WO1998017400A1

WO1998017400A1 - Device suitable for activating a high pressure fluid pump, and also a method for activating a high pressure fluid pump

Info

Publication number: WO1998017400A1
Application number: PCT/NL1997/000578
Authority: WO
Inventors: Leonardus Johannes Gerardus Peeters
Original assignee: Houben, Johannes, Mathias, Hendrikus
Priority date: 1996-10-18
Filing date: 1997-10-15
Publication date: 1998-04-30
Also published as: AU4576897A; NL1004785C2

Abstract

A device and a method for activating a high pressure fluid pump (2), which device comprises a high pressure fluid pump (2), a fluid squirting tool connected to said high pressure fluid pump via at least one line, and a valve disposed in a passage of said line, which valve can be changed over by means of a pedal (8) from a first position, in which said passage is closed, to a second position, in which said passage is open, and vice versa. A control unit (5) operating on low-pressure fluid is disposed between the pedal (8) and the high pressure fluid line, which control unit (5) is connected to the pedal (8) via at least one low pressure fluid line. The valve disposed in the high pressure fluid line can be changed over from the first, closed position to a second, open position, and vice versa, by means of the control unit (5) operating on low pressure fluid.

Description

Device suitable for activating a high pressure fluid pump, and also a method for activating a high pressure fluid pump.

The invention relates to a device suitable for activating a high pressure fluid pump, which device comprises a high pressure fluid pump, a fluid squirting tool connected to said high pressure fluid pump via at least one line, and a valve disposed in a passage of said line, which valve can be changed over by means of a pedal from a first position, in which said passage is closed, to a second position, in which said passage is open, and vice versa.

The invention also relates to a method for activating a high pressure fluid pump which is connected to a fluid squirting tool via a high pressure fluid line, wherein a valve is disposed in a passage of said high pressure fluid line, which valve can be changed over by means of a pedal from a first, closed position to a second, open position.

Such a method and device, which are known per se, are for example used for high pressure cleaning, wherein water, for example, is squirted under a relatively high pressure (600 - 2000 bar) from the high pressure fluid tool against a building to be cleaned. Water is thereby pressurized to a relatively high pressure by means of the high pressure fluid pump, which water is then carried to the tool through the high pressure fluid line. A valve is disposed in said fluid line, which valve can be selectively opened or closed by the tool operator by means of a pedal. The pedal may be operated by hand or by foot, for example. With the known devices the valve is disposed in the pedal, whereby relatively large forces are exerted on the pedal by the highly pressurized fluid, which forces inter alia lead to vibrations in the pedal. Furthermore the operation of the pedal requires a relatively great force. In the event of a malfunction of the pedal the forces being exerted on the pedal due to the use of high pressure fluid may lead to dangerous situations, and thus to accidents.

The object of the invention is to provide a device wherein the high pressure fluid pump can be activated by means of the pedal in a simple and safe manner. This object is achieved with the device according to the invention in that a control unit operating on low-pressure fluid is disposed between the pedal and the high pressure fluid line, which control unit is connected to the pedal via at least one low pressure fluid line, whereby the valve disposed in said high pressure fluid line can be changed over from the first, closed position to a second, open position, and vice versa, by means of the control unit operating on low pressure fluid. As a result of the use of the low pressure fluid only relatively small forces are exerted on the pedal, which forces cannot lead to dangerous situations in the event of a malfunction. The low pressure fluid may be air, for example. For the sake of simplicity pneumatic control by means of air is discussed herein. The low pressure fluid may also be a fluid other than air, however. The valve is opened or closed by means of the control unit, which may be remote from the pedal. Pneumatic safety devices may be incorporated in the control unit in a simple manner.

One embodiment of the device according to the invention is characterized in that the pedal is electrically connected to the high pressure fluid pump via the control unit.

In this manner the control unit is electrically and pneumatically controlled by means of the pedal. There is no direct connection between the pedal and the high pressure fluid pump.

Another embodiment of the device according to the invention is characterized in that the valve comprises a safety pin, which can be moved under high fluid pressure, by means of which pin a safety switch being electrically connected to the high pressure fluid pump can be switched.

If the high pressure fluid pump is turned on and the expected high pressure in the valve is actually available, the safety switch will be in the on position. If the expected high pressure is not available, however, due to malfunction and/or incorrect connection of the high pressure lines to the valve, the movable safety pin will turn the safety switch to the off position, as a result of which also the high pressure fluid pump will be turned off. This enhances the safety of the device.

