Abstract: The steam valve driving apparatus according to an embodiment is a steam valve driving apparatus regulating open and close position of a valve body. The steam valve driving apparatus includes: a plurality of hydraulic cylinders that presses the valve body in an opening direction. Each of the hydraulic cylinders includes: a piston rod extending outward from a piston in the opening direction; and an open-side cylinder chamber arranged in the opposite side of the piston with respect to the piston and to which hydraulic oil is supplied. The hydraulic cylinder is disposed on a side opposite to the valve body with respect to a closing spring pressing the valve body in a closing direction.

Abstract: The hydraulic shock-absorber comprises a hydraulic stop member having a cup-shaped body, which is adapted to be mounted in a compression chamber, and a plunger, mounted at an end of a rod of the shock-absorber so as to slide in the cup-shaped body when the shock-absorber moves towards the compression end-of-travel position. The cup-shaped body comprises a side wall and a bottom wall which define, along with the plunger, a working chamber in which a damping fluid of the shock-absorber is compressed by the plunger when the latter slides in the working chamber towards the bottom wall of the body. Axial channels are formed on the inner surface of the side wall of the body and allow the damping fluid to flow axially out of the working chamber when the plunger slides in the working chamber towards the bottom wall of the cup-shaped body.

Abstract: A hydraulic cylinder includes a rod inner passage that is formed in a piston rod along an axial direction and communicates a fluid pressure source and an interior of a cylinder tube; a plug that is inserted from an open end that opens to the interior of the cylinder tube of the rod inner passage; a lateral hole that is formed in the piston rod along a radial direction and extends so as to cross the rod inner passage; and a pin that is inserted into the lateral hole. In the piston rod, an inner-circumference screw portion is formed on an inner circumference of the rod inner passage, and on the plug, an outer-circumference screw portion that is screwed into the inner-circumference screw portion and an engagement portion that is engaged with the pin and locks rotation of the plug are formed.

Abstract: A port shield assembly includes a cup, a fitting, and a retaining pin. The cup includes a top with a hole, a sidewall, a cavity defined by the top and the sidewall, and a side port in the side wall. The fitting includes a body with a first end and a second end, a flange at the first end, and a central bore extending from the first end. The fitting also includes a port that communicates with the central bore, and a cross bore near the second end. The fitting extends through the hole of the cup and a retaining pin is disposed in the cross bore to retain the cup between the first end and the second end of the fitting.

Abstract: The vibration damper including a hydraulic end stop that has a sealing ring which is arranged between the end stop ring and the closure element, is supported axially on one side at the end stop ring, engages radially around the piston rod, is mounted in a sliding manner at the piston rod, and with its outer circumferential surface radially contacts the inner wall of the control space, wherein the sealing ring has at least one radial throttle groove which takes effect when the end stop with the sealing ring moves into the control space and ensures a defined flow of damping medium between the control chamber and the first working space, and wherein the sealing ring has a plurality of spring tongues which are supported at a supporting surface on the piston rod side.

Abstract: A piston assembly including an integral piston chamber with an increased volume that is maximized by providing a mounting arrangement whereby the piston can be mounted to a structural member such that the piston chamber surrounds at least two sides of the structural member. A gas damping passage is disposed in fluid communication with the piston chamber and is dimensioned such that pressurized gas transferred through the gas damping passage can dissipate kinetic energy acting on the piston assembly. The piston chamber can therefore utilize space adjacent the structural member to which it is mounted thereby resulting in a piston chamber of a greater volume than prior art designs. A gas spring and gas damper assembly utilizing such a piston assembly is also included.

Abstract: A flow restrictor (1) for application in bearing formation between a piston (2) and a cylinder (3) of a gas compressor (4). The gas compressor (4) includes a pad (5) externally surrounding the cylinder (3) and an inner cavity (6), arranged between the pad (5) and the cylinder (3), fluidly fed by a discharge flow arising from a compression movement exerted by the piston (2) within the cylinder (3). The gas compressor (4) includes a bearing formation gap (7) separating a piston outer wall (2) and an inner cylinder wall (3), and a flow restrictor (1) is provided with a housing (12) fluidly associating the inner cavity (6) to the bearing formation gap (7). The flow restrictor (1) includes a porous element (8), associated to the housing (12), provided with at least a restrictor part provided with a porosity sized to limit the gas flow flowing from the inner cavity (6) to the bearing formation gap (7).

