Fluid transfer device Field of the Invention The invention relates to a fluid transfer device, especially to a device using reciprocal movement of the piston to transfer fluid. 5 Description of prior art The working prcess of the internal combustion engine is roughly such, the piston moves downward, the mixed combustible gas goes into the cylinder; the piston moves upward to compress 10 combustible gas, the spark plug ignites combustible gas to explode the gas, the exploded gas with high temperature and high pressure drives the piton moving downward, the linear movement of the piston is converted to the rotational movement of the crankshaft by the connecting rod; the crankshaft goes on rotating because of the 15 inertia, the rotational movement of the crankshaft is converted to the linear movement of the piston by the connecting rod, the piston moves upward to push exhaust gas out of the cylinder. In brief, inhale- compression -work- exhaust. 20 Whether we can make some reconstruction based on the structure of the current internal combustion engine, saving the process of " compression-work", keeping the precess of " inhale- exhaust", such that the reconstructed device can be used in the field of pumping air, or compressing air, or drawing water or pumping water. 25 Summary of the present invention The object of the invention is to provide a device to transfer fluid by reciprocal movement of the piston so as to solve the above problem. 30 1/20 In the following, the technical solution will be discribed. A fluid transfer device includes a body, a switching unit, a triggering unit, a piston unit and a transmission unit; the device further 5 includes a receiving chamber, a input passage, a output passage and a valve chamber, the end of the receiving chamber in the body, the end of the input passage and the end of the output passage are configured to communicate with the valve chamber. The switching unit includes a swinging arm having a triggering end and a fixed end, 10 a cartridge having a first passage, a second passage and a manifold chamber, and a reset component for reseting the switching unit. The fixed end of the swinging arm of the switching unit removably connects with the cartridge, the triggering end of the swinging arm is configured to mate with the triggering wheel of the triggering 15 unit, the cartridge is configured to freely hermetically rotate in the valve chamber, the end of the first passage and the end of the second passage are configured to communicate with the manifold chamber, the first passage always communicates with the receiving chamber of the body, the second passage of the cartridge is 20 configured to mate with the triggering unit with the help of the triggering end, and the reset component alternatively communicates with the input passage of the body or the output passage. The triggering unit includes a triggering wheel having a triggering block, a fourth belt wheel, a fourth support board and a 25 fifth belt wheel. The piston unit further includes a piston with a piston ring, a connecting rod, a crankshaft and a cylinder casing without cover or bottom, the receiving chamber of the body is surrounded by the cylinder casing of the piston unit, the rotation of the crankshaft is configured to drive the piston reciprocally moving 30 in the receiving chamber, the crankshaft interacts with the fourth belt wheel through the belt wheel. The transmission unit includes a first support board, a second support board, a third support board, a first gear, a second gear, a first belt wheel, a second belt wheel, a third belt wheel, a first support pillar, a second support pillar, a vane, 2/20 a belt and a bushing, the first support board of the transmission unit at the middle portion thereof has a first belt wheel, the end of the second support board at the middle portion thereof having a second belt wheel, the head of the second support board at the middle 5 portion thereof having a third belt wheel, the second and third belt wheels interacted with each other by belt, the first and second belt wheels interacted with each other by the engagement between the first and second gears, the first belt wheel connected with the outside power source through the belt, the third belt wheel rotating 10 in unison with the crankshaft through the key connection. The heat generated by the device is taken away by the vane. Specifically, the triggering end of the swinging arm of the switching unit is configured to mate with the triggering block of the triggering 15 unit, the triggering block is configured to rotate around the axis of the fourth belt wheel and having an arcuate surface for matting with triggering end of the switching unit, the rotation of the fourth belt wheel makes engagement between the triggering block and the triggering end of the switching unit, the triggering block drives the 20 triggering end moving and then driving the cartridge rotating, the passage communicated with end of the second passage is switched from the output passage of the body to the input passage. The head of the reset component communicates with the swinging arm and the end of the reset component communicates with the body, the 25 reset component drives the switching unit moving, and then the passage communicated with the end of the second passage is switched from the