Another embodiment of the device according to the invention is characterized in that the control unit comprises a starting unit, by means of which the safety switch is short-circuited in use during a starting period stored in the control unit.

As a result of this the high pressure fluid pump is kept on in a simple manner during the starting period, when the expected high pressure in the valve is not available yet. The high pressure fluid pump would otherwise be turned off by the safety switch during starting, since the expected high pressure in the valve is not available yet.

Yet another embodiment of the device according to the invention is characterized in that the pedal comprises a main pedal and at least two auxiliary pedals to be engaged after the main pedal is engaged, whereby a low pressure valve provided in the control unit as well as an electrical switch connected to the high pressure pump can be controlled by means of said two simultaneously operated auxiliary pedals. In this manner a pneumatic and an electric signal will be delivered to the control unit only if the main pedal is operated and the two auxiliary pedals are operated simultaneously. This further enhances the safety of the device.

Another object of the invention is to improve a known method such that the high pressure fluid pump can be controlled in a simple and safe manner.

This objective is accomplished with the method according to the invention in that a control unit operating on low pressure fluid is activated by means of the pedal, after which the high pressure fluid pump and the valve are controlled by the control unit.

A signal delivered by the pedal is converted by the control unit into an control signal for the valve by pneumatic means.

Another embodiment of the method according to the invention is characterized in that the high pressure fluid pump is started by means of the control unit, after which the valve is kept open during a predetermined starting period stored in the control unit, whereby the high pressure is built up in the valve during the starting period, by means of which high pressure a safety switch is activated, whereby the high pressure pump will be turned off after the starting period if the safety switch has not been activated.

If the expected high pressure is not available in the valve within the starting period, the high pressure fluid pump will be turned off. The absence of the high pressure indicates malfunction. By turning off the high pressure fluid pump before work can be continued such malfunction must first be remedied. This makes it impossible to use a device which is not functioning properly. The invention will be explained in more detail hereafter with reference to the drawings, in which:

Figure 1 is a block diagram of the device according to the invention; Figure 2 is a plan view of a foot pedal of the device shown in Figure 1;

Figure 3 is a longitudinal sectional view of the foot pedal shown in Figure 2, in the direction indicated by arrows III— III;

Figure 4 is a longitudinal sectional view of the foot pedal shown in Figure 2, in the direction indicated by arrows IV- IV;

Figure 5 is a longitudinal sectional view of the foot pedal shown in Figure 2, in the direction indicated by arrows V-V;

Figures 6 and 7 are details of the device illustrated in Figure 5, showing the pedal in the non-depressed position and in the depressed position respectively;

Figure 8 shows a valve and associated control elements of the device shown in Figure 1;

Figures 9A-9C are cross-sectional views of the device of Figure 8, showing said device in the directions indicated by arrows A-A, B-B and C-C respectively;

Figure 10 is a pneumatic control diagram of the control unit shown in Figure 1; and

Figure 11 shows an electric control diagram of the control unit shown in Figure 1. In the figures like parts are numbered alike.

The blocks in Figure 1 show the various components of the device 1 according to the invention. Device 1 comprises a high pressure fluid pump 2 (400 - 2000 bar), which is connected to a control unit 5 via a high pressure fluid line 3 and an electric lead 4. A tool 7 operating on high pressure fluid is connected to control unit 5 via a high pressure fluid line 6. Furthermore a control element, for example a pedal 8, is connected to control unit 5 via an electric lead 9 and pneumatic supply and discharge lines 10, 11. Furthermore connected to control unit 5 is a pneumatic main supply line 12 (4 - 8 bar). High pressure pump 2 comprises a pump 13, which is driven by means of a drive unit 14. High pressure pump 2 is connected to a bypass valve 16 via a line 15, which bypass valve is connected to high pressure fluid line 3. Bypass valve 16 is in communication with a fluid supply line 18 via a line 17, which line 18 is furthermore connected to pump 13. High pressure fluid pump 2 does not form part of the present invention and consequently will not be explained in more detail herein. The exact operation of device 1 according to the invention will be explained in detail with reference to detailed Figures 2 - 11. Now a global description of the operation of device 1 according to the invention will be given in order to provide a better understanding of the device 1. When pedal 8 is operated, an electric signal and a pneumatic signal will be delivered to control unit 5 via lines 9 and 11 respectively. Then control unit 5 will deliver an electric signal to high pressure pump 2 via line 4, which signal will activate high pressure pump 2. A fluid, for example water, will be carried under high pressure to control unit 5 by high pressure pump 2. Control unit 5 will open a valve disposed in control unit 5, after which the high pressure fluid will be delivered to tool 7 via line 6.

