Abstract: A gas spring-powered fastener driver includes a first chamber, and a movable piston positioned within the first chamber. The fastener driver also includes a driver blade attached to the piston and movable therewith between a ready position and a driven position. The fastener driver further includes a second chamber containing pressurized gas. The second chamber is in fluid communication with the first chamber via a flow passage. The fastener driver also includes a throttle mechanism configured to throttle flow of the pressurized gas through the flow passage.

Abstract: Pistons and related methods may be configured to separate fluids and to at least partially prohibit one fluid from traveling to one side of the piston from another side of the piston. Pressure exchange devices and systems may include such pistons.

Abstract: A self-adjusting end position damping arrangement includes a stroke space 9 which is delimited by a movable stroke element 7, 24 and a part of the pneumatic cylinder 1, with the stroke space 9 being connected via a connecting duct 14 to the working pressure P1 which acts on the cylinder piston 22 or to the ventilation pressure (P3) in the outlet duct 3 and the stroke element 7, 24 being acted on via a damping duct 16 by the damping pressure P2 in the damping volume 19, a non-return valve 12 is arranged in the connecting duct 14 upstream of the stroke space 9, which non-return valve 12 blocks in the direction of the working pressure P1 or the ventilation pressure (P3), respectively, and a ventilation duct 5 is provided, which ventilation duct 5 can be opened by means of the movable stroke element 7, 24 and which is connected to an outlet duct 3.

Abstract: An air logic controller for increasing the efficiency of an air operated double diaphragm pump. The air logic controller may increase the efficiency of the pump by controlling the supply of compressed fluid to the pump. In one embodiment, the air logic controller may control the supply of compressed fluid to the pump by replacing the continuous, large volume supply of compressed fluid supplied to conventional air operated pumps during a single pumping stroke with a varied supply of compressed fluid. The varied supply of compressed fluid may comprise a supply of compressed fluid that alternates between a large volume supply and a small volume supply of compressed fluid. The air logic controller may vary the supply of compressed fluid to the pump based at least partially on the position of a main air valve spool and the setting on an adjustable pneumatic time delay relay.

Abstract: A fluid pressure powered apparatus comprises a double-acting member, a first pilot valve, a second pilot valve, and a switchable valve is disclosed. The double-acting member is operable between a first stroke end and a second stroke end by fluid pressure from the switchable valve. The first and second pilot valves are configured to establish a biasing fluid pressure to first and second bias surfaces, respectively, of the switchable valve. The first and second pilot valves are actuatable by the double-acting member when at the first and second stroke ends, respectively, to reduce the biasing fluid pressure on the first bias surface. In operation, the reduction of biasing fluid pressure on either the first bias surface or the second bias surface, respectively, triggers the switchable valve to switch between a first stroke position and a second stroke position, respectively. A method of reciprocating a fluid pressure powered apparatus is also disclosed.

Abstract: A fastener driving tool includes a frame defining therein an accumulator that accumulates compressed air, a cylinder, a piston movable between a top dead center and a bottom dead center, a main valve section having a main valve movable between a top dead center and a bottom dead center to alternately open and block fluid communication between a piston upper chamber and the accumulator, a trigger valve section having a plunger movable between a top dead center and a bottom dead center so as to alternately open and block fluid communication from the accumulator to a main valve chamber, and fluid communication from the main valve chamber to atmosphere, and a trigger adapted to press the plunger when operated by a user. The piston moves from the top dead center to the bottom dead center within 11.3 msec when the plunger is pressed.

Abstract: A pilot control valve for controlling a reciprocating pump has a valve member shiftable within a valve body between a first or “downstroke” position and a second or “upstroke” position. In its first and second positions, the valve member positions slide valves to allow communication of control fluid to move the piston to a second and first position, respectively. When the piston reaches its second position a poppet disposed in a rod attached to the piston allows control fluid acting on the valve member to depressurize. Pressurized control fluid then acts on the valve member to move to its second position. When the piston returns to its first position, the poppet allows pressurized control fluid acting on the upper surface of the piston to act on the valve member to move the valve member back to its first position and repeat the process.

Abstract: A double acting pneumatic motor having a cylinder, a piston within the cylinder that divides the cylinder into two cavities that vary in volume with movement of the piston, a source of fluid under pressure, and a valve assembly for alternately directing fluid to one cavity while exhausting the other cavity to make the piston reciprocate. The valve assembly resides in a housing, and includes a cylindrical spool that moves axially between two positions with at least one enlarged diameter portion between smaller diameter portions at each end. The pneumatic motor may be provided with a cover for attenuating sound from the exhaust.

