the variable displacement hydraulic drive pump and in fluid communication with the proportional pressure control valve. The electro-hydraulic water bypass valve may include: a needle valve having an inlet in fluid communication with the discharge conduit, an outlet in fluid communication with the water supply tank, and a valve stem; a valve spring configured for urging the valve stem in a first direction; and a hydraulic cylinder having a cylinder output shaft configured for urging the valve stem in a second direction opposite the first direction, thereby moving the needle valve between an open position and a closed position; wherein the proportional pressure control valve is in fluid communication with and adapted for controlling the hydraulic cylinder, thereby regulating bypass water from the discharge conduit to the water supply tank in response to output from the computer. In some embodiments, the needle valve may be biased toward the open position by the valve spring. In some embodiments, the valve spring may be compressed by a spring plate, the valve stem may include a threaded portion having a nut threaded thereon, the nut may be engaged with the spring plate, and the valve stem may be slidably disposed through the spring plate.
In some embodiments, a method of controlling a pressurized water system may be provided. The system may have a variable speed water pump in fluid communication with a water reservoir and a discharge conduit, a nozzle in fluid communication with the discharge conduit, a safety relief valve in fluid communication with the discharge conduit, the safety relief valve having a pressure limit and being configured to divert water from the discharge conduit to the water reservoir if a pressure in the discharge conduit exceeds the pressure limit, a bypass valve in fluid communication with the discharge conduit, a hydraulic pressure control valve configured for controlling the bypass valve, a hydraulic controller configured for controlling a hydraulic motor, the hydraulic motor being configured for driving the water pump, and a computer in communication with the hydraulic controller and the hydraulic pressure control valve. The method may include: setting a preselected water pressure for the system in the computer via an operator interface, the preselected water pressure being less than the pressure limit; activating the water pump; sensing a pressure in the discharge conduit using a pressure transducer; sending a first signal representative of the pressure as a first input to the computer; sensing a speed of the water pump using a speed sensor; sending a second signal representative of the speed as a second input to the computer; and in response to the first and second signals, sending a first output signal from the computer to the hydraulic controller thereby controlling the speed of the water pump within a range of speeds and sending a second output signal from the computer to the hydraulic pressure control valve thereby controlling the bypass valve in a manner that tends to maintain the pressure in the discharge conduit at the preselected water pressure.
In some embodiments, the water pump may have a minimum speed, and the method may further include reducing the speed of the water pump if the pressure in the discharge conduit is greater than the preselected water pressure and the speed of the water pump is greater than the minimum speed.
In some embodiments, the method may further include diverting water from the discharge conduit through the bypass valve if the pressure in the discharge conduit is greater than the preselected water pressure and the speed of the water pump is less than or equal to the minimum speed.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of a system for regulation and control of water pressure and flow rate in a high pressure water application is shown in the accompanying drawings in which:

FIG. 1 is a schematic diagram of a water control and regulation system.

FIG. 2 is a front elevation view in partial cross-section of the EHW bypass valve of the system of FIG. 1.

FIG. 3 is a side elevation view of the EHW bypass valve of the system of FIG. 1.

FIG. 4 is a top front perspective view of the EHW bypass valve of the system of FIG. 1.

FIG. 5 is a top back perspective view of the EHW bypass valve of the system of FIG. 1.

