PUMP WITH CONTINUOUS INFLOW AND PULSATING OUTFLOW

Abstract: A pump with a continuous inflow and a pulsating outflow comprises a first chamber and a second chamber with a passage between them and made from a flexible material, provided with an inlet to the first chamber and an outlet from the second chamber, the passage between the chambers being provided with a one-way valve permitting flow in direction from the first to the second chamber only, and a second one-way valve arranged at the outlet permitting flow out of the second chamber only. The chambers are movably supported in a pump casing with a first and a second opening, in that the inlet is connected to and penetrates the first opening, and in that the outlet is connected to and penetrates the second opening. Drive means cyclically affect the second chamber and reduce its volume under expulsion of the medium which is pumped while simultaneously affecting the walls of the first chamber causing its volume to increase and medium to flow through the inlet into the chamber. The drive means include a drivering surrounding said passage and fixed to it, and which drivering has surfaces engagable with the first and the second chamber walls in a way that the medium taken in between periods when the drive means is affecting the chamber walls controls the output of the pump by defining the receding movement of the drive ring, which movement is a function of the differential pressure force resulting from the difference in areas of engagement with the respective chamber wall on both sides of the drive ring.

Description: The present invention regards a pump with continuous inflow and pulsating outflow for use in industry, mining, agriculture, water supply, heating, sanitation, and similar areas. Background In various industrial and other areas there is a need for pumping where the prevailing fluid pressure is intended to control the flow of the medium to be pumped ("pumping medium"). This may regard water and other liquids as well as solutions and suspensions of various kinds. At present, such pumping is controlled by sensors monitoring the pressure of the medium being pumped at the inflow side of the pump, and which sensors control the pumping rate in pumps whose capacity may be varied, e.g. piston pumps with a variable stroke rate. Such monitors may cease functioning without the pump necessarily stopping. This results in the pump pumping either too much or too little, possibly resulting in severe consequences with regard to safety. In case safety is decisive, double safety measures have to be incorporated into the design, e.g. by doubling the sensors. Obviously this will make the pump more expensive and more prone to succumb to electrical faults. Description of the invention It is the aim of the invention to provide a self-regulating pump for use as an industrial, mining, agricultural, water supply, sanitation, or similar pump, which gives a pulsative outflow at essentially constant inflow, and which has a displacement volume varying according to filling pressure. This aim is attained according to the present invention by a pump with two rooms (chambers), each at least partially consisting of flexible walls, with an inlet and an outlet and a passage between both rooms, which passage at the same time is the outlet of the first room and the inlet of the second room, the outlet of which is in fact the outlet of the pump, and which pump furthermore has a first one-way valve arranged in the passage between both rooms, allowing flow from the first room to the second room only, and which pump has a second one-way valve arranged in the outlet of the second room, which valve allows flow out of the second room only. Both rooms (chambers) are movably supported in a casing with first and second openings where the inlet to the first room is fastened in the first opening of the casing and the outlet of the second room is fastened in the second opening of the casing. Drive means are arranged so that they periodically and selectively affect the walls of the second room in a way that makes its volume decrease and liquid to be expelled from it, while simultaneously the volume of the first room is affected by the drive means in a way that allows it to increase and to permit inflow of liquid through the inlet of the pump. The drive means include a drivering surrounding the passage between the two rooms and joined to it, which drivering has a surface affecting the wall of the second room over a selected area in a way that the pressure of the medium to be pumped entering into the rooms of the pump during the forward movement of the drive means controls the amount of medium being pumped in that this pressure determines the size of the receding movement of the drive ring and, thereby, of the passage between the two rooms as a function of a pressure force affecting the area of engagement between the drive ring and the walls of the second room. One preferred embodiment of the invention includes the following characteristics individually or in combination: 1. The drive means affect the driving only during their forward movement when expelling pumping medium out from the second room. During the return move, the drivering disengages from the other part of the drive means, the power transmission means, which recede independently be being retracted by a force applied in the direction opposite to the forward movement, for example by a spring. 