Abstract: A control system of a pneumatic oscillation cylinder (1) to produce the oscillating motion of a scraper (3) used in paper machines in particular. There is in the oscillation cylinder motion rod (18) motion stoppers (4), which in both wanted reversing points of the rod (18) motion open an own pressure discharge valve (5) for the said stopper in the pilot operation line (9), whereby the opening of both pressure discharge valves (5) in turns causes a reversing function in a pneumatic reversing valve (10) known as such.

Abstract: A pneumatically operated fastener driving device which includes a control valve module having i) a control module housing assembly mounted with respect to the housing and providing an exhaust passage which can be opened to communicate the one end of the cylinder with atmosphere, and ii) a main valve mounted with respect to the control module housing assembly for movement between opened and closed positions to open and close the passageway. The control module is a selected one of the standard type, full cycle type, automatic type, and automatic with remote type. The selected one control module is constructed and arranged with respect to the main frame portion of the housing so as to be removable therefrom as a unit. After removal of the selected one control module as a unit, another one of the types of control modules can be positioned with respect to the main frame portion of the housing as a unit to as to be operable therewith.

Abstract: For the oscillating triggering of a double acting operating cylinder (4), a reversing valve (6) has been provided and has been inserted between the pressure supply connector (5) and the two operating cylinder drive connectors (2,3) that is driven via two NOT elements (7,8), that each have been assigned to an operating position and connected with a drive connector (2,3). The reversing valve (6) is caused by pressure to periodically switch between the two operating positions. In order to stop oscillating with a defined final position of the operating cylinder (4) or start it up again, at least one of the NOT elements (7) has been provided with a pressure supply connector that can be triggered independently from the supply connector (5).

Abstract: The present invention relates to an ejection switch for a nailer, which allows for precise controlling of the ejection of nails by having a gliding bar vertically gliding within a gliding seat in a cavity on a valve seat, wherein, after ejecting a nail, the gliding seat moves against the gliding bar, such that the triggering of a loading state and of an ejection state follows the position of the moving bar in a hysteresis-like behavior and unwanted ejection of nails is prevented.

Abstract: The compressed-air nail firing tool with head valve operates with single firing or repeat firing through valves comprising a selector, a distributor, and a shunt valve that can be operated through a trigger. The selector has two positions that can be selected from the outside by the user actuating a lever and correspond to single-firing or repeat-firing operation.

Abstract: A release mechanism for a compressed-air nail firing tool which includes a trigger that is adapted to act on a pilot valve shutter that activates the nail firing tool. A lever is mounted on the trigger and is operatively associated with a probe that detects the resting position of the nail firing tool on a part being treated. A stem is pivoted on the probe and, in cooperation with a cap that can be applied thereto and as a function of its orientation with respect to the lever, selects single-firing or repeated-firing operation of the nail firing tool.

Abstract: A pneumatically operated fastener driving device includes a pilot pressure operated main valve movable from a normally closed position into an opened position closing an exhaust path and allowing a supply of air under pressure to be communicated with a piston chamber to initiate and effect the movement of a piston and fastener driving element through a fastener drive stroke. First passage structure is provided between a pilot pressure chamber and an exhaust port. A secondary valve member is mounted with respect to the first passage structure so as to be movable between an opened position permitting communication between the pilot pressure chamber and the exhaust port and a closed position preventing communication between the pilot pressure chamber and the exhaust port. Second passage structure communicates the piston chamber with the secondary valve member and with the exhaust path.

Abstract: A pneumatically operated driving device is constructed and arranged to operate in a single actuation sequence and an automatic actuation sequence. The device includes an improved control valve assembly for communicating reservoir pressure to move a piston in a direction to effect a drive stroke of a fastener driving element and for permitting the piston to move in a direction to effect the return stroke of the fastener driving element. The control valve assembly includes a main valve, a secondary valve, and first and second actuating members for controlling movement of the main and secondary valves, a trigger member for moving the actuating members, and trigger member adjustment structure constructed and arranged to adjust pivotal movement of the trigger member thereby providing operator selection of single actuation followed by automatic actuation of the device, or automatic actuation thereof only. The control valve assembly may be removed from the device as a unit.

Abstract: A control module for a pneumatically operated fastener driving device is constructed and arranged to be mounted with respect to a main frame portion of the device housing so as to open a passageway to operate the device.