DETAILED DESCRIPTION

The following terms as used herein should be understood to have the indicated meanings unless the context requires otherwise.
When an item is introduced by “a” or “an,” it should be understood to mean one or more of that item.
“Communication” means the transmission of one or more signals from one point to another point. Communication between two objects may be direct, or it may be indirect through one or more intermediate objects. Communication in and among computers, I/O devices and network devices may be accomplished using a variety of protocols. Protocols may include, for example, signaling, error detection and correction, data formatting and address mapping. For example, protocols may be provided according to the seven-layer Open Systems Interconnection model (OSI model), the TCP/IP model, or any other suitable model.
“Comprises” means includes but is not limited to.
“Comprising” means including but not limited to.
“Computer” means any programmable machine capable of executing machine-readable instructions. A computer may include but is not limited to a general purpose computer, mainframe computer, microprocessor, computer server, digital signal processor, personal computer (PC), personal digital assistant (PDA), laptop computer, desktop computer, notebook computer, smartphone (such as Apple's iPhone™, Motorola's Atrix™ 4G, and Research In Motion's Blackberry™ devices, for example), tablet computer, netbook computer, portable computer, portable media player with network communication capabilities (such as Microsoft's Zune HD™ and Apple's iPod Touch™ devices, for example), camera with network communication capability, wearable computer, point of sale device, or a combination thereof. A computer may comprise one or more processors, which may comprise part of a single machine or multiple machines.
“Computer readable medium” means an article of manufacture having a capacity for storing one or more computer programs, one or more pieces of data, or a combination thereof. A computer readable medium may include but is not limited to a computer memory, hard disk, memory stick, magnetic tape, floppy disk, optical disk (such as a CD or DVD), zip drive, or combination thereof.
“GUI” means graphical user interface.
“Having” means including but not limited to.
“Interface” means a portion of a computer processing system that serves as a point of interaction between or among two or more other components. An interface may be embodied in hardware, software, firmware, or a combination thereof.
“I/O device” may comprise any hardware that can be used to provide information to and/or receive information from a computer. Exemplary I/O devices may include disk drives, keyboards, video display screens, mouse pointers, joysticks, trackballs, printers, card readers, scanners (such as barcode, fingerprint, iris, QR code, and other types of scanners), RFID devices, tape drives, touch screens, cameras, movement sensors, network cards, storage devices, microphones, audio speakers, styli and transducers, and associated interfaces and drivers.
“Memory” may comprise any computer readable medium in which information can be temporarily or permanently stored and retrieved. Examples of memory include various types of RAM and ROM, such as SRAM, DRAM, Z-RAM, flash, optical disks, magnetic tape, punch cards, EEPROM, and combinations thereof. Memory may be virtualized, and may be provided in or across one or more devices and/or geographic locations, such as RAID technology, for example.
“Module” means a portion of a program.
“Program” may comprise any sequence of instructions, such as an algorithm, for example, whether in a form that can be executed by a computer (object code), in a form that can be read by humans (source code), or otherwise. A program may comprise or call one or more data structures and variables. A program may be embodied in hardware, software, firmware, or a combination thereof. A program may be created using any suitable programming language, such as C, C++, Java, Perl, PHP, Ruby, SQL, other languages, and combinations thereof. Computer software may comprise one or more programs and related data. Examples of computer software may include system software (such as operating system software, device drivers and utilities), middleware (such as web servers, data access software and enterprise messaging software), application software (such as databases, video games and media players), firmware (such as software installed on calculators, keyboards and mobile phones), and programming tools (such as debuggers, compilers and text editors).
“Signal” means a detectable physical phenomenon that is capable of conveying information. A signal may include but is not limited to an electrical signal, an electromagnetic signal, an optical signal, an acoustic signal, or a combination thereof.
For exemplary purposes only, an embodiment of the present invention is described as associated with a mobile, highway speed, hydroexcavating machine. One such machine is the VacAll Industries unit identified as the VacAll AllExcavate™ machine. In a particular environment, the excavating system may derive its power from any source adapted to drive a hydrostatic drive pump. In some embodiments described herein, the power may be derived from a power takeoff connected to the transmission of a truck which transports the chassis-mounted machine.
