Patent Publication Number: US-2021172437-A1

Title: Liquid sending device

Description:
TECHNICAL FIELD 
     The present invention relates to a liquid sending device that sends liquid by repeating intake and discharge of the liquid by a plunger pump. 
     BACKGROUND ART 
     In an analysis device such as a liquid chromatograph, a liquid sending device that causes two plunger pumps to operate in a complementary manner and continuously sends a mobile phase is often used. In such a liquid sending device, a check valve for preventing the liquid from flowing backward is provided at an inlet port or an outlet port of each plunger pump. Generally, the check valve has a spherical valve element provided to be movable in the direction in which the liquid flows and a valve seat on which the valve element is to be seated. The valve seat is a hollow cylindrical member through which the liquid flows. A liquid flow path is closed when the spherical valve element is seated on the edge of an opening of the valve seat. 
     As for the check valve at the inlet port of the plunger pump, in a case where the plunger pump performs a discharge operation, the pressure in the pump chamber becomes positive (higher than an atmospheric pressure), and the valve element is pressed toward the valve seat by the pressure in the pump chamber to be seated. On the contrary, in a case where the plunger pump performs an intake operation, the pressure in the pump chamber becomes negative (lower than the atmospheric pressure), and the valve element is attracted toward the pump chamber by the negative pressure to be detached from the valve seat. 
     As described above, in the check valve in which the valve element passively operates due to the pressure in the pump chamber, in a case where the valve element is attached to the valve seat due to contamination on the surface of the valve element or the contact surface between the valve element and the valve seat or the like, the check valve at the inlet port might not open only by the negative pressure generated in the pump chamber when the intake operation is performed, and liquid might not be sent. 
     As such, it has been proposed to cause the valve element to actively operate by using a solenoid or the like (see Patent Documents 1 and 2). Even in a case where the valve element is attached to the valve seat, it is possible to cause the valve element to detach from the valve seat reliably and open the valve by causing the valve element to actively operate. 
     [Patent Document 1] JP 2001-235052 A 
     [Patent Document 2] WO 2017/046861 A1 
     SUMMARY OF INVENTION 
     Technical Problem 
     The check valve disclosed in Patent Document 1 or 2 is configured to cause a valve element to actively detach from a valve seat by pressing of the valve element with a pin provided inside of the valve seat in such a direction that the valve element is detached from the valve seat. The valve seat is made of a hard material such as sapphire or zirconia, and the pin is made of material such as stainless steel, which has lower hardness than the valve seat. Thus, when sliding inside of the valve seat, the pin wears. In a case where all of the operations of causing the valve element to detach from the valve seat are actively performed, the number of times the pin slides inside of the valve seat increases, and the pin wears out quickly. 
     Thus, although it was preferable to actively drive the valve element only when the valve element was attached to the valve seat, because attachment of the valve element to the valve seat could not be detected conventionally, the check valve had to actively perform all of the opening operations. Further, in a case where abrasion powder generated due to wear of the pin is caught between the valve seat and the valve element, the liquid-tightness might be lowered when the check valve is closed, and the check valve might lose its function as a check valve. 
     As such, the present invention was conceived considering the above-mentioned problems, and an object of the present invention is to enable detection of attachment of a valve element to a valve seat in a check valve. 
     Solution to Problem 
     A liquid sending device according to the present invention includes a plunger pump, which performs an intake operation of liquid to and a discharge operation of liquid from a pump chamber and in which pressure in the pump chamber in a case where the intake operation is performed is lower compared to a case where the discharge operation is performed, a check valve that is provided at an inlet port of the plunger pump, has a spherical valve element and a valve seat on which the valve element is to be seated, and passively operates according to the pressure in the pump chamber in such a direction that the valve element is seated on or detached from the valve seat, a pressure sensor that detects the pressure in the pump chamber of the plunger pump, and an attachment detector that is configured to compare the pressure in the pump chamber detected by the pressure sensor with a preset threshold value, and detect attachment of the valve element to the valve seat in a case where the pressure in the pump chamber is equal to or lower than the threshold value. 
