Reverse permeation membrane device

Abstract

To provide a reverse osmosis membrane device where noise can be suppressed.SOLUTION: In a reverse osmosis membrane device 1 having a reverse osmosis membrane tank 2, a reciprocating pump 3 and a drive mechanism 5,: the reciprocating pump 3 has a piston 31 which can perform reciprocating movement between a first pump chamber 33 connected to a treatment liquid introduction port 23 and a concentrated liquid lead-out port 24 of the reverse osmosis membrane tank 2 and a second pump chamber 34; the drive mechanism 5 has an electric cylinder 50 connected so that a rod 51 performs reciprocating movement by rotation drive power of a motor 52 and the rod 51 communicates the reciprocating movement to the piston 31 of the reciprocating pump 3; control means 53 controls a rotation speed of the motor 52; and the control means 53 controls the rotation speed of the motor 52 so as to move in a direction opposite to a direction, until then while performing at least one of the increasing and decreasing of the speed of the piston 31 when the movement of the piston 31 to a forward direction is switched to a backward direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004] , ,

[0005] , ,

[0001] The present disclosure relates to a reverse osmosis membrane device that performs a process of supplying a liquid to be treated to a reverse osmosis membrane at high pressure and separating it into a permeate that passes through the reverse osmosis membrane and a concentrate that does not pass through the reverse osmosis membrane.

Background Art

[0002] Conventionally, fresh water has been obtained from seawater using a reverse osmosis membrane. A conventional reverse osmosis membrane device 100 shown in FIG. 5 includes a reverse osmosis membrane tank 110 having a reverse osmosis membrane 111 inside, a reciprocating pump 120, a drive mechanism 130 for driving the reciprocating pump 120, and a switching valve mechanism 150 (see, for example, Patent Document 1).

[0003] The reciprocating pump 120 includes a cylinder 121 and a piston 122 that reciprocates inside the cylinder 121. The inside of the cylinder 121 is divided into two pump chambers 123 and 124 by the piston 122 interposed therebetween. The first pump chamber 123 is connected to the liquid supply port 112 of the reverse osmosis membrane tank 110 by a liquid introduction passage for the liquid to be treated, and the second pump chamber 124 is connected to the liquid discharge port 113 of the reverse osmosis membrane tank 110 via the switching valve mechanism 150 by a concentrate discharge passage. The drive mechanism 130 consists of a hydraulic cylinder.

[0004] In the conventional reverse osmosis membrane device 100, when the piston 122 moves in one direction (left direction in FIG. 5) inside the cylinder 121 by the drive mechanism 130, the liquid to be treated in the first pump chamber 123 is supplied to the reverse osmosis membrane tank 110 at high pressure, and the concentrate discharged from the reverse osmosis membrane tank 110 is introduced into the second pump chamber 124 via the switching valve mechanism 150. When the piston 122 moves in the reverse direction (right direction in FIG. 5) inside the cylinder 121, the concentrate in the second pump chamber 124 is discharged through the switching valve mechanism 150, and new liquid to be treated is supplied into the first pump chamber 123.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Special Publication No. 7-49096 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The hydraulic cylinder constituting the drive mechanism 130 includes a hydraulic oil tank 131 for storing hydraulic oil, a hydraulic pump 132 for pumping the hydraulic oil from the hydraulic oil tank 131, a hydraulic oil switching valve 133, a cylinder 134, and a piston 135. The rod 136 of the piston 135 of the hydraulic cylinder is connected to the rod 125 of the piston 122 of the reciprocating pump 120 via a coupling 137. The inside of the cylinder 134 of the hydraulic cylinder is divided into two cylinder chambers 138 and 139 with the piston 135 in between, and the two cylinder chambers 138 and 139 are connected to the hydraulic oil tank 131 via a hydraulic oil switching valve 133 for supplying and discharging hydraulic oil.

[0007] When the hydraulic fluid switching valve 133 is driven, the first cylinder chamber 138 of the hydraulic cylinder and the hydraulic fluid tank 131 are connected by a hydraulic fluid supply passage, and the second cylinder chamber 139 of the hydraulic cylinder and the hydraulic fluid tank 131 are connected by a hydraulic fluid discharge passage. High-pressure hydraulic fluid is then supplied from the hydraulic fluid tank 131 into the first cylinder chamber 138, causing the piston 135 to move in one direction (leftward in Figure 5) within the cylinder 134. In conjunction with this, the piston 122 of the reciprocating pump 120 moves in one direction (leftward in Figure 5) within the cylinder 121. At this time, the hydraulic fluid in the second cylinder chamber 139 of the hydraulic cylinder is discharged into the hydraulic fluid tank 131.

[0008] The reciprocating movement of the piston 135 of the hydraulic cylinder is monitored by limit switches 140 and 141. When the limit switch 140 detects the piston 135 moving in the aforementioned one direction (leftward in Figure 5), the hydraulic fluid switching valve 133 is activated, connecting the first cylinder chamber 138 of the hydraulic cylinder to the hydraulic fluid tank 131 via a hydraulic fluid discharge passage, and connecting the second cylinder chamber 139 of the hydraulic cylinder to the hydraulic fluid tank 131 via a hydraulic fluid supply passage. As a result, hydraulic fluid is supplied at high pressure from the hydraulic fluid tank 131 into the second cylinder chamber 139 of the hydraulic cylinder, causing the piston 135 to move in the reverse direction (rightward in Figure 5) within the cylinder 134. In conjunction with this, the piston 122 of the reciprocating pump 120 moves in the reverse direction (rightward in Figure 5) within the cylinder 121. At this time, the hydraulic fluid in the first cylinder chamber 138 of the hydraulic cylinder is discharged to the hydraulic fluid tank 131. Then, when the limit switch 141 detects the movement of the piston 135 in the reverse direction (to the right in Figure 5) as described above, the hydraulic fluid switching valve 133 is activated, and the first cylinder chamber 138 of the hydraulic cylinder and the hydraulic fluid tank 131 are again connected by the hydraulic fluid supply passage, and the second cylinder chamber 139 of the hydraulic cylinder and the hydraulic fluid tank 131 are connected by the hydraulic fluid discharge passage, causing the piston 135 to move again in one direction (to the left in Figure 5) inside the cylinder 134, and in conjunction with this, the piston 122 moves in one direction (to the left in Figure 5) inside the cylinder 121.

