US3433415A

US3433415A - Hydraulic systems

Info

Publication number: US3433415A
Authority: US
Inventors: Bruno Eugen Enssle
Original assignee: Binks Res & Dev
Current assignee: Binks Res & Dev; Binks Research & Dev Corp
Priority date: 1966-03-18
Filing date: 1966-03-18
Publication date: 1969-03-18
Anticipated expiration: 1986-03-18

Description

March 18, 1969 B. E. ENSSLE HYDRAULIC SYSTEMS I of 5 Sheet Filed March 18. 1966 zwmza/ March 18, 1969 B. E. ENSSLE 3,433,415

HYDRAULIC SYSTEMS Filed March 18, 1966 Sheet g of 5 2 i I J 7% k I 1 O C i I, I 2 134 -ifive/7101:

March 18, 1969 a. E. ENSSLE 3,433,415

HYDRAULIC SYSTEMS Filed March 18, 1966 Sheet Q of 5 March 18, 1969 B. E. ENSSLE 3,433,415

HYDRAULIC SYSTEMS Filed March 18, 1966 Sheet 4 of 5 7 46 J42 450 144% li 55/155 fr jfia March 18, 1969 B. E. ENSSLE HYDRAULIC SYSTEMS Sheet 5 of 5 Filed March 18. 1966 United States Patent ABSTRACT OF THE DISCLOSURE A hydraulic system for airless spraying of liquids at high pressure including by-pass means for by-p-assing the fluid at low pressure while maintaining a predetermined high pressure available at a spray gun member and including improved control apparatus for controlling the starting and stopping of the system and for regulating the pressures developed therein.

The present invention relates to hydraulic systems, and to apparatus for producing and regulating the pressure in a hydraulic system. More specifically, the invention relates to apparatus which provides for the supply of fluids at high pressure, the accumulation of fluid volume and pressure to a predetermined value at one portion of the hydraulic system, and thereafter, the by-passing of the fluid supply at low pressure while maintaining the predetermined pressure in said portion of the system. While the pressure regulating apparatus of the present invention may be used to advantage in various applications, it is particularly useful in conjunction with the airless or hydraulic spraying of paint and other coating materials.

In airless spray painting, the paint is supplied at high pressure, e.g. 1000 to 3000 p.s.i., to an atomizing nozzle having a small elliptically shaped orifice therethrough, the paint being atomized hydraulically upon passage through said orifice into a fan-shaped spray as is known in the art. In spray painting, it is conventional to spray intermittently, and a valve is associated with the nozzle to accommodate starting and stopping of the spray as desired or required. Manifestly, whenever the valve is opened, spraying should commence substantially instantaneously. Consequently, it is necessary to maintain the high pressure supply of paint to the nozzle at all times and to maintain the pressure within close limits both when spraying and when not spraying.

One of the principal problems heretofore encountered in the use of airless spraying devices has been due to maintaining a high pressure available at the spray gun, i.e. the assembly of the nozzle and the valve, even when the gun is temporarily not spraying. It has therefore been customary to provide a by-pass line which is connected with the passage leading to the spray gun, and to incorporate a restricted orifice in the by-pass so that when the spray gun is not being triggered fluid material will be forced at high pressure through the by-pass orifice and thereby recirculated until the spray gun is again operated. In this manner, the restricted by-pass orifice creates a back pressure so as to maintain the desired high pressure at the spray gun, while the fluid material is continuously recirculated through the by-pass. However, such an arrangement has serious disadvantages since the pump is subjected to a heavy load at all times even when the spray gun is not operating. Moreover, such conice tinuous recirculation of the fluid material at high pressure through a restricted orifice causes the material to become unduly heated and in many cases to disintegrate. Thus, only certain carefully selected fluid materials can be utilized in such apparatus.

Due to the above described problem, electric motor operated pumps have not found acceptance in the airless spray painting art since they would have, at best, very limited application and would suffer the disadvantage of high operational and maintenance costs due to the necessity for continuous operation at full load. As a consequence, air motor operated pumps, with their inherent inefliciencies and the necessity for a high pressure air compressor and reservoir, have been utilized substantially exclusively in the airless spray painting art simply because an air motor can stall-out harmlessly upon attainment of a predetermined pressure and yet be available for substantially instantaneous operation upon a decrease in pressure, as caused for example by resumption of spraying.

The objects of the present invention are to provide improved fluid pressure apparatus which substantially overcomes the foregoing problems, and especially accommodates an electric motor pump device, and an improved high pressure electric pump embodying said apparatus and especially adapted for supplying fluids for airless spray painting systems and the like.

A more specific object of the invention is to provide a device, e.g. a pump, which accumulates fluid volume and pressure to a predetermined value at one portion of a hydraulic system, eg a spray gun, and thereafter permits by-passing of the fluid source at a substantially reduced pressure, i.e. low load, While maintaining the predetermined pressure at the one portion of the system until the latter requires replenishing.