Abstract: Provided is a connector which can facilitate tuning of frequency of pulsation to be reduced and prevent sealing performance from degrading when a piston moves. A pulsation reducing member adopts a structure in which the piston moves in a cylinder. The cylinder has an annular flange portion projecting in a radially inner direction of a hollow cylindrical shape. An elastic sealing member is sandwiched in a compressed state between an end surface of the flange portion of the cylinder and an end surface of the piston. An urging body is disposed in a region in the cylinder on a side of the piston opposite to a passage and applies urging force to move the piston toward the passage and compress the elastic sealing member.

Abstract: A cylinder accumulator system is disclosed. The system includes a cylinder comprising a cylinder rod, a cylinder barrel coaxial to the cylinder rod, a cylinder end cap coupled to the cylinder barrel and the cylinder rod, and a cylinder piston assembly disposed within the cylinder barrel. The cylinder piston assembly further includes a dynamic sealing arrangement, which comprises one or more dynamic seals. The system further includes a first annular volume coaxial to the cylinder rod and the cylinder barrel, and a second volume disposed within the cylinder piston assembly. The system also includes a piston disposed within a bore of the second volume and between a hydraulic fluid located on a first side of the piston and a gas media located on a second side of the piston. The system also includes an external high-pressure accumulator, a low-pressure accumulator, and one or more tube manifolds coupling the external high-pressure accumulator and low-pressure accumulator to the cylinder.

Abstract: Disclosed is an actuator damping control system for reducing shocks imparted to a hydraulic actuator caused by a change in load resulting from an abrupt manipulation of a boom or other working device.

Abstract: A piston pump assembly in which a piston-forming element to be received in a piston chamber of a piston chamber-forming member carries a removable stop flange member which may be secured to the piston chamber-forming member to provide a retention stop to prevent the piston-forming element from being removed from the piston chamber.

Abstract: The mounting arrangement is applied to a compressor which comprises: a piston having a cylindrical tubular body; and an actuating means connected to the piston to drive the latter in a reciprocating movement. The suction muffler comprises two tubular inserts, longitudinally disposed in the interior of the piston and having spaced apart open adjacent ends, and closed opposite ends respectively affixed to the top wall of the piston and to the actuating means, and defining, in the interior of the piston, a muffling chamber (C) and an annular passage medianly opened to the muffling chamber (C) and communicating an open rear end of the piston with a suction valve provided in a top wall of said piston.

Abstract: A delay mechanism of a main rod of a gas spring is described, having an inner rod and a series of gas chambers which are defined in the interior of the body of the spring in such a manner that, by controlling the passage of gas between said chambers, the speed and delay of the main rod of the spring is controlled.

Abstract: A piston pump assembly in which a piston-forming element to be received in a piston chamber of a piston chamber-forming member carries a removable stop flange member which may be secured to the piston chamber-forming member to provide a retention stop to prevent the piston-forming element from being removed from the piston chamber.

Abstract: The system according to the invention for controlling a stabilizing foot (112) includes a hydraulic cylinder (116) and a hydraulic circuit (124) for supplying hydraulic fluid to the hydraulic cylinder, the hydraulic cylinder (116) including a cylinder rod (114), at the end of which the stabilizing foot (112) can be attached, and at least one hydraulic chamber (118) controlling the position of the cylinder rod (114), the hydraulic supply circuit (124) including an arm (126) for supplying to the hydraulic chamber (118), comprising first means (138) that can be selectively actuated to prevent the flow of the hydraulic fluid from the hydraulic cylinder, and second means (130, 136) for preventing a flow of the hydraulic fluid from the hydraulic cylinder while the pressure of the hydraulic fluid in the hydraulic chamber is lower than a predetermined threshold value, the second means (136) being arranged between the first means (138) and the hydraulic chamber (118).

Abstract: A machine such as an external combustion engine in an electrical power and heat cogeneration unit comprises multiple cylinders, each driving an independent load or being independently driven, and a balance shaft comprising one or more off-center balancing mass(es) to counteract rocking motion created by the piston motion and thereby assist in dynamically balancing the machine.