[0009] Conventional reverse osmosis membrane systems use a hydraulic cylinder in the drive mechanism 130, and the hydraulic fluid switching valve 133, which switches the supply of hydraulic fluid to the first cylinder chamber 138 and the second cylinder chamber 139 of the hydraulic cylinder, vibrates and emits noise each time it switches. In addition, in the reciprocating pump 120 and the hydraulic cylinder, the pistons 122 and 135 respectively vibrate and generate noise when the direction of movement of the hydraulic fluid switching valve 133 is momentarily reversed. Furthermore, at the connection between the rod 125 of the reciprocating pump 120 and the rod 136 of the hydraulic cylinder of the drive mechanism 130, a high-pressure load is momentarily applied when the hydraulic fluid switching valve 133 is switched, which may damage the joint 137 and the respective rods 125 and 136.

[0010] This disclosure aims to provide a reverse osmosis membrane apparatus that can solve the above-mentioned problems. [Means for solving the problem]

[0011] This disclosure relates to a reverse osmosis membrane apparatus comprising: a reverse osmosis membrane tank for separating a liquid to be treated into a permeate and a concentrate by a reverse osmosis membrane; a reciprocating pump for pressurizing the liquid to be treated and supplying it to the reverse osmosis membrane tank; and a drive mechanism for driving the reciprocating pump. The reverse osmosis membrane apparatus of the present disclosure comprises a reciprocating pump comprising a first pump chamber connected to the liquid to be treated inlet of the reverse osmosis membrane tank, a second pump chamber connected to the concentrated liquid outlet of the reverse osmosis membrane tank, and at least one piston capable of reciprocating movement, wherein movement in the forward direction reduces the volume of the first pump chamber and increases the volume of the second pump chamber, and movement in the reverse direction increases the volume of the first pump chamber and decreases the volume of the second pump chamber; the drive mechanism comprising an electric cylinder in which a rod moves back and forth by the rotational driving force of a motor, the electric cylinder in which the rod is connected to the piston of the reciprocating pump so as to transmit reciprocating movement; and control means for controlling the rotational speed of the motor, wherein the control means controls the rotational speed of the motor such that when switching between forward and reverse movement of the piston, the piston moves in the opposite direction while decelerating and accelerating at least one of the two.

[0012] Preferably, in the reverse osmosis membrane apparatus of the present disclosure, the control means controls the rotational speed of the motor such that when the piston starts moving in the opposite direction at the end position of both the forward and return movements, the piston gradually accelerates and its movement speed increases to a maximum speed over a predetermined period of time.

[0013] Furthermore, preferably in the reverse osmosis membrane apparatus of the present disclosure, the control means can be configured to control the rotational speed of the motor such that, when the piston reaches the respective end positions of forward and reverse movement and stops forward and reverse movement, the piston gradually decelerates from just before the end position so that the movement speed decreases to zero over a predetermined period of time until it reaches the end position.

[0014] Furthermore, in the reverse osmosis membrane apparatus of the present disclosure, the control means may be configured to control the rotational speed of the motor such that, after the piston reaches the respective end positions of its forward and reverse movements and stops moving in the forward and reverse directions, it starts moving in the opposite direction after a predetermined time interval.

[0015] Furthermore, in the reverse osmosis membrane apparatus of the present disclosure, the control means may be configured to include an inverter for changing the rotational speed of the motor and a controller for outputting a control signal to the inverter for controlling the rotational speed of the motor.

[0016] Furthermore, in the reverse osmosis membrane apparatus of the present disclosure, the motor is preferably positioned above the electric cylinder, a drive pulley is fixed to the output shaft of the motor, the electric cylinder has an input shaft protruding from it, a driven pulley is fixed to the input shaft, an endless belt is wrapped around the drive pulley and the driven pulley, and the rotational driving force of the motor is transmitted to the electric cylinder via the drive pulley, the endless belt and the driven pulley.

[0017] Also, in the reverse osmosis membrane device of the present disclosure, preferably, the first pump chamber and the second pump chamber of the reciprocating pump are provided at both ends of the electric cylinder, each of the first pump chamber and the second pump chamber includes the piston capable of reciprocating movement, a pair of the pistons are fixed to both ends of the rod of the electric cylinder, and the pair of pistons reciprocate in the same direction, and it can be configured to be characterized in this way.

Advantages of the Invention

[0018] According to the reverse osmosis membrane device of the present disclosure, noise can be suppressed.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic configuration diagram of a reverse osmosis membrane device according to an embodiment of the present disclosure. [Figure 2] It is a schematic configuration diagram of a reverse osmosis membrane device according to a modification of the present disclosure. [Figure 3] It is a schematic configuration diagram of a reverse osmosis membrane device according to a modification of the present disclosure. [Figure 4] It is a schematic configuration diagram of a reverse osmosis membrane device according to a modification of the present disclosure. [Figure 5] It is a schematic configuration diagram of a reverse osmosis membrane device of a conventional example.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the reverse osmosis membrane device of the present disclosure will be described with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a reverse osmosis membrane device 1 according to an embodiment of the present disclosure. The reverse osmosis membrane device 1 can be used, for example, for applications such as concentrating seawater to produce fresh water and concentrated seawater. Note that the application of the reverse osmosis membrane device 1 is not limited to seawater desalination. For example, it can be used to obtain clean water from wastewater containing impurities such as groundwater or landfill leachate, to produce highly purified pure water, to obtain concentrated oral liquids (beverages, liquid foods, liquid health supplements, oral pharmaceuticals, etc.) or external use liquids (liquid cosmetics, liquid pharmaceuticals, etc.).

[0021] The reverse osmosis membrane device 1 includes a reverse osmosis membrane tank 2, a reciprocating pump 3, a switching valve mechanism 4, and a drive mechanism 5. Hereinafter, each constituent means of the reverse osmosis membrane device 1 will be described.

[0022] Reverse osmosis membrane tank The reverse osmosis membrane tank 2 has a reverse osmosis membrane 20 inside, and separates the liquid to be treated into a permeate and a concentrate by the reverse osmosis membrane 20. Inside the reverse osmosis membrane tank 2, it is partitioned into a first chamber 21 and a second chamber 22 by the reverse osmosis membrane 20. The reverse osmosis membrane 20 can be made of conventionally known materials such as cellulose acetate, polyamide, polysulfone, aquaporin (protein), etc. Also, the reverse osmosis membrane 20 can be of a conventionally known structure such as a flat membrane, hollow fiber membrane, etc.