A further object is to provide an improved airless spraying system incorporating fluid pressure regulating means of the type last above-mentioned.

An additional object is to provide a pump, especially a compact electric pump, including adjustable means for adjusting the discharge pressure, means for automatically reducing the load on the pump whenever the selected discharge pressure =is attained, and means for substantially instantaneously and continuously maintaining the discharge pressure at the selected value.

:The foregoing and other objects and advantages of the invention will be apparent from the following description of a preferred embodiment thereof.

Now, in order to acquaint those skilled in the art with the manner of making and using my invention, I shall describe, in conjunction with the accompanying drawings, the best mode contemplated by me of carrying out the invention.

In the drawings:

FIGURE 1 is a perspective view of a self-contained pump and hydraulic pressure apparatus constructed in accordance with the present invention, the housing being partly broken away to illustrate various internal components;

FIGURE 2 is an enlarged fragmentary top plan view of the apparatus of FIGURE 1, with portions thereof partly broken away;

FIGURE 3 is a fragmentary vertical sectional view, partly in elevation, taken substantially along the line 3-3 of FIGURE 4;

FIGURE 4 is a fragmentary front end elevational view, partly in section, looking approximately in the direction of the arrows 44 of FIGURE 3;

FIGURE 4A is an enlarged fragmentary vertical sectional view taken substantially along the line 4A-4A of FIGURE 2, showing a check valve assembly which comprises one component of the apparatus of FIGURE 1;

FIGURE 5 is a top plan view of a manifold body which comprises one component of the apparatus of FIGURE 1;

FIGURE 6 is a vertical sectional view taken substantially along the line 66 of FIGURE 5;

FIGURE 7 is a fragmentary vertical sectional view taken substantially along the line 77 of FIGURE 5',

FIGURE 8 is a rear elevational view of the manifold body of FIGURE 5; and

FIGURES 9 to 12 are schematic views showing an airless spray painting system including the apparatus of FIGURE 1 in various sequential stages of operation in accordance with this invention.

As previously stated, the fluid pressure regulating device of the present invention can be used to advantage in various types of hydraulic systems where it is desired to provide for adjustable system pressure control and for by-passing of a fluid source when pressure in a portion of the system such as in the discharge area reaches a predetermined desired value. In one application thereof, the regulator is embodied in the high pressure electrically operated pump provided in accordance with the present invention and especially adapted for use in the airless or hydraulic spraying of paint or various other fluid materials.

Referring now to the drawings, and in particular to FIGURES 1 to 4, there is shown a portable electric airless pump 20 comprising a housing 22 mounted on a pair of rear wheels 24 and a pair of forward support legs 26, a pair of handle bars 28 which are fixed to the housing 22, an electric pump motor 30 and a pump drive housing 32. As shown in FIGURE 3, the electric motor 30 drives a motor pulley 34 and the latter drives a larger diameter pulley 36 by means of endless belts 38. The pulley 36 is fixedly mounted to one end of a drive shaft 40 which extends upwardly therefrom into the drive housing 32 and is supported by bearings 42 and 44. A crank hub 46 is fixedly mounted on the drive shaft 40 and secured by retainer plates 47 between a pair of counterweights 48 and 50, and one end of a connecting rod 52 encompasses the crank hub 46 while the other end of the rod is secured to a connecting rod adapter 54. A further rod 56 has one end threaded into the adapter 54 and its other end is pivotally connected by means of a universal ball joint or the like 58 to a cylindrical crosshead shaft 60 which reciprocates in a tubular sleeve 62.

A piston rod 64 made of long-wearing material, preferably ceramic, has a cup-shaped adapter 66 glued or otherwise fixedly secured on one end thereof, and the adapter is anchored by a screw or other suitable means within the forward end of the crosshead shaft 60 in such a manner as to be pivotable therein a limited amount. In this manner, the forward end of the piston 64 is free to move radially a limited amount relative to the crosshead shaft 60 as may be necessary to permit optimum alignment of the piston. The piston 64 extends through a hearing member 68 and into a bore 70 formed in the rear face of a manifold body 72. A seal 74, which is preferably a unitary tubular ceramic seal, is mounted within the rear end of the bearing member 68 and held therein by a cup-shaped collar 69 confined between the housing 32 and the manifold 72. The piston 64 passes through said seal, the outer diameter of the piston and the inner diameter of the seal (when ceramic) being manufactured to close tolerances so as to prevent leakage of fluid material therebetween. However, any fluid material which might leak past the seal 74 due to the high pressures developed will simply pass downwardly into a drive housing drain tube 75 and be returned thereby to the fluid supply container (not shown). It will be understood from the foregoing that when the electric pump motor 30 is operating it will cause the piston 64 to reciprocate continuously with the nose of the piston moving back and forth in the bore 70 provided in the manifold body 72, and as will be explained more fully later herein the fluid piston 64 acts as a pump in drawing fluid material up from the supply container through a suction tube and pumping such fluid under pressure through the manifold.

