Abstract:
A pressure washer is provided. The pressure washer includes a water inlet port for receiving water from a water source. A water outlet port is in fluid communication with the water inlet port. A pump is in fluid communication with the water inlet port and the water outlet port for pressurizing the water received through the water inlet port and pumping the pressurized water through the water outlet port. An internal combustion engine powers the pump. A heat transfer unit is interposed between and in fluid communication with the water inlet port and the water outlet port. The heat transfer unit receives exhaust gas from the internal combustion engine and uses the exhaust gas to heat the water as it travels between the water inlet port and the water outlet port.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to pressure washers, and more particularly, to gasoline-powered pressure washers commonly used for household power spraying and washing applications. 
       BACKGROUND OF THE INVENTION 
       [0002]    Gasoline-powered pressure washers have become increasingly popular for use in household cleaning applications, including cleaning decks, patios, siding, automobiles, and the like. Such pressure washers now are economically manufactured and available to the consumer in most hardware and home improvement retail stores. Such gasoline-powered pressure washers basically comprise a movable cart or stand, a water pump, an internal combustion engine for powering the pump, and a spray wand and nozzle assembly. Operation of the pressure washer, following coupling of a common garden hose between a home water outlet and the inlet to the pressure washer pump, generates a high pressure liquid discharge up to 1000 psi and more, for power spraying applications. A chemical inlet port also can be provided on the pressure washer for enabling the introduction of cleaning chemicals into the liquid flow stream to enhance a cleaning operation. 
         [0003]    While chemical intermixing and cleaning effectiveness can be greatly enhanced by use of hot water, inexpensive consumer type pressure washers typically only are available for cold water use operation, such as when connected to a household water outlet. While commercial grade pressure washers are available for directing hot water, these systems require that the pressurized liquid be directed through a downstream heat exchanger separately powered from a fuel other than gasoline, such as propane gas, natural gas or electricity. Such systems are prohibitively expensive for the consumer market. Relatively inexpensive gasoline-powered pressure washers sold in the household or consumer market also can suffer from environmental problems, including excessive noise and inefficient fuel consumption and emissions. 
       OBJECTS AND BRIEF SUMMARY OF THE INVENTION 
       [0004]    It is an object of the present invention to provide an economical gasoline-powered pressure washer for the consumer market which is adapted for improved cleaning efficiency. 
         [0005]    Another object is to provide a gasoline-powered pressure washer as characterized above which is operable for directing a hot water discharge for intermixing with cleaning chemicals and more effective cleaning. 
         [0006]    A further object is to provide a gasoline-powered pressure washer of the above kind which permits heating of the liquid discharge without the necessity for an expensive heat exchanger that requires a separate fuel source. 
         [0007]    Still another object is to provide a gasoline-powered pressure washer of the foregoing type that can be selectively operated for directing either a hot or a lower temperature pressurized liquid discharge. 
         [0008]    Yet a further object is to provide a gasoline-powered pressure washer of such type in which the hot liquid discharge is directed in a high frequency pulsating stream for enhanced cleaning. A related object such as a gasoline-powered pressure washer in which the hot liquid discharge pulsates up to 1000 impulses per minute. 
         [0009]    Another object is to provide a gasoline-powered pressure washer of the above kind that can be operated with reduced noise and fuel emissions. 
         [0010]    Yet a further object is to provide a heat exchanger that can be economically retrofit onto conventional consumer pressure washers for enabling the discharge of high pressure hot water. 
         [0011]    Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         [0012]      FIG. 1  is a perspective of an illustrative pressure washer having a heat transfer unit in accordance with the invention; 
           [0013]      FIG. 2  is a further perspective of the pressure washer shown in  FIG. 1 ; 
           [0014]      FIG. 3  is an enlarged longitudinal section of the heat transfer unit of the illustrated pressure washer; 
           [0015]      FIG. 4  is a diagrammatic depiction of the piston pump of the illustrated pressure washer; 
           [0016]      FIG. 4A  is a diagrammatic depiction of the piston pump of the pressure washer with a selectively lockable valve for disabling operation of one of the pistons; 
           [0017]      FIG. 5  is a flow diagram of the illustrated pressure washer having a piston pump as shown in  FIG. 4 ; 
           [0018]      FIG. 6  is a diagrammatic depiction of an alternative piston pump control that can be used with the illustrated pressure washer; 
           [0019]      FIG. 7  is a flow diagram of the operation of a flow diagram of the pressure washer having the piston pump shown in  FIG. 6 ; and 
           [0020]      FIG. 8  is an enlarged longitudinal section of an alternative embodiment of heat transfer unit usable with the illustrated pressure washer. 