     That is, the present invention is a liquid sending device that is provided with the function of detecting attachment of the valve element to the valve seat in the check valve provided at the inlet port of the plunger pump. The check valve in which the attachment of the valve element to the valve seat is to be detected is the check valve provided at the inlet port of the plunger pump in which the pressure in the pump chamber in a case where the intake operation is performed is lower compared to a case where the discharge operation is performed. “the plunger pump in which the pressure in the pump chamber in a case where the intake operation is performed is lower compared to a case where the discharge operation is performed” is the pump in which the pressure in the pump chamber is reduced to a pressure lower than a liquid sending pressure because the outlet port is closed by another check valve in a case where the intake operation is performed. In a case where the liquid sending device of the present invention is constituted by a serial-type double plunger pump in which two plunger pumps are connected in series to each other, the upstream (primary) plunger pump corresponds to it. On the other hand, in a case where the liquid sending device of the present invention is constituted by a parallel-type double plunger pump in which two plunger pumps are connected in parallel to each other, both of the plunger pumps correspond to it. 
     As for the above-mentioned plunger pump, in a case where the check valve is opened normally in a case where the intake operation is performed, the pressure in the pump chamber is to be maintained at about the atmospheric pressure. However, in a case where the check valve is closed due to attachment of the valve element to the valve seat, the pressure in the pump chamber is reduced to be lower than the atmospheric pressure. This phenomenon is utilized in the present invention. A value slightly lower than the atmospheric pressure is set as a threshold value, and the pressure in the pump chamber in a case where the intake operation is performed is compared with the threshold value. Thus, whether the check valve is normally operated, that is, whether the valve element is attached to the valve seat is determined. 
     The present invention is especially effective in a case where the check valve has a valve element driver for actively driving the valve element seated on the valve seat in such a direction that the valve element is detached from the valve seat. In this case, the liquid sending device preferably includes a valve element drive controller for controlling an operation of the valve element driver, and the valve element drive controller is preferably configured to actively drive the valve element by the valve element driver in such a direction that the valve element is detached from the valve seat, only in a case where the attachment detector detects attachment of the valve element to the valve seat when the intake operation is performed. Thus, the number of times the valve element of the check valve is caused by the valve element driver to actively operate can be reduced, and wear of the member that constitutes the valve element driver can be suppressed. 
     The valve element driver may include a pin provided to be movable inside of the valve seat and an operating element that causes the pin to operate and press the valve element in such a direction that the valve element is detached from the valve seat. In that case, at least a portion, which slides inside of the valve seat, of the pin is preferably made of a same material as the valve seat. This can further suppress the wear in a case where the pin slides inside of the valve seat. 
     Further, diamond-like carbon coating may be applied to at least one of an outer peripheral surface of the pin and an inner side surface of the valve seat. Diamond-like carbon has excellent slidability and wear resistance, thereby being able to further suppress the wear in a case where the pin slides inside of the valve seat. 
     Advantageous Effects of Invention 
     In the liquid sending device according to the present invention, attachment of the valve element to the valve seat can be easily detected based on whether the pressure in the pump chamber of the plunger pump detected by the pressure sensor is equal to or lower than the preset threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A schematic diagram showing the configuration of one inventive example of a liquid sending device. 
         FIG. 2  Graphs showing one example of the temporal change of the pressure in a primary pump, and  FIG. 2(A)  shows the pressure in a case where a first check valve operates normally, and  FIG. 2(B)  shows the pressure in a case where the first check valve does not operate normally. 
         FIG. 3  A flow chart for explaining one example of the drive control of the first check valve in the same inventive example. 
         FIG. 4  A cross sectional view showing the structure of the first check valve in the same inventive example. 
         FIG. 5  A cross sectional view of the first check valve taken along the line X-X shown in  FIG. 2 . 
         FIG. 6  A cross sectional view showing the first check valve being actively opened. 
         FIG. 7  A cross sectional view showing one example of another structure of a first check valve. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one inventive example of a liquid sending device according to the present invention will be described below with reference to the drawings. 
