Pneumatic Reciprocating Tool

Abstract

A pneumatic reciprocating tool in which a reciprocating piston is slidingly disposed through a slide valve with its ends extending therebeyond and formed to be slidingly received within a piston bore independently of the slide valve for a predetermined extent of travel. Fluid passageways are formed in the tool body from a fluid intake valve to spaced intermediate locations in the piston bore and are interconnected by the slide valve to passageways leading to the opposite ends of the piston bore. The piston and an underlying tool carriage are formed with opposing rack gears and a gear wheel is disposed in mesh with the rack gears thereby interconnecting the tool carriage and piston for inverse movement of the tool carriage relative to the piston.

Description

FIELD OF THE INVENTION

The fields of art to which the invention pertains include the fields of reciprocating piston air motors and abrading tools.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention provides a pneumatic reciprocating tool of relatively simple and reliable construction and which requires only a small number of moving parts during reciprocation. In particular embodiments, the tool includes a housing body defining a piston bore, a piston reciprocal in the bore, a fluid pressure intake and exhausts operatively associated with the bore. Fluid is admitted under pressure to opposite ends of the piston bore to effect reciprocation of the piston and sequential venting to ambient of the exhausts. The piston and an underlying tool carriage are formed with opposing rack gears and the gear wheel is disposed in mesh with the rack gears thereby interconnecting the tool carriage and piston for inverse movement of the tool carriage relative to the piston.

In specific embodiments a slide valve is reciprocally received within the piston bore to direct fluid under pressure alternately to the opposite ends of the piston bore. A piston is slidingly disposed through the slide valve and has ends which extend beyond the slide valve and which are formed to be slidingly received within the piston bore independently of the slide valve for a predetermined extent of its travel. Passageways are formed from a fluid intake valve to intermediate spaced locations defining inlet ports in the piston bore and are connected by means of reduced diameter portions on the slide valve to other passageways leading to opposite ends of the piston bore. Fluid under pressure directed to one side of the piston bore effects movement of the piston in the opposite direction within the slide valve and which causes inverse movement of the tool carriage by means of the rack and wheel gears. As the piston is displaced from its position it contacts the slide valve and carries it along in the same direction to effect valving of the fluid to the opposite side of the piston bore to thereby reverse the direction of piston travel. The piston is massive relative to the slide valve and overtravels its null position, the extent of overtravel increasing with the number of strokes after start-up until a maximum is reached.

A fluid intake valve is provided which sequentially directs fluid under pressure first to one side only of the piston bore, whereby to assure displacement of the piston from a null position, and then alternately to opposite sides of the piston bore whereby to effect reciprocation of the piston. This sequence is accomplished by providing an intake valve member which is formed to sequentially interconnect the fluid intake passageway (1) briefly to a passageway leading directly into one side of the piston bore and then (2) to a passageway leading to the aforementioned inlet ports. In a particular embodiment, the fluid intake valve defines an elongate bore and includes a plunger carrying a slide within the bore. The slide initially closes the passageway leading to the inlet ports but in that position exposes the passageway leading to one piston bore end. The intake valve plunger is slidable to displace a valve ball from its seat to thereby open communication between the last-mentioned passageway and a fluid intake passageway. However, as the plunger is further displaced the slide closes the passageway leading to the piston bore and opens the passageway which leads to the inlet ports. The result is a sequential operation in which fluid under pressure is initially directed to one side of the piston bore and, upon further displacement of the valve plunger, the fluid is then directed to alternate sides of the piston bore in sequence with the reciprocation of the piston as hereinabove described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a pneumatic reciprocating tool of this invention;

FIG. 2 is a vertical sectional view of the tool of FIG. 1;

FIGS. 3a and 3b are vertical sectional views of the valve portion of the tool of FIG. 1 in sequential operative positions;

FIGS. 4a-c are schematic representations of reciprocating components of the tool at start-up; and

FIGS. 5a-d are schematic representations of reciprocating components of the tool during operation.