Turning to FIG. 1, a schematic of a water pressure and flow control system 10 is illustrated. Broadly described, a high pressure water pump 12 may draw water from a water supply tank or reservoir 14 and deliver the water via a discharge conduit 16 to a lance or handgun 21 having a discharge nozzle 18. The operator may control the water discharge by activation of a trigger or controller at the lance 21.
System 10 may have a water pressure safety relief valve 20 in fluid communication at an upstream location 15 of the discharge conduit 16 to allow water to flow back to the water supply tank 14 in situations where the water pressure in the discharge conduit 16 exceeds a prescribed, high pressure limit. Without EHW bypass valve 22 as described below, if the operator were to reduce the water flow from the nozzle 18 below a certain threshold, a back pressure may be created in the output conduit 16 because the speed of the water pump 12 may not be able to be reduced sufficiently due to pump lubrication requirements. When the back pressure exceeds the safety limit set on relief valve 20, the excess water flow would be dumped back to the water supply tank 14 via safety relief conduit 19. Thus, without EHW bypass valve 22, it would be difficult to control the water discharge flow over a broad range of pump speeds.
In light of that, the system 10, as shown in FIG. 1, may incorporate a unique EHW bypass valve 22 disposed at a downstream location 17 of the discharge conduit 16. This bypass valve 22 may open and close in response to water pressure sensed in discharge conduit 16 and the speed of the high pressure water pump 12. As described further below, this bypass valve 22 may allow the operator to reduce the flow rate from the nozzle 18 over a broad range of pump speeds.
As shown in FIG. 1, an operator interface device 24 may allow the operator to enter a prescribed or preselected water discharge pressure setting. A microprocessor or other suitable computer 26, well known and understood in the art, may receive input from a water pump speed sensor 28 operatively disposed at the pump input shaft 30. Interface device 24 may be part of or separate from computer 26. The computer 26 may also receive data from a water pressure transducer 32 operatively disposed in fluid communication with an upstream location 15 of discharge conduit 16. The computer 26 may utilize the data received from both sensor 28 and transducer 32 to control and regulate a variable displacement pump 34 and a proportional pressure control valve 36 which operatively controls the EHW bypass valve 22, as will be described further below. Thus, by utilizing data from the sensor 28 and transducer 32, the speed of the water pump 12 may be varied and water pressure in the discharge conduit 16 (and, ultimately the nozzle 18) may be controlled via the EHW bypass valve 22, thereby controlling and regulating the water flow rate over a wide range of values.
As will be appreciated by persons of ordinary skill in the art, computer 26 may have one or more memories programmed with one or more programs on one or more computer readable media configured for carrying out the control processes described herein. Computer 26 may also have one or more I/O devices (such as interface device 24) and one or more GUI's or other user interfaces configured for allowing a user to operate computer 26 as described herein. Although only one computer 26 is shown, two or more such computers may be employed, depending on the needs of the particular application.
Operation of the present system 10 may be achieved when, based on the required water flow, the operator installs a nozzle 18 into a water handgun or lance 21, selects the pressure required at the operator interface 24 for the specific application, and activates the high pressure water pump 12. A signal is sent to a hydraulic controller 35 which controls variable displacement hydraulic pump 34 (driven by the power take off 13 on the truck). The hydraulic pump 34 may power a hydraulic motor 40 with an output shaft 30 which in turn drives the high pressure water pump 12.
It should be understood that various hydraulic reservoirs 99 may be used to supply the system with hydraulic fluid. The water pump 12 may be driven to the required speed for the desired operation. The speed range of water pump 12 may vary depending on operating conditions. The computer 26 may receive pump speed data from sensor 28 and water pressure data from pressure transducer 32 and may adjust the water pump speed to ensure the most efficient operation for the selected pressure. If the speed for the output flow rate (controlled by the operator at the lance or handgun 21) is within the operating parameter of the water pump 12 (as dictated by the pump lubrication system), and the pressure is at the operator's preselected setting, then no further action may be required.
If, however, the pressure noted at the transducer 32 is higher than the preselected pressure and less than the safety relief set point limit of relief valve 20, the computer 26 may adjust the displacement of the variable displacement hydraulic drive pump 34 via the hydraulic controller 35 to reduce the speed of the motor 40 and high pressure water pump 12 to a minimum speed recommended by the water pump manufacturer. After the water pump 12 reaches the minimum allowable speed and the preselected pressure (via interface device 24) is not achieved, the EHW bypass valve 22 may activate and divert excess water back to the water supply tank 14. Once the preselected pressure is reached, the EHW bypass valve 22 may maintain this pressure and water flow rate until the condition is no longer valid. As the operator increases or decreases the discharge of water through the nozzle 18, as conditions change, based on data from the pressure transducer 32 and speed sensor 28, the computer 26 may send a signal to the EHW bypass valve 22 to increase or decrease the bypass water flow, as needed, in order to maintain the desired pressure and flow rate in line 16.