input passage of the body to the output passage. Advantageously, the width of the second passage is less than the 30 minimal distance between the the end of the output passage of the body and the end of the input passage. The width of the swinging range formed by the rotation of the head of the first passage with the cartridge is less than the constriction width of the end of the receiving chamber of the body. 3/20 Specifically, the head of the input passage and the head of the output passage are configured to extend to exterior surface of the body. The head of the first passage and the head of the second passage are configured to radially extend to exterior surface of the 5 cartridge. Specifically, the first gear rotates in unison with the first belt wheel through the key connection, the second gear rotates in unison with the second belt wheel through the key connection. 10 Specifically, the head of the first support pillar removably partly inserts into the first support board, the end of the fist support pillar removably partly inserts into the body, the end of the second support board is removably mounted to the first support board, the 15 bolt sequentially passes through the second support board, the first support board and the first suport pillar, and fastens the three to the body; two sides of the second support pillar respectively removably connects with the first support board and the second support board, and two ends of the the second support pillar partly 20 inserts into the corresponding support board, the fist support board, the second support board and the second support pillar are fastened together by bolts. In the following, the working process of the device will be 25 described. The outside power source drives the first belt wheel rotating through the belt, the first belt wheel drives the second belt wheel rotating through the engagement between the first and second 30 gears, the second belt wheel drives the third belt wheel rotating through the belt, the third belt wheel drives the crankshaft rotating through the key connection, the crankshaft dirves the piston reciprocally move through the conecting rod, the crankshaft drives the fifth belt wheel rotating through the key connection, that is the 4/20 triggering block rotates around the axis of the fourth belt wheel. The triggering block touches the triggering end of the swinging arm and then drives the triggering end rotate, that is the swinging arm drives the cartridge rotating, the second passage is switched from 5 the output passage of the body to the input passage during the rotational movement of the cartridge, when the arcuate surface of the triggering block is tangent to the triggering end, the triggering end is not rotated any longer, the first passage of the cartridge keeps communicating with the input passage, while the first 10 passage always communicates with the receiving chamber. The piston moves upward to make fluid sequentially flow through the input passage, the second passage, the manifold chamber, the first passage and the receiving chamber. The triggering block goes on rotating, when the triggering block is separated from the triggering 15 end of the swinging arm, the swinging arm returns to the initial position under the effect of the reset component, meanwhile, the cartridge rotates back to the initial position, that is the second passage of the cartridge is switched back to the output passage from the input passage of the body and keeps communicating with 20 the output passage, while the fisrt passage always communicates with the receiveing chamber, the piston moves downward to compress the fluid therein out of the receiving chamber, fluid sequentially passes through the first passage, the manifold chamber, the second passage and the output passage. 25 Advantageous Effects Through the intermittent linkage between the triggering block and the triggering end, upward and downward movements of the piston combines with the rotation of the cartridge achieve that the 30 receiving chamber switchingly independently communicates with the input passage or the output passage, that is the second passage alternatively communicates with the input passage or the output passage, while the receiving chamber always communicates with the first passage. Therefore, 5 / 20 1. When the input passage communicates with the water source, the piston moves upward to creat a negative pressure area in the receiving chamber, water near the input passage is compressed into the receiving chamber through the second and first passages by the 5 effect of the atmosphere. The downward movement of the piston within the receiving chamber compresses water therein out of the output passage opening through the first and second passages, due to the near incompressibility of fluid, the output passage can ouput water flow with equal pressure, so the device can be used as a 10 water pump, even there is some air left in the waterpipe conected with the input passage. 2. When the input passage communicates with the atmosphere, the piston moves upward to creat a negative pressure area in the 15 receiving chamber, air near the inlet opening is compressed into the receiving chamber through the second and first passages by the effect of the atmosphere. The downward movement of the piston within the receiving chamber compresses air therein out of the output passage opening through the first and second passages, due 20 to the compressibility of air, the output passage can ouput air flow with a little pressure, if the output passage connects with a gas tank, so the device can be used as an air compressor. 