Abstract: A fuel gallery has a first opening port communicated to a variable volume chamber formed at a lower side of a plunger and a second opening port communicated to a fuel pressurizing chamber formed at an upper side of the plunger. A connecting tube member is provided in the fuel gallery for communicating the first and second opening ports with each other. During a fuel amount adjusting stroke, for example, in which the plunger is moved in an upward direction, a part of excessive fuel from the fuel pressurizing chamber is supplied to the variable volume chamber through the connecting tube member and the remaining part of the excessive fuel is discharged from the connecting tube member into the fuel gallery through a communication through-hole formed in the connecting tube member.

Abstract: The invention relates to a device having a pneumatic actuating cylinder (1), wherein the actuating cylinder (1) has at least one pneumatic piston (2) and a brake element (15) which can be actuated in an arbitrary manner and which is connected to the pneumatic piston (2) or to a component (3, 7) which can be moved by means of the pneumatic piston (2), wherein a movement of the pneumatic piston (2) can be braked or suppressed by an actuation of the brake element (15). The invention also relates to a method for controlling a device of said type.

Abstract: A diaphragm pump (1) having a diaphragm (11), a solenoid with a movable magnetic armature (8) as a drive element for the diaphragm (11), and a stop element (9) for adjusting the stroke for the drive element (8). The diaphragm pump includes at least one elastic damper (36) between the drive element (8) and the stop element (9), which elastic damper (36) has at least one compression chamber (26) which is surrounded and formed by at least one elastic boundary wall and by at least one rigid boundary wall of the drive element (8) and/or stop element (9).

Abstract: A cylinder stroke system with a laser proximity detector including a pressure containing tube. The pressure containing tube can include a first tube end and a second tube end. A cylinder rod can be movably disposed within the pressure containing tube. The system can also include a piston disposed on the cylinder rod first end; a first fluid port formed in the pressure containing tube; a second fluid disposed within the pressure containing tube; a blind end cap and mount; a laser secured to the pressure containing tube; at least one optic guide; a lens separating the at least one optic guide from the second fluid. The cylinder stroke system can also include a camera in communication with a main controller. The camera can receive the reflection from the piston and convert the reflection into a reflection signal.

Abstract: A force limiting device comprises a housing defining an axially extending chamber containing a working fluid. A force transmitting member may be mounted for linear reciprocable movement inside the chamber under the action of external loads. An axial array of plates is floatingly disposed in the chamber between the force transmitting member and an end wall of the chamber. At rest, each plate is spaced from an adjacent plate by a gap occupied by the working fluid. When the force transmitting member is displaced towards the array of plates, the fluid in the chamber causes the plates to be successively pushed against each other, thereby causing some of the fluid to be squeezed out from between the plates.

Abstract: A fluid cylinder actuator assembly is provided. The assembly includes a cylinder tube and a cushion control needle assembly. The cushion control needle assembly is configured to extend into the fluid cylinder actuator assembly to control fluid that exits the cylinder tube and comprises: a threaded cushion control differential screw that selectively screws into a retainer having corresponding threads; a control needle that includes a stem selectively extendable through a bore in the retainer opposite of the cushion control differential screw; wherein the stem of the control needle is engageable with a threaded bore inside the cushion control differential screw that is complimentary to the threads formed on the stem so that rotating the threaded cushion control differential screw will selectively extend or retract the control needle back and forth; and wherein threads of the threaded cushion control differential screw is different than the threads in its threaded bore.

Abstract: A control system for a reciprocating device which includes a switching valve for directing fluid supply under pressure to one of two drive lines in an alternating manner, means for alternating the switching valve, and an exhaust circuit including and exhaust outlet, a first flow restrictor disposed between one drive line and the exhaust outlet, and a second flow restrictor disposed between the other drive line and the exhaust outlet. The system may include a selection valve for alternately connecting one of two drivelines to the exhaust outlet.

Abstract: A piston and cylinder assembly includes a housing defining a bore. A piston is sized to reciprocate in the bore. A first sealing member provides a sealing engagement between the piston and a wall of the bore. A first bushing, of a first material, is around a first portion of the piston toward a first end of the piston. A second bushing, of a second material, is around a second portion of the piston toward a second end of the piston. The first and second bushings guide the piston within the bore. The first material is different than the second material.