     As shown in  FIG. 1 , the liquid sending device  1  in this inventive example includes two plunger pumps including a primary pump  2  and a secondary pump  22 . The primary pump  2  and the secondary pump  22  are connected in series to each other. The primary pump  2  and the secondary pump  22  operate in a complementary manner so as to continuously send the liquid through a discharge flow path  38 . While a serial-type double plunger pump in which two plunger pumps  2  and  22  are connected in series to each other will be described in this inventive example by way of example, the present invention is not limited to this. The present invention can be applied to a parallel-type double plunger pump in which two plunger pumps are connected in parallel to each other. 
     The primary pump  2  includes a pump head  3  having a pump chamber  4  therein and a pump body  6 . The pump head  3  is provided at the tip of the pump body  6 . The pump head  3  is provided with an inlet port through which liquid flows into the pump chamber  4  and an outlet port through which liquid flows out of the pump chamber  4 . A first check valve  16  for preventing liquid from flowing backward is provided at the inlet port of the pump head  3 . The check valve  16  has a spherical valve element that passively operates according to a pressure state in the pump chamber  4 . In a case where the primary pump  2  performs a liquid intake operation, the valve element is detached from a valve seat to open the inlet port. In a case where the primary pump  2  performs a liquid discharge operation, the valve element is seated on the valve seat to close the inlet port. 
     Although not shown in  FIG. 1 , the first check valve  16  includes a valve element driver that actively drives the valve element, and the closed first check valve  16  can be forcibly opened. The operation of the first check valve  16  is controlled by a controller  40  mentioned below. The specific structure of the check valve  16  will be described below. 
     The tip of a plunger  10  is slidably inserted into the pump chamber  4 . The proximal end of the plunger  10  is held by a crosshead  8  stored in the pump body  6 . The crosshead  8  moves in one direction (the left-and-right direction in the diagram) in the pump body  6  by rotation of a feed screw  14 , and the plunger  10  moves in the one direction accordingly. A primary pump drive motor  12  that rotates the feed screw  14  is provided at the proximal end of the pump body  6 . The primary pump drive motor  12  is a stepping motor. 
     The secondary pump  22  includes a pump head  23  having a pump chamber  24  therein, and a pump body  28 . The pump head  23  is provided at the tip of the pump body  28 . The pump head  23  is provided with an inlet port through which liquid flows into the pump chamber  24  and an outlet port through which liquid flows out of the pump chamber  24 . A second check valve  26  for preventing liquid from flowing backward is provided at the inlet port of the pump head  23 . The second check valve  26  has a spherical valve element that passively operates according to a pressure state in the pump chamber  24 . In a case where the secondary pump  22  performs a liquid intake operation, the valve element is detached from a valve seat to open the inlet port. In a case where the secondary pump  22  performs a liquid discharge operation, the valve element is seated on the valve seat to close the inlet port. 
     The tip of a plunger  32  is slidably inserted into the pump chamber  24 . The proximal end of the plunger  32  is held by a crosshead  30  stored in the pump body  28 . The crosshead  30  moves in one direction (the left-and-right direction in the diagram) in the pump body  28  by rotation of a feed screw  36 , and the plunger  32  moves in the one direction accordingly. A secondary pump drive motor  34  that rotates the feed screw  36  is provided at the proximal end of the pump body  28 . The secondary pump drive motor  34  is a stepping motor. 
     The inlet port of the pump head  3  is connected to a container (not shown), storing the liquid to be sent, via a flow path. The inlet port of the pump head  23  is connected to the outlet port of the pump head  3  via a connection flow path  18 . A first pressure sensor  20  for detecting the pressure (P1) in the pump chamber  4  is provided on the connection flow path  18 . 
     A discharge flow path  38  is connected to the outlet port of the pump head  23 . The discharge flow path  38  communicates with an analysis flow path of a liquid chromatograph, for example. A second pressure sensor  39  for detecting a liquid sending pressure (P2) is provided on the discharge flow path  38 . 