[0023] The reverse osmosis membrane tank 2 is provided with a liquid to be treated inlet 23 at one end (the left end in FIG. 1) of the first chamber 21. A liquid to be treated introduction flow path L1 is connected to the liquid to be treated inlet 23. The liquid to be treated introduction flow path L1 is connected to the first pump chamber 33 of the reciprocating pump 3. The liquid to be treated pumped from the first pump chamber 33 of the reciprocating pump 3 is introduced into the first chamber 21 of the reverse osmosis membrane tank 2 through the liquid to be treated introduction flow path L1. A check valve 11 is provided in the liquid to be treated introduction flow path L1 so as to open only in the direction from the first pump chamber 33 of the reciprocating pump 3 to the first chamber 21 of the reverse osmosis membrane tank 2. Inside the first chamber 21, when pressure acts on the liquid to be treated, a part of the moisture in the liquid to be treated permeates from the first chamber 21 through the reverse osmosis membrane 2 and moves to the second chamber 22. As a result, the liquid to be treated is concentrated by the separation of moisture and becomes a concentrate.

[0024] A concentrate outlet 24 is provided at the other end (the right end in FIG. 1) of the first chamber 21 of the reverse osmosis membrane tank 2, which is opposite to the one side. A concentrate discharge flow path L2 is connected to the concentrate outlet 24. The concentrate discharge flow path L2 is connected to the second pump chamber 34 of the reciprocating pump 3 via the switching valve mechanism 4, and the concentrate generated in the first chamber 21 of the reverse osmosis membrane tank 2 is discharged to the reciprocating pump 3 through the concentrate discharge flow path L2 via the switching valve mechanism 4. The description of the switching valve mechanism 4 will be given later.

[0025] A permeate outlet 25 is provided in the second chamber 22 of the reverse osmosis membrane tank 2. A permeate outlet channel L3 is connected to the permeate outlet 25. In the reverse osmosis membrane tank 2, the permeate that has passed through the reverse osmosis membrane 20 is collected through the permeate outlet channel L3 and used, for example, as fresh water.

[0026] Reciprocating pump The reciprocating pump 3 pressurizes the liquid to be treated and supplies it to the reverse osmosis membrane tank 2. The reciprocating pump 3 comprises a cylinder 30, a piston 31 that moves back and forth within the cylinder 30, and a rod 32 connected to the piston 31.

[0027] The cylinder 30 has a cylindrical shape with both ends closed. The internal space of the cylinder 30 is divided into a first pump chamber 33 and a second pump chamber 34 by a piston 31. The first pump chamber 33 on one side (left side in Figure 1) is connected to the liquid to be treated inlet 23 of the reverse osmosis membrane tank 2, and the second pump chamber 34 on the opposite side (right side in Figure 1) is connected to the concentrated liquid outlet 24 of the reverse osmosis membrane tank 2. A liquid to be treated supply channel L4 is also connected to the first pump chamber 33, and the liquid to be treated is supplied from outside the system through the liquid to be treated inlet channel L4. The liquid to be treated supply channel L4 is provided with a check valve type supply valve 10 that closes when the piston 31 of the reciprocating pump 3 moves inside the cylinder 30 in the direction of the first pump chamber 33 (left direction in Figure 1, and referred to as the "forward direction" in this disclosure).

[0028] The piston 31 is disc-shaped. The piston 31 reciprocates within the cylinder 30 in close contact with the inner wall of the cylinder 30. By moving forward within the cylinder 30, the piston 31 decreases the volume of the first pump chamber 33 and increases the volume of the second pump chamber 34. On the other hand, by moving forward within the cylinder 30 in the direction of the second pump chamber 34 (to the right in Figure 1, which is referred to as the "returning direction" in this disclosure, and the "returning direction" is the opposite direction to the "forward direction"), the piston 31 increases the volume of the first pump chamber 33 and decreases the volume of the second pump chamber 34.

[0029] As the piston 31 moves forward within the cylinder 30, the liquid to be treated is pumped from the first pump chamber 33 and supplied at high pressure to the first chamber 21 of the reverse osmosis membrane tank 2. At the same time, the concentrated liquid discharged from the concentrated liquid outlet 24 is introduced into the second pump chamber 34 via the switching valve mechanism 4. Meanwhile, as the piston 31 moves backward within the cylinder 30, the concentrated liquid in the second pump chamber 34 is discharged via the switching valve mechanism 4, and new liquid to be treated is supplied into the first pump chamber 33.

[0030] The rod 32 is a straight, rod-shaped object. The rod 32 extends horizontally from the center of the plate surface of the piston 31, passes through the cylinder 30, and protrudes from the other end of the cylinder 30 (the right end in Figure 1). As a result, the internal volume of the second pump chamber 34 in the cylinder 30 is smaller than the internal volume of the first pump chamber 33 by the volume of the rod 32. The rod 32 is connected to the rod 51 of the drive mechanism 5 via a known connecting means 6 such as a coupling.

[0031] Switching valve mechanism The switching valve mechanism 4 comprises a valve body 40, a spool 41, a piston 43, and a connecting rod 46. The connecting rod 46 is a straight rod and connects the spool 41 and the piston 43. The switching valve mechanism 4 switches the flow path by switching the reciprocating movement of the piston 31 of the reciprocating pump 3, which causes the spool 41, piston 43, and connecting rod 46 to reciprocate (move to the left and to the right in Figure 1).

[0032] The valve body 40 is cylindrical with both ends closed. The internal space of the valve body 40 is divided into pilot chambers 44, 45 and a spool chamber 47 by a partition wall 42. A piston 43 is slidably housed in the pilot chambers 44, 45 on one side (left side in Figure 1), and a spool 41 is slidably housed in the spool chamber 47 on the other side (right side in Figure 1). A through hole is formed in the partition wall 42 through which a connecting rod 46 can be inserted.

[0033] A concentrated liquid outlet channel L2 is connected to the end of the spool chamber 47 of the valve body 40 that is on the side of the partition wall 42. In other words, the spool chamber 47 of the valve body 40 is interposed in the middle of the concentrated liquid outlet channel L2. A concentrated liquid discharge channel L5 is connected to the end of the spool chamber 47 of the valve body 40 that is on the side opposite to the partition wall 42.

[0034] The spool 41 is disc-shaped. The spool 41 reciprocates within the spool chamber 47 in close contact with the inner wall of the valve body 40. By moving within the spool chamber 47 toward the partition wall 42, the spool 41 blocks the concentrated liquid outlet channel L2 and opens the concentrated liquid discharge channel L5. On the other hand, by moving within the spool chamber 47 in the opposite direction to the partition wall 42, the spool 41 blocks the concentrated liquid discharge channel L5 and opens the concentrated liquid outlet channel L2, connecting the first chamber 21 of the reverse osmosis membrane tank 2 to the second pump chamber 34 of the reciprocating pump 3.