DETAILED DESCRIPTION

Referring to FIG. 1, a pneumatic reciprocating tool 10 of this invention is shown wherein an abrading member 12, such as a sandpaper panel, is secured to the underside of a sanding plate 14 (shown partially broken away for clarification) which, in turn, is secured by threaded screws (not shown) and nuts 16 to the ends of an elongate tool carrier shoe 18. The sandpaper panel 12 is retained in place, backed by a cushioning pad 20, by means of spring clamps 22 which are of conventional structure, including ready-release members 24. A pair of elongated L-shaped guide members 26 are received in recesses on opposite lower sides of the pneumatic tool and are secured in place by screwthreaded fasteners 28 or the like. The lower edges of the guide members 26 are inturned under the shoe 18 which is cut away at its elongate bottom edge 30 to form elongate shelves 32, one on each side thereof, for receiving the inturned portions of the guide members 26. Thus, as the shoe 18 and sanding plate 14 are reciprocated, the movement thereof is guided by the L-shaped guide members 26 sandwiched between the shelf edges of the shoe 18 and the sanding plate 14 whereby the structure is retained in assembled and aligned relationship. The foregoing aspects of the tool 10 undercarriage are of conventional design and are included here only for purposes of completeness.

The tool 10 includes a body or housing 34 which carries reciprocating members as will hereinafter be detailed. The housing 34 is formed with hollow passageways and bores which are closed at one end by a front end cap 36 carrying a forward round, knurled handle 38, secured by screwthreaded fasteners (not shown). The rear end of the housing 34 is closed by a rear cap 40 having a forwardly curved handle 42 secured thereto by screwthreaded fasteners 44 and including a trigger 46 for controlling air pressure as hereinafter described.

Referring to FIG. 2, details of construction of the tool 10 are shown. The body or housing 34 of the tool 10 has a bore 48 formed longitudinally therein and seated within the bore is a piston sleeve 50 which is shown as a single component but which can be composed of a plurality of sections. The piston sleeve 50 functions as a bearing surface for sliding reciprocation of an aluminum slide valve 52 and steel piston rod 54 within the bore 48. The housing 34 defines a main fluid passageway 56 from the rear end thereof lengthwise of the piston bore 48. A pair of conduits 58 and 60 are formed intersecting the main passageway 56 and open into the piston bore 48 through the sleeve 50, at intermediate locations defining inlet ports 55 and 57 spaced symmetrically on opposite sides of centerline (centerline being indicated by the dashed line 62). Another pair of conduits 64 and 66 are formed opening into the piston bore 48 through the sleeve 50 at intermediate locations therein, also spaced symmetrically on opposite sides of centerline 62 and defining load ports 69 and 71. The load ports 69 and 71 are defined laterally from the inlet ports 55 and 57 without vertical overlap therewith, but with their inner edges precisely in line with the outer edges of the inlet ports 55 and 57. Drive plugs 59, 61, 65 and 67 are inserted into the bore holes which would otherwise open exteriorly of the housing. Fluid passageways 68 and 70 are formed from the conduits 64 and 66 to the front and rear ends respectively of the housing 34 which, in conjunction with recesses 72 and 74 in the front and rear end caps 36 and 40 open into the respective end chambers 76 and 78 of the piston bore 48.

The end chambers 76 and 78 are defined by the disposition of a pair of piston caps 80 and 82 carried at opposite ends of the piston rod 54 and secured thereto by means of flat head screws 84 and 86 respectively. Valve rings 88 and 90 are carried by the piston caps for close fitting sliding engagement with the piston sleeve 50.

The slide valve 52 is an elongate hollow cylindrical member which is formed internally with a bore 92 for slidingly and reciprocally receiving the piston rod 54. The slide valve 52 is formed with reduced diameter portions 94 and 96 symmetrically on opposite sides of its centerline. The slide valve 52 and piston rod 54 are shown in FIG. 2 in a null position wherein they are disposed exactly symmetrical with respect to centerline 62. This is a position which would occur rarely and only by coincidence of the components. The null position is shown in FIG. 2 only to clearly illustrate the disposition of the reduced diameter portions 94 and 96 relative to the inlet and outlet ports 55, 57, 69 and 71. As shown, the reduced diameter portions 94 and 96 are formed coincident with the outer edges of the inlet ports 55 and 57 and with the inner edges of the outlet ports 69 and 71. This arrangement enables the slide valve 52 to interconnect one or the other of the inlet ports 55 or 57 to the respective outlet ports 69 or 71 immediately upon displacement from centerline. The manner of such interconnection and the effect of reciprocation of the slide valve will be described in more detail hereinafter. The slide valve 52 is formed with valve rings 98, 100, 102 and 104 on opposite sides of the reduced diameter portions 94 and 96 to effect a slidingly close fit with the piston sleeve 60.