Abstract: A swivel motor has a plurality of work chambers and a join system between the work chambers that joins the work chambers at least by pairs. The arrangement of the joined work chambers is carried out in such a way that the work chambers which are connected to the first pressure medium connection alternate with those which are connected to the second pressure medium connection. At least two work chambers associated with different pressure medium connections are connected to a pressure compensation element, and the pressure compensation element is formed by a compensation space that is divided by a movable dividing element. A partial compensation space is connected in each instance to at least one work chamber of a pressure medium connection, and the dividing element is held in an initial position by oppositely acting springs. The spring force characteristic is formed by a spring arrangement which comprises a plurality of springs and has at least one coil spring and one elastomer spring.

Abstract: The invention concerns a method and an arrangement for a suspension system that may be, but does not necessarily need to be, constituted by a harvesting unit of a forestry harvester and which suspension system is of the type that has an arm (2) on which a wheel (4) is supported and provided with an angle sensor (4a) in order to form a measurement wheel for the measurement of length, and which arm is attached in a manner that allows it to pivot to a frame (3) in such a manner that the wheel can be adjusted from positions in contact with and out of contact with a surface (5) of the object whose length is to be measured while the object is fed in its longitudinal direction (5a) past the measurement wheel running against the circumference of the measurement wheel, whereby the said object may be, but does not necessarily need to be, constituted by a tree trunk taken up into a harvester unit.

Abstract: An apparatus for pivoting a boom relative to a frame of a pipe handling system between a first position and a second position has a hydraulic actuator assembly connected to the boom and to the skid, and a pneumatic spring connected to the boom and to the skid. The pneumatic spring has a cylinder with an end pivotally connected to the boom, and a piston with an end pivotally connected to the skid. The hydraulic actuator assembly has a cylinder pivotally connected to the skid, and a piston with an end pivotally connected to the boom. The pneumatic spring urges the boom from the first position toward the second position while resisting movement of the boom from the second position toward the second position.

Abstract: A machine such as an external combustion engine in an electrical power and heat cogeneration unit comprises multiple cylinders, each driving an independent load or being independently driven, and a balance shaft comprising one or more off-centre balancing mass(es) to counteract rocking motion created by the piston motion and thereby assist in dynamically balancing the machine.

Abstract: The present invention provides a telescopic hoist comprising a series of telescopically arranged tubular sections wherein the tubular sections are made in nitrided steel.

Abstract: A linear motor of the present invention has: a stator having a stationary iron core and a magnet wire; a mover having a moving iron core and a magnet; and a plate-shaped elastic member for supporting the mover in a manner to rock in the rocking directions. This construction eliminates a sliding portion for supporting the mover so that it can reduce the loss, which might otherwise accompany the reciprocation of the mover. Moreover, a linear compressor using this linear motor is high in efficiency and reliability.

Abstract: A regulating unit for accomplishing a linear movement includes a cylindrical frame part (1) having a cylinder part (11) and cylinder head (12), which define a piston space (131, 132), and a piston unit (2) to be moved by a pressurized medium in the piston space. The height of a first space (131), in which a piston part (22) is moveable, is bigger than the height of a piston part, the cross section area is bigger than a cross section area of a piston rod. A cross section area of a second space (132) is smaller that the cross section area of the piston part. Pressurized medium may be fed into a cavity space (15), which is between the facing surfaces of the piston part and the piston space, for moving the piston unit towards the cylinder head (12) or vice versa.

Abstract: There is provided a free-piston device, comprising at least one piston chamber in which at least one piston assembly is arranged for linear displacement, the at least one piston assembly being drivable under the action of a medium which expands in an expansion space, and the at least one piston chamber having a resilience space, in which a compressible gas is contained for exerting a returning force on the at least one piston assembly, and at which a control member is arranged for controlling the returning force while the free-piston device is in operation. A method for operating a free-piston device is also proposed.

Abstract: The present invention provides an off-chip apparatus and a method for driving micro fluid wherein one or a plurality of impedance members, plunger positioning members and pressure difference design are used to drive the fluid and control the flow speed in a microfluidic system. The present invention also provides a method for driving fluid and controlling flow speed, wherein a slow pressure balancing mechanism is produced by the foregoing device so the flow speed of fluid can be controlled.

Abstract: The invention relates to a reciprocating-piston pump having an electromagnetically driveable reciprocating piston, which is mounted with a restoring spring, for feeding a liquid, an impact damper composed of an elastomer for damping an impact of the reciprocating piston at the end of a feed phase, a core flange which is situated opposite the reciprocating piston, with a gap which is dependent on the position of the reciprocating piston being provided between the reciprocating piston and the core flange. Here, the invention is characterized in that the kinetic energy of the reciprocating piston during an early feed interval of a feed phase is absorbed primarily by the restoring spring and the feed of the liquid, and in that the kinetic energy of the reciprocating piston during a late feed interval of a feed phase is absorbed primarily by the hydraulic damping of the liquid present in the gap.