As best shown in FIGURE 2, an accumulator shaft 7 is disposed within a bore 78 in the manifold body 72 for longitudinal sliding movement therein, and a bearing 80 and seal 82 are positionel in a counterbore at the rear of the manifold body for cooperation with the shaft 76. The rear end of the accumulator shaft 76 has a reduced diameter projec ion 83 on which is mounted a spring retainer 84, and a coiled compression spring 86 has one end seated in the retainer 84. The other end of the compression spring 86 is seated in a second spring retainer member 88, and the latter is mounted on an adapter 90 which in turn is supported from a fixed wall 92 by means of an adjustable screw member 94. It will thus be understood that the screw member 94 may be rotated to adjust the initial compression in the accumulator spring 86. It should also be understood, as will be explained more fully later herein, that during operation the forward end of the accumulator shaft 76 is subjected to the system pressure, and thus whenever the system pressure builds up it will act on the shaft 76 and tend to move the latter rearwardly against the force of the spring 86. Other means such as a closed chamber of gas may be utilized in place of the spring 86 to act against the accumulator shaft 76.

A control rod 96 (see FIGURES 2 and 3) extends through a bore 97 in the manifold body 72 and has one end which projects beyond the front of the manifold body and has a manually operable pressure control knob 98 mounted thereon for rotation of the rod. The other end of the control rod 96 approximately abuts against a switch button 100 comprising an element of a push-on push-01f switch 102 for controlling the operation of the electric pump motor 30. The control rod 96 includes a threaded portion 104 on which is mounted a pressure indicator 106. The indicator 106 includes an upright indicator pin 108 which is movable in a guide slot 110 provided therefor in a top cover plate 112, and if desired the cover plate may be calibrated in pressure increments corresponding to the location of the indicator pin. It will be understood that the pin 108 retains the indicator 106 against rotation so that the indicator 106 is movable forwardly and rearwardly on the threaded part 104 of the control rod 96 upon manual rotation of the knob 98. A washer 113 is fixed on the control rod immediately rearwardly of the threaded portion 104 so as to retain the indicator on the threaded portion of the rod. As will become more clear later herein, the knob 98 is rotated in order to regulate the discharge pressure of the pump. The indicator 106 extends laterally toward the accumulator spring 86 and includes an arcuate portion 114 which is located in close proximity to the spring so as to be en gageable by the spring retainer 84 when the latter is moved rearwardly with the accumulator shaft 76. Accordingly, when the accumulator shaft 76 is moved rearwardly due to a build-up of fluid pressure in the discharge area of the pump, the spring retainer 84 will engage the indicator member 106 and thereby cause the control rod 96 to be moved rearwardly, although as will be explained more fully hereinafter such movement of the control rod will not normally be suflicient to actuate the switch 102.

FIGURE 2 shows a by-pass valve assembly 116 including a valve member which is normally biased toward a closed or seated position in the manifold body by a spring 118 and which is adapted to be pulled away from the manifold body in order to open the valve. Preferably, the valve assembly 116 is of essentially the same structure as disclosed in my copending application Ser. No. 467,- 635, filed June 28, 1965. The end of the valve member extends through a fixed retainer 120 and includes a nut 122. One end of a valve actuating lever 124 is mounted over the end of the valve between the fixed retainer 120 and the nut 122, and the other end of the lever is mounted on the control rod 96 and bears at its front face against a shoulder on the rod so that rearward movement of the control rod will produce rearward movement of the adjacent end of the lever 124. Accordingly, when the control rod 96 is moved rearwardly by the accumulator shaft 76, it moves the adjacent end of the valve-actuating lever 124 rearwardly so as to pivot the lever about its opposite end, and in this manner the lever 124 acts upon the nut 122 to pull the valve 116 away from the manifold head 72 and thereby open the valve for a by-pass function.

It should be noted that when the control rod 96 is rotated so as to move the indicator 106 forwardly on the threaded portion 104 of the rod toward the manifold body 72, a short stroke will be required of the accumulator shaft 76 before the spring retainer 84 engages the indicator 106 and moves the control rod 96 and the lever 124 so as to open the by-pass valve 116. On the other hand, when the control rod 96 is rotated in the opposite direction so as to move the indicator 106 away from the manifold body 72, a greater stroke will be required of the accumulator shaft 76 before the spring retainer 84 engages the indicator and effects opening of the by-pass valve 116. It will be understood that a greater fluid pressure is required to move the accumulator shaft 76 a greater distance against the force of the compression spring 86, and thus the further the indicator 106 is located rearwardly away from the manifold body 72 the greater the pressure required in the discharge area of the pump 20 before the by-pass valve 116 will be opened. Accordingly, with the by-pass valve connected to the pump outlet, rotation of the control rod 96 in one direction will increase the discharge pressure of the pump 20, while rotation in the opposite direction will decrease such pressure. It should further be understood that as the control rod 96 is moved rearwardly due to engagement of the spring retainer 84 with the indicator 106, the by-pass valve 116 will be opened before the rod has moved a sufficient distance to actuate the on-olf switch 102, and once the by-pass valve has opened the pressure build-up in the discharge area of the pump will cease and the rearward movement of the control rod will be discontinued. Thus, the switch 102 will normally be actuated only when the control rod 96 is manually pushed to its extreme rearward position to turn the motor 30 of if it is off, and off if it is on.