3. When the input passage communicates with a sealing container 25 while the output passage communicates with the atmosphere, the piston moves upward to creat a negative pressure area in the receiving chamber, the air in the sealing container is compressed into the receiving chamber through the second and first passage by the current air pressure in the container. The downward movement 30 of the piston within the receiving chamber compresses air therein out of the output passage opening through the first and second passages,and then into the atmosphere, so the device can be used as an air-extractor. 6/20 Brief description of the drawing In the following, the invention will be described in greater detail by means of some embodiments with reference to the accompanying drawings, in which 5 Fig.1 is a 3d-drawing of the fluid transfer device of the invention; Fig.2 is a 3d-drawing of the device in Fig.1 from another view angle; Fig.3 is an exploded 3d-drawing of main parts of the device in Fig.1; Fig.4 is a 3d-drawing of the device in Fig.1 with the body, the switching unit, the triggering unit and the piston unit; 10 Fig.5 is a sectional 3d-drawing of Fig.4; Fig.6-9 are the front views of the Fig.5, wherein the piston is at different positions; Fig.10 is a 3d-drawing of the body; Fig.11 is a sectional front view of the body; 15 Fig.12 is an exploded 3d-drawing of the switching unit; Fig.13-14 is sectional 3d-drawing of the cartridge from different view angles; Fig.15 is a 3d-drawing of the triggering wheel; Fig.16 is a front view of the triggering wheel without a fixed sheet in 20 Fig.15; Fig.17 is an exploded 3d-drawing of the triggering wheel in Fig.15; Fig.18 is an exploded 3d-drawing of the transmission unit; 1. the body; 101. the receiving chamber; 102. the valve chamber; 103. the input passage; 104. the output passage; 105. the aspirail; 25 2. the switching unit; 201. the swinging arm; 201a. the triggering end; 201b. the fixed end; 201c. the beak-like rod; 201d. the beak; 201e. the rod; 202. the cartridge; 202a. the first passage; 202b. the second passage; 202c. the manifold chamber; 30 203. the reset component; 3. the triggering unit; 301. the triggering block; 302. the fourth belt wheel; 303. the fourth support board; 304. the fifth belt wheel; 305. the triggering wheel; 306. the fixed sheet; 7/20 4. the pistion unit; 401. the piston; 402. the connecting rod; 403. the crankshaft; 404. the cylinder casing; 5. the transmission unit; 501. the first support board; 502. the second support board; 503. the third support board; 5 504. the first gear; 505. the second gear; 506. the first belt wheel; 507. the second belt wheel; 508. the third belt wheel; 509. the first support pillar; 510. the second support pillar; 511. the vane; 512. the first rotating shaft; 513. the second rotating shaft; 10 6. the inlet opeing; 7. the outlet opening. Detailed description of the preferred embodiment In order to distinguish between the head and the end of the component, the portion near the axis of the cartridge 202 is called 15 the end, and the portion away from the axis of the cartridge 202 is called the head. Referring to Fig.1 to Fig.3, a fluid transfer device includes a body, a switching unit 2, a triggering unit3, a piston unit 4 and a 20 transmission unit 5. Power is transmissioned to the transmission unit 5 from the electric motor mounted by the belt, the transmission unit 5 transfers power to the piston unit 4 through the belt, the piston unit 4 transfers power to the switching unit 2, the linkage between the switching unit 2 and the piston unit 4 achieves 25 that fluid is indrafted through the inlet opening 6 of the transfer device and then released from the outlet opening 7 of the transfer device. Inorder to increase the transferring efficiency of the device, the 30 device includes four piston units 4, four piston units 4 are uniformly arranged in a ring array, the axis of the array is the axis of the cartridge 202. Three of the four input passages 103 of the body 1 are sealed by plugs, and three of the four output passages 104 of 8/20 the body 1 are sealed by plugs, the transfer device only keeps one input passage 103 and one output passage 104, a pipe connects with the head of the input passage 103 to form an input opening 6 of the transfer device, a pipe connects with the head of the output 5 passage 104 to form an output opening 7 of the transfer device. The heat created by the device during working is taken away by the vane 511 arranged in the front of the device. 