Figures 2 - 7 show various views of a foot pedal 8 according to the invention. Foot pedal 8 comprises a bottom plate 20, a main pedal 22, which pivots about a pin 21, and two auxiliary pedals 24, 25, which pivot about a pin 23 extending parallel to pin 21. Main pedal 22 comprises two parallel bars 26, which are pivotally connected to pin 21 on one side and which are interconnected by a bridge part 27 on another side. Pedal 22 is maintained in the upwardly tilted position shown in Figures 3, 4 by means of a spring 28 (Figure 5). Auxiliary pedal 24 surrounds auxiliary pedal 25 in a U shape. Auxiliary pedal 24 is maintained in the position shown in Figure 4 by means of a spring 29. Auxiliary pedal 25 is maintained in the position shown in Figure 4 by means of a spring 30. Near the ends of bars 26 of main pedal 22 foot pedal

8 is provided with a lever 32 capable of pivoting movement about a pin 31, which lever is maintained in the position shown in Figures 5, 6 by means of a spring 33. Pins 34 connected to bars 26 butt against the upper side of levers 32. A rod 35 connected to levers 32 is capable of pivoting movement about pin 31, which rod is provided with a flange 36, which extends in vertical direction in the position of rod 35 shown in Figures 3, 4.

U-shaped auxiliary pedal 24 is provided on one leg 37 with a plate-shaped extension 38, which extends above a pneumatic valve

39, whilst another extension 40 extends below an electric switch 41. Extension 40 abuts against a pin 42, which is urged in a direction towards switch 41 by means of a spring 43.

The auxiliary pedal 25 located within U-shaped pedal 24 abuts against a pneumatic valve 45 provided with a hold-down roller 44 between pins 23, 31, and against pneumatic valve 39 on a side remote from pin 31. Auxiliary pedal 25 is provided with an extension 46, which abuts against a pin 47, which surrounds pin 42 concentrically and which is urged towards switch 41 by means of a spring 48. Pin 47 is provided with a slotted recess 49, in which a pin 50 connected to pin 42 is capable of movement. The operation of foot pedal 8 is as follows.

Bridge portion 27 of main pedal 22 is pivoted about pin 21, in a direction indicated by arrow PI, by a heel of a foot, until the bridge portion 27 is positioned within a recess 51 in bottom plate 20. During said pivoting of main pedal 22 the levers 32 are pivoted about pin 31, in a direction indicated by arrow P2 from the position as shown in Figure 6 to the position of Figure 7, by means of pins 34 abutting against levers 32. Also rod 35 and the flange 36 attached thereto are thereby pivoted in the direction indicated by arrow P2, whereby flange 36 occupies a substantially horizontal position. Auxiliary pedals 24, 25 can be pressed down by foot the moment flange 36 occupies this horizontal position. As long as the flange 36 occupies the position shown in Figures 3, 4 the auxiliary pedals can not be pressed down. When the auxiliary pedals 24, 25 are pressed down simultaneously, said pedals are pivoted about pin 23 in the direction indicated by arrow P3 against the spring force of springs 29, 30. Pivoting of auxiliary pedal 25 will cause pneumatic valve 45 to be pressed down, whilst pneumatic valve 39 is released. Said releasing of pneumatic valve 39 will only take place if both portion 46 connected to auxiliary pedal 25 and portion 40 connected to auxiliary pedal 24 are moved in a direction indicated by arrow P4. Pneumatic valve 39 will not be released if only one of the auxiliary pedals 24, 25 is pressed down. If both portions 40, 46 are moved in the direction indicated by arrow P4, the spring force of springs 43, 48 will cause pins 42, 47 to move in a direction indicated by arrow P5, towards switch 41, and activate said switch 41. If only one of the portions 40, 46 is moved in a direction indicated by arrow P5, whilst the other portion will remain in the position shown in Figure 4, the interconnection of pins 42, 47 by means of pin-slot connection 49, 50 will prevent the upper side of pin 42 coming into contact with switch 41. Only if both auxiliary pedals 24, 25 are pressed down simultaneously, pneumatic valve 39 will be released and switch 41 will be excited. In this way a pedal 8 has been obtained where only the conscious pressing down of two auxil iary pedals will actuate pneumatic valve 39 and switch 41.