As best shown in FIGURE 4, a suction tube 126 is connected at the underside of the manifold body 72 so as to communicate with a cartridge or check valve assembly 128 (see FIGURE 4A) positioned Within a vertical opening 130 provided therefor in the manifold body. Also connected to the underside of the manifold body 72 are a hy-pass conduit 132, and a pressure relief conduit 134 which includes a manually operable pressure relief ball valve 136. The three conduits or

tubes

126, 132 and 134 are all intended to have their lower ends comrnunicating with a container C of fluid material (see FIGURES 9l2) so that the latter can be drawn up into the pump through the suction tub 126, and can also be returned to the supply container at appropriate times through the bypass conduit 132 or the pressure relief conduit 134.

It will be seen from FIGURE 4A that the cartridge or check valve assembly 128 includes four vertically spaced

balls

138, 140, 142 and 144 each of which cooperates with a corresponding valve seat therebelow to control the flow of fluid material in the manifold body 72. FIGURES 2 and 4A further show a bracket 146 which is secured to the upper end of the cartridge assembl 128 and includes a pair of notched

arms

148 and 150 which fit under the heads of a pair of tightening

bolts

152 and 154 threaded into the top of the manifold body 72. Accordingly, by loosening the two

bolts

152 and 154, it is possible to grip the handle portion of the bracket 146 and rotate the cartridge 128 slightly, after which the entire cartridge assembly may be lifted upwardly out of the manifold body 72 for inspection or repair or replacement.

The manifold body 72 will now be described in detail, and for this purpose reference is made to FIGURES 5-8. There is shown the vertical opening 130 which contains the ball check assembly 128, and it will be seen from FIGURE 6 that there are provided a lower passageway 156, an intermediate passageway 158, and an upper passageway 160, each of which communicates with the vertical cartridge opening 130. The lowermost passage 156 communicates directly with the bore in which the nose of the piston 64 reciprocates. FIGURES 7 shows the manner in which the intermediate passage 158 extends upwardly along an inclined path to a horizontal by-pass passageway 1 62 which extends to the rear face of the manifold body 72, and it is important to understand from FIGURE 2 that the by-pass valve 116 controls communication between the upper end of the inclined passageway 158 and the rearward end of passageway 162. The horizontal by-pass passage 162 extends forwardly and then communicates with a vertical bypass 164 (see FIGURE 6). The previously described by-pass hose or conduit 132 connects to the underside of the manifold body 72 at the lower end of the passageway 164, so that when the by-pass valve 116 is open it is possible for fluid material to be forced by the piston 64 out through the intermediate passage 158 to the by-pass conduit 132 and back to the fluid supply container C.

FIGURE 6 further shows that the upper passageway 160 in the cartridge opening extends downwardly along an inclined path to a relatively large diameter chamber 166, the outer end of the latter normally being plugged at 168. The chamber 166 communicates with a downwardly extending passage 170, and it should be understood that the previously described pressure relief hose 134 connects to the underside of the manifold body 72 at the lower end of the passage 170. The chamber 166 also connects with a short horizontal passageway 172 which in turn connects with a pump outlet passage 174 leading forwardly to the front face of the manifold body 72. It is to be noted that a spray gun 176 (see FIGURES 9-12) is connected by means of a discharge hose 178 to the front of the manifold body 72 at the opening 174, and thus fluid material pumped through the passageway will be supplied to the spray gun 176 if th pressure relief valve 136 is closed. In addition, the chamber 166- connects with an upwardly extending passageway 180 which communicates with the accumulator shaft bore 78 forwardly of the end of the accumulator shaft 76, and thus fluid material pumped through the passage 160 is not only supplied to the spray gun 176 but is also conducted to the bore 78 so as to urge the accumulator shaft 76 rearwardly against the force of the compression spring 86. Consequently, the pressure acting upon the accumulator shaft 76 will be approximately equal to the discharge pressure at the spray gun 176.