10 Referring to Fig.18, the transfer device provides one first support board 501, four second support boards 502, one third support board 503, one first gear 504, four second gears 505, one first belt wheel 506, four second belt wheels 507, four third belt wheels 508, eight first support pillars 509, four second support pillars 510, one 15 vane 511, five belts and a plurality of bushings. Four second support pillars 502 are uniformly arranged in a ring array, the axis of the array is the axis of the first support board 501, two mounting holes located at the end of the first support board 20 501 removably connects with the first support board 501, the end of the second support board 502 at the middle portion thereof has a second belt wheel 507, the head of the second support board 502 at the middle portion thereof has a third belt wheel 508, the second and third belt wheels 507, 508 interacted with each other by equal 25 transmission ratio through the belt. The second belt wheel 507 coaxially provides a second gear 505, which rotates in unison with the second belt wheel 507 through the key connection. The first support board 501 at the middle portion thereof has a first 30 belt wheel 506, which coaxially provides a first gear 504, which rotates in unison with the first belt wheel 506 through the key connection. The linkage between the first and second belt wheels 506, 507 is 9/20 achieved by the engagement between the first and second gears 504, 505, the transmission ratio thereof is 2. The first belt wheel 506 connects with outside power source through the belt, the transmission ratio thereof is 2. The third belt wheel 508 and the 5 crankshaft 403 interact with each other by equal transmission ratio through the key connection, due to such arrangement, finally the transmission ratio between the crankshaft 403 and the electric motor is 4, due to peed reduction, the crankshaft 403 can output large torque to the connecting rod 402, therefore, the piston 401 10 has large force to pull and compress fluid, so as to do more work to fluid. The heat created by the gears and belts during working is taken away by the rotating vane 511 configured to rotate in unison with first belt wheel 506 through the key connection. 15 The second rotating shaft 513 connected with the second belt wheel 507 and the second gear 505 passes through the second support board 502, each end of two ends of the second rotating shaft 513 respectively partly inserts into the first support board 501 and the third support board 503, such arrangement can limit the 20 aixal movement of the second rotating shaft 513 so as to save extra limiting parts like antiextrusion rings or screws or nuts. Each end of two ends of the first rotating shaft 512 connected with the first belt wheel 506 and the first gear 504 respectively connects 25 with the first support board 501 and the third support board 503 through bearings, the bearing has interference fitting with the first support board 501 or the third support board 503, the bearing has interference fitting with the first rotating shaft 512. The vane 511 is mounted to the first rotating shaft 512 near the side of the third 30 support board 503, the vane 511 is fastened to the first rotating shaft 512 by the screw. The first support board 501 removably connects with the third support board 503 through the second support pillar 510, each end 10/20 of two ends of the second support pillar 510 respectively inserts into the first support board 501 and the third support board 503, such arrangement has such advantages: 1. limiting the axial and radial movements of the second support 5 pillar 510 for avoiding the device shaking created by the displacement of parts during the transmission unit 5 working. 2. Increasing the assemble convenience, the second support pillar 510 can be quickly conveniently situated by the the prefabricate counterbore on the first support board 501, then the prefabricate 10 counterbore on the third support board 503 can be quickly conveniently slipped into the second support pillar 510. 3. The support effect of the second support board 510 can be maximized, the cylinder formed by that the first support pillar 510 inserts into the first support board 501 or the third support board 15 503 supports each other for preventing the fastening screws from the effect of radial shear force so as to make the screw only take the effect of axial force . The second support pillar 510 separates the first support borad 501 20 from the third support board 503 to form a space for arranging the gear and the belt wheel. The first gear 504 and the second gear 505 are aligned with eacher by face, the first belt wheel 506, the second belt wheel 507 and the third belt wheel 508 are aligned with one another by face, such aligning arrangement can be achieved by 25 bushings adjusting heights of the gear or the belt wheel. The first support board 501 removably connects with the body 1 through the first support pillar 509, each end of two ends of the first support pillar 509 respectively partly inserts into the first support 30 board 501 and the body 1, such arrangement has above advantages. Referrign to Fig.10 to Fig.11, the body 1 has four receiving chambers 101, four input passages 103, four output passages 104 and one valve chamber 102. Four receiving chambers 101, four input 11/20 passages 103 and four output passages 104 are uniformly arranged in a ring array, the axis of the array is the axis of the valve chamber 102. One input passage 103 and one output passage 104 are arranged in the middle area between the two receiving chambers 5 101, the input passage 103 and the output passage 104 are mirror-images. The end of the receiving chamber 101, the end of the input passage 103 and the end of the output passage 104 are configured to 10 communicate with the