The operation of the EHW bypass valve 22 may be controlled by a proportional pressure control valve 36. Hydraulic pressure may be supplied to the proportional control valve 36 from the control pressure circuit 41 of the hydraulic drive pump 34. The control circuit 41 for the hydraulic drive pump 35 may be supplied by a charge pump 42 that is integral to the hydraulic drive pump 34, as shown in FIG. 1. Alternatively, charge pump 42 may be separate from drive pump 34.
FIGS. 2-5 illustrate an exemplary structural configuration of the EHW bypass valve 22. The valve 22 may include a ball tip stem needle valve 60 or other suitable valve that is biased toward an open position by a spring 52 and forced closed by a hydraulic cylinder 54. The pressure to cylinder 54 may be supplied via an input line 53 by the charge pump 42 and controlled by an electro-proportional valve 36 which receives a control signal from output 80 of computer 26. As would be understood by one skilled in the art, hydraulic cylinder 54 may urge valve stem 56 downwardly against the opposing compression force of the spring 52. As the stem 56 moves upwardly or downwardly, needle valve 60 may open and close thereby controlling water flow from the water inlet side 62 to the water outlet side 64 of valve 60. The water passing through valve 60 may be dumped back to the water supply tank 14 as described above.
FIGS. 2 and 3 further illustrate an exemplary construction of EHW bypass valve 22. Hydraulic cylinder 54 may be mounted on a plate 63 with an inlet hydraulic tube 53 connected to the cylinder 54 by an adapter 55. A pair of hex nut and jam nut 70 may be attached to the cylinder output shaft 69 to interact with (e.g., bear downward on) a similar hex nut and jam nut pair 71, which may be attached to a threaded portion of valve stem 56 in order to capture the spring plate 72. The valve stem 56 may slidingly pass through the spring plate 72, with spring 52 urging the spring plate 72 upwardly by compressive forces. The movement of spring plate 72 may result in the movement of the valve stem 56 within the needle valve 60. Needle valve 60 may be mounted to the EHW bypass valve 22 on a water valve mounting plate 61. When the hydraulic cylinder 54 urges shaft 69 downwardly, the spring plate 72 may move downwardly, compressing the spring 52, and the valve 60 may be closed. Thus, in response to the control signals from computer 26, valve 60 may be placed in any desired state, from fully closed, to partially open, to fully open, depending on how much excess water needs to be diverted to the tank 14 in order to maintain the desired flow rate and pressure at nozzle 18.
As noted above, hydraulic cylinder 54 may be operated by proportional control valve 36. Hydraulic fluid pressure may be supplied to a manifold 37 (see FIG. 5) of the control valve 36 from the control pressure circuit 41 from a charge pump 42 (see FIG. 1) of the hydraulic pump 34. The proportional control valve 36 may receive an output signal 80 from the computer 26 in response to data received from the pressure transducer 32 in the discharge conduit 16. FIG. 3 shows a side elevation view of the EHW bypass valve 22 with the manifold 37 and the proportional control valve 36 mounted on hydraulic mounting plate 63. Mounting plate 63 may be held in a rigid, space-apart relationship with needle valve mounting plate 61 by spacer tubes 65. Needle valve 60 may be mounted on mounting plate 61.
The EHW bypass valve 22 of the present system may allow the operator to regulate water flow through nozzle 18 from 25 gpm to 0 gpm, for example, at a preset pressure with a single (one size) water pump 12. As noted above, in previous systems, the maximum/minimum flows were completely dependent on the size of the water pump mounted on the chassis of the truck or trailer. For example, a 25 gpm-sized high pressure water pump, due to minimum speed requirements set by the manufacturer because of pump lubrication limits, may have a minimum flow rate of approximately 10 gpm. To obtain flow rates below 10 gpm, such as down to the 3-5 gpm range, for example, a smaller sized pump, perhaps a 10 gpm pump, would be required. Thus, a 25 gpm sized pump included in an embodiment of the present inventive system can do the job of several machines based on jobsite requirements. For example, when using a hydroexcavator system around fiber optics, the water flow and pressure is often dictated by the municipality or telecommunications provider. With a hydroexcavator equipped with an embodiment of the present EHW bypass valve 22, there are fewer limitations preventing the machine from adapting to the particular jobsite conditions.
The embodiments described herein are some examples of the current invention. Various modifications and changes of the current invention will be apparent to persons of ordinary skill in the art. Among other things, any feature described for one embodiment may be used in any other embodiment. The scope of the invention is defined by the attached claims and other claims to be drawn to this invention, considering the doctrine of equivalents, and is not limited to the specific examples described herein.