Abstract: A fluid pressure piston-cylinder drive unit is reciprocated automatically by coupling the opposite ends of the cylinder through delivery conduits to a source of fluid pressure and exhaust through a switching valve in which a longitudinally reciprocative spool has a pair of passageways which reversibly couple one end of the cylinder to the source of fluid pressure and the other end of the cylinder to an exhaust conduit. The opposite ends of the switching valve contain shift pistons each of which engages an end of the spool through a coil spring. The shift pistons abut the opposite ends of an elongated rod which extends freely through a bore in the spool. Bypass conduits couple the opposite ends of the cylinder through the delivery conduits one to each end of the valve body such that fluid pressure in one delivery conduit from the source is coupled to one end of the valve body while exhaust fluid pressure from the other delivery conduit is coupled to the other end of the valve body.

Abstract: A pilot control relay valve to change the directional flow of fluid to a piston (such as, for example, the piston of a chemical injection pump for injecting chemicals at a slow or rapid rate over a long period of time), but also allow the recovery of exhaust fluids under significant back pressure. The pilot control relay valve comprises an elongated valve member shiftable within a valve body between a first and second position. The first position allows communication of control fluid to a first pressure receiving surface while allowing exhausting of fluid from a third or opposing pressure receiving surface, thereby to initiate movement of the valve member against the back pressure of the exhaust fluid from its first position to a position equalizing the pressure acting on a second pressure receiving surface with the pressure of the control fluid, thereby causing the valve member to move to its second position.

Abstract: An improved hydraulic motor includes a cylinder having a head end and a rod end, and a piston reciprocable in the cylinder dividing it into a first expansible chamber toward the head end and a second expansible chamber toward the rod end. Fluid under pressure from a supply source is continually delivered to the second chamber. A fluid directional valve controls the delivery of fluid to and exhaust of fluid from the first chamber for reciprocating the piston within the cylinder. The piston has valving associated therewith for controlling the operation, in conjunction with a relay valve, of the fluid directional valve.

Abstract: A hydrofluidic oscillator including a momentum exchange fluidic amplifier coupled to a four-way reciprocal valve. The four-way valve is connected to control flow of hydraulic fluid from a source thereof to a using apparatus. The fluidic amplifier is connected to provide input signals to the four-way valve to cause the four-way valve to reciprocate responsive to the input signals. Both negative and positive feedback paths are provided from each outlet of the fluidic amplifier to the respective control ports to control oscillation of the four-way valve.

Abstract: A cylinder including a housing disposed between a head and a board, a body disposed in the housing and closely contacted with the head, a piston slidably disposed in the housing, a piston rod coupled to the piston, a valve including five rings being disposed in the head, a valve including five annular grooves being disposed in the body, an inlet being formed in the head for continuously supplying hydraulic oil into the cylinder, the piston can be urged to move in a reciprocating action without changing the supplying direction of the hydraulic oil.

Abstract: A two stage fluid compressor is operated by a pneumatically operated relay valve controlled by a fluidic switching device in which switching pulses of pressurized control air are obtained automatically on movement of a compression piston in one of the compression stages.

Abstract: A fluid operable engine has a cylinder in which a piston slides up and down. The cylinder has a cylindrical wall and two end walls. The piston divides the cylinder into two chambers. The piston is hollow, has a cylindrical wall and two end walls, with a rigid tube extending from and through one end wall of the piston through an adjacent end wall of the cylinder so that the interior of the piston communicates with the exterior through the tube. The cylinder has an aperture in each end wall or in its cylindrical wall close to the end walls and the piston has an opening in each of its end walls. A closure member is provided for alternately closing the openings or the apertures as the piston reaches each end wall. The engine is operated either in a positive or negative manner, with fluid being charged into or sucked from the piston or the cylinder. The openings may be closed from within or without and the apertures may be closed from inside or outside. The closure member may be mechanically or fluid operable.

Abstract: Control valve means for a driving tool operated with compressed air for the driving of fasteners into workpieces. Through a specific design of the main and the auxiliary valve and through a connection to the piston return chamber the control of the valves are brought into synchronization with the movement of the working piston. By this, high repetition frequencies can be achieved. Further, in the mode "automatic operation" also single shot operation is possible.