       
    
    
       [0021]    While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    Referring now more particularly to the drawings, there is shown an illustrative pressure washer  10  in accordance with the invention which basically includes a wheeled frame  11  that carries a liquid pump  12 , a gasoline powered internal combustion engine  14  for operating the pump  12 , and a operator wand or spray gun  15  connected to the pressure washer via a high pressure fluid transfer hose  18 . The pump  12  has an inlet  16  connectable to a liquid supply source, such as a home water outlet, by a garden hose  17  or the like. The operator wand  15  typically includes a nozzle  15   a  and a trigger valve  15   b  of a known type for allowing the operator to controllably direct a stream of pressurized liquid toward a substrate surface for cleaning. The high pressure hose  18  preferably has a reinforced construction, such a disclosed in U.S. Pat. No. 5,964,409, the disclosure of which is incorporated herein by reference. The hose  18  and wand  15  each may be provided with conventional fittings and couplings to effect appropriate fluid type connections therebetween. 
         [0023]    In accordance with the invention, the gasoline-powered pressure washer has a heat transfer unit that is operable without a separate fuel source for efficiently and economically heating water for more effective cleaning. To this end, the illustrated pressure washer  10  has a heat transfer unit  20  interposed between the liquid pump  12  and the high pressure outlet hose  18  which utilizes exhaust gas of the gasoline powered engine  14  for heating the liquid exiting from the pump  12  prior to direction to and discharge from the spray wand  15 . The heat transfer unit  20  in this case comprises a liquid heat transfer coil  21  preferably formed by a continuous, seamless stainless steel tube contained within an outer cylindrical casing  22  having end caps  24 , at opposite axial ends. The heat transfer coil  21  in this instance has an inlet end  26  connected to a liquid outlet  28  of the pump  12  via a high pressure hose  30  and a liquid discharge end  31  coupled to the high pressure hose  18  communicating with the spray wand  15 . The coil  21  preferably defines a plurality of concentric layers or rows of windings of the continuous wound tubing. The illustrated coil  21  comprises three concentric layers or rows of  21   a ,  21   b ,  21   c  of windings. The liquid inlet  26  in this case communicates with an inner layer or row  21   a  of windings, which in turn communicates at a downstream end with a second layer  21   b  of windings, which in turn communicates with an outer or third row layer  21   c  of windings, which in turn communicates with the discharge end outlet  31  of the coil. It will be seen that liquid directed through the heat transfer coil  21  will travel in serpentine fashion, first being directed from the inlet  26  through the inner row  21   a  of coil windings from left to right as viewed in  FIG. 3 , then through the second row  21   b  of coil windings in an opposite right to left direction, and then through the outer row or layer  21   c  of coil windings again in an opposite direction left to right to the coil outlet  31 . The coil  21  preferably may be formed of 3/16″ or ⅛″ stainless steel seamless tubing, and preferably, the individual rounds are spaced apart slightly to provide air flow therebetween, as will become apparent. The coil  21  in this case is disposed within an inner tubular jacket  35 , also preferably made of stainless steel, which in turn is disposed within the outer tubular jacket  22  with a layer of insulation  36  there between. The insulation preferably is a ceramic fiber type. 
         [0024]    In carrying out the invention, the heat transfer unit  20  is directly coupled to the exhaust port of the internal combustion engine  14  for receiving exhaust gases during operation of the pressure washer and includes an exhaust gas flow distributor tube  40  centrally within the heat transfer coil  21  for facilitating the flow of the exhaust gases through the heat transfer coil  21  for efficient heat transfer to liquid passing through the coil  21  prior to direction of the pressurized liquid to the outlet hose  18  and control wand  15 . The gas flow distributor tube  40  in this case preferably has an uninterrupted tubular side wall concentrically disposed within the heat transfer coil  21  with an end plate  41  at an upstream end formed with a central gas flow passageway  42 . The gas flow distributor tube  40  has an open discharge end  43  that is fixed in sealed relation within the downstream end plate  25  of the heat transfer unit  20 . 