When main pedal 27 is released, the spring force of spring 28 will cause pedal 27 to return to the position shown in Figures 3, 4, whereby levers 32 are pivoted in a direction opposed to arrow P2 by a force exerted by spring 33, whereby levers 32 move from the position shown in Figure 7 to the position shown in Figure 6.

Figures 8, 9A-9C are a (partially sectional) side view and cross-sectional views respectively of a part of the control unit 5 according to the invention. Control unit 5 comprises a valve 60, which is provided with a high pressure fluid inlet 61, a high pressure fluid outlet 62 and a passage 63 between inlet 61 and outlet 62, which accom modates a slide 65, which is movable against spring force 64. Slide 65 comprises a central cylindrical portion 66 and extensions 68 extending on either side of cylindrical portion 66, which extensions are provided with slots 67. In the position shown in Figure 8 cylindrical portion 66 abuts against a sleeve 69. Valve 60 is provided with a sleeve 70 on a side remote from sleeve 69. Valve 60 is furthermore provided with a chamber 71, which is in communication with a chamber 72, in which a piston 73 is present. Piston 73 is connected to a pin 74, which is provided with a conical element 75 on a side remote from chamber 72. Conical element 75 abuts against an electric safety switch 76. A pin 78 connected to a pneumatic cylinder 77 is positioned opposite the end of pin 74.

One end 79 of a pin 80 terminates in chamber 71, while the other end of said pin 80 abuts against a lever 81, which pivots about a pin 82. Lever 81 is connected to a frame 84 via a spring 83. Furthermore connected to frame 84 is a pneumatic cylinder 85, which abuts against lever 81 with a pin 86. A pneumatic valve 87 and an electric switch 88 are disposed on a side of lever 81 remote from cylinder 85.

The operation of valve 60 is as follows. Actuation of pneumatic cylinder 85 will cause pin 86 to move in the direction indicated by arrow P6, as a result of which lever 81 is pivoted about pin 82 in the direction indicated by arrow P7. Said pivoting of lever 81 causes pin 80 to move against the spring force of spring 89 in a direction indicated by arrow P8, whereby cylindrical portion 66 takes up a position between sleeves 69, 70. Fluid being supplied under high pressure flows into the slots 67 in left-hand portion 68 via inlet 61, to slots 67 in the right- hand portion 68, and, via chamber 71, to outlet 62. A valve 90 is disposed near outlet 62, which valve is moved in the direction of flow P9 by the high fluid pressure, as a result of which the passage in outlet 62 is released. The fluid exits valve 60 via conical bores 91. The highly pressurized fluid exerts a force on piston 73, as a result of which pin

74 is moved in a direction indicated by arrow P10. When pin 74 moves sufficiently far in the direction indicated by arrow P10, conical portion

75 will excite switch 76. A counter pressure can be exerted on pin 74, via pin 78, by means of air cylinder 77, whereby pin 74 will not move in the direction indicated by arrow P10 until the pressure in chamber 71 is sufficiently high.

Figure 10 shows a pneumatic control diagram of control unit 5 of the device shown in Figure 1. Control unit 5 comprises an air pre-treatment unit 100, in which air supplied in direction Pll via line 12 is pre-treated. The air from said pre-treatment unit is supplied, via a line 101, to a starting unit 102, which is provided with three pneumatic valves 103, 104, 105 and three pneumatic-electric switches 106, 107, 108. Valve 103 is in communication with switch 107 via a line 109. Connected to switch 107 is a line 110, which branches into a line 111, which is connected to valve 104, and a line 112, which is connected to switch 108. Valve 104 is furthermore connected to ingoing line 101 and to an outgoing line 113. Valve 105 is connected to switch 108 via a line 114 and to line 113 via a line 115. Non-return valves 116 are disposed in lines 110 and 115. Line 113 opens into a buffer tank 117, which is in communication with ingoing line 10 to foot pedal 8 via a throttle valve 118. Line 10 is connected to valve 45, an outgoing line 119 of which is connected to valve 39 and also to outgoing pneumatic line 11. Pneumatic line 11 is connected to a quick-release valve 120, which is also connected to air cylinder 85. Line 113 coming from valve 104 is connected to air cylinder 77 via a line 121 and to valve 87. Valve 87 is in communication with a buffer tank 123 via a line 122, which buffer tank 123 is connected with an outgoing side thereof to switch 106 via a line 124.

Figure 11 shows an electric diagram of control unit 5. Electric switches 107, 108, 88 are arranged in series, they are series- connected to switches 76 and 106, which are arranged in parallel. The electric circuit furthermore comprises a transistor 130 and a resistor 131.