2. The casing is hermetically sealed and contains a compressible fluid, preferably a gas, between it and both rooms. The pressure of said fluid varies in dependence of the total volume of both rooms, and therefore affects the inflow of pumping medium during the receding movement of the drive means. The pressure in the volume between the casing and both chambers can be controlled by a valve arranged in the casing. 3. The room in the casing between the casing wall and the chambers which room contains the drive means is in communication with a further room which, e.g., may consist of a completely or partially enclosing envelope, and where the volume of the further room communicates with the interior of the casing through a pressure control valve. 4. The first and the second rooms and the passage between these rooms are parts of a hose-like member (sock) provided with bulgings and made of flexible material which is preferentially non-elastic. When the hose is inflated, the bulgings will approximately take the form of a biconvex lens or a sphere. 5. The inlet into the first room and the outlet from the second room are preferentially arranged at opposite sides of the casing and generally also at sides opposite to the passage between both rooms. 6. Both rooms and the passage between them are essentially rotationally symmetric around an axis of symmetry defined by a line joining the inlet, the passage between both rooms, and the outlet. Also the drivering and the casing are preferentially symmetric with respect to this axis. 7. Part of the walls of the first and the second rooms will engage with a surface of the drivering and an interior wall surface of the casing, and the surfaces engaging with the walls of each chamber are of generally complementary shape. The drivering advantageously has the form of a dish. The surface of the drivering engaging with one chamber is preferentially convex and that engaging with the other chamber is preferentially concave. The area of the drivering engaging with the wall of the other chamber during a substantial part of the return stroke of the pump is substantially larger than the area of the drivering engaging with the first room, whereby the volume taken in into the pump between strokes of the power transmission means acting unidirectionally on the drivering is a function of the dynamic and static forces of the incoming medium. As mentioned above, it is desirable for the walls of the first and second room to be not only flexible but also essentially non-elastic. Because it is difficult to find materials with these properties, some elasticity must be tolerated. The walls should be made of a material which is not or only very slightly affected chemically by the medium to be pumped, which resists wear and is not soluble, swelling in the medium, or allowing substantial diffusion of the medium. Generally, materials like polymers are acceptable, eventually reinforced by fibres of various kinds. Suitable polymer materials are, e.g., rubber, silicone rubber, and polyurethanes. Because of the self-regulating properties of the pump, it can dispense with sensors that control its capacity, for example by affecting the stroke rate. If desired, the pump may however be provided with sensors as control members in addition to the built-in autoregulation. Two or several pumps of this sort may be coupled in series or in parallel while maintaining the self-regulating properties. Thereby, the pumping within complex systems may be achieved by preset pressure values for each individual pump. Such systems with several pumps may be driven synchronously or with different stroke frequencies. The pulsating outflow of the pump may, if desired, be smoothed by arranging next to the outlet an element with flexible walls, preferentially elastic, surrounded by a compressible fluid. In order to provide a better understanding of the invention, there is given below a description of two preferred but not limiting embodiments illustrated by attached drawings. Description of the Drawings Figure 1 is a first preferred embodiment in cross-sectional view along the axis of symmetry, showing certain parts sketched out only. Figure 2 is an exploded view of the same first preferred embodiment, and Figures 3A to 3D show schematically the first preferred embodiment in different parts of the pumping cycle. Figure 4 shows a second preferred embodiment in cross-sectional view along the axis of rotational symmetry in that certain parts are only shown schematically. Description of the preferred embodiments The first preferred embodiment is shown in Figures 1 to 3, which embodiment as well is the best embodiment known to the inventor as a laboratory-built prototype. It is based on a hose-type member 6 with bulgings, made from a material