Claims

What is claimed is:

1. A system for regulation and control of water pressure and flow rate in high pressure water applications, comprising:

a variable speed water pump configured for receiving water from a water reservoir;

a discharge conduit configured for passing water from said water pump to a nozzle;

a relief valve in fluid communication with said discharge conduit, said relief valve having a pressure limit, wherein said relief valve is configured to divert water from said discharge conduit to the water reservoir if a water pressure in said discharge conduit exceeds said pressure limit;

a variable flow bypass valve in fluid communication with said discharge conduit, said bypass valve being controllable between a closed position and a fully open position, said bypass valve being configured to divert water from said discharge conduit to the water reservoir when said bypass valve is in an open position;

a speed sensor configured for sensing a speed of said water pump;

a pressure transducer configured for sensing a pressure in said discharge conduit; and

a computer configured for

setting a preselected water pressure via an operator interface, said preselected water pressure being less than said pressure limit;

receiving a speed input signal from said speed sensor;

receiving a pressure input signal from said pressure transducer; and

in response to said input signals, controlling the speed of said water pump within a range of speeds and controlling said bypass valve in a manner that tends to maintain said pressure in said discharge conduit at said preselected water pressure.

2. The system of claim 1 further comprising a hydraulic control system comprising:

a hydraulic drive pump configured for engagement with a power takeoff of a vehicle;

a hydraulic drive motor operatively connected to said hydraulic drive pump, said hydraulic drive motor being operatively engaged with said water pump;

a hydraulic controller configured for receiving a first output signal from said computer, said hydraulic controller being operatively engaged with said hydraulic drive pump; and

a proportional hydraulic pressure control valve configured for receiving a second output signal from said computer, said proportional hydraulic pressure control valve being operatively engaged with said bypass valve;

wherein said hydraulic controller is configured for controlling the speed of said water pump via said hydraulic drive pump and said hydraulic drive motor in response to said first output signal; and

wherein said proportional hydraulic pressure control valve is configured for controlling said bypass valve in response to said second output signal.

3. The system of claim 2 further comprising a hydraulic charge pump operatively engaged with said hydraulic drive pump and in fluid communication with said hydraulic controller and said proportional hydraulic pressure control valve.

4. The system of claim 1 wherein said water pump comprises a minimum speed, and wherein said computer is further configured to reduce the speed of said water pump if said pressure in said discharge conduit is greater than said preselected water pressure and the speed of said water pump is greater than said minimum speed.

5. The system of claim 4 wherein said computer is further configured to divert water from said discharge conduit through said bypass valve if said pressure in said discharge conduit is greater than said preselected water pressure and the speed of said water pump is less than or equal to said minimum speed.