The operation of the device and the method according to the invention will now be explained in more detail.

When device 1 is started, valve 103 is manually operated, as a result of which switch 107 is opened and switch 108 is closed. Valve 104 is opened and buffer tank 107 is pressurized. The opening of valve 104 will cause air cylinder 77 to move outward, whereby pin 78 will come into contact with pin 74. This will open electric switch 76. Buffer tank 123 is pressurized via valve 87. The air pressure supplied to switch 106 via line 124 will close switch 106. Knob 141 of valve 103 is now released, as a result of which line 109 is vented and switch 107 is closed.

Then pedal 27 is pressed down, as a result of which levers 32 pivot in the directions indicated by arrow P2 and pedals 24, 25 are unlocked. Then pedals 24, 25 are pressed down, as a result of which valve 45 is opened and air cylinder 85 is moved out via line 11 and quick-release valve 120. Said moving out of air cylinder 85 causes lever 81 to pivot in the direction indicated by arrow P7, as a result of which pin 80 is moved in the direction indicated by arrow P8 and cylindrical portion 66 is put in a central position. This puts inlet 61 and outlet 62 in communication with each other. When valve 45 is opened, valve 39 is at the same time closed and put in the position shown in Figure 10. Electric switch 88 and valve 87 are closed by the tilting of lever 81.

Electric switches 107, 108, 88 and 106 are now closed. When auxiliary pedals 24, 25 are depressed, this not only causes valve 45 to open and valve 39 to close, but it also activates switch 41. The electric circuit shown in Figure 11 now delivers a signal to the high pressure fluid pump, as a result of which the high pressure fluid pump starts to pressurize fluid. During the time that fluid is being pressurized by the high pressure fluid pump, buffer tank 123 blows off via line 122 and valve 87, as a result of which the air pressure on switch 106 is released and switch 106 opens. The time required for venting line 124 depends on a unidirectional throttle valve 132 disposed in line 122. This time has been set such that the high pressure fluid pump will have moved the fluid under pressure into valve 60 via inlet 61 before switch 106 opens, whereby the high pressure will have moved pin 74 in a direction indicated by arrow P10, against the force exerted by pneumatic cylinder 77, and switch 76 will have been closed. If the pressure in valve 60 was insufficient at the time that switch 106 opened, so that switch 76 has not been closed, the starting procedure must be repeated. The fact that switch 76 has not been closed within the desired time may indicate a malfunction.

Upon stopping the foot is removed from the foot pedal, as a result of which main pedal 22 is pivoted in a direction opposite to arrow PI. Lever 32 then pivots in a direction opposite to arrow P2, causing rod 35 and flange 36 attached thereto to take up the positions shown in Figures 3 and 4 and pedals 24, 25 to be locked in the positions shown in Figures 3 and 4. Switch 41 is no longer activated, as a result of which the high pressure fluid pump is turned off. Valve 45 is closed, as a result of which cylinder 85 is made pressureless via quick-release valve 120 and line 111. Spring 83 pivots lever 81 in a direction opposite to arrow P7, whereby pin 80 is moved in a direction opposite to arrow P8 by spring 89. Portion 66 of slide 65 takes up the position shown in Figure 8, whereby the passage from inlet 61 to outlet 62 is closed. The pivoting of lever 81 causes switch 88 and valve 87 to open. The opening of valve 87 causes buffer tank 123 to become pressurized, as a result of which switch 106 is closed.

The pressure in chamber 71 is released via a passage 133 provided in valve 90, after which pin 74 is moved in a direction opposite to arrow P10 by air cylinder 77, whereby switch 76 is opened. The squirting tool 7 connected to outlet 62 becomes pressureless. Valve 105 is manually operated and locked in order to exchange the squirting tool. The control pressure for valve 104 is made pressureless via lines 111, 112 and 114, as a result of which valve 104 is closed. Switch 108 is opened thereby. The buffer tank 117 is made pressureless via valve 104. The same applies to cylinder 77. Buffer tank 123 is made pressureless via valve 87 and valve 104. The pneumatically operated switch 106 is opened. As long as the manually operated valve 105 remains locked in its closed position, the entire pneumatic control system 5 will remain pressureless. All electric switches, with the exception of switch 107, remain open and the high pressure fluid pump cannot be activated. As a result of this measure foot pedal 8 cannot be depressed by a third person whilst tool 7 is being exchanged by the operator. A restriction 134 is present near valve 104, via which air can escape. If valve 104 is not open after valve 103 has closed, the air will escape via restriction 134, as a result of which switch 108 is opened. This signals the occurrence of a malfunction in valve 104.