which is flexible but essentially non-resilient, and which is mounted in a casing 1 consisting of parts 1a and 1b. Part 6 which in its general form is best understood from Figure 1 is a hose with a smaller bulging 6a and a larger bulging 6v, both in the form of a convex lens, and made from polyurethane reinforced by cellulose acetate silk. At the constriction 9 between bulgings 6a and 6v there is mounted a dish-like drivering 10. Furthermore, two one-way valves are arranged, the first one-way valve 5 in the construction 9 and the other one-way valve 4 in the casing at the outlet from the room defined by bulging 6v. The one-way valves can be of various sorts and should be adapted to the type of medium to be pumped. As is evident from the drawings, the hose-like member 6 is connected with other parts of the pump in three places that is, with valve 5 in the constriction 9, and with openings 7 and 8 in casing 1. Regarding opening 7 in the casing, a ring 20 with an external grove has been inserted into the hose-like member 6, and a resilient O-ring 21 has been mounted in the same place on its outside. A retaining ring 30 secured with screws 31 in casing 1 is keeping O-ring 21 and thereby ring 20 in place. Besides their valve function, valves 4 and 5 also have the function of participating in securing the hose-like member 6 at drive ring 10 and opening 8 in casing 1. Both valves have an outer circular grove which accepts an 0-ring and thereby keeps the interposed hose-like member 6 in place. Drive ring 10 consists of two plate-like parts which are pressed against O-ring 13 around valve 5, and which are kept together by screws 32. O-ring 14 at valve 4 is pressed against the casing at opening 8 by a retainer ring 22 secured in the casing by screws 34. The entire arrangement in assembled state is shown in Fig. 1. Drive ring 10 is able to move freely along the walls in casing 1, which has grooves 15 on its inside permitting free flow of the medium in the casing between the volumes at either side of the drive ring. The smaller lens-like bulging 6a on hose 6 defines a first room "A", and the larger bulging 6v a second room "V". The inlet to room "A" is mounted in the casing at opening 7. The constriction 9 between the two rooms "A" and "V" is a passage through which the medium to be pumped can only flow in the direction from room "A" to room "V" through one-way valve 5. Opening 8 with one-way valve 4 is the outlet of the pump through which the medium to be pumped is discharged under pressure. The volume of both chambers is controlled during parts of the pumping cycle by engagement of bulgings 6a and 6v with the lower, 25, and upper, 26, walls of casing 1 and the lower and upper surfaces 28 and 27 of drive ring 10. The inner wall surface 25 of the casing is concave whereas the surface 28 of the drive ring 10 is convex. In the same way the bulging 6a during part of the pumping cycle is engaging with a convex surface 26 of the inner wall of the casing and a concave surface 27 on drive ring 10. In other words, each lens-shaped bulging is in contact with complementary and generally dish-shaped surfaces on the inside of the casing and on the drive ring. It is possible for both sides of the drive ring to have convex form, in which case the surface of the house engaging with bulging 6a should have a concave form, but this embodiment is not preferred because the connection between both chambers A and V would become too long and entail an unintended loss in pressure. It is fully possible but not preferred to have the hose-like member 6, the casing, and drive ring 10 in an asymmetric shape. On the other hand, it is fully possible and may be advantageous for certain applications to have the inlet and the outlet of the hose-like member arranged not in line but at an angle. It is also possible to omit all or certain parts of the hose-like member 6 which during the entire pump cycle abut against wall surfaces 25 and 26, and against ring surfaces 27 and 28. It is preferred to omit the part of the hose-like member 6 which permanently engages with the lower wall 25 as well as the part of the hose-like member 6 which permanently engages with the upper surface 27 of drive ring 10. Figure 4 shows a second preferred embodiment in accordance with these requirements. The ends of the remaining parts of the flexible hose are secured at surfaces 27 and 25 by concentric fixtures 44 and 45 provided with a number of concentrically arranged screws 46 and 47, and at the outer grove in valves 4 and 5 as well as in ring 20 by the pressure effect of O-rings 14, 13, and 21. The omitted parts of the flexible hose have thus been replaced by parts of surfaces 25 and 27. This other preferred embodiment is advantageous with respect to the manufacture of the flexible parts of hose 6. The pump can be driven by an electrical, pneumatic or mechanical driving means 17 as schematically shown in Fig. 1. The unidirectional driving force is transmitted to drive ring 10 by a pressure ring (thrust collar) 12b which is rigidly connected to a pair of pusher rods 12a at opposite sides of the