The piston rod 54 is somewhat longer than the slide valve 52 so that its ends extend therebeyond with a small overlap. For example, for a bore 48 of 8 inches in length and a slide valve 5 eleven-sixteenths inches long, a piston rod 54 which is 6 inches long can be utilized for a total overlap (with one side flush) of 5/16 inch. Accordingly, the piston rod 54 overrides the slide valve 52 by five-sixteenths inch during operation of the tool 10. In the null position as shown in FIG. 2, the piston caps 80 and 82 are disposed so as to cover a pair of exhaust conduits, shown in shadow at 106 and 108, formed through the piston sleeve 50 and housing 34 and opening exteriorally of the housing 34 at the other side thereof. The piston caps 80 and 82 have their outer edges flush with the outer edges of the exhaust conduits 106 and 108 so that displacement of the piston rods 54 from centerline immediately vents one or the other of the chambers 76 or 78 to ambient, as will be detailed hereinafter. An elongate bearing strip 110 is disposed on the underside of the housing 34 on each side thereof between the housing 34 and the tool carrier shoe 18, which strip 110 serves as a spacer between the housing 34 and shoe 18, allowing the escape of the fluid from the exhaust conduits 106 and 108 and also serving to reduce friction during reciprocation of the shoe 18.

The tool carrier shoe 18 and the piston rod 54 are formed with opposing rack gears 112 and 114 respectively which are interconnected by a gear wheel 116 rotatably journaled on a bearing 118 fixed within the housing 34 (by means not shown). The gear wheel 116 is disposed in mesh with the rack gears 112 and 114 to thereby interconnect the tool carrier shoe 18 and piston rod 54 for inverse movement of the tool carrier shoe 18 relative to the piston rod 54 when the piston rod 54 is reciprocated. The lower central portions of the housing 34 and piston sleeve 50 are cut away to accommodate the gear wheel 116. The rack gears 112 and 114 are secured by rivets 120 and 122 through the tool carrier shoe and piston rod respectively. In assembly, the slide valve and piston rod are inserted within the piston sleeve 50, the gear wheel 116 is secured in place on the bearing 118 in mesh with the rack gear 114 and the tool carrier shoe 18 is then disposed with its gear rack 112 in mesh with the gear wheel. Thereafter, the L-shaped guide members 26 (FIG. 1) are fastened into place.

Referring now to other details of construction, a gasket 124 is placed over the front end of the housing 34 and the front end cap 36 is secured to the forward end of the housing 34 by means of threadscrew fasteners, not shown. The front end cap is formed with an oil reservoir 126 which is closed by means of a threaded plug 128. A conduit 130 is formed from the reservoir 126 and connects to a passageway 132 formed through the housing 34 paralleling the main fluid passageway 56 as shown by the dashed lines 134 and connecting with the main fluid passageway 56 rearwardly of the inlet conduit 60 through a small opening 135 thereto. Fluid traveling under pressure from rear to front of the main fluid passageway 56 draws sufficient oil through the oil passageway opening 135 to adequately lubricate the reciprocating components.

The rear end cap is formed to contain an intake valve 136 and a trigger 46 which is contained within the rear handle 42. The trigger 46 is carried on a pivot and is formed with a flat bottom member 140 abutting the top of the spring loaded valve plunger 142. The trigger 46 extends through an opening 143 defined in the handle 142 and is restrained from rear movement by the action of the lower rear edge 144 thereof against the internal base surface 146 of the trigger 46. A portion of the trigger 46 is cut away to form a recess 147. A set screw 148 having a rough textured head 150 is threaded through an opening 152 through the recessed area of the trigger 46 and compresses a spring 154 carried on the shank of the set screw 148. By such construction, the rough textured head screw 150 can be rotated to extend or withdraw the set screw internally of the handle 42 thereby governing the extent of travel of the trigger 46 to constitute a speed control for the reciprocating tool 10.