If valve 87 is not opened after cylinder 85 has been made pressureless, buffer tank 123 cannot be pressurized, as a result of which switch 106 cannot be closed. First the malfunction occurring in valve 87 will have to be remedied before the device will function properly again.

If valve 45 remains stuck in the open position after foot pedal 8 has been released, the venting of air cylinder 85 will take place via the open valve 39. The function of valve 45 is taken over by valve 39, as it were. If valve 39 remains stuck in the open position when the foot pedal is pressed down, both valve 45 and valve 39 will be open. This means that valve 39 attempts to vent cylinder 85, whilst valve 45 attempts to pressurize the cylinder. In order to achieve that cylinder 85 is made or will remain pressureless, so that it can be indicated that a malfunction has occurred, the amount of air being supplied via valve 45 must be smaller than the amount of air being vented via valve 39. This can be achieved by suitably adjusting restriction 118.

Valve 104 is opened by valve 103 and, after being opened, provides its own control pressure via lines 115, 114 and 112.

If valve 103 remains stuck in the open position after being released, switch 107 will remain open, as a result of which no controlling of the high pressure fluid pump can take place.

The non-return valve 116 provided in line 10 prevents supply and discharge lines from being incorrectly connected to foot pedal 8. If line 11 has buckled, for example, as a result of which the supply to cylinder 85 stagnates or the discharge via valve 45, 39 stagnates during venting, cylinder 85 is made pressureless via blow-off restriction 140.

The pedal may also be operated by hand rather than by foot.

Claims

CLAIMS ,

1. A device suitable for activating a high pressure fluid pump, which device comprises a high pressure fluid pump, a fluid squirting tool connected to said high pressure fluid pump via at least one line, and a valve disposed in a passage of said line, which valve can be changed over by means of a pedal from a first position, in which said passage is closed, to a second position, in which said passage is open, and vice versa, characterized in that a control unit operating on low-pressure fluid is disposed between the pedal and the high pressure fluid line, which control unit is connected to the pedal via at least one low pressure fluid line, whereby the valve disposed in said high pressure fluid line can be changed over from the first, closed position to a second, open position, and vice versa, by means of the control unit operating on low pressure fluid.

2. A device according to claim 1, characterized in that the pedal is electrically connected to the high pressure fluid pump via the control unit.

3. A device according to claim 1 or 2, characterized in that the valve comprises a safety pin, which can be moved under high fluid pressure, by means of which pin a safety switch being electrically connected to the high pressure fluid pump can be switched.

4. A device according to claim 3, characterized in that the safety pin abuts against a low pressure cylinder in the control unit on a side remote from the valve, whereby the safety pin is capable of movement in a direction away from the valve against a force exerted by the cylinder during operation.

5. A device according to claim 3 or 4, characterized in that the control unit comprises a starting unit, by means of which the safety switch is short-circuited in use during a starting period stored in the control unit.

6. A device according to any one of the preceding claims, characterized in that the valve comprises a slide capable of movement against spring force, which slide is disposed in the passage of the high pressure line, and which can be moved by means of a low pressure cylinder in the control unit.

7. A device according to any one of the preceding claims, characterized in that the pedal comprises a main pedal and at least two auxiliary pedals to be engaged after the main pedal is engaged, whereby a low pressure valve provided in the control unit as well as an electrical switch connected to the high pressure pump can be controlled by means of said two simultaneously operated auxiliary pedals.

8. A method for activating a high pressure fluid pump which is connected to a fluid squirting tool via a high pressure fluid line, wherein a valve is disposed in a passage of said high pressure fluid line, which valve can be changed over by means of a pedal from a first, closed position to a second, open position, characterized in that a control unit operating on low pressure fluid is activated by means of the pedal, after which the high pressure fluid pump and the valve are controlled by the control unit.

9. A method according to claim 8, characterized in that the high pressure fluid pump is started by means of the control unit, after which the valve is kept open during a predetermined starting period stored in the control unit, whereby the high pressure is built up in the valve during the starting period, by means of which high pressure a safety switch is activated, whereby the high pressure pump will be turned off after the starting period if the safety switch has not been activated.

10. A pedal according to any one of the preceding claims 1 - 7.

11. A valve according to any one of the preceding claims 1 - 7.