hose. These pusher rods penetrate through holes in the wall of the casing which wall entrances may be made hermetically sealing. The pusher rods can be actuated by a suitable electrical motor or by a mechanical or pneumatic driving arrangement. When the driving force is affecting the push rods, they press down pressure ring 12b so that it makes contact with drive ring 10 and carries the drive ring with it. When pressure ring 12 with the push rods has reached its extreme position, it recedes from drive ring 10 and is retracted back to the starting position by a restoring resilient force (not shown in the drawings). During each active thrust of the pressure ring onto the drive ring, the volume of chamber "V" is diminished and the pressure within it thus increased, which results in the closing of one-way valve 5 and the opening of one-way valve 4. Thereby medium is pumped out from the pump. Simultaneously, the volume in chamber "A" has increased so that pumping medium has been taken in into the pump under the same active phase. When the end of the active phase has been reached and the thrust collar has been retracted to the starting position, the compressive strain on chamber "V" ceases. A short period after that pumping medium continues to flow out of the pump because of the kinetic energy in the direction of the outlet imparted to it during the active phase. When the pressure in chamber "V" has decreased sufficiently valve 5 opens, and pumping medium via constriction 9 will fill chamber "V". When the impulse effecting the ongoing outflow of pumping medium ceases, valve 4 closes. The pressure of the incoming medium in combination with the kinetic component in chamber "V" will give rise to forces directed upwardly towards constriction 9 affecting the lower side 28 of drive ring 10. The area of contact between bulging 6v and the lower surface of drive ring 10 (normalized by projection onto an imaginary plane perpendicular to the direction of movement of drive ring 10) is then larger than the area of contact of bulging 6a against the upper surface 27 of the drive ring. This results in ring 10 being moved upwards and further pumping medium being transferred to chamber "V". The degree of filling of chamber "V" is dependent on the pressure of the incoming pumping medium which thereby also controls the capacity of the pump at constant stroke rate. One qualification for the pump to have this regulating function is the fulfillment of the requirement that the frequency must be adapted in such a way that each stroke (or thrust) begins before the chambers have reached their maximum total volume. After that, evidently, no more pumping medium can be taken in by the pump. The extent to which the chambers of the pump are filled during each pumping cycle is also affected by the pressure of the gas or the like occupying the room between the hose-like member and the casing. During each pumping stroke said volume increases, and, in case the casing is hermetically sealed, the pressure in that volume correspondingly decreases. This decrease in pressure raises the pressure difference between the incoming pumping medium and the medium at the outside of the hose, and thereby increases the inflow of pumping medium. During the retrograde movement the opposite is the case, in that the volume in the casing outside the hose is decreasing and the pressure correspondingly increases. The pressure outside the hose gradually approaches the pressure of the incoming medium, and the filling rate decreases. Thus a controlling effect of the pressure variations inside the casing on the filling of the rooms of the pump is obtained during the retrograde phase of the pumping cycle. The pressure in the casing is determined on the one hand by the relationship between the displacement volumes in the pump, and by the volume inside the casing interlinked with them that is, the geometric qualifications of the pump. The amount of compressible fluid in the casing can be controlled by a pressure control valve, e.g. in form of two one-way valves operating in opposite directions, which make possible the setting of a highest and a lowest pressure inside the casing. Figs. 3A to 3D schematically show the preferred embodiment at four points of the pumping cycle. Fig. 3A shows the pump at the end of the stroke that is, of the active propulsion of pressure ring 12b when it has reached the limit of its downward movement as shown by arrows D which indicate the downward force applied onto the drive ring. During the downward stroke of the pressure ring, drive ring 10 is compressing chamber "V" and thereby brings about a pressure affecting the medium in the chamber, resulting in it being pumped out from the chamber through one-way valve 4 arranged at outlet 8. The same pressure is keeping one-way valve 5 closed during this phase. The downward movement of drivering 10 changes the geometry of chamber "A" in a way that its volume can expand, thereby making possible during this phase the intake of medium through inlet 7 into said chamber. The combined total volume of chambers "A" and "V" decreases in