Abstract: An air-operated expansible chamber motor comprising a cylinder having first and second end heads, a piston reciprocable in the cylinder, a spool valve for controlling the supply to and exhaust of air from opposite ends of the cylinder, a relay valve mounted in one of the end heads for controlling the spool valve, a pilot valve in each end head having a stem engageable by the piston for controlling the relay valve via pressurization and exhaust of a pilot line, and a bleed for feedback of pressure air to the pilot line.

Abstract: A percussive tool comprising a housing (1) accommodating a movable striker (2) and connected with a power cylinder (6) in which is arranged a striker shank (4) with a gripping mechanism (14) and a drive in the form of a hydraulic cylinder (8). The percussive tool is provided with a control unit having a spool valve means (18) to control a distribution means (19). The spool valve means (18) has a casing (22) and a spool (23) taking two positions in the casing and defining two chambers (25, 26) interconnected through a throttling means (24). One chamber (25) constantly communicates with a discharge line (21), and the other chamber (26) is periodically put in communication with the space of the hydraulic cylinder (8). The spool (23) is spring-loaded with respect to the casing (22) on the side of one chamber (25) and takes in this case its first position.

Abstract: A hydraulic percussion device comprises a housing defining a longitudinal cylinder, a piston longitudinally reciprocal in the cylinder and subdividing same into a front compartment and a rear compartment, and a tool engageable longitudinally with the piston at the front compartment. The compartments are alternately and oppositely hydraulically pressurized to move the piston forward to strike the tool while traveling at an end speed and to move the piston backward away from the tool, the rate of alternation being a frequency parameter and the speed being a force parameter. A controller varies at least one of the parameters by detecting how much the piston rebounds from the tool after striking same and operating the control means in accordance with how much rebound is detected. How much the piston rebounds can be detected by sensing the pressure in one of the compartments immediately after the piston strikes the tool.

Abstract: The present invention relates to an improved cylinder pump. The cylinder pump includes air hoists enabling the entire pump assembly to be lifted so that a container may be placed thereunder and thereafter the air hoists may be biased downwardly so that the follower plate of the pump mechanism will bear down on top of the liquid contained within the container. Thereafter, the air cylinder of the pump is activated and reciprocated up and down through the provision of a four port reversing valve activated through the use of air sensors to cause the pump to pump fluid out of the container while the downward bias of the air hoists keeps the follower plate in contact with the surface of the liquid within the container. By separating the air cylinder actuator for the pump mechanism from the four port reversing valve thereof, improved reliability and quietness are attained.

Abstract: A pilot control valve comprising an elongated valve member shiftable within a valve body between a first and a second position. The first position allows communication of control fluid to a first pressure receiving surface to initiate movement of the valve member from its first position to a position equalizing the pressure acting on a second pressure receiving surface with the pressure of the control fluid, thereby causing the valve member to move to its second position. The valve member when in its second position allows communication with a third pressure receiving surface for initially moving the valve member from its second position while equalizing the pressure acting on the second pressure receiving surface to move the valve member to a position equalizing the pressure acting on the second pressure receiving surface with a pressure lower than the pressure of the control fluid for moving the valve member to its first position whereby the operation is repeated at infinitum.

Abstract: A pilot control relay valve having first and second elongated valve members coaxially and independently longitudinally shiftable within a valve body between a first position of the first or leading valve member thereby allowing communication of actuating fluid from a supply to a first pressure receiving surface of the second or following valve member to initiate movment of the second valve member from its first position to a second position thereby allowing communication of the actuating fluid to a first pressure receiving surface of a main piston to initiate movement of the first valve member to a second position of the first valve member thereby allowing communication of supply fluid to the second pressure receiving surface of the second valve member thereby initiating movement of the second valve member from its second to its first position thereby allowing communication of supply fluid to a second pressure receiving surface of the main piston to initiate movement of the first valve member to its first pos

Abstract: The pump or pumps for supplying fluid to the two ends of a double-acting cylinder include a direction control, such as a direction control valve, shiftable between extend and retract conditions. A drive mechanism for the direction control includes a rotary hydraulic motor and a driven rotary drive mechanism for shifting the direction control. Hydraulic fluid is supplied to the drive motor through parallel connected start and stop valves. The start valve is opened in response to the movements of the hydraulic cylinder toward a stroke limit. The stop valve is operated in response to the shifting of the direction control, so that the motor is operated intermittently to reverse the direction control when the cylinder reaches the limit of an extend or retract stroke. The stop valve is controlled by the drive mechanism in timed relation with the shifting of the direction control. The start valve may be closed by that drive mechanism in timed relation with the opening of the stop valve.