     The operations of the primary pump drive motor  12  and the secondary pump drive motor  34  are controlled by the controller  40 . The controller  40  causes the primary pump  2  and the secondary pump  22  to operate in a complementary manner such that the flow rate of the liquid sent through the discharge flow path  38  is a preset target flow rate. The controller  40  is realized by a dedicated computer or a general-purpose personal computer that stores an arithmetic element and a program that realizes a specific function when being executed by the arithmetic element. 
     The controller  40  includes an attachment detector  41  and a valve element drive controller  42 . The attachment detector  41  and the valve element drive controller  42  are the functions obtained when the arithmetic element executes a predetermined program. 
     The attachment detector  41  is configured to detect the attachment of the valve element to the valve seat in the first check valve  16  based on the pressure (P1) in the pump chamber  4  detected by the first pressure sensor  20 . Only in a case where the attachment detector  41  detects the attachment of the valve element to the valve seat in the first check valve  16 , the valve element drive controller  42  is configured to drive the valve element driver of the first check valve  16  and cause the valve element to actively detach from the valve seat and forcibly open the first check valve  16 . 
     As shown in  FIG. 2(A) , in a case where the first check valve  16  operates normally, when the primary pump  2  starts performing the intake operation, and the pressure in the pump chamber  4  becomes negative, the first check valve  16  is opened, and the liquid flows into the pump chamber  4 . The pressure in the pump chamber  4  is maintained close to an atmospheric pressure while the primary pump  2  is performing the intake operation. 
     Meanwhile, in a case where the valve element is attached to the valve seat in the first check valve  16 , and the first check valve  16  stops operating normally, even when the primary pump  2  starts performing the intake operation, and the pressure in the pump chamber  4  becomes negative, the first check valve  16  stays closed, and the pressure in the pump chamber  4  further decreases. As such, it is possible to determine whether the valve element is attached to the valve seat in the first check valve  16  by setting a value slightly lower than the atmospheric pressure as a threshold value and comparing the pressure (P1) in the pump chamber  4  with the threshold value. 
     In this inventive example, as shown in  FIG. 2(B) , in a case where the pressure (P1) in the pump chamber  4  detected by the first pressure sensor  20  becomes equal to or lower than the preset threshold value, the attachment detector  41  detects the attachment of the valve element to the valve seat in the first check valve  16 . Further, the valve element drive controller  42  is configured to actively drive the valve element to forcibly open the first check valve  16  when the attachment of the valve element to the valve seat is detected. 
     The flowchart of  FIG. 3  shows a drive control operation of the first check valve  16  realized by the attachment detector  41  and the valve element drive controller  42 . 
     The controller  40  receives the output of the first pressure sensor  20  at short time intervals (step S 1 ). The attachment detector  41  compares the output of the first pressure sensor  20  received by the controller  40  with the preset threshold value (step S 2 ). In a case where the output of the first pressure sensor  20  is equal to or lower than the threshold value, the attachment detector  41  detects the attachment of the valve element to the valve seat in the first check valve  16  (step S 4 ). The valve element drive controller  42  actively drives the valve element of the first check valve  16  to forcibly open the first check valve  16  only when the attachment detector  41  detects the attachment of the valve element to the valve seat (step S 5 ). 
     In the above operation, the “output of the first pressure sensor  20 ,” which the attachment detector  41  compares with the threshold value does not only mean one output value received by the controller  40  but may mean the average value of a plurality of output values of the first pressure sensor  20  most recently received by the controller  40 . Further, the attachment detector  41  may also detect attachment of the valve element to the valve seat only in a case where the predetermined number of output values successively received by the controller  40  are equal to or lower than the threshold value. 
     Next, one example of structure of the first check valve  16  will be described with reference to  FIGS. 3, 4 and 5 . 
     The first check valve  16  includes the T-shape valve body  43  that has a convex portion projecting upward and a drive mechanism  70  attached to the lower surface of the valve body  43 . The valve body  43  has a hollow inside, and provided with a liquid inlet port  46  through which liquid flows into the hollow from a side surface and a liquid outlet port  47  through which liquid flows out in the upper end surface. 