6. The system of claim 5 wherein said system is part of a mobile hydroexcavating machine.

7. The system of claim 1 wherein said bypass valve is disposed downstream along said discharge conduit from said pressure transducer.

8. The system of claim 7 wherein said bypass valve is disposed downstream along said discharge conduit from said relief valve.

9. An electro-hydraulic water bypass valve for use in a system having a water pressure safety relief valve for regulation and control of water pressure applications, said system comprising an operator interface for setting a preselected water pressure, a computer receiving input from a water pump speed sensor and a water pressure transducer, wherein output from said computer regulates a variable displacement hydraulic drive pump and a proportional pressure control valve, a hydrostatic drive motor operatively connected to said variable displacement hydraulic drive pump and a high pressure water pump, said high pressure water pump being in fluid communication with a water intake conduit extending from a water supply tank, a discharge conduit extending from an output side of said high pressure water pump to a discharge nozzle, said discharge conduit being in fluid communication with said water pressure safety relief valve, a fixed displacement charge pump engaged with said variable displacement hydraulic drive pump and in fluid communication with said proportional pressure control valve, said electro-hydraulic water bypass valve comprising:

a needle valve having an inlet in fluid communication with said discharge conduit, an outlet in fluid communication with said water supply tank, and a valve stem;

a valve spring configured for urging said valve stem in a first direction; and

a hydraulic cylinder having a cylinder output shaft configured for urging said valve stem in a second direction opposite said first direction, thereby moving said needle valve between an open position and a closed position;

wherein said proportional pressure control valve is in fluid communication with and adapted for controlling said hydraulic cylinder, thereby regulating bypass water from said discharge conduit to said water supply tank in response to output from said computer.

10. The bypass valve of claim 9 wherein said needle valve is biased toward said open position by said valve spring.

11. The bypass valve of claim 10 wherein said valve spring is compressed by a spring plate, said valve stem comprises a threaded portion having a nut threaded thereon, said nut being engaged with said spring plate, and said valve stem is slidably disposed through said spring plate.

12. A method of controlling a pressurized water system having a variable speed water pump in fluid communication with a water reservoir and a discharge conduit, a nozzle in fluid communication with the discharge conduit, a safety relief valve in fluid communication with the discharge conduit, the safety relief valve having a pressure limit and being configured to divert water from the discharge conduit to the water reservoir if a pressure in the discharge conduit exceeds the pressure limit, a bypass valve in fluid communication with the discharge conduit, a hydraulic pressure control valve configured for controlling the bypass valve, a hydraulic controller configured for controlling a hydraulic motor, the hydraulic motor being configured for driving the water pump, and a computer in communication with the hydraulic controller and the hydraulic pressure control valve, the method comprising:

setting a preselected water pressure for said system in said computer via an operator interface, said preselected water pressure being less than said pressure limit;

activating said water pump;

sensing a pressure in the discharge conduit using a pressure transducer;

sending a first signal representative of said pressure as a first input to said computer;

sensing a speed of said water pump using a speed sensor;

sending a second signal representative of said speed as a second input to said computer; and

in response to said first and second signals, sending a first output signal from said computer to said hydraulic controller thereby controlling the speed of said water pump within a range of speeds and sending a second output signal from said computer to said hydraulic pressure control valve thereby controlling said bypass valve in a manner that tends to maintain said pressure in said discharge conduit at said preselected water pressure.

13. The method of claim 12 wherein said water pump comprises a minimum speed, and wherein said method further comprises reducing the speed of said water pump if said pressure in said discharge conduit is greater than said preselected water pressure and the speed of said water pump is greater than said minimum speed.

14. The method of claim 13 further comprising diverting water from said discharge conduit through said bypass valve if said pressure in said discharge conduit is greater than said preselected water pressure and the speed of said water pump is less than or equal to said minimum speed.