The rear end cap 40 is formed with a bore 156 vertically therethrough for receiving the components of the fluid intake valve 136 as will be detailed hereinafter. The end cap 40 also defines a fluid inlet passageway 158 intersecting the bore 156 from the rear end of the tool 10 and into which is threaded an inlet fitting 160 for coupling to a source of fluid under pressure. A relatively wide conduit 162 is drilled through the end cap 40 from the forward end thereof to intersect the valve bore 156 and for alignment with the main fluid passageway 56. A relatively narrow conduit 164 is drilled into the end cap 40 parallel to the wider conduit 162 and is formed to interconnect the valve bore 156 with the piston bore end chamber 78. A gasket 166 is placed on the rear end of the tool housing 34 and the rear end cap 40 is placed thereover and secured to the housing 34 by means of threadscrew fasteners (not shown).

Parallel narrow and wide fluid conduits 164 and 162 are provided to prevent a null position by sequential actuation of the piston. When the trigger 46 is depressed, the valve mechanism 136 operates in such a manner as to initially introduce fluid under pressure through the narrow conduit 164 into the right hand end chamber 78 thereby assuring displacement of the piston rod 54 from a null position. Thus, although the manner of construction herein makes it unlikely that the null position would be encountered, in the rare instances in which the tool is initially in a null position, the burst of fluid under pressure through the conduit 164 into the end chamber 78 assures an operative disposition of the components. The valve 136 is designed so that upon further depression of the trigger 46 the fluid under pressure is diverted from the narrow conduit to the main fluid passageway where it effects reciprocation of the operative components.

Referring to FIGS. 3a and 3b, there is more clearly illustrated the manner of construction and operation of the intake valve 136. A brass sleeve 168 is threadably disposed within the valve bore 156 and is formed at its end with a hexagonal head 170 whereby it may be tightly positioned within the bore 156. The head 170 is formed with an opening 172 through which the top end of the valve plunger 142 extends. The valve sleeve 168 is formed with openings 174 and 176 for mating in alignment with the fluid conduits 162 and 164 respectively. The plunger 142 carries a cylindrical slide 178 which is slidingly received close fit within the valve sleeve 168. A threaded plug 180 is threaded into the bottom of the valve bore 156 and carries a spring 182 within a central recess 184. The spring 182 supports a valve ball 186 which is thrust upwardly by the spring 182 against the bottom of the plunger 142.

The slide 178 is formed so that when the plunger 142 is in a closed position, i.e., the trigger is completely released, it covers the opening 174 thereby closing the top fluid conduit 162. In that position, there is sufficient clearance between the bottom of the slide 178 and the opening 176 so that the lower, narrower conduit 164 remains open for a small extent of travel of the slide 178. When in a closed position, the valve bore 186 seats against the bottom surface 188 of the sleeve 168, thereby closing off communication with the fluid inlet passageway 158. FIG. 3a illustrates the valve components after depression of the trigger, but before substantial travel downwardly of the slide 178. When the plunger 142 is depressed by movement of the trigger 46, it effects movement of the valve bore 186 out of its seat, thereby opening communication between the fluid inlet passageway 158 and the narrow conduit 164, resulting in passage of fluid therethrough as indicated by the arrow 190. Referring momentarily back to FIG. 2, the fluid thus admitted is conducted under pressure to the piston end chamber 78 whereupon it effects displacement of the piston rod 54 to initiate reciprocation of the operative tool components.

Referring to FIG. 3b, after the trigger 46 has been further depressed, thereby causing further downward travel of the plunger 142, the slide 178 is in a position whereby it covers the sleeve opening 176 thereby closing the narrow passageway 164. Simultaneously, the slide uncovers the sleeve opening 174 thereby opening the relatively wide passageway 162 leading to the main fluid passageway 56. The slide 178 is formed with a number of conduits 192 effecting communication between the bottom and top ends thereof and which serve to conduct fluid from the inlet passageway 158 to the conduit 162 as indicated by the arrow 194. The slide conduits 192 are operative to pass fluids only when there is communication between the top of the slide 178 and the conduit 162. The passage of fluid from the inlet passageway 158 to the conduit 162 and from there to the main fluid passageway 56 effects reciprocation of the operative components of the tool. At that point the right hand piston chamber 78 is sealed with respect to the conduit 164 and exhaust from the chamber is effective only through the exhaust conduit 108 (see FIG. 2). When the trigger 46 is released, the force of the valve spring 182 carries the valve ball 186 upwardly to carry the plunger 142 back to its original position, thereby closing the conduit 162 and again opening the narrow conduit 164.