Abstract: A cushion ring which is used between a rod-side cylinder head and a piston rod of a fluid-pressure cylinder and which is externally fitted on the piston rod to cushion a shock in the vicinity of the farthest extended end of cylinder includes a throttling groove that has a V-shaped cross section. The throttling groove extends from an appropriate position of the cushion ring to a rod-side end part and functions to throttle the flow of a working fluid flowing from a rod-side fluid chamber to an input/output port provided in a rod-side cylinder head. The throttling groove is provided at the outer periphery of the cushion ring. The throttling groove terminates at a rod-side end part with an end guide face that guides the working fluid toward a slantwise outward direction of the cushion ring.

Abstract: A depth compensated passive eave compensator comprises a first cylinder connected at its upper end to a vessel. A piston rod extends from a piston located within the first cylinder through the lower end thereof and is connected to subsea equipment. A second cylinder contains a compressed gas which maintains pressure beneath the piston of the first cylinder. The upper end of the first cylinder is connected to the upper end of a third cylinder having a piston mounted therein. A piston rod extending from the piston of third cylinder extends through the lower end thereof thereby applying the pressure of the sea to the piston of the third cylinder.

Abstract: A regulating unit for accomplishing a linear movement includes a cylindrical frame part (1) having a cylinder part (11) and cylinder head (12), which define a piston space (131, 132), and a piston unit (2) to be moved by a pressurized medium in the piston space. The height of a first space (131), in which a piston part (22) is moveable, is bigger than the height of a piston part, the cross section area is bigger than a cross section area of a piston rod. A cross section area of a second space (132) is smaller that the cross section area of the piston part. Pressurized medium may be fed into a cavity space (15), which is between the facing surfaces of the piston part and the piston space, for moving the piston unit towards the cylinder head (12) or vice versa.

Abstract: A vibration damper including a cylinder filled with damping medium; a piston rod axially moveable in the cylinder; a piston mounted on the piston rod in the cylinder, the piston dividing the cylinder into a first working space around the piston rod and a second working space away from the piston rod; a valve opening communicating with the first working space; a valve ring on the piston rod and in the first working space, the valve ring being configured to influence an inflow into the valve opening; and a valve sleeve surrounding the piston rod. The valve ring is axially moveable in the valve sleeve.

Abstract: The invention relates to a piston engine which is essentially comprised of an engine shaft and a set of modules, each of which comprises a cylinder and a piston powered by the engine shaft in the cylinder, each module resulting in vibratory excitation of the engine at a determined fundamental frequency. Rather than introducing phase differences between the various vibratory excitations, as is the case in prior art, the invention introduces a frequency offset between the fundamental frequencies thereof in order to avoid a high-amplitude vibration at a common excitation frequency, arising from the spectral spread thus obtained.

Abstract: A piston type compressor includes a housing forming a cylinder bore. A drive shaft is supported by the housing. A cam plate is coupled to the drive shaft and is rotated by the rotation of the drive shaft. A piston is accommodated in the cylinder bore and is coupled to the cam plate. The rotation of the cam plate is converted into the reciprocating movement of the piston. In accordance with the reciprocating movement of the piston, gas is introduced into the cylinder bore, is compressed and is discharged from the cylinder bore. Compression reactive force is generated in compressing the gas by the piston, is transmitted to the housing through a compression reactive force transmission path and is received by the housing. A vibration damping member is made of a predetermined vibration damping alloy and is placed at least one location along the compression reactive force transmission path.

Abstract: A hybrid of the pneumatic and hydraulic actuators for combining pneumatically powered actuation with incompressible and controllable hydraulic damping in order to achieve smooth displacement, rapid stopping and steady and accurate positioning of the hybrid actuator in which hydraulic damping of a pneumatic actuator is obtained through utilizing positive-displacement hydraulic actuator means with zero volumetric differential.