[0035] The internal space of the pilot chambers 44 and 45 of the valve body 40 is divided into a first pilot chamber 44 and a second pilot chamber 45 by a piston 43. The first pilot chamber 44 on one side (left side in Figure 1) is connected to a first pilot passage L6, and the pressure from the first pump chamber 33 of the reciprocating pump 3 is introduced into the first pilot chamber 44 via the first pilot passage L6. The second pilot chamber 45 on the other side (right side in Figure 1) is connected to a second pilot passage L7, and the pressure from the second pump chamber 34 of the reciprocating pump 3 is introduced into the second pilot chamber 45 via the second pilot passage L7.

[0036] In the first pilot chamber 44 and the second pilot chamber 45, with the piston 43 in between, if the pressure acting on the first pilot chamber 44 is higher, the piston 43 moves to the first switching position in the direction of the partition wall 42 (the position shown by the dashed line in Figure 1). This connects the first chamber 21 of the reverse osmosis membrane tank 2 and the second pump chamber 34 of the reciprocating pump 3 via the concentrated liquid discharge channel L2 and the spool chamber 47. On the other hand, if the pressure acting on the second pilot chamber 45 is higher, the piston 43 moves to the second switching position in the direction opposite to the partition wall 42 (the position shown by the solid line in Figure 1). This connects the concentrated liquid discharge channel L5 and the second pump chamber 34 of the reciprocating pump 3 via the spool chamber 47.

[0037] When the piston 31 of the reciprocating pump 3 is at the end of its return movement position (the position shown by the solid line in Figure 1, hereinafter referred to as the "return movement end position"), the piston 43 of the switching valve mechanism 4 is at the second switching position (the position shown by the solid line in Figure 1), and the piston 41 is blocking the concentrated liquid discharge channel L2. Therefore, the flow of liquid from the first chamber 21 of the reverse osmosis membrane tank 2 to the second pump chamber 34 of the reciprocating pump 3 is blocked, and the piston 31 of the reciprocating pump 3 does not start moving in the forward direction. When a force from the drive mechanism 5 acts on the piston 31 of the reciprocating pump 3 to encourage forward movement, the pressure in the first pump chamber 33 of the reciprocating pump 3 increases, and this pressure increase is transmitted to the first pilot chamber 44 via the first pilot passage L6, causing the piston 43 of the switching valve mechanism 4 to move to the first switching position (the position shown by the dashed line in Figure 1). This enables the flow of concentrated liquid from the first chamber 21 of the reverse osmosis membrane tank 2 to the second pump chamber 34 of the reciprocating mobile pump 3.

[0038] On the other hand, when the piston 31 of the reciprocating pump 3 is at the end of its forward movement position (the position shown by the dashed line in Figure 1, hereinafter referred to as the "end of forward movement position"), the piston 43 of the switching valve mechanism 4 is at the first switching position (the position shown by the dashed line in Figure 1), and the concentrated liquid outlet passage L2 is open, but the flow of liquid from the first chamber 21 of the reverse osmosis membrane tank 2 to the first pump chamber 33 of the reciprocating pump 3 is blocked by the check valve 11, so the piston 31 of the reciprocating pump 3 does not start moving in the reverse direction. When a force from the drive mechanism 5 acts on the piston 31 of the reciprocating pump 3 to encourage movement in the reverse direction, the pressure in the second pump chamber 34 of the reciprocating pump 3 rises, and this pressure rise is transmitted to the second pilot chamber 45 via the second pilot passage L7, causing the piston 43 of the switching valve mechanism 4 to move to the second switching position (the position shown by the solid line in Figure 1). This enables the flow of concentrated liquid from the second pump chamber 34 of the reciprocating pump 3 through the spool chamber 47 of the switching valve mechanism 4 to the concentrated liquid discharge channel L5.

[0039] Drive mechanism The drive mechanism 5 drives the reciprocating pump 3, specifically, it drives the reciprocating movement of the piston 31 of the reciprocating pump 3 within the cylinder 30. The drive mechanism 5 includes an electric cylinder 50 and a control means 53 for controlling the rotational speed of the motor 52, which is the drive source for the electric cylinder 50.

[0040] The electric cylinder 50 has a rod 51 that moves back and forth when driven by a motor 52, and a ball screw and ball screw nut (not shown) convert the rotational driving force of the motor 52 into linear motion. The electric cylinder 50 in this embodiment can be of a conventionally known structure. The rod 51 of the electric cylinder 50 is connected to the piston 31 of the reciprocating pump 3 to transmit its reciprocating movement, and in this embodiment, the rod 51 of the electric cylinder 50 and the rod 32 of the reciprocating pump 3 are connected in a linear fashion.

[0041] In this embodiment, the electric cylinder 50 has an input shaft that protrudes from the electric cylinder 50, and a driven pulley 56 is fixed to the input shaft. The motor 52 is positioned above the electric cylinder 50, and a drive pulley 57 is fixed to the output shaft of the motor 52. An endless belt 58 is wrapped around the drive pulley 57 and the driven pulley 56. The rotational driving force of the motor 52 is transmitted to the input shaft of the electric cylinder 50 via the drive pulley 57, the endless belt 58, and the driven pulley 56.

[0042] The motor 52 is rotatable in both forward and reverse directions and is not particularly limited, but in this embodiment it is a three-phase motor.

[0043] The control means 53 controls the rotational speed (rotational speed) of the motor 52, which is the drive source for the electric cylinder 50. In this embodiment, the control means 53 includes an inverter 54 connected to the motor 52 and a controller 55 connected to the inverter 54.

[0044] The inverter 54 includes a converter circuit, a capacitor, and an inverter circuit, and changes the rotational speed of the motor 52 by freely changing the frequency and voltage of the commercial power supply and outputting it to the motor 52. By changing the rotational speed of the motor 52 with the inverter 54, the reciprocating speed of the rod 51 of the electric cylinder 5 can be changed, and the reciprocating speed of the piston 31 of the reciprocating pump 3 can be changed. Note that the inverter 54 in this embodiment is not special; it can be any inverter that can generate an alternating current of any frequency and voltage from the commercial power supply.

[0045] The controller 55 outputs a control signal to the inverter 54 to control the rotational speed (rotational rate) of the motor 52. The controller 55 mainly consists of a microcontroller or microcomputer having one or more processors and one or more memories. In other words, the controller 55 realizes the function of controlling the rotational speed (rotational rate) of the motor 52 by executing a program stored in the memory by the processor.

[0046] The controller 55 controls the rotational speed (rotational speed) of the motor 52 via the inverter 54 so that the piston 31 of the reciprocating pump 3 moves back and forth between the return-direction end position (the position shown by the solid line in Figure 1) and the forward-direction end position (the position shown by the dashed line in Figure 1).