         [0025]    Exhaust gases from the internal combustion engine  14  in this case are transferred via a rigid manifold pipe  45 , preferably made of metal, which communicated through a side of the heat transfer unit  20  near an upstream end into an axial space  46  between the heat transfer end plate  24  and the upstream ends of the heat transfer coil  21  and exhaust gas flow distributor tube  40 . Hot exhaust gases discharging from the engine during operation of the pressure washer thereby are directly introduced into the heat transfer unit  20  for circulation about the layers  21   a ,  21   b ,  21   c  of windings of the heat transfer coil  21  along its length. The exhaust gas ultimately will flow through the central gas passageway  42  in the upstream end of the exhaust gas flow distributor tube  40  for ultimate discharge to the atmosphere from the open downstream discharge end  43  thereof. It will be understood that the arrangement of the inner and outer tubular casings  35 ,  22  with the interposed insulation  36  not only maintains heat within the heat transfer unit  20  for more efficient heating of liquid passing through the heat transfer coil  21 , but also prevents dangerous overheating of the exterior surface of the outer tubular casing  22 . In the illustrated embodiment, a shroud  48  also is provided over the heat transfer unit  20  for enhanced aesthetic appearance as well as for preventing inadvertent manual contact with the heat transfer unit. It further has been unexpectedly found that the heat transfer unit  20  effectively muffles sound from the engine such that the pressure washer can be operated at reduced noise levels without the necessity for further muffling. Transmission of the hot exhaust gases through the heat transfer unit further is believed to enhance efficient fuel utilization while facilitating complete combustion with reduced exhaust gas admissions. 
         [0026]    In accordance with a further aspect of the invention, the pressure washer  10  is selectively operable in a pulsating, hot water pressurized liquid dispensing mode or in a higher volume, lower temperature liquid dispensing mode. To this end, the illustrated pump  12  ( FIG. 4 ) is a piston pump having three cylinders  50   a ,  50   b ,  50   c  each having a respective piston  51   a ,  51   b ,  51   c  operated by a respective crank from a common crank shaft driven from the gas powered motor  20  in a conventional manner. During each operating cycle, reciprocating movement of the pistons  51   a ,  51   c  sequentially opens an inlet valve  54  to the cylinder chamber to draw in a predetermined quantity of liquid, while a respective outlet valve  55   a ,  55   b ,  55   c  is closed, and reverse movement closes the inlet valve while directing liquid under pressure into a manifold chamber  61  of the pump. The sequential operation of the pistons creates a uniform, high volume, high pressure, liquid flow from the pump. 
         [0027]    In carrying out the invention, at least one of the piston chamber inlet valves can be selectively locked in a closed position for reducing the liquid flow rate through the pump to facilitate heating of the liquid to a relatively higher temperature. In addition, the resulting asymmetrical action of the remaining pistons driving liquid through the pump causes a pulsating discharge to occur, up to 1000 pulses per minute. In the illustrated embodiment shown in  FIG. 4 , the inlet valve  54   b  to the second or middle piston  51   b  of the pump  21  is a disabling valve  13 , which can be selectively locked into a closed position, thus making the piston inoperable. The remaining two pistons  51   a ,  51   c  remain operational, causing the pump to “pulse” by throwing the system into an imbalanced configuration. It also causes the flow volume to lower, thus allowing the waters to spend more time in the heat transfer unit  20  for heating to a higher temperature. The valve  13 , which may be of a known type commercially available under the name Jetter, can be rotatably adjusted in the pump housing for preventing opening of the valve during an intake stroke. Selective rotation of the valve in an opposite direction releases the locking action permitting the piston to operate in its normal fashion. 
         [0028]    It will be understood by one skilled in the art that the combination of the higher water temperature and forcible pulsation of the discharging stream will enhance effective cleaning action of the discharging stream notwithstanding its lower flow rate. In practice, it has been found that the pressure washer can be operated in the high temperature mode at a rate of 1 to 1.5 gpm at a pressure of 1,000 psi. These parameters result in an outlet liquid temperature of between 130° and 140° F. 
         [0029]    To further enhance cleaning, the pressure washer has a chemical injection port  60  which enables cleaning chemicals to be added into the flow stream prior to direction to the heat transfer unit  20 , such as by a conventional siphon intake. Subsequent heating of the water chemical solution and the pulsating direction of the liquid onto a substrate surface further effectively enhances cleaning. 