Referring again to FIGURE 4A, it will be observed that the carriage 128 comprises an outer cylinder having four annular lands each equipped with a seal engaging the wall of the bore or opening 130 and respectively sealing the upper end of said bore above the passage 160, between the

passages

158 and 160, between the

passages

156 and 158 and the lower end of said bore below the passage 156. Disposed seriatim' within the interior of said outer cylinder, and sealed with respect thereto, are a body and a seat for each of the

balls

138, 140, 142

7 and 144, the bodies, seats and balls being confined within said outer cylinder by screw threaded plugs inserted in the opposite ends of said cylinder.

The body for the ball 142 and aligned portions of Said outer cylinder are ported for communication with the passage 156 and the cylinder 70 of the pump, and the two

balls

142 and 144 located below said ports serve jointly and severally as inlet check valves for the pump. The body of the next upward ball 140 and aligned portions of said outer cylinder are ported for communication with the by-pass passage 158, so that the ball 140 serves as an outlet check valve for the pump between the pump cylinder 70 and the by-pass 158. The body of the top ball valve 138 and aligned portions of said outer cylinder are ported for communication with the passage 160, and the ball 138 serves (i) as a pump outlet check valve between the cylinder 70 and the passage 160 and (ii) as a return check valve for the accumulator cylinder 78 and chamber 166 as will presently appear.

The operation of the apparatus of the present invention will be most easily understood in conjunction with an illustrative use thereof as depicted in FIGURES 9- 12 which comprise schematic illustrations of the apparatus in four different stages of its operation as a high pressure supply means for airless paint spraying equipment. First, the pressure relief valve 136 is opened, and the pump motor 30 is started by pushing the control rod 96 rearwardly until it actuates the switch button 100 (see FIGURE 3), whereupon the motor operates to reciprocate the piston 64. Since the pressure relief conduit 134 is open, fluid material, as shown in FIGURE 9, will be drawn up through the suction tube 126 past the

inlet check balls

142 and 144 on the rearward or suction stroke of the piston, and on the forward or compression stroke of the piston will be forced past the upper two

balls

138 and 140 out through the passage 160 and chamber 166 back to the supply container C through the pressure relief port 170 and hose 134. Accordingly, the fluid material will be continuously recirculated through the pressure relief hose 134, and since there is no pressure head opposing the piston, the electric motor 30 will be operating against no load and will essentially idle.

It will be understood that when the control rod 96 is manually pushed rearwardly as described above, it will act through the lever 124 to open the bypass valve 116 momentarily, the by-pass valve being held open only as long as the control rod is held in its rearward position. It is important to note that at this stage all air will be bled out of the system through the pressure relief hose 134 and through the momentarily open by-pass line 132 so as to facilitate initial priming of the apparatus, and if necessary the control rod 96 may be held for a time in its rearward position to assist in purging air from the system. Moreover, because the control rod 96 is designed to operate both the on-off switch 102 and the by-pass valve 116, a safety feature is provided to assure that when the pump motor 30 is started it will not have to operate the pump against a high pressure head, and this would be true even if the pressure relief valve 136 were closed.

The pressure release valve 136 is then manually closed (FIGURE thereby causing the fluid material delivered by the pump to passage 160 to pass to the spray gun 176 and through the passage 180 to the accumulator shaft 76. Assuming the spray gun 176 is not operating, (i.e. the valve thereof is closed) the pressure will build up at the gun and at the accumulator shaft 76 until the resultant movement of the latter is sufficient to engage the spring retainer 84 against the indicator 106 and thereby effect opening of the bypass valve 116 in the manner previously described, it being understood that the pressure at which the by-pass valve 16 will open is determined by rotating the control rod 96 and thereby adjusting the position of the indicator 106. Thus, when a desired predetermined pressure is developed at the spray gun 176, the by-pass valve 116 will be opened automatically,

whereupon fluid material discharged by the pump piston 64 may be circulated through the low pressure by-

pass line

158, 162, 164, 132. When the by-pass valve 116 is opened, said by-pass line establishes communication between a location at atmospheric pressure and the body of ball valve 140, whereupon the fluid under substantial pressure (e.g. 2000 psi.) in the chamber 166 and accumulator cylinder 78 will cause the valve ball member 138 to close, thereby preventing loss of pressure throughout the

circuit

160, 166, 180, 78, 172, 174, 178 and at the spray gun 176 until such time as the gun is triggered. Accordingly, a desired predetermined high pressure will be maintained at the gun 176, and yet the pump operates simply to circulate fluid material as substantially no pressure head through the unrestricted by-pass line 132, whereby the motor 30 simply idles. The upper ball member 138 thus constitutes one-way valve means located between the pump and the spray gun 176 and positioned downstream of the bypass conduit 158 so that during by-passing of the fluid material the ball 138 will remain closed to prevent loss of fluid pressure down-stream thereof except through the spray gun while by-passing occurs upstream of the ball 138. The foregoing arrangement eliminates heating and disintegration of the fluid material as normally occurs during recirculation thereof through a restricted orifice, and it also unloads the pump during such recirculation of the fluid and permits the motor to operate with essentially no load and at low current draw.