[0047] Furthermore, when switching between the forward and reverse movement of the piston 31 of the reciprocating pump 3, the controller 55 controls the rotational speed (rotational speed) of the motor 52 via the inverter 54 so that the piston 31 moves in the opposite direction while decelerating and accelerating at least one of the two directions, that is, so that the direction of movement does not momentarily reverse during the switching.

[0048] Specifically, when the piston 31 of the reciprocating pump 3 reaches the end position in the forward direction (the position shown by the dashed line in Figure 1) and begins to move in the reverse direction, and when the piston 31 reaches the end position in the reverse direction (the position shown by the solid line in Figure 1) and begins to move in the forward direction, that is, when the piston 31 switches from reciprocating movement to moving in the opposite direction, the controller 55 controls the rotational speed (rotational speed) of the motor 52 so that the movement speed does not instantaneously increase to the maximum speed (the initial speed becomes the maximum speed), but rather the piston 31 gradually accelerates and the movement speed gradually increases from zero to the maximum speed over a predetermined time (referred to as the "rise time" in this disclosure). Furthermore, once the movement speed of the piston 31 reaches the maximum speed, the controller 55 controls the rotational speed (rotational speed) of the motor 52 so that the movement speed is maintained at the maximum speed.

[0049] By setting the rise time as described above, the direction of movement of the piston 31 of the reciprocating pump 3 does not momentarily reverse when the direction of movement is switched. Therefore, unlike conventional reverse osmosis membrane devices, the reverse osmosis membrane device 1 of this embodiment suppresses vibrations generated in the reciprocating pump 3, thus suppressing noise.

[0050] Alternatively, when the piston 31 of the reciprocating pump 3 approaches the forward end position (the position shown by the dashed line in Figure 1) and ends its forward movement, and when the piston 31 approaches the return end position (the position shown by the solid line in Figure 1) and ends its return movement, that is, when the piston 31 stops reciprocating movement when switching between reciprocating movement, it is preferable that the controller 55 controls the rotational speed (rotational speed) of the motor 52 so that the movement speed does not instantaneously drop from the maximum speed to zero at each end position, but rather the piston 31 gradually decelerates from just before each end position, and the movement speed gradually drops from the maximum speed to zero over a predetermined time (referred to as the "fall time" in this disclosure) until it reaches each end position.

[0051] By setting the fall time as described above, the direction of movement of the piston 31 of the reciprocating pump 3 does not momentarily reverse when the direction of movement is switched. Therefore, unlike conventional reverse osmosis membrane devices, the reverse osmosis membrane device 1 of this embodiment suppresses vibrations generated in the reciprocating pump 3, thus suppressing noise.

[0052] Furthermore, by setting both the rise time and fall time as described above, the direction of movement of the piston 31 of the reciprocating pump 3 can be reversed more gradually when switching directions of movement. As a result, vibrations generated in the reciprocating pump 3 can be suppressed more effectively, and thus noise can be suppressed more effectively.

[0053] The rise time and fall time mentioned above are not particularly limited and should be greater than zero. However, in order to effectively suppress vibrations generated when the direction of movement of the piston 31 of the reciprocating pump 3 is switched, thereby effectively reducing noise, and to ensure a sufficient volume of liquid to be pumped to the reverse osmosis membrane, it is preferable that the rise time and fall time be between 0.5S and 1.5S.

[0054] Furthermore, the controller 55 can also control the rotational speed (rotational speed) of the motor 52 via the inverter 54 as follows. Specifically, when the direction of movement of the piston 31 of the reciprocating pump 3 is switched, that is, when the piston 31 reaches the end position of each reciprocating movement and stops reciprocating, the controller 55 can control the rotational speed (rotational speed) of the motor 52 so that it starts moving in the opposite direction after a predetermined time (referred to as the "interval time" in this disclosure).

[0055] The interval time mentioned above is not particularly limited and can be greater than zero, but in order to suppress vibrations that occur when the direction of movement of the piston 31 of the reciprocating pump 3 is switched, thereby keeping noise down well, and to ensure a sufficient amount of liquid to be treated is pumped to the reverse osmosis membrane, it is preferable that the interval time be between 0.5S and 1.5S.

[0056] Operation of a reverse osmosis membrane device Next, the operation of the reverse osmosis membrane apparatus 1 of this embodiment will be described. The controller 55 of the drive mechanism 5 controls the rotational speed (rotational rate) of the motor 52, so that when the piston 31 of the reciprocating pump 3 moves from the return-direction end position (position shown by the solid line in Figure 1) to the forward direction, the liquid to be treated is pumped from the first pump chamber 33 of the reciprocating pump 3. As a result, the liquid to be treated is supplied to the first chamber 21 of the reverse osmosis membrane tank 2 through the liquid to be treated introduction channel L1. Since the liquid to be treated is pressurized to a high pressure due to the difference in internal volume between the first pump chamber 33 and the second pump chamber 34, the liquid to be treated is separated in the reverse osmosis membrane tank 2 into permeate that passes through the reverse osmosis membrane 20 and concentrated liquid that does not pass through the reverse osmosis membrane 20. The permeate is recovered as permeate from the second chamber 22 via the permeate outlet channel L3. The concentrated liquid is introduced from the first chamber 21 through the concentrated liquid discharge channel L2 and the spool chamber 47 of the switching valve mechanism 4 into the second pump chamber 34 of the reciprocating pump 3, because the concentrated liquid discharge channel L2 is opened when the piston 43 of the switching valve mechanism 4 moves from the second switching position (the position shown by the solid line in Figure 1) to the first switching position (the position shown by the dashed line in Figure 1).

[0057] As the piston 31 of the reciprocating pump 3 approaches the end position in the forward direction (the position shown by the dashed line in Figure 1), the controller 55 of the drive mechanism 5 controls the rotational speed (rotational speed) of the motor 52, gradually reducing the movement speed of the piston 31. Over a predetermined period of time, the piston 31's movement speed is reduced from its maximum speed to zero as it approaches the end position in the forward direction. As a result, the piston 31 gradually decelerates and stops at the end position in the forward direction.

[0058] When the piston 31 reaches the forward end position, the controller 55 of the drive mechanism 5 controls the rotational speed (rotational rate) of the motor 52, causing the piston 31 of the reciprocating pump 3 to move from the forward end position to the return position. At this time, the controller 55 of the drive mechanism 5 gradually accelerates the movement speed of the piston 31, increasing the movement speed of the piston 31 from zero to the maximum speed over a predetermined period of time from the forward end position. As a result, the piston 31 moves from the forward end position while gradually accelerating. Due to the return movement of the piston 31, the concentrated liquid is pumped from the second pump chamber 34 of the reciprocating pump 3. At this time, the piston 43 of the switching valve mechanism 4 moves from the first switching position (indicated by the dashed line in Figure 1) to the second switching position (indicated by the solid line in Figure 1), and since the concentrated liquid discharge channel L5 is open, the concentrated liquid is discharged outside the system through the switching valve mechanism 4 and the concentrated liquid discharge channel L5.