         [0030]    In keeping with the invention, the pressure washer may be selectively operated at a higher volume, lower water temperature operation by simply unlocking the jitter valve  54   b . In that case, each of the three pistons  51   a - 51   c  is operational in directing water from the supply source. It will be understood that the higher volume flow will result in a lower temperature elevation as it is directed to the heat transfer unit. Nevertheless, the higher volume, lower temperature discharge may be preferred, such as during rinsing operations, and the operating mode of the pressure washer is easily changed by selective adjustment of the jitter valve  54   b.    
         [0031]    An alternative embodiment of control for selectively operating that pressure washer in a relatively high temperature pulsating flow stream and a relatively lower temperature high volume flow stream is depicted in  FIGS. 6 and 7 . In this case, each of the inlet valves  54   a - 54   c  are conventional, spring operated and a bypass passageway line  63  is provided between the outlet manifold passage  61  of the pump  20  and the liquid inlet of the pump  20 . The bypass line  63  in this case communicates in diametrically opposed relation to the outlet valve  55   b  of the piston  51   b  such that a significant portion of the discharge from that piston will be directed into the bypass line  63 . Through operation of a needle valve  62 , the bypass line  63  may be opened to permit a portion of the liquid to be drawn from the liquid passage manifold  61  and recirculated through the system. It will be understood, like in the previously described embodiment, the effective discharge rate of liquid from the pressure washer is reduced resulting in heating of the remaining liquid to a higher temperature during its passage through the heat transfer unit. By reason of the imbalanced state of the pumping system, the discharging flow again has a pulsating effect to at least some degree for enhanced cleaning. Selectively adjusting the needle valve to a bypass passage closed position again enables the pump to operate at a higher volume lower temperature operating mode for rinsing or other cleaning applications. 
         [0032]    In carrying out still a further aspect of the invention, the heat transfer unit  20  can be used in retrofitting existing pressure washers. In such case, the heat transfer unit would be appropriately mounted on the pressure washer, a manifold pipe for connecting the exhaust port of the internal combustion engine to the inlet port of the heat transfer unit and the liquid outlet of the heat transfer unit would be connected to the high pressure hose of the control wand. It will be appreciated that the heat transfer unit can be mounted on most existing internal combustion engine powered pressure washers in such manner with little or minimal modifications. The relatively simple mounting procedure can be carried out by a user of the pressure washer with common tools and limited technical knowledge of the pressure washer, allowing a cold water pressure washer unit to be easily converted to an economical high water unit through such retrofitting of a fixed heat transfer unit. 
         [0033]    Referring now to  FIG. 8  of the drawings, there is shown an alternative and preferred embodiment of a heat transfer unit  20 ′ usable in the pressure washer  10  in accordance with the invention, wherein items similar to those described above have been given similar reference numerals with the distinguishing suffix “′”. The heat transfer unit  20 ′ again has a housing defined by an outer cylindrical casing  22 ′ and end plates  24 ′,  25 ′ at opposite axial ends thereof. The heat transfer unit  20 ′ in this case utilizes a dual coil longitudinally-spaced liquid heat transfer tubing without a central exhaust gas flow distributor tube. To this end, the heat transfer unit  20 ′ includes a first upstream heat transfer coil  21 ′ formed of relatively large diameter tubing, such as ¼″ tubing, having an inlet  26 ′ communicating with the cold water liquid supply, in this case from the outlet of the pressure washer pump. The coil  21 ′ is defined by three concentrically wound continuous layers or rows  21   a ′,  21   b ′,  21   c ′ of windings, similar to that described above, with the liquid inlet  26 ′ communicating with the inner layer  21   a ′ of windings, which in turn communicates at a downstream end with a second or intermediate layer  21   b ′ of windings, which in turn communicates with an outer or third layer  21   c ′ of windings. 