When the spray gun 176 is operated, the pressure and volume accumulated at the gun and at the accumulator shaft 76 are immediately available for supplying the spray gun requirements, and as the accumulator shaft gradually returns toward its original position the by-pass valve 116 is closed whereupon the pump will build up pressure at the upper ball 138 and again deliver fluid material directly to the spray gun at the desired pressure. Thus, as shown in FIGURE 11, when the gun 176 is triggered the by-pass 116 closes automatically and the pump resumes pressure supply of fluid. Whenever the spray gun 176 is closed, the pressure will again build up at the gun and at the accumulator shaft 76 until the predetermined adjustable pressure is reached, and then the movement of the accumulator shaft will open the by-pass valve 116 and the operation will again be as illustrated in FIGURE 10.

It is important to understand that the by-pass system is operative not only when the spray gun 176 is shut off, but also during a spraying operation at any time the pressure at the gun and at the accumulator shaft 76 reaches a predetermined desired pressure. Where the capacity of the particular nozzle (not shown) being utilized in the spray gun is at the selected pressure substantially equal to the capacity of the pump, then the spray gun could be operated continuously without a pressure build-up sufficient to open the by-pass valve 116. However, in most situations the capacity of the pump will exceed the capacity of the nozzle, and this will cause a pressure build-up or back pressure at the nozzle and at the accumulator shaft 76 thereby moving the latter and opening the by-pass valve 116, after which the fluid material delivered by the pump will be temporarily recirculated through the by-pass tube 132 until the pressure downstream of the upper ball 138 diminishes and requires replenishing. Thus, any excess capacity of the pump is diverted through the by-pass 132 while maintaining the approximate desired discharge pressure at the spray gun 176 at all times. It will thus be understood that during a spraying operation, assuming the capacity of the pump exceeds the capacity of the nozzle, the by-pass valve 116 will automatically open each time the back pressure developed by the nozzle reaches a predetermined adjustable value, and such valve will again close when due to such by-passing the pressure at the nozzle diminishes. Accordingly, during such a spraying operation the by-pass valve 116 will intermittently open and close, as depicted in FIGURE 11,

and if the pump capacity substantially exceeds the nozzle capacity, the by-pass valve 116 may be open most of the time during a spraying operation, particularly if the indicator 106 is located to provide a relatively low discharge pressure. There is no pressure variation noticeable at the nozzle and the fluid pressure control system described herein provides an approximately constant dis charge pressure at the spray gun 176.

When it is desired to shut off the pump 20, the control rod 96 is manually pushed rearwardly to actuate the switch 102 and shut off the pump motor 30. If the pressure relief valve 136 has been opened, then the entire system will be relieved of pressure. If the pressure relief valve 136 remains closed, then the spray gun 176 and the accumulator shaft 76 will remain under pressure, and, with reference to FIGURE 2, the spring retainer 84 will be in a rearward position so as to act on the indicator 106 and prevent the control rod 96 from returning to its extreme forward position after the same has been pushed to its rearward position to shut off the pump motor 30. The switch 102 is designed so that the switch button 100 must come out all the way before it can again be actuated. Accordingly, the high pressure at the accumulator shaft 76 will prevent the switch 102 from again being actuated a second time to turn on the motor 30 until the pressure release valve 136 has been opened. This is a further safety feature of the system since it will normally require an operator to open the pressure release valve 136 be fore he will be able to start the pump motor 30. However, as previously described, there is an added safety feature provided since whenever the control rod 96 is pushed rearwardly to start the motor 30, the by-pass valve 116 is temporarily opened. It is also of interest to note that if with the pump operating the lever 124 should fail to operate and open the by-pass valve 116 at the appropriate time, the continuous pressure build-up will continue to move the accumulator shaft 76 and control rod 96 rearwardly until the latter engages the switch button 100 and turns off the motor, although in the usual situation the by-pass valve 116 will be opened before the control rod has moved rearwardly far enough to actuate the on-oif switch.

It will be seen that I have provided a hydraulic apparatus wherein the power developed by the pump motor is applied directly to the fluid material being pumped without the use of air or hydraulic oils as intermediate stages. As a result, there are fewer moving parts, no air compressor is required, and due to the increased efliciency a smaller horsepower motor may be utilized. The desired discharge pressure is readily adjustable, e.g. between 1000 p.s.i. and 3000 p.s.i., and the low pressure bypass arrangement automatically unloads the pump when the predetermined desired pressure is attained, both when the spray is shut off and also during the course of actual spray. The low pressure by-pass eliminates temperature rises during recirculation of the fluid material and thereby substantially increases the number of different types of fluid materials which can be used in the apparatus without any adverse effects, and yet it maintains full pressure at the spray gun with sufficient reserve accumulation. Moreover, the low pressure by-pass arrangement described herein is not limited to use in sprayers and may be used to advantage in various other applications as a fluid pressure regulator.