[0059] As the piston 31 of the reciprocating pump 3 approaches the return-direction end position (the position shown by the solid line in Figure 1), the controller 55 of the drive mechanism 5 controls the rotational speed (rotational speed) of the motor 52, gradually reducing the movement speed of the piston 31. Over a predetermined period of time, the piston 31's movement speed is reduced from its maximum speed to zero as it approaches the return-direction end position. As a result, the piston 31 gradually decelerates and stops at the return-direction end position.

[0060] When the piston 31 reaches the return-direction end position, the controller 55 of the drive mechanism 5 controls the rotational speed (rotational rate) of the motor 52, causing the piston 31 of the reciprocating pump 3 to move again in the forward direction from the return-direction end position. At this time, the controller 55 of the drive mechanism 5 gradually accelerates the movement speed of the piston 31, increasing the movement speed of the piston 31 from zero to the maximum speed over a predetermined period of time from the return-direction end position. As a result, the piston 31 moves from the return-direction end position while gradually accelerating. The forward movement of the piston 31 causes the liquid to be processed to be pumped again from the first pump chamber 33 of the reciprocating pump 3. Thereafter, the reciprocating movement of the piston 31 of the reciprocating pump 3 as described above is repeated.

[0061] Actions and effects of reverse osmosis membrane devices The reverse osmosis membrane apparatus 1 of this embodiment is characterized in that the control means 53 controls the rotational speed of the motor 52 so that when the piston 31 of the reciprocating pump 3 starts moving in the opposite direction at the end of its forward and reverse movements, the piston 31 gradually accelerates and its movement speed increases to the maximum speed over a predetermined period of time. Therefore, the direction of movement of the piston 31 of the reciprocating pump 3 does not momentarily reverse when the direction of movement is switched. Thus, unlike conventional reverse osmosis membrane apparatuses, the reverse osmosis membrane apparatus 1 of this embodiment suppresses vibrations generated in the reciprocating pump 3, and thus noise can be suppressed.

[0062] Furthermore, the control means 53 controls the rotational speed of the motor 52 so that when the piston 31 of the reciprocating pump 3 reaches the respective end position of its forward and reverse movement and stops its forward and reverse movement, the piston 31 gradually decelerates from just before each end position, and the movement speed decreases to zero over a predetermined period of time until it reaches each end position. Therefore, when the direction of movement of the piston 31 of the reciprocating pump 3 is switched, the direction of movement does not momentarily reverse. Thus, according to the reverse osmosis membrane apparatus 1 of this embodiment, unlike conventional reverse osmosis membrane apparatuses, vibrations generated in the reciprocating pump 3 are suppressed, and thus noise can be suppressed.

[0063] Thus, according to the reverse osmosis membrane apparatus 1 of this embodiment, noise can be suppressed by having the piston 31 of the reciprocating pump 3 move in the opposite direction while decelerating and accelerating at least one of the two directions when switching between forward and reverse movement.

[0064] Furthermore, in this embodiment, the reverse osmosis membrane apparatus 1 adjusts (deceleration and acceleration) the movement speed of the piston 31 of the reciprocating pump 3 before and after switching the direction of movement of the piston 31. Therefore, when switching the direction of movement of the piston 31 of the reciprocating pump 3, the direction of movement can be reversed more smoothly. Thus, according to the reverse osmosis membrane apparatus 1 of this embodiment, vibrations generated in the reciprocating pump 3 can be suppressed more effectively, and noise can be suppressed more effectively.

[0065] Furthermore, in this embodiment of the reverse osmosis membrane apparatus 1, the direction of movement does not momentarily reverse when the reciprocating movement of the piston 31 of the reciprocating pump 3 is switched. Therefore, a momentary high-pressure load is not applied at the connection between the rod 32 of the reciprocating pump 3 and the rod 51 of the electric cylinder 50 of the drive mechanism 5 during the switching. Thus, with this embodiment of the reverse osmosis membrane apparatus 1, damage to connecting means 6 such as joints and each rod 32, 51 can be suppressed.

[0066] Furthermore, in this embodiment, the reverse osmosis membrane apparatus 1 uses an electric cylinder 50 as the drive mechanism 5 that drives the reciprocating pump 3. Therefore, according to this embodiment, unlike conventional reverse osmosis membrane apparatuses that use a hydraulic cylinder as the drive mechanism 5, the hydraulic cylinder's hydraulic fluid switching valve does not vibrate and generate noise each time it switches, nor does it vibrate and generate noise when the direction of movement of the hydraulic cylinder's piston is switched, thus enabling quiet operation.

[0067] Furthermore, the reverse osmosis membrane apparatus 1 of this embodiment allows for easy adjustment of the amount and speed of movement of the piston 31 of the reciprocating pump 3 during its reciprocating motion. In addition, it eliminates the need for equipment such as limit switches, hydraulic fluid switching valves, and hydraulic fluid tanks, and eliminates the need for hydraulic fluid management and replenishment. Moreover, malfunctions of these devices will not cause malfunctions in the reciprocating pump 3.

[0068] Modified Reverse Osmosis Membrane Apparatus Although one embodiment of the reverse osmosis membrane apparatus of this disclosure has been described above, the reverse osmosis membrane apparatus of this disclosure is not limited to the above embodiment, and various modifications are possible without departing from the spirit of this disclosure.

[0069] In the reverse osmosis membrane apparatus 1 of the above embodiment, the rotational driving force of the motor 52 is transmitted to the electric cylinder 50 via the drive pulley 57, endless belt 58, and driven pulley 56. As a modification, the reverse osmosis membrane apparatus 1 shown in Figure 2 may be configured to transmit the rotational driving force of the motor 52 to the electric cylinder 50 without going through the drive pulley 57, endless belt 58, and driven pulley 56. The reverse osmosis membrane apparatus 1 shown in Figure 2 can also solve the above-mentioned problems of this disclosure, similar to the reverse osmosis membrane apparatus 1 of the above embodiment. Furthermore, the configuration of the reverse osmosis membrane apparatus 1 shown in Figure 2, other than the configuration described above, is the same as that of the reverse osmosis membrane apparatus 1 shown in Figure 1, and a detailed explanation is omitted here, but the parts that have the same configuration as the reverse osmosis membrane apparatus 1 shown in Figure 1 will have the same function and effect.