     A cylindrical housing  44  is inserted from the tip of the convex portion of the valve body  43 . A linear flow path through which the liquid, that has flown in from the liquid inlet port  46  of the valve body  42 , flows in the one direction toward the liquid outlet port  47  is formed inside of the housing  44 . A ring-shape gasket  49  is attached to the upper end surface of the housing  44 , and a through hole inside the gasket  49  serves as the liquid outlet port  47  through which the liquid flows out. 
     A valve seat  50 , a valve element  52 , a valve seat  54  and a valve element  56  are stored in the axial direction (the vertical direction) of the housing  44  from below in the hollow inside of the housing  44 . The valve seats  50  and  54  are cylindrical members that constitute part of the linear flow path in the housing  44 . The positions of the valve seats  50  and  54  are fixed, and the valve elements  52  and  56  are seated at the respective openings in the upper surfaces of the valve seats  50  and  54 . 
     A spacer  53  is interposed between the valve seats  50  and  54 . The spacer  53  has an inner diameter slightly larger than the outer diameter of the valve element  52 . The valve element  52  is arranged inside of the spacer  53  so as to be movable in the axial direction of the housing  44 . The valve element  56  is also arranged above the valve seat  54  so as to be movable in the axial direction of the housing  44 . Members in other shapes such as conical plugs may be used as the first and second valve elements instead of the valve elements  52  and  56 . The valve seats  50  and  54  are made of the same material, and the valve elements  52  and  56  are made of the same material. 
     The valve body  42  has a cylinder  48  at a position directly below the housing  44 . The cylinder  48  is a space for movement of an operating element  60 , in which a permanent magnet  58  is buried, in the housing  44  in the axial direction (vertical direction). The operating element  60  is stored in the cylinder  48  so as to be movable in the vertical direction. The operating element  60  holds the proximal end of a pin  62 . The pin  62  is arranged vertically so as to extend toward the valve element  52 . With the valve element  52  seated on the valve seat  50 , a clearance of about 0.4 mm, for example, is present between the pin  62  and the valve element  52 . A sheet  65  made of PTFE (polytetrafluoroethylene), for example, is provided as a bottom surface of the cylinder  48 . The operating element  60  is supported by the sheet  65 . 
     A pin  64  is vertically arranged between the valve elements  52  and  56  to extend in the axial direction of the housing  44 . The pin  64  is provided inside the valve seat  54  so as to be vertically movable. The length of the pin  64  is shorter than the clearance between the valve elements  52  and  56 . When the valve element  52  is seated on the valve seat  50 , and the valve element  56  is seated on the valve seat  54 , the clearance of about 0.3 mm, for example, is present between the pin  64  and the valve element  56 . 
     As shown in  FIG. 5 , the shape of the cross section of the pin  64  is a circle having an outer diameter substantially equal to the inner diameter of the valve seat  54  with partially missing parts. Thus, when the pin  64  moves in the vertical direction inside the valve seat  54 , the axis of the pin  64  is not inclined with respect to the vertical direction, and the inner peripheral surface of the valve seat  54  and the pin  64  are prevented from locally coming into contact with each other and wearing out. 
     Further, the pin  64  is made of the same material as the valve seat  54  (sapphire or zirconia, for example). Although the pin  64  slides on the inner peripheral surface of the valve seat  54 , significant wear of one of the pin  64  and the valve seat  54  is prevented because the pin  64  and the valve seat  54  are both made of the same material. Further, the pin  62  and the valve seat  50  are also made of the same material (sapphire or zirconia, for example), so that significant wear of one of the pin  62  and the valve seat  50  is prevented. 
     Further, as shown in  FIG. 7 , a diamond-like carbon (DLC) film may be formed on the outer peripheral surfaces of the pins  62  and  64  in order to prevent wear caused by sliding between the pin  62  and the valve seat  50  and wear caused by sliding between the pin  64  and the valve seat  54 . The DLC film may be formed on the inner peripheral surfaces of the valve seats  50  and  54 . 