Abstract: A fluid operated pumping system which includes a main power cylinder divided into a power chamber and a pump chamber by a reciprocally mounted power piston. An actuator piston is connected to the power piston for synchronous movement therewith and is reciprocably mounted in an actuator cylinder. A diaphragm type four-way transfer valve is interposed between a power fluid source and the main power cylinder and actuator cylinder, to both of which the valve is connected, and functions to alternately and cyclically charge power fluid at a relatively high pressure to the power cylinder and actuator cylinder, and to concurrently discharge power fluid at a relatively low pressure. The system further includes a needle valve controlled, diaphragm-type, astable pneumatic amplifier which is connected to, and controls the movement of, the transfer valve.

Abstract: A pneumatically actuated diaphragm type metering pump is controlled by a pneumatic control circuit including a pilot actuated two position valve for pressurizing and venting the pump power piston chamber and which is controlled by a second pilot actuated two position valve. Timing chambers and a flow control valve in the control circuit operate to vary the frequency of the pumping cycle. The control circuit is included in a manifold assembly made up of a series of circular plate members assembled in staked relationship and including all of the fluid passages of the control circuit as well as the pneumatic timing chambers. The manifold assembly is mounted directly on an end wall of the pump body which provides for a single control fluid inlet passage and a single discharge passage for venting control and power piston fluid from the pump.

Abstract: A valve mechanism for a water actuated waste disposal unit includes a reciprocating control valve for actuating an operating piston with cutters attached thereto. The control valve is cycled by a pilot valve. Passages in the valve mechanism are constructed and arranged for optimum operation and cycle time with minimum leakage.

Abstract: A fluid operated ram comprises a striker body guided in an upright housing between an active stroke and a return stroke and striking at the end of its active stroke an impact transmitter resting on a member to be driven into the ground by the ram. The striker body is connected by a piston rod to a working piston reciprocatedly arranged in a cylinder coaxially mounted on the upper end of the housing, so that the striker body is driven during reciprocation of the working piston. The working piston is a differential piston and divides the cylinder into a first chamber above the upper larger face of the working piston and a second chamber below the smaller annular face of the differential piston.

Abstract: A hammer or impactor apparatus including improved motive fluid means cooperable with spring bias means to reciprocably drive a hammer element and an improved process of hammer cycling achieved thereby.

Abstract: A cylinder control device of a hydraulic cylinder apparatus including a main directional control valve having a pilot chamber for controlling the reciprocatory movement of the piston, and a first valve including a plurality valve members for selectively communicating the pilot chamber, via an auxiliary directional control valve, to the fluid discharging tank side of the working fluid circuit when the piston reaches a predetermined position in its rearward stroke. The pilot chamber is brought into communication, via a passage, to the pump side of the working fluid circuit by a second valve when the piston reaches the end of its forward stroke. A control valve using the pump side pressure as a pilot pressure is mounted in the passage connecting the second valve to the pilot chamber or in the passage connecting the pilot chamber to the auxiliary directional control valve.

Abstract: Automatically Self-Reciprocating sequencing valve for use with pneumatic power cylinders/actuators in systems operated at frequencies of a few cycles to a few thousand cycles per minute comprises a valve housing with a central bore adaptable to receive a shuttle member that makes or breaks fluid communication between a fluid supply source and a receiver such as a power cylinder or an actuator of a positive displacement pump in response to fluid pressures acting over surfaces such shuttle member entails as controlled by appropriate slave valve housed alongside therein including fluid supply and exhaust ports entering and leaving said valve housing, and together with said slave valve allowing an automatic reciprocating-valve-operation for as long as the pressurized fluid is supplied thereto to result in self-reciprocating operator responsive to not only system pressures for cycle regulation but also to an externally provided biasing flow regulator for an easy control of cycle frequencies within the desired prac

Abstract: A pressure fluid-actuated oscillator, especially suitable for use in lung ventilation equipment for emergency use, comprises a double-piloted 5-port valve and biased timer valves controlling the supply to its pilots to provide for repeated changeover of the 5-port valve at intervals determined by the respective timing periods of the timer valves. One of the timer valves has an adjustable timing period whereas the other has a nominally fixed timing period but is made sensitive to the duration of the immediately preceding timing period determined by the adjustable timer valve so as automatically to change its timing period in the same sense as adjustment of the adjustable timer valve.In lung ventilation equipment using such an oscillator, therefore, a single control may serve for directly setting the critical inhalation phase duration and to cause a complementary alteration of the exhalation phase duration that maintains the ratio of duration of the respective phases within desirably close limits.