         [0034]    In keeping with the invention, the first heat transfer coil  21 ′ communicates with a downstream longitudinally adjacent second coil  23  formed of relatively smaller diameter tubing, such as 3/16″ diameter tubing. The downstream smaller diameter tubing coil  23  again has three concentric layers or rows  23   a ,  23   b ,  23   c  of windings with an upstream end of the outer layer  23   c  communicating with the downstream end of the outer layer  21   c  of the first coil  21 , which in turn communicates at a downstream end with the intermediate or second layer  23   b  of windings, which in turn communicates with an upstream end with the inner layer  23   a  of windings, which in turn communicates with the liquid discharge end outlet  31 ′ of the heat transfer unit  20 ′ coupled to the high pressure hose of the spray control wand or gun. It will be seen that liquid directed through the heat transfer unit will travel in two distinct serpentine paths, first being directed through the successive layers  21   a ′,  12   b ′,  21   c ′, from outer to inner layers of the first heat transfer coil  21  and then through successive layers  23   c ,  23   b ,  23   a  from the inner to the outer layers of the relatively smaller diameter downstream coil  23 , prior to being transferred to the spray wand or gun. 
         [0035]    In keeping with the invention, the exhaust manifold duct from the internal combustion engine of the pressure washer communicates through a cylindrical side of the heat transfer unit  20 ′ into an axial space  46 ′ between a downstream end of the smaller diameter heat transfer coil  23  and the axial end of the heat transfer unit. The heat transfer unit  20 ′ in this case has an exhaust outlet tube  67  mounted in off-centered relation to the end plate  25 ′ in diametrically opposed relation to the liquid inlet  26 ′. 
         [0036]    For enhancing heat transfer efficiency, the heat transfer unit  20 ′ in this instance has relatively thick insulation layers, which include an outer cylindrical insulation layer  36 ′ having a thickness of at least ⅕ th  the radius of the heat transfer unit interposed between the outer casing  22 ′ and an inner cylindrical casing  35 ′ of the heat transfer unit, an axial heat transfer layer  70  adjacent the end plate  25 ′, a relatively thick end insulating layer  71  adjacent the end plate  24 ′ and the exhaust manifold inlet  45 ′, and an intermediate insulating layer  74  between the longitudinally spaced upstream and downstream liquid heat transfer coils  21 ′,  23 . The intermediate insulating layer  74  is annular shaped with an internal opening corresponding with the diameter of the inner layers of the heat transfer coils  21 ′,  23 . 
         [0037]    In further carrying out this aspect of the invention, to facilitate circulation of exhaust gas through the heat transfer unit  20 ′ for enhanced heat transfer to liquid passing through the longitudinally aligned coils  21 ′,  23 , end caps  75 ,  76  are respectively mounted in opposite ends of the heat transfer coils  21 ′,  23  for preventing the direct axial flow of exhaust gas through the coils  21 ′,  23  and a plurality of circumferentially spaced longitudinal extending spaced gas distribution strips  78  are interposed between the layers of the coils for facilitating circulation of gas through the coils for efficient heat transfer. 
         [0038]    It has been found that during operation of the pressure washer with the heat transfer unit  20 ′, exhaust gas is forced to circulate throughout the heat transfer coils  21 ′,  23  with hotter gases effecting heat transfer between the smaller diameter tubing of the heat transfer coil  23  and the larger surface area of the larger diameter tubing of the coil  21 ′ effecting enhanced heat transfer even while the temperature is being lowered prior to discharge through the exhaust outlet tube. The heat transfer unit  20 ′ again is of relatively simple construction and lends itself to economical manufacture, efficient use, and easy retrofitting on existing pressure washers. 
         [0039]    From the foregoing, it can be seen that an economical gasoline powered pressure washer is provided that has particular utility in the consume market. It further enables improved cleaning efficiency through utilization of a pulsating high temperature liquid discharge which can be premixed with cleaning. The pressure washer permits heating of the liquid discharge without the necessity for expensive heat exchangers that require a separate fuel source. The pressure washer also can be selectively operated in either hot or a lower temperature liquid discharge modes. The pressure washer is economical in design and the heat transfer unit according to the invention lends itself to economical retrofitting on conventional pressure washers. 
         [0040]    It will be understood that while in the illustrative embodiment a pump is disclosed which has a plurality of pistons driven by a crank shank disposed in perpendicular relation to piston movement, alternatively, an axial piston pump may be utilized in which pistons are driven by a wobble plate having a rotary access parallel to the piston movement. Moreover, while the illustrated gas flow distribution tube in the embodiment of  FIG. 3  has an uninterrupted outer tubular construction, alternatively, axially-spaced air flow apertures may be provided in the perimeter of the tube to facilitate passage of gas through the heat transfer coil into the gas flow distributor tube along the length thereof.