     A weight  66  is provided between the gasket  49  attached to the upper end of the housing  44  and the valve element  56 . The weight  66  is biased vertically in the downward direction by an elastic member  68  made of a coil spring, for example. Thus, the valve element  56  is pressed toward the valve seat  54  at all times. 
     The drive mechanism  70  includes an iron core  72  provided directly below the sheet  65  that supports the operating element  60 , and a coil  74  arranged to be spaced apart from the side surface of the iron core  72 . When a current flows through the coil  74 , a magnetic field passing through the operating element  60  is generated, and the operating element  60  is lifted upward from the sheet  65  by 0.9 mm, for example. 
     When the operating element  60  is lifted upwardly, the pin  62  presses the valve element  52  upwardly as shown in  FIG. 6 , and the valve element  52  is lifted from the valve seat  50  by 0.5 mm. When the valve element  52  is lifted from the valve seat  50 , the pin  64  is accordingly lifted and presses the valve element  56  upward. Thus, the valve element  56  is lifted from the position of the valve element  56  being seated on the valve seat  54  by 0.2 mm. Therefore, the first check valve  16  is opened. 
     When the first check valve  16  is to be opened, the pin  62  is put in an open state by generation of a magnetic field in a direction that repels the permanent magnet  58  such that the operating element  60  moves upward by the drive mechanism  70 . The valve element  52  is lifted by the pin  62 , and the valve element  56  is lifted by the pin  64 . Therefore, the valve elements  52  and  56  are actively lifted by the pins  62  and  64 , respectively. Thus, even in a case where the valve seat  50  is attached to the valve element  52 , or the valve element  56  is attached to the valve seat  54 , the valve can be opened reliably. 
     On the contrary, when the valve is to be closed, the drive mechanism  70  does not generate a magnetic field. Thus, the operating element  60  is lowered to the sheet  65  by its own weight. When the operating element  60  is lowered, the valve element  52  is lowered by its own weight and the weight of the pin  64  to be seated on the valve seat  50 . The valve element  56  is seated on the valve seat  54  since the inside of the pump chamber  8   a  is pressurized, and the valve element  56  is pressed downward by the weight  66 . 
     The operating element  60 , the pins  62  and  64  and the drive mechanism  70  constitute a valve element driver for actively operating the valve elements  52  and  56 . 
     In the first check valve  16  described with reference to  FIGS. 3 to 7 , when an attempt is made to actively drive the valve elements  52  and  56 , the operating element  60  operates and wear of the operating element  60  itself and the pin  62  is promoted. However, the liquid sending device  1  of this inventive example causes the drive mechanism  70  to generate a magnetic field and drive the operating element  60  only in a case where the attachment of the valve element  52  to the valve seat  50  and/or the attachment of the valve element  56  to the valve seat  54  is detected. Thus, the wear of the operating element  60  and the pin  62  is suppressed to the minimum. 
     DESCRIPTION OF REFERENCE NUMERALS 
       1  Liquid Sending Device 
       2  Primary Pump 
       3 ,  23  Pump Heads 
       4 ,  24  Pump Chambers 
       6 ,  28  Pump Bodies 
       8 ,  30  Crossheads 
       10 ,  32  Plungers 
       12 ,  34  Motors 
       14 ,  36  Feed Screws 
       16 ,  26  Check Valves 
       20 , 39  Pressure Sensors 
       22  Secondary Pump 
       40  Controller 
       41  Attachment Detector 
       42  Valve Element Driver 
       43  Valve Body 
       44  Housing 
       46  Liquid Inlet Port 
       47  Liquid Outlet Port 
       48  Cylinder 
       49  Gasket 
       50 ,  54  Valve Seats 
       52 ,  56  Valve Elements 
       53  Spacer 
       58  Permanent Magnet 
       60  Operating Element 
       62 ,  64  Pins 
       66  Weight 
       68  Elastic Member 
       70  Drive Mechanism 
       72  Iron Core 
       74  Coil