valve chamber 102, the head of the input passage 103 and the head of the output passage 104 are configured to extend to exterior surface of the body 1, the diameters of the heads of the input and output passages 103,104 are greater than the diameters of the ends thereof, heads of the input and output 15 passages 103,104 have thread for connecting. The end of the receiving chamber 101 has a constriction, the distance between the ends of the input and output passage 103,104 is less than the distance between the heads of input and output passages 103,104, a aspirail 105 is arranged between the input passage 103 or the 20 output passage 104 and the receiving chamber 101, the heat created by the body can be taken away by the air flow through the aspirail 105. Referring to Fig.12 to Fig.14 and Fig.4, the switching unit 2 25 comprises a swinging arm 201 having a triggering end 201a and a fixed end 201b, a cartridge 202 having a first passage 202a, a second passage 202b and a manifold chamber 202c, a reset component 203 for reseting the switching unit 2, the reset component here is a extension spring 203. The fixed end of the swinging arm 201 30 removable connects with the cartridge 202 through four groups of bolts, the triggering end 201a of the swinging arm 201 mates with the triggering unit 3. The switching unit 2 is configured to freely hermetically rotate in the cartridge 102, the cartridge 102 is axially limited in the valve chamber 102 by the antiextrusion ring arranged 12/20 at the ends of the cartridge 202. Referring to Fig.12, the fixed end 201b of the swinging arm 201 is parallel to the triggering end 201a, the triggering end 201a connects 5 with the fixed end 201b through a vertical arm, which is vertical to the fixed end 201b, the triggering end 201a at the middle portion has a through hole for mating with the extension spring 203, a beak-like rod 201c is arranged to the triggering end 201a away from the vertical arm, the angle made with the beak 201d and the rod 10 201e of the beak-like rod 201c is an obtuse angle, the end portion of the beak 201d is round, the connecting portion between the beak 201d and the rod 201e is round. Referring to Fig.13, the cartridge 202 has contour corresponding to 15 the valve chamber 102 of the body 1, the manifold chamber 202c is arranged in the middle portion of the cartridge 202, the cartridge 202 uniformly radially arranges eight cylindrical passages, four of passages are called the first passages 202a, the rest four of passages are called the second passages 202b, the diameters of the first and 20 second passages 202a, 202b are equal, the first and second passages 202a, 202b are alternately arranged. The ends of the first and second passages 202a, 202b are configured to communicate with the manifold chamber 202c, the heads of the first and second passages 202a, 202b are configured to raidally extend to the 25 exterior surface of the cartridge 202, the manifold chamber 202c in the middle portion of the cartridge 202 can only communicate with outside through the first passage 202a or the second passage 202b. The cartridge 202 also includes four threaded holes for fastening the fixed end 201b of the swinging arm 201. The cartridge 202 also 30 includes a aspirail 105 therethrough located between the first passage 202a and the second passage 202b, the aspirail 105 do not communicate with the first or second passages 202a, 202b. Referring to Fig.3, the triggering unit 3 includes triggering wheel 305, 13/20 a fourth belt wheel 302, a fourth support board 303 and a fifth belt wheel 304. The triggering wheel 305 rotates in unison with the fourth belt wheel 302 through the key connection, the fourth belt wheel 302 and the fifth belt wheel 304 interacts with each other 5 through the belt, the transmission ratio thereof is 2, the fifth belt wheel 304 rotates in unison with the crankshaft 403 through the key connection. The transmission shaft connecting with triggering wheel 305 and the fourth belt wheel 302 passes through the fourth support board 303 and freely rotates within the correspoding hole 10 of the fourth support board 303, the fourth support board 303 is removably mounted to the second support board 502 through two groups of screws. Referring to Fig.15 to Fig.17, the triggering wheel 305 includes two 15 fixed sheets 306 with a form of circular disc, two arcuate triggering blocks 301 and four rivets. Two triggering blocks 301 are radially uniformly and symmetrically arranged to the fixed sheet 306, the arcuate openings of the triggering blocks 301 are opposite. Two triggering blocks 301 are clamped between two fixed sheets 306, 20 the head and end of each triggering block 301 is fastened to two fixed sheets by the rivet. Each fixed sheet 306 at the middle portion thereof has a through hole for matting with the rotary shaft and the key. 25 Referring to Fig.4 to Fig.9, they show the different rotational positions of the switching unit 2 when the piston 401 is at different positions, and the matting situation between the triggering end 201a and the triggering wheel 305, and the communication situation bewteen the receiving chamber 101, the first passage 202a, 30 the second passage 202b, the input passage 103 and the output passage 104. The piston unit 4 includes a piston 401 with a piston ring, a connecting rod 