While I have described my invention in a preferred form, I do not intend to be limited to such form, except insofar as the appended claims are so limited, since modifications coming within the scope of my invention will readily occur to others, particularly with my disclosure before them.

I claim:

1. In a hydraulic system, the improvement comprising, in combination, a fluid source for supplying fluid under pressure, a pressure chamber, one-way valve means interposed between said fluid source and said pressure chamber and arranged to permit fluid flow from said source to said pressure chamber, low pressure by-pass means disposed between said fluid source and said valve means for diverting fluid from said source away from said pressure chamber, pressure control means located downstream of said valve means in conjunction with said pressure chamber for sensing the fluid pressure thereat and for automatically rendering said by-pass means operative when said pressure attains a pre-determined value, said fluid source including a pump which operates under substantially reduced load when said low pressure by-pass means is operative, on-off means for controlling the starting and stopping of said pump, manually operable pump control means for actuating said on-otf means, and means interconnecting said pump control means with said by-pass means so that said by-pass means Will be rendered operative whenever said pump control means is manually actuated to start or stop said pump whereby said pump will be started and stopped under reduced load with said low pressure by-pass open.

2. The invention of claim 1 wherein said by-pass means includes a by-pass valve and wherein said pump control means is interconnected with said by-pass valve for opening and closing the latter.

3. In a hydraulic system, the improvement comprising, in combination, a fluid source including a pump for supplying fluid under pressure, a pressure chamber, one-Way valve means interposed between said fluid source and said pressure chamber and arranged to permit fluid flow from said source to said pressure chamber, low pressure by-pass means disposed between said source and said one-way valve means for diverting fluid from said source away from said pressure chamber, on-ofl means for controlling the starting and stopping of said pump, manually operable pump control means for actuating said on-off means, means interconnecting said pump control means with said by-pass means so that said by-pass means will be rendered operative whenever said pump control means is manually actuated to start or stop said pump whereby said pump will be started and stopped under reduced load with said low pressure by-pass open, and pressure control means located downstream of said one-way valve means in conjunction with said pressure chamber for sensing the fluid pressure thereat and for automatically rendering said by-pass means operative when said pressure attains a predetermined value, said pressure control means being interconnected with said pump control means for moving the latter an amount sufficient to open said by-pass means but normally insufficient to actuate said on-off means, whereby said pump control means is manually operable to start and stop said pump and to open said by-pass means and is also automatically operable upon attainment of a predetermined pressure in said pressure chamber to open said by-pass means.

4. The invention of claim 3 wherein said pressure control means includes a slidable accumulator shaft one end of which is subjected to the pressure in said pressure chamber which urges said shaft in one longitudinal direction, compressible means acting on the other end of said accumulator shaft biasing said shaft in the opposite longitudinal direction, said accumulator shaft being interconnected with said pump control means for moving the latter an amount sufficient to open said by-pass means but normally insufficient to actuate said on-otf means, whereby when said shaft is moved a predetermined distance in said one direction under the influence of the pressure in said pressure chamber and against the force of said compressible means said shaft will effect opening of said by-pass means.

5. The invention of claim 4 wherein the interconnecting means between said accumulator shaft and said pump control means includes adjustable means for varying the stroke required of said accumulator shaft to actuate said pump control means and open said by-pass means whereby said adjustable means serves to vary the pressure in said pressure chamber.

6. In a hydraulic system, the improvement comprising, in combination, a fluid source for supplying fluid under pressure, a pressure chamber, one-way valve means interposed between said fluid source and said pressure chamber and arranged to permit fluid flow from said source to said pressure chamber, low pressure by-pass means including a by-pass valve disposed between said fluid source and said one-way valve means for diverting fluid from said source away from said pressure chamber, pressure control means located downstream of said one-way valve means in conjunction with said pressure chamber for sensing the fluid pressure thereat and for automatically opening said by-pass valve when said pressure attains a predetermined value, said pressure control means including a slidable accumulator shaft one end of which is subjected to the pressure in said pressure chamber which urges said shaft in one longitudinal direction, compressible means acting on the other end of said accumulator shaft biasing said shaft in the opposite longitudinal direction, and means interconnecting said accumulator shaft with said by-pass valve whereby when said shaft is moved a predetermined distance in said one direction under the influence of the pressure in said pressure chamber and against the force of said compressible means said shaft will effect opening of said by-pass valve, said interconnecting means including adjustable means for varying the stroke required of said accumulator shaft to open said by-pass valve whereby said adjustable means serves to vary the pressure in said pressure chamber.