[0070] Furthermore, in the reverse osmosis membrane apparatus 1 of the above embodiment, the piston 31 of the reciprocating pump 3 moves back and forth within the cylinder 30 by connecting a rod 32 protruding from the cylinder 30 to a rod 51 of the electric cylinder 50. As one modification, as shown in Figure 3 of the reverse osmosis membrane apparatus 1, the piston 31 of the reciprocating pump 3 may be configured to move back and forth within the cylinder 30 by connecting the piston 31 of the electric cylinder 50 to a rod 51. This modification will be described in detail below.

[0071] In the reverse osmosis membrane apparatus 1 shown in Figure 3, the reciprocating pump 3 comprises a pair of cylinders 30 and a pair of pistons 31 that reciprocate within each cylinder 30. The pair of cylinders 30 are cylindrical with one end closed and are connected to both ends of an electric cylinder 50. The pair of cylinders 30 and the electric cylinder 50 are sealed by connecting plates 59. The internal space on one side of the pair of cylinders 30 (left side in Figure 3) is the first pump chamber 33, and the internal space on the other side of the pair of cylinders 30 (right side in Figure 3) is the second pump chamber 34. The first pump chamber 33 is connected to the liquid to be treated inlet 23 of the reverse osmosis membrane tank 2, and the second pump chamber 34 is connected to the concentrated liquid outlet 24 of the reverse osmosis membrane tank 2. A liquid to be treated supply channel L4 is also connected to the first pump chamber 33. A concentrated liquid discharge channel L5 is also connected to the second pump chamber 34. A concentrated liquid discharge valve 12 is provided in the concentrated liquid discharge channel L5. Furthermore, the second pump chamber 34 contains the rod 51 of the electric cylinder 50, which will be described later. The rod 51 passes through one of the pistons 31 (the right side in Figure 3) and protrudes from the end of the cylinder 30 that contains the second pump chamber 34. As a result, the internal volume of the second pump chamber 34 is smaller than the internal volume of the first pump chamber 33 by the volume of the rod 51.

[0072] The concentrated liquid discharge valve 12 is configured to close when the pair of pistons 31 of the reciprocating pump 3 move in the forward direction (left side in Figure 3) within their respective cylinders 30, and to open when they move in the return direction (right side in Figure 3). The concentrated liquid discharge valve 12 can be connected to, for example, a controller 55, and the controller 55 can be configured to control the opening and closing of the concentrated liquid discharge valve 12 in relation to the reciprocating movement of the pistons 31. However, the opening and closing operation of the concentrated liquid discharge valve 12 is not limited to electrical control by the controller 55.

[0073] The pair of pistons 31 reciprocate within their respective cylinders 30, maintaining close contact with the inner walls of the cylinders 30. The pair of pistons 31 move in the same direction, and by moving forward within their respective cylinders 30, they decrease the volume of the first pump chamber 33 and increase the volume of the second pump chamber 34. On the other hand, by moving backward within their respective cylinders 30, the pair of pistons 31 increase the volume of the first pump chamber 33 and decrease the volume of the second pump chamber 34.

[0074] As a pair of pistons 31 move forward within their respective cylinders 30, the liquid to be treated is pumped from the first pump chamber 33 to the liquid to be treated introduction channel L1, and supplied to the first chamber 21 of the reverse osmosis membrane tank 2. Because the liquid to be treated is pressurized to a high pressure due to the difference in internal volume between the first pump chamber 33 and the second pump chamber 34, the liquid to be treated is separated in the reverse osmosis membrane tank 2 into permeate that passes through the reverse osmosis membrane 20 and concentrated liquid that does not pass through the reverse osmosis membrane 20. The permeate is recovered as permeate from the second chamber 22 via the permeate outlet channel L3. The concentrated liquid is introduced into the second pump chamber 34 from the first chamber 21 via the concentrated liquid outlet channel L2. Meanwhile, as the pair of pistons 31 move backward within their respective cylinders 30, the concentrated liquid in the second pump chamber 34 is discharged out of the system via the concentrated liquid discharge channel L5, and new liquid to be treated is supplied into the first pump chamber 33 via the liquid to be treated supply channel L4.

[0075] The rod 51 of the electric cylinder 50 protrudes from both ends of the electric cylinder 50, and a pair of pistons 31 are fixed to both ends of the rod 51. When the rod 51 moves back and forth, this reciprocating motion is transmitted to the pair of pistons 31, causing the pair of pistons 31 to also move back and forth. A screw shaft 60 is formed on the rod 51, at least in a portion of the electric cylinder 50. The motor 52 is fixed inside the electric cylinder 50. The electric cylinder 50 is equipped with a first gear 61 and a second gear 62. The first gear 61 meshes with the screw shaft 60, and the second gear 62 meshes with the first gear 61 while fixed to the output shaft of the motor 52. The rotational driving force of the motor 52 is transmitted to the rod 51 of the electric cylinder 50 via the first gear 61 and the second gear 62, and at this time the rotational motion is converted into linear motion, causing the rod 51 to move back and forth. Note that the configuration for transmitting the rotational driving force of the motor 52 to the rod 51 of the electric cylinder 50 and converting it into linear motion is not limited to the above configuration, and various known configurations can be used.

[0076] In the modified example shown in Figure 3, the problems described above in this disclosure can be solved in the same way as in the reverse osmosis membrane apparatus 1 of the above embodiment. Furthermore, in the reverse osmosis membrane apparatus 1 shown in Figure 3, the same reference numerals are used for components that are the same as those for the reverse osmosis membrane apparatus 1 shown in Figure 1. Although the differences between each component and the above embodiment have been explained here, the parts that have the same configuration as the reverse osmosis membrane apparatus 1 shown in Figure 1 will have the same function and effect. In addition, according to the reverse osmosis membrane apparatus 1 shown in Figure 3, since the first pump chamber 33 and the second pump chamber 34 of the reciprocating pump 3 are provided at both ends of the electric cylinder 50, the apparatus can be made smaller, replacement parts such as rods 32 and connecting means 6 such as joints are not required, and the switching valve mechanism 4 is also not required, thus reducing costs.

[0077] In the modified example shown in Figure 3, the internal volume of the second pump chamber 34 is smaller than the internal volume of the first pump chamber 33 by the volume of the rod 51. However, as shown in the modified example in Figure 4, the size of the cylinder 30 including the second pump chamber 34 may be smaller than the size of the cylinder 30 including the first pump chamber 33.

[0078] In the modified examples shown in Figures 3 and 4, the liquid to be treated is pressurized to a high pressure due to the difference in internal volume between the first pump chamber 33 and the second pump chamber 34. However, the pressure of the liquid to be treated may be adjusted by, for example, providing a pressure regulating valve in the concentrated liquid discharge channel L5.