402, a crankshaft 403 and a cylinder casing 404 14/20 without cover or bottom, the receiving chamber 101 of the body 1 is surrounded by the cylindercasing 404, the rotation of the crankshaft 403 drives the piston 401 reciprocally moving in the receiving chamber 101, the crankshaft 403 interacts with the fourth 5 belt wheel 302 of the triggering unit 3 through the belt wheel. Referring to Fig.4, the piston 401 is at the upward extreme position, that is the top dead center. A through hole arranged on the middle portion of the triggering end 201a connects with the extension 10 spring 203, the other end of the extension spring 203 connects with the first support pillar 509 of the body 1, due to the elastic force of the extension spring 203, the triggering end 201a rotates in a counterclockwise direction till the beak-like rod 201c of the triggering end 201a touches the first support pillar 509 on the left 15 side thereof, at this time the end of the beak 201d of the triggering end 201a is at the middle portion between the two triggering blocks 301, and there is a certain distance from the triggering block 301. The second passage 202b of the cartridge 202 communicates with the output passage 104 of the body 1, the first passage 202a of the 20 cartridge 202 communicates with the receiving chamber 101 of the body 1. Referring to Fig.7, the triggering wheel 305 rotates in a clockwise direction during the piston 401 moving downward, when the 25 triggering wheel 305 rotates a certain angle, the piston 401 is near to the constriction of the receiving chamber 101, the triggering block 301 touches the end portion of the beak 201d of the triggering end 201a, after this, the piston 401 goes on moving downward, meanwhile the triggering block 301 pushes the 30 triggering end 201a to rotate, the cartridge rotates as the triggering end 201a rotates, the second passage 202b and the output passage 104 are gradually staggered till the piston 401 moves downward to the extreme position, that is the bottom dead center, the second passage 202b do not communicate with output passage 104 at all, 15/20 see Fig.8. The piston 401 moves from the bottom dead center to the top dead center with the help of the crankshaft 403, meanwhile, the 5 triggering wheel 305 goes on rotating, the triggering block 301 goes on driving the cartridge 202 rotating, the second passage 202b gradually turns to the input passage 103 till the second passage 202b totally communicates with the input passage 103, at this time, the piston 401 is at the pistion shown in dashed line in the Fig.9, the 10 triggering block 301 is at the pistion shown in dashed line in the Fig.9. The piston 401 goes on moving upward, the triggering wheel 305 goes on rotating in clockwise direction, because the arcuate surface 15 of the triggering block 301 is tangent to the end portion of the beak 201d of the triggering end 201a. the arcuate surface of the rotating triggering block 301 do not go on pushing the end portion of the beak 201d of the triggering end 201a to rotate, that is the cartridge 202 stops rotating to leave the second passage 202b communicate 20 with the input passage 103 Referring to Fig.9, the piston 401 goes on moving upward, the triggering wheel 305 goes on rotating in clockwise direction, when the piston 401 moves upward to the top dead center, the triggering 25 block 301 of the triggering wheel 305 separates from the triggering end 201a, due to the elastic force of the extension spring 203, the cartridge 202 rotates in clockwise direction till the beak-like rod 201c of the triggering end 201a touches the first support pillar 509 on the left side thereof, that is the second passage 202b is switched 30 from the input passage 104 to the output passage 104 and maintained a communication with the output passage 104, so far, a single cycle of motion is done. In a single cycle of motion, the second passage 202b is switched 16/20 from the output passage 104 to the input passage 103, and then from the input passage 103 to the output passage 104, the second passage 202b of the cartridge 202 is configured to mate with the triggering unit 3 with the help of the triggering end 201a, and the 5 reset component 203 alternatively communicates with the input passage 103 of the body 1 or the output passage 104. The first passage 202a always communicates with the receiving chamber 101 during the cartridge 202 rotating. Such result can be achieved by such arrangement, the width of the second passage 202b is less 10 than the minimal distance between the the end of the output passage 104 of the body 1 and the end of the input passage 103. The width of the swinging range formed by the rotation of the head of the first passage 202a with the cartridge 202 is less than the constriction width of the end of the receiving chamber 101 of the 15 body 1. In the following, the working process of the fluid transfer device will be discribed. 