connection with the forced stroke of pressure ring 12b, and the volume between the hole and the casing is thereby increased so that the pressure in it will be decreasing. When the pumping stroke has been brought to completion, the pressure ring 12b is immediately retracted, for example by a spring (not shown) forming an integral part of the drive means (Fig. 3B). For a short time period after the drive ring had been retracted, the movement of the pumping medium flowing through outlet 8 is keeping valve 4 in an open position, and additional medium will therefore leave chamber "V". However, the hydrostatic pressure in this chamber will rapidly decrease which makes valve 5 to open under the action of the static and hydrodynamic pressure of the medium flowing into chamber "A". In consequence, the flexible walls in bulging 6v exert a pressure force on surface 28 at the lower side of drive ring 10. A pressure force of the same type, although smaller, will be exerted on the walls of bulging 6a at the upper surface 27 of the drivering. An upward force component during the time period between active pump strokes thus results. This force component makes drivering 10 rise. The convex surface 26 is progressively affecting the adjacent portions of bulging 6a when drive ring 10 is moving in the direction of said surface, and the differential decrease of the volume in bulging 6a is approaching the differential increase of the volume in bulging 6v. In a certain point, both become equal. The upward movement thus ceases, no matter how large the pressure difference between chambers "A" and "V" be, on the one hand, and the room surrounding them, on the other. This arrangement of surfaces affecting chambers "A" and "V" in such a way that their maximum volume is reached before drive ring 10 has moved to the upper point of arrival in the direction of the inlet has a protecting effect with respect to the flexible material in hose 6, this effect being especially advantageous when the pump is working continuously in form of an embodiment with a casing not hermetically sealed agaist the ambient atmosphere, e.g. at atmospheric pressure. As shown in Fig. 3C, the force of the inflowing medium acting upwards raises the drivering and allows the volume in "V" to increase. The size and geometry of both chambers is such that even when the volume of chamber "A" is decreasing, the total combined volume of "A" and "V" increases. The higher the position of drivering 10, the larger the total combined volume of the chambers, and the larger the increase of pressure within the casing. Before the drivering reaches the position where the total volume of the chambers attains its maximum (in case the pressure within the casing being kept constant) or, when the pressure in chambers "A" and "V", on the one, hand, and the pressure in the room surrounding them, on the other hand, have become equal (the pressure in the casing varying dependent on the volume of chambers "A" and "V" and their dependence on the static and dynamic forces of the incoming medium), the next pump stroke is started by the downward movement of pressure ring 12b through the force effected by the drive means (arrows D) as shown in Fig. 3D. At a higher stroke rate, dynamic forces will become more important, and equilibrium is no longer attained, but the pumping effect nevertheless will be proportional to the pressure of the pumping medium at the inlet side of the pump. The pump may be executed in form of various embodiments. It may be made immersible by surrounding it with a flexible polymer bag which, in addition, has the function of an outer volume enabling exchange of fluid surrounding hose 6 by means of a pressure control valve 16 according to Fig. 1. Pressure control valve 16 may, e.g. be given the form of two one-way valves, one in each direction, which connect the room inside the casing with the room between the casing and said polymer bag, and which valves may have preset opening and closing pressure levels. Said polymer bag has been indicated in Fig. 1 by dashed line 35. The pump can be provided with means of detection of the highest position of drive ring 10 during a pumping cycle, for example in order to control the stroke rate of the pump. The invention thus offers a pump in which a valve plane is raised by the forces of the incoming medium that is, the fluid pressure and the dynamic forces which result from the active phase of the pumping cycle. When the valve plane has reached its lowest position and is about to start its return movement due to the continuing inflow of the medium, the valve functions as a collapsible wall moving in direction counter to that of the inflowing medium until a new stroke starts. The valve at the outlet closes as soon as the flow through it ceases which, depending on flow rate, may be later that the moment when the valve plane in the pump has reached its lowest position. The higher the stroke rate, the more the dynamic forces in the flowing medium will affect the pumping function, though not violating the basic principle that the pressure at the inflow side controls output.