[0079] Furthermore, in the above embodiment and modified reverse osmosis membrane apparatus 1, the control means 53 is equipped with an inverter 54, and the rotational speed of the motor 52 is changed by inverter control. As one modification, although not shown in the figures, a servo motor may be used for the motor 52, and a rotary encoder as a position detector may be connected to the servo motor, and the controller 55 may be configured to control the rotational speed of the motor 52 to follow a commanded rotational speed while grasping the rotational position of the motor 52 by detection of the rotary encoder. In this modified reverse osmosis membrane apparatus 1 as well as in the above embodiment, the above-mentioned problems of this disclosure can be solved and the same effects as in the above embodiment and modified reverse osmosis membrane apparatus 1 can be achieved. [Examples]

[0080] The noise reduction effect of the reverse osmosis membrane apparatus of this disclosure will be explained below with reference to examples. However, the reverse osmosis membrane apparatus of this disclosure is not limited to the following examples.

[0081] As an example, using a reverse osmosis membrane apparatus with the same configuration as the reverse osmosis membrane apparatus shown in Figure 1, the sound level generated when the piston movement speed of a reciprocating pump was adjusted during the switching of the piston's reciprocating movement was measured. As a comparative example, using a reverse osmosis membrane apparatus with the same configuration as the reverse osmosis membrane apparatus shown in Figure 5, the sound level generated when the piston of a reciprocating pump was moved back and forth by a hydraulic cylinder was measured. Furthermore, as a reference example, using a reverse osmosis membrane apparatus with the same configuration as the reverse osmosis membrane apparatus shown in Figure 1, the sound level generated when the piston movement speed of the reciprocating pump was not adjusted during the switching of the piston's reciprocating movement was measured. In all examples, the sound level was measured within the same facility, at the same distance from the apparatus, and using the same measuring equipment. The results are shown in Table 1. The units for rise time, fall time, and interval time in Table 1 are seconds. The speed in Table 1 is the maximum piston movement speed, and the unit is mm / second. The processing volume in Table 1 is the amount of water to be treated supplied to the reverse osmosis membrane apparatus, and is shown as a percentage based on the value of the comparative example. The sound levels in Table 1 represent the maximum sound levels measured and are shown as percentages relative to the comparative values. The reduction rates in Table 1 are shown as the amount of decrease from the comparative sound level.

[0082] [Table 1]

[0083] Comparing Examples 2 and 3 with the Comparative Examples and Reference Examples, it can be seen that by adjusting the piston's movement speed before or after switching the direction of movement of the reciprocating pump's piston, the sound level generated can be reduced compared to the case where the piston instantaneously reverses direction of movement without either deceleration or acceleration during the switching of the piston's movement direction, thus suppressing noise. Furthermore, Examples 2 and 3 achieve a reduction in the generated sound level despite having a higher maximum piston speed during reciprocating movement than the Comparative Examples and Reference Examples, and if the maximum speed is the same, a noise reduction effect greater than the reduction rate shown in Table 1 can be expected.

[0084] Furthermore, according to Example 1, by adjusting the piston's movement speed both before and after switching the direction of movement of the piston in a reciprocating pump, the noise level generated can be significantly reduced even though the maximum speed during piston reciprocating movement is at its highest, demonstrating that noise can be effectively suppressed. [Explanation of Symbols]

[0085] 1 Reverse osmosis membrane device 2 Reverse osmosis membrane tank 3. Reciprocating pump 5. Drive mechanism 20 Reverse osmosis membrane 23 Inlet for liquid to be treated 24 Concentrate outlet 31 pistons 33 First Pump Room 34. Second Pump Room 50 Electric Cylinder 51 Electric cylinder rod 52 Motors 53 Control means 54 Inverter 55 Controllers 56 Driven pulley 57 Drive pulley 58 Endless Belt

Claims

1. A reverse osmosis membrane tank separates the liquid to be treated into a permeate and a concentrate using a reverse osmosis membrane, A reciprocating pump that pressurizes the liquid to be treated and supplies it to the reverse osmosis membrane tank, A drive mechanism for driving the aforementioned reciprocating pump, A reverse osmosis membrane apparatus equipped with, The aforementioned reciprocating pump is A first pump chamber connected to the liquid to be treated inlet of the reverse osmosis membrane tank, A second pump chamber connected to the concentrated liquid outlet of the reverse osmosis membrane tank, A piston capable of reciprocating motion, wherein movement in the forward direction reduces the volume of the first pump chamber and increases the volume of the second pump chamber, and movement in the reverse direction increases the volume of the first pump chamber and decreases the volume of the second pump chamber, Equipped with, The aforementioned drive mechanism is An electric cylinder in which a rod moves back and forth due to the rotational driving force of a motor, wherein the rod is connected to the piston of the reciprocating pump so as to transmit the reciprocating motion, The motor comprises control means for controlling the rotational speed of the motor, The control means comprises an inverter for changing the rotational speed of the motor and a controller for outputting a control signal to the inverter for controlling the rotational speed of the motor, and controls the rotational speed of the motor such that when switching between forward and reverse movement of the piston, the piston moves in the opposite direction while decelerating and accelerating at least one of the two.

2. The reverse osmosis membrane apparatus according to claim 1, wherein the control means controls the rotational speed of the motor such that when the piston starts moving in the opposite direction at the end position of both the forward and return movements, the piston gradually accelerates and its movement speed increases to a maximum speed over a predetermined period of time.

3. The reverse osmosis membrane apparatus according to claim 1 or 2, wherein the control means controls the rotational speed of the motor such that when the piston stops moving at the respective end positions of forward and reverse movement, the piston gradually decelerates from just before the end position so that the movement speed decreases to zero over a predetermined period of time until it reaches the end position.

4. The motor is positioned above the electric cylinder, and a drive pulley is fixed to the output shaft of the motor. The electric cylinder has an input shaft protruding from it, and a driven pulley is fixed to the input shaft. The reverse osmosis membrane apparatus according to any one of claims 1 to 3, wherein an endless belt is wrapped around the drive pulley and the driven pulley, and the rotational driving force of the motor is transmitted to the electric cylinder via the drive pulley, the endless belt, and the driven pulley.

5. The first pump chamber and the second pump chamber of the reciprocating pump are provided at both ends of the electric cylinder, and each of the first pump chamber and the second pump chamber is equipped with a piston that can move back and forth. The reverse osmosis membrane apparatus according to any one of claims 1 to 3, wherein a pair of pistons are fixed to both ends of the rod of the electric cylinder, and the pair of pistons reciprocate in the same direction.

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