Abstract: A hybrid of the pneumatic and hydraulic actuators for combining pneumatically powered actuation with incompressible and controllable hydraulic damping in order to achieve smooth displacement, rapid stopping and steady and accurate positioning of the hybrid actuator in which hydraulic damping of a pneumatic actuator is obtained through utilizing positive-displacement hydraulic actuator means with zero volumetric differential.

Abstract: A hybrid of the pneumatic and hydraulic actuators for combining pneumatically powered actuation with incompressible and controllable hydraulic damping in order to achieve smooth displacement, rapid stopping and steady and accurate positioning of the hybrid actuator in which hydraulic damping of a pneumatic actuator is obtained through utilizing positive-displacement hydraulic actuator means with zero volumetric differential.

Abstract: A hybrid of the pneumatic and hydraulic actuators for combining pneumatically powered actuation with incompressible and controllable hydraulic damping in order to achieve smooth displacement, rapid stopping and steady and accurate positioning of the hybrid actuator in which hydraulic damping of a pneumatic actuator is obtained through utilizing positive-displacement hydraulic actuator means with zero volumetric differential.

Abstract: The invention provides a rotary actuator having a rack driven in an oscillating manner by an air pressure, a pinion engaged with the rack, and a cushion mechanism for stopping the rack to at least one normal or inverse stroke end in a cushioning manner. The cushion mechanism has an exhaust port open to a pressure chamber at a position close to a chamber end rather than a port hole, a flow amount adjusting mechanism for restricting a flow amount of the exhaust air discharged from the exhaust port, and a cushion packing mounted to an outer peripheral surface of the piston and operating so as to shut the port hole from the pressure chamber immediately before the piston reaches the stroke end, thereby discharging the air within the pressure chamber through the flow amount adjusting mechanism.

Abstract: A damping device for installation in a hydraulic adjustment device such, for example, as for motor vehicle clutches. The hydraulic adjustment device has a cylinder that is either an input cylinder or actuator or an output cylinder. The input cylinder or actuator, which is connected to an operating pedal of the motor vehicle, is also connected to the output cylinder via a hydraulic line filled with fluid. The damping device opposes a throttle resistance to the flow of the fluid in both flow directions. The damping device comprises a disk having first and second spring washers on either side of the disk. The disk has passage openings, which are covered on the respective sides by one of the first and second spring washers. The damping device is installed in the hydraulic adjustment device to suppress disturbing vibrations acts as both a vibration filter and an operating speed limiter. In addition, a constant throttle resistance is maintained relative to the fluid at all ambient temperatures.

Abstract: The downhole pump has a barrel with a reciprocating plunger therein. The barrel has a first one-way valve, while the plunger has a second one-way valve. A barrel chamber is formed between the two one-way valves. The barrel chamber expands when the reciprocal movement between the plunger and the barrel is an upstroke movement and then contracts when the reciprocal movement is a downstroke movement. A bypass channel is provided between the barrel and the plunger so as to provide communication around the plunger and its one-way valve. The bypass channel is open when the reciprocal movement is near an end of the upstroke movement. When open, pressure across the plunger can equalize and gas inside the barrel chamber can vent around the plunger and/or pressure can equalize across the plunger one-way valve so as to prevent gas lock and minimize stress on the sucker rods.

Abstract: The present invention is intended to prevent vibration of a piston while reciprocating the piston without frictional contact by replacing a cross head for preventing the vibration of the piston with a leaf spring fixed by a rod at the lower end of the piston and a cylinder, and applied to a stirling cycle machine.

Abstract: A fluid pressure cylinder of the kind including a cylinder tube (23) with a slot and being shielded and sealed by an outer (11) and an inner (10) sealing band and with a cylinder bore (23') and a piston (2,5) which is movably arranged inside the tube and a transfer means (3) for transferring the piston movement through the slot to means (4) at the outside of the cylinder tube, wherein the piston comprises a seat (7) for a piston sealing member (6). The piston comprises a central body (2) and two piston end units (5) surrounding the respective end of the piston body and lying (17) against the cylinder bore, wherein each piston end unit (5) is fitted with play (s) onto the body (2) in order to allow a relative movement between these elements in directions essentially perpendicular to the cylinder axis.

Abstract: A trim-tilt device for a marine propulsion device includes a piston having a valve device for stopping a trim action by bringing a piston-side chamber and a rod-side chamber into communication with each other at an end of a trim region before a propeller of the marine propulsion device rises higher than the surface of the water when the marine propulsion device is generating a propulsive force.