Referring now to FIGS. 4a-c, the manner of operation of the reciprocating tool is schematically illustrated. For purposes of illustration, it is assumed that the tool has come to rest with the components thereof in a null position, that is, the slide valve 52 and piston rod 54 are disposed exactly in the center of their travel so as to be symmetrical about the centerline 62. Upon depressing the trigger 46, fluid under pressure is admitted through the conduit 164 into the right hand piston chamber 78, as indicated by the arrow 190. Referring to FIG. 4b, the fluid pressure as represented by the arrow 190 reacts against the right hand piston cap 82 displacing it leftwardly into engagement with the right hand end of the slide valve 52, opening access to the right hand exhaust conduit 108 whereupon the fluid 190 can escape from the chamber 78. simultaneously, the left hand reduced diameter portion 94 of the slide valve 52 is pushed into communication with the outlet passageway 68 leading to the left hand piston chamber 76. At that point, the passageway 164 has been closed by downward movement of the valve plunger 142 so that the valve 136 is in the operative condition as illustrated in FIG. 3b. Accordingly, as shown in FIG. 4b, open communication is established between the fluid inlet passageway 158 and the main fluid passageway 56 causing fluid under pressure 194 to enter the inlet conduits 58 and 60. The right hand outlet passageway 70 is closed by the land 53 adjacent the reduced diameter portion 96, however, the left hand conduit 58 communicates via the reduced diameter portion 94 with the outlet passageway 68. Fluid under pressure 194 is thus conducted into the left hand piston chamber 76, as indicated by the arrow 194'.

Referring to FIG. 4c, as a result of pressurizing the left hand chamber 76, the piston rod 54 is caused to be displaced rightwardly as shown until the left hand piston cap 80 is flush with the left hand land 55 of the slide valve 52. During this overtravel the slide valve 52 has not moved and at the point of flush contact the right hand piston cap 82 slides sufficiently to the right to cover the right hand exhaust conduit 108. However, the momentum of the steel piston rod 54 is sufficiently great to carry the aluminum slide valve 52 past the point shown so that communication is effected between the right hand inlet conduit 60 and the passageway 70 leading into the right hand piston chamber 78. At this point, the components assume the position in reverse of that depicted in FIG. 4b and the piston rod 54 starts its travel toward the left. The components would thus reciprocate only a small amount initially but the construction herein is such that the extent of travel within the piston bore 48 increases until after a small plurality of such strokes an equilibrium is reached wherein the components are reciprocating substantially the length of the piston bore 48.

Referring to FIGS. 5a-d, the manner of operation of the tool components, following establishment of equilibrium, is further illustrated. In FIG. 5a, the components are shown after the piston rod 54 has carried the slide valve 52 to the right and after sufficient fluid under pressure 194 has been conducted into the right hand piston chamber 78, as indicated by the arrow 194" so that the piston rod 54 is carried leftward again to the extent of its overtravel. In that position the right hand piston cap 82 is flush with the right hand land 53 of the slide valve 52. Also at that point, the left hand exhaust conduit 106 is open thereby venting the left hand piston chamber 76 to atmosphere, as indicated by the arrow 196. Subsequently, the piston rod 54 and slide valve 52 are caused to move leftwardly under the fluid pressure indicated by the arrow 194" during venting of the left hand chamber 76 as indicated by the arrow 196. This movement, together with the prior override movement of the piston rod 54 constitutes the power stroke of the tool in that more power is transmitted during this interval of movement than during other modes of operation.

In FIG. 5b, a modified power stroke is illustrated as the next operative step. The power stroke is modified since the further movement of the piston rod 54 leftwardly carries the right hand piston cap 82 past the exhaust conduit 108 causing a portion of the fluid 194" to escape through the exhaust conduit 108. Furthermore, the left hand exhaust conduit 106 is now closed by movement of the left hand piston cap 80 thereover. However, the momentum of the steel piston rod 54 is sufficiently great as to carry it substantially to the end of the piston chamber 76 and this is illustrated in FIG. 5c. At that point, communication is established between the intermediate inlet conduit 58 and the passageway 68 leading to the left hand piston chamber 76 so that fluid under pressure 194' is conducted into the left hand piston chamber 76. Also at that point, the right hand exhaust conduit 108 has been opened completely, allowing for complete exhaust from the right hand piston chamber 78 as indicated by the arrow 198. In this position of the components, the valve is at the very beginning stages of its return power stroke.