20 The outside power source drives the first belt wheel 506 rotating through the belt, the first belt wheel 506 drives the second belt wheel 507 rotating through the engagement between the first and second gears 504, 505, the second belt wheel 507 drives the third belt wheel 508 rotating through the belt, the third belt wheel 508 25 drives the crankshaft 403 rotating through the key connection, the crankshaft 403 dirves the piston 401 reciprocally move through the conecting rod 402, the crankshaft 403 drives the fifth belt wheel 304 rotating through the key connection, that is the triggering block 301 rotates around the axis of the fourth belt wheel 302. The 30 triggering block 301 touches the triggering end 201a of the swinging arm 201 and then drives the triggering end 201a rotating, that is the swinging arm 201 drives the cartridge 202 rotating, during the rotational movement of the cartridge 202, the second passage 202b is switched from the output passage 104 of the body 1 to the input 17/20 passage 103 and maintained a communication with the input passage 103, while the first passage 202a always communicates with the receiving chamber 101. The piston 401 moves upward to make fluid sequentially flow through the input passage 103, the 5 second passage 202b, the manifold chamber 202c, the first passage 202a and the receiving chamber 101. The triggering block 301 goes on rotating, when the triggering block 301 is separated from the triggering end 201a of the swinging arm 201, the swinging arm 201 returns to the initial position under the effect of the reset 10 component, meanwhile, the cartridge 202 rotates back to the initial position, that is the second passage 202b of the cartridge 202 is switched back to the output passage 104 from the input passage 103 of the body 1 and keeps communicating with the output passage 104, while the fisrt passage 202a always communicates 15 with the receiveing chamber 101, the piston 401 moves downward to compress the fluid therein out of the receiving chamber 101, fluid sequentially passes through the first passage 202a, the manifold chamber 202c, the second passage 202b and the output passage 104. 20 In the following, the application of the fluid transfer device will be discribed. 1. The inlet opening 6 of the device connects to the water well 25 through pipes, the outlet opening 7 connects to the water tower. The piston 401 in the receiving chamber 101 moves upward to creat a negative pressure area in the receiving chamber 101, under the effect of the atmosphere, the air in the pipe connected with the inlet opening 6 goes into the second passage 202b through the 30 input passage 103, then goes into the first passage 202a through the manifold chamber 202c, finally the air is pressed into the receiving chamber 101. Due to the downward movement of the piston 401 in the receiving chamber 101, the air in the receiving chamber 101 is pressed into manifold chamber 202c through the first passage 202a, 18/20 then into the output passage 104 through the second passage 202b, finally into the water tower along the pipe connected with the outlet opening 7. 5 After the air in the pipe connected with the inlet opening 6 is totally pressed out, the piston 401 in the receiving chamber 101 moves upward to creat a negative pressure area in the receiving chamber 101, under the effect of the atmosphere, water in the well is compressed into the receiving chamber 101 through the second and 10 first passages 202b, 202a. The downward movement of the piston 401 within the receiving chamber 101 compresses water therein out of the output passage 104 opening through the first and second passages202a, 202b, due 15 to the near incompressibility of water, the output passage 104 can ouput water flow with equal pressure, the water flow at the outlet opening 7 can climb a certain height along the pipe with the help of the pressure into the water tower. So the device can transfer water in a well with a certain depth to a water tower with a certain height, 20 even there is some air left in the pipe connected with the inlet opening 6, the device can still draw and pump water. 2. The inlet opening 6 of the device connects with the atmosphere, the outlet opening 7 connects with a gas tank through pipes. The 25 piston 401 moves upward to creat a negative pressure area in the receiving chamber 101, air near the inlet opening 6 is compressed into the receiving chamber 101 through the second and first passages 202b, 202a by the effect of the atmosphere. The downward movement of the piston 401 within the receiving 30 chamber 101 compresses air therein out of the output passage 104 opening through the first and second passages 202a, 202b, due to the compressibility of air, the output passage 104 can ouput air flow with a little pressure, which is collected in the gas tank little by little, such that air mass with a certain pressure is finally formed in the 19/20 tank, so the device can be used as an air compressor. 3. The inlet opening 6 of the device connects with a sealing container, while the outlet opening 7 connects with the atmosphere, 5 the piston 401 moves upward to creat a negative pressure area in the receiving chamber 101, the air in the sealing container is compressed into the receiving chamber 101 through the second and first passage 202b, 202a by the current air pressure in the container. The downward movement of the piston 401 within the receiving 10 chamber 101 compresses air therein out of the output passage 104 opening through the first and second passages 202a, 202b,and then into the atmosphere, so the device can draw air out of the sealing container to reduce air pressure in the container. So the device can be used as an air-extractor. 20 / 20