Claims: 1. A pump for use as an industrial, mining, agricultural, water supply, sanitation, or similar pump, with continuous inflow and pulsating outflow which comprises two chambers with flexible walls, a passage arranged between them with a first one-way valve, an intake tube to the first chamber, an output tube to the other chamber, a one-way valve arranged at the output tube, a motor, drive means coupled to the motor for change of the volume of the second chamber, and a casing enclosing the chambers with the intake tube and the output tube emanating from the casing through openings in it and secured in the openings, characterized in that the drive means are fastened at the passage and in combination with the passage are freely movable inside the casing in such a way that the effect of motion in the direction towards the outlet on the second chamber causes its volume to decrease by expelling pumping medium through the outlet from said chamber, whereby the first chamber is increasing its volume allowing pumping medium to be taken in, which drive means comprise a drivering surrounding said passage and fixed to it, and which further comprise power transmission means between the motor and the drivering, which drivering has surfaces that during the pumping cycle engage variably with the walls of the first and the second chamber, in such a way that the pressure of the incoming medium controls the flow in the pump by determining the extent of the return movement of the drivering as a function of the pressure force acting over the area of engagement between the drivering and the respective chamber. 2. A pump according to claim 1, characterized in that the power transmission means affect the drivering only in one direction, and thereafter disengage from the drivering and move to the start position. 3. A pump according to claim 1, characterized in that the pump casing is hermetically sealed and contains a compressible fluid between the chambers and the casing, the pressure of which varies as a function of the variation in total volume of the chambers, and which pressure thereby simultaneously affects the inflow of pumping medium. 4. A pump according to claim 3, characterized in that it includes means for control of the pressure within the casing. 5. A pump according to claim 4, characterized in that it comprises an enclosure containing part of or the entire pump casing with the means for control of the pressure in the casing, which control means constitute a passage between the casing and said enclosure. 6. A pump according to claim 1, characterized in that the chambers and the passage between them are part of a hose-like member made of flexible and preferentially non-elastic material. 7. A pump according to claim 1, characterized in that the chambers are made from a flexible and preferentially non-elastic material. 8. A pump according to claim 1, characterized in that the surface of the drivering engaging with one chamber is convex and the surface of the drivering engaging with the other chamber is concave. 9. A pump according to claim 8, characterized in that a wall portion of each chamber during the pumping cycle engages with a portion of the inner wall of the casing, said casing wall portion being complementary in form to the drivering surface facing it. 10. A pump according to claim 1, characterized in that the portions of the chamber walls being, during a pumping cycle, in permanent contact with part of the inner wall of the casing or with a surface of the drivering are wholly or partly replaced by said portions of the inner wall of the casing or said surface of the drive ring. 11. A pump for use as an industrial, mining, agricultural, water supply, sanitation, or similar pump, with continuous inflow and pulsating outflow, which comprises a casing enclosing two chambers with flexible walls and containing a compressible fluid in the space between the casing inner wall and the walls of said chambers, a passage with a first one-way valve arranged between the chambers, and which further com-­ prises an intake tube to the first chamber penetrating the casing and secured at it, an outlet tube from the second chamber penetrating the casing and secured at it, a second one-way valve arranged in the outlet tube, a motor, means for change of the volume of the chambers coupled to the motor, characterized in that said means comprise a drivering mounted at said passage and surrounding it, the surface of the drive ring facing the first chamber being concave with respect to that chamber and the surface of the drivering facing the seco-­ nd chamber being convex with respect to that chamber, which surfaces par-­ tially engage with wall portions of the respective chambers, and further comprising a convex casing inner wall portion facing the first chamber, which wall portion is arranged symmetrically around the inlet and engages with part of the wall of said chamber, and a concave casing inner wall portion facing the second chamber, which wall portion engages with part of the wall of said chamber. 12. A pump according to claim 11. characterized in that it includes a thrust collar arranged for unidirectional dis-­ placement of the drivering, and which collar faces the drivering surface turned towards the intake tube to the first chamber, said collar being arranged for undirectional actuation by the motor in the direction of the outlet, and for immediate retraction at the end of actuation. 13. A pump according to claim 11, characterized in that the casing is hermetically sealed. 14. A pump according to claim 13, characterized in that it comprises means for control of the pressure within the casing. 15. A pump according to claim 14, characterized in that it comprises an enclosure enclosing part of or the entire pump casing with the means for control of the pressure in the casing, which control means constitute a passage between the casing and said enclosure. 16. A pump according to claim 11, characterized in that the intake tube, the outlet tube, the chambers, and the passage between the chambers are part of a hose-type member made of flexible but essentially non-elastic material. 17. A pump according to claim 11, characterized in that part of the flexible walls of the chambers are replaced by portions of the inner casing wall and the drivering surface. 18. A pump according to claim 16, characterized in that the chambers when inflated and not restricted in their expansion take the approximate form of a biconvex lens or a sphere. 19. A pump according to claim 17, characterized in that the portions of the flexible walls of the chambers not replaced by portions of the inner casing wall when inflated and not restricted in their expansion take the approximate form of the corresponding portions of a biconvex lens or a sphere. 20. A pump according to claim 11, characterized in that the volume of the first chamber is smaller than that of the second chamber. 21. A pump according to claim 19, characterized in that the volume of the first chamber is smaller than the volume of the second chamber.

Inventors: LUNDBACK, STIG, Lundbäck, Stig 
Applicants: ASTRA-TECH AKTIEBOLAG
Application year: 1986
Main classification: F04B43
IPC codes: E03B5, F04B43, E03F5