Referring to FIG. 5d, the fluid under pressure 194' effects rightward movement of the piston rod 54, carrying the left hand piston cap 80 into contact with the left hand land 55 of the slide valve 52. Comparing FIG. 5d with FIG. 5a it will be recognized that the components as depicted in FIG. 5d are in exact reverse of the components as depicted in FIG. 5a and that one half cycle of reciprocation has been effected. Reciprocation proceeds in reverse of the sequence as set forth in FIGS. 5b and 5c to effect a full power stroke and a modified power stroke.

Referring back to FIG. 2, it will be seen that reciprocation of the piston rod 54 is transmitted via the rack gears 112 and 114 and gear wheel 118 to the tool carrier shoe 18. The result is that the tool carrier shoe 18 reciprocates in inverse sequence to the reciprocation of the piston rod 54.

As required, a detailed illustrative embodiment of the invention has been disclosed. However, it is to be understood that the foregoing embodiment merely exemplifies the invention which may take many different forms that are radically different from the specific illustrative embodiment. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims which define the scope of the invention.

Claims

I claim:

1. A pneumatic reciprocating tool, comprising:

a body having a wall defining an elongate bore in said body;

fluid pressure intake means;

a passageway formed in said body from said fluid pressure intake means to first and second intermediate bore locations through said wall;

passageways formed in said body from third and fourth intermediate bore locations through said wall to respective ends of said bore;

reciprocating means in said bore having end portions in sliding, fluid-sealing engagement with said wall to define fluid chambers with said bore ends and formed to alternately interconnect said first and third bore locations and second and fourth bore locations whereby to direct fluid under pressure to alternate ones of said fluid chambers in sequence with its reciprocation; and

means for venting opposite alternate ones of said fluid chambers to ambient atmosphere;

said reciprocating means comprising a hollow slide valve for effecting said interconnection and a piston slidably disposed through said slide valve, said piston having ends extending beyond said reciprocating means end portions and formed to be slidingly received within said bore in fluid-sealing engagement with said wall independently of said reciprocating means end portions for a predetermined extent of travel.

2. A pneumatic reciprocating tool, comprising:

a body having a wall defining a piston bore in said body;

fluid pressure intake means and exhausts operatively associated with said bore;

a hollow slide valve slidingly received in said piston bore having end portions in sliding, fluid-sealing engagement with said wall to define fluid chambers with respective ends of said bore; and

a piston slidingly disposed through said slide valve and having ends extending beyond respective ones of said slide valve end portions and formed to be slidingly received within said piston bore in fluid-sealing engagement with said wall independently of said slide valve end portions for a predetermined extent of travel;

said slide valve being formed to be operable in conjunction with said intake means to alternately admit fluid under pressure to the opposite ones of said fluid chambers to effect reciprocation of said piston and sequential venting to ambient of said exhausts;

said fluid pressure intake means comprising an inlet valve, a first passageway formed in said body from said inlet valve to said piston bore whereby to operate in conjunction with said valve to admit fluid under pressure to opposite ends of said piston bore for effecting reciprocation of said piston, and a second passageway formed in said body from said inlet valve to one end of said piston bore;

said inlet valve being formed to sequentially direct fluid under pressure into said second passageway, whereby to assure displacement of said piston from a null position, and then into said first passageway.

3. A pneumatic reciprocating tool, comprising:

a body having a wall defining a piston bore in said body;

a piston reciprocal in said bore having end portions in sliding, fluid-sealing engagement with said wall to define fluid chambers with respective ends of said bore; and

fluid pressure means and exhausts operatively associated with said bore, said fluid pressure means including a fluid intake valve, means for sequentially directing fluid under pressure from said valve to one of said fluid chambers, whereby to assure displacement of said piston from a null position, and then alternately to opposite ones of said fluid chambers whereby to effect reciprocation of said piston;

said sequentially directing means comprising means defining an intake valve bore, means defining a first passageway from said intake valve bore to said piston bore, means operable in conjunction with said first passageway whereby to direct fluid to alternate sides of said piston bore, means defining a second passageway from said intake valve bore to one end of said piston bore whereby to direct fluid to said one end, means defining a third passageway opening into said intake valve bore for the intake of fluid under pressure, and a valve member in said intake valve bore formed to sequentially interconnect said third and second passageways and then said third and first passageways.