Abstract: A waste disposal unit having cutters which are driven with a rotary reciprocating motion by a water powered piston moving in a toroidal chamber. An automatic servo controlled valve, responsive to differential pressure on opposite sides of the piston, reverses the piston direction at the end of a stroke, or when an obstruction is encountered. The driving water is exhausted into the cutting chamber to flush waste material through the stacked cutters, which are arranged to reduce the waste material progressively to small particles.

Abstract: A hammer and more particularly a fluid operable hammer wherein alternating impetus provided by pressurized liquid and gas means actuates a reciprocable hammer piston to generate repetitive impact loads.

Abstract: A high pressure pump comprising a valve body having a first housing secured at one of its ends to one end of the valve body and having a body member secured to the other end thereof. A second housing is secured to the body member with a piston rod movably extending through the body member and the first and second housings. A first piston secured to the piston rod and movably positioned in the first housing defines first and second chambers. A second piston secured to the piston rod and movably positioned in the second housing defines third and fourth chambers. Check valve means are in communication with the third and fourth chambers and sources of fluid to be pumped. The valve body has a pilot valve therein. The pilot valve means is connected to the piston rod so that the pilot valve means will be moved from a first position to a second position when the piston rod moves from a first position to a second position and vice versa. The valve body also has a main valve therein.

Abstract: The disclosure concerns a hydraulically driven impactor in which the operng cycle of a reciprocating piston is determined by the retraction velocity and displacement of the piston itself. Energy is conserved and heat dissipation minimised by the utilization of hydraulic spring accumulators to decelerate the piston. The drive to the piston is switched into a forward direction at such a point in each displacement cycle that the rebound energy of the piston is always re-absorbed into the drive fluid. The impactor operates at optimum acceleration and frequency at all times, whether or not impact occurs, and this feature combined with high energy conservation makes the impactor particularly suitable for use in a full-face tunnelling machine where high power density is required and individual impactors are often constrained to operate without impacting the rock face for considerable periods.

Abstract: In a percussion tool a means is provided for delaying the manifestation, on a valve means sensitive to such change in pressure, of a change in pressure of the fluid applied to the hammer piston at one end thereof and which drives such hammer piston in its working stroke, the valve means being that means which serves to control the inlet and exhaust parts of the fluid circuit which applies pressure to the other end of the piston.

Abstract: The piston of a pneumatic cylinder is reciprocated with a controllable dwell time at each end of its stroke, under the control of a digital fluidic circuit which responds to the termination of exhaust flow at the end of each piston stroke to initiate the reverse piston stroke. The air for driving the piston is supplied alternately to opposite ends of the piston through respective cylinder ports, by way of a corresponding pair of pilot valves which are controlled by the fluidic circuit so that one or the other of the pilot valves may supply driving air to the piston at any time.

Abstract: In a hydraulic percussion rock drill the operation of the working fluid distributing valve is controlled to effect a variation in percussive blow energy and blow frequency by varying the piston hammer stroke. Actuation of the distributing valve is controlled by a remote controlled hydraulically actuated pressure control valve interposed in a fluid passage which conducts hydraulic fluid from the hammer bore to actuate the distributing valve. Substantially infinite variation of hammer impact blow energy between high and low limits provides for selecting the maximum penetration rate of the drill for any type of rock conditions. The hydraulic rock drill is connected to a source of hydraulic fluid supplied to the drill at substantially constant fluid power by a variable displacement constant power hydraulic pump.

Abstract: A fluid operable engine has a cylinder in which a piston slides up and down. The cylinder has a cylinder wall and two end walls. The piston divides the cylinder into two chambers. The piston is hollow, has a cylindrical wall and two end walls, with a rigid tube extending from and through one end wall of the piston through an adjacent end wall of the cylinder so that the interior of the piston communicates with the exterior through the tube. The cylinder has an aperture in each end wall or in its cylindrical wall close to the end walls and the piston has an opening in each of its end walls. A closure member is provided for alternately closing the openings or the apertures as the piston reaches each end wall. The engine is operated either in a positive or negative manner, with fluid being charged into or sucked from the piston or the cylinder. The openings may be closed from within or without and the apertures may be closed from inside or outside. The closure member may be mechanically or fluid operable.