7. In a spraying device for pumping fluid from a container and atomizing the fluid into a spray, the improvement comprising, in combination, manifold means, a pump for supplying fluid from a container to said manifold means, a spray gun connected with said manifold means, one-way valve means interposed between said pump and said spray gun and arranged to permit fluid flow from said pump to said spray gun, low pressure bypass means disposed between said pump and said one-way valve means for diverting fluid delivered by said pump away from said spray gun, pressure control means associated with said manifold means between said one-way valve means and said spray gun for sensing the fluid pressure thereat and for automatically rendering said by-pass means operative when said pressure attains a predetermined value thereby controlling the pressure at said spray gun 'both 'when said spray gun is shut off and during the course of actual spray, on-off means for controlling the starting and stopping of said pump, manually operable pump control means for actuating said on-oif means, and means interconnecting said pump control means with said by-pass means so that said by-pass means will be rendered operative whenever said pump control means is manually actuated to start or stop said pump whereby said pump will be started and stopped under reduced load with said low pressure by-pass open.

'8. In a spraying device for pumping fluid from a container and atomizing the fluid into a spray, the improvement comprising, in combination, manifold means, a pump for supplying fluid from a container to said manifold means, a spray gun connected with said manifold means, one-way valve means interposed between said pump and said spray gun and arranged to permit fluid flow from said pump to said spray gun, low pressure bypass means disposed between said pump and said one-way valve means for diverting fluid delivered by said pump away from said spray gun, on-off means for controlling the starting and stopping of said pump, manually per able pump control means for actuating said on-off means, means interconnecting said pump control means with said by-pass means so that said by-pass means will be rendered operative \whenever said pump control means is manually actuated to start or stop said pump whereby said pump will be started and stopped under reduced load with said low pressure by-pass open, and pressure control means associated with said manifold means between said oneway valve means and said spray gun for sensing the fluid pressure thereat and for automatically rendering said by-pass means operative when said pressure attains a predetermined value thereby controlling the pressure at said spray gun both when said spray gun is shut off and during the course of actual spray, said pressure control means being interconnected with said pump control meansfor moving the latter an amount suflicient to open said bypass means but normally insufficient to actuate said on-oif means, whereby said pump control means is manually operable to start and stop said pump and to open said by-pass means and is also automatically operable upon attainment of a predetermined pressure at said spray gun to open said by-pass means.

9. In a spraying device for pumping fluid from a container and atomizing the fluid into a spray, the improvement comprising, in combination, manifold means, a pump for supplying fluid from a container to said manifold means, a spray gun connected with said manifold means, one-way valve means interposed between said pump and said spray gun and arranged to permit fluid flow from said pump to said spray gun, low pressure bypass means including a hy-pass valve disposed between said pump and said one-way valve means for diverting fluid delivered by said pump away from said spray gun, pressure control means associated with said manifold means between said one-way valve means and said spray gun for sensing the fluid pressure thereat and for automatically opening said by-pass valve when said pressure attains a predetermined value thereby controlling the pressure at said spray gun both when said spray gun is shut off and during the course of actual spray, said pressure control means including a slidable accumulator shaft one end of which is subjected to the pressure at said pressure control means which urges said shaft in one longitudinal direction, compressible means acting on the other end of said accumulator shaft biasing said shaft in the opposite longitudinal direction, and means interconnecting said accumulator shaft with said by-pass valve whereby when said shaft is moved a predetermined distance in said one direction under the influence of the pressure acting on said shaft and against the force of said compressible means said shaft will effect opening of said bypass valve, said interconnecting means including adjustable means for varying the stroke required of said accumulator shaft to open said by-pass valve whereby said adjustable means serves to vary the pressure at said spray gun.

10. In an airless spray system for pumping fluid from a container and atomizing the fluid into a spray, the improvement comprising, in combination, manifold means, an electric pump for pumping fluid material from a container to said manifold means, an airless spray gun connected to said manifold means, one-way valve means interposed between said electric pump and said airless spray gun and arranged to permit fluid flow from said pump to said spray gun, low pressure by-pass means disposed between said pump and said one-way valve means for diverting fluid delivered by said pump away from said spray gun and delivering the same back to said container, pressure control means associated with said manifold means between said one-way valve means and said spray gun for sensing the fluid pressure thereat and for automatically rendering said by-pass means operative when said pressure attains a predetermined value thereby controlling the pressure at said spray gun both when said spray gun is shut off and during the course of actual spray, said electric pump including a reciprocating piston which acts directly on the fluid material to be pumped, and an electric motor for driving said piston.

11. The invention of claim 10 wherein said piston comprises a cylindrical shaft made of ceramic material and mounted at its rear end in such a manner as to permit limited radial movement of its forward and relative to M. HENSON WOOD, 111., Primary Examiner.

sald rear end as necessary for optunum ahgnment of sand MICHAEL Y M AR, Assistant Examiner.

piston.

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