JP2011001843A - Fixed volume type solenoid pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixed volume type solenoid pump, causing less change in delivery quantity characteristic even when back pressure fluctuates and the temperature of a fluid changes.SOLUTION: A back pressure valve is provided in a series on the downstream side of a delivery valve, a valve element of the delivery valve is made of a lightweight material, and a valve seat is made of an elastic body such as rubber. A valve element of the back pressure valve is made of a lightweight material, and a valve seat is made of a hard material. Thus, the back pressure is shared between the back pressure valve and the delivery valve, the high valve closing speed of the back pressure valve is attained, and leakage of the delivery valve is eliminated, whereby a back flow in the valve closing process is reduced.

Description

  The present invention relates to an in-line type electromagnetic pump, and more particularly to an electromagnetic pump capable of stably supplying a constant capacity.

  The electromagnetic pump generates intermittent magnetic force by the pulse current supplied to the electromagnetic coil, and when not excited, the electromagnetic plunger is returned to the return spring and reciprocated by such a continuous action. The piston connected to the plunger is driven to change the volume in the pump chamber, and the pump action is performed by the cooperation of a pair of check valves (suction valve and discharge valve).

  Constant volume electromagnetic pumps are used in, for example, reformed water pumps for fuel cell systems, urea water pumps for NOx reduction devices (SCRs) for internal combustion engines, DPF pumps for diesel engines, and the like. The requirement is that the change in the discharge amount is slight with respect to the back pressure on the discharge side or the fluctuation of the discharge pressure. That is, in addition to the flat PQ characteristic (discharge back pressure-discharge amount characteristic), the change in the discharge amount is slight with respect to fluctuations in the fluid temperature and the ambient temperature. The TQ characteristic (temperature-discharge amount characteristic) is flat.

  Furthermore, the continuous stability of the discharge amount, the change in the discharge amount when starting and stopping the pump for a long time, and the fluctuation of the power supply voltage (in many cases ± 10%) That is, the change in the discharge amount accompanying the above is slight. In addition to these, long-term durability and low power consumption during operation are required. For example, in the reforming water pump of the fuel cell system, each of the above requirements is within ± 3%.

  As a conventional technique, Patent Document 1 (Japanese Patent Publication No. 5-67793) is disclosed. This conventional example has a suction valve 14 and an overflow flow valve 20 provided on a movable piston 5, and the piston 7 is fluctuated by the electromagnet unit 5, pressurizing the fluid at the time of excitation, and supplying the fluid from the outlet 4. The fluid is sucked from the inlet 3 by the return spring 8 when discharged and demagnetized. Then, when stopped, the piston 7 takes the basic position of FIG. 1, and the elastic stopper 9 abuts on the outlet side end 12a, whereby the outlet 4 is closed and the outflow of fluid is prevented.

  Further, Patent Document 2 (Japanese Patent Laid-Open No. 11-218076) is disclosed as a conventional technique. This conventional example has a suction valve body 18 provided on a movable discharge plunger 11 and a discharge valve body 20 provided on a fixed side, and the discharge plunger 11 driven by a constant reciprocation of the electromagnetic plunger 10 A pumping action is performed, and fluid is sucked from the suction hole 23 and discharged from the discharge orifice 37. When the pump is stationary, the closing valve body 31 is seated on the closing valve seat 30 to close the passage.

  Further, Patent Document 3 (Japanese Patent Laid-Open No. 2007-278148) is disclosed as a conventional technique. In this conventional example, the suction valve 20 is provided on the fixed side, the movable piston 27 has the discharge valve 29, and the pump 27 is driven by the reciprocating motion of the electromagnetic plunger 41, and the fluid is discharged from the suction passage 13. And is discharged from the discharge passage 49. The electromagnetic plunger 41 has a closing valve 44 at the end opposite to the piston (downstream from the discharge valve 29), repeatedly opens and closes with the valve seat 46, and has a backflow prevention valve 51 in the discharge passage 49 downstream thereof. Yes.

Japanese Patent Publication No. 5-67793 Japanese Patent Laid-Open No. 11-218076 JP 2007-278148 A

  However, the pump used in the paragraph (0003) described above is different from a pressure electromagnetic pump in which a load such as a nozzle is provided on the discharge side, and the load back pressure is always static during the non-pressurization process of the pump. And the back pressure fluctuates frequently.

  Next, the problem will be described for each prior patent document. In Patent Document 1, the overflow valve 20 is provided in the sleeve portion 35 of the piston 7 and functions as a discharge valve. 7 has a closing valve composed of the outlet end 12a and the elastic stopper 9, but there is no check valve (check valve) downstream thereof.

  The pump in such a state is driven by PFM, but the pulse width with respect to the cycle of the pulse voltage, that is, the pulse duty is preferably 10% to 20% from the transient characteristics of the coil current, power consumption, the operation time of each check valve, etc. ing. In particular, the effect of the check valve is significant, including chattering when seated, depending on the viscosity of the fluid and the design of the check valve, but it takes several ms to settle down completely. In the pump of this form, the behavior of the overflow valve 14 is applicable, and it is difficult to satisfy the above requirements unless this drawback is solved. In particular, the influence on the PQ characteristic is great.

  Further, in the pump of this form, the space constituted by the suction valve 14, the outlet end 12a of the piston 7 and the elastic stopper 9 is hermetically closed when the operation is stopped. When the ambient temperature rises in such a state, the inside of the pump becomes a high pressure due to the thermal expansion of the internal fluid, and malfunctions and liquid leakage may occur. When the fluid is water, the same problem may occur due to freezing, and the fuel cell system is in a range of 0 to 60 ° C. and the diesel engine DPF is in the temperature range of −30 to 90 ° C., so it cannot be used.

  In Patent Document 2, since the load back pressure is received by the discharge valve seat 49, the valve closing speed of the discharge valve body 20 is fast, and particularly good TQ characteristics are easily obtained. However, the delay in closing the discharge valve main body 20 should not be completely eliminated, and it is still insufficient to satisfy the PQ characteristics other than the TQ characteristics.

  Patent Document 3 discloses an operation in which a backflow prevention valve 51 is provided to oppose back pressure. In this pump, a closing valve 44 that also serves as a stopper is provided at the upstream end of the plunger 41, and the drive pulse width applied to the coil 3 is 10 to 20% of the same period. During this period, the stop valve 44 is in a closed state. Therefore, the backflow prevention valve is in a stable closed state at the start of the piston drawing process, and the closing time of the backflow prevention valve is not a problem, but the volumetric efficiency of transferring to the downstream portion of the discharge valve (29) is important. There is no change in performance, and the sealing performance of the discharge valve 29 and the backflow prevention valve 51 is important.

  The discharge valve 29 is in the piston 27 and cannot satisfy the above requirements due to space and other constraints. As an alternative means, a small lip is formed on the valve seat 46 of the backflow prevention valve by using an elastomer such as rubber to increase the surface pressure when contacting the valve body. As described above, in this embodiment, the valve seat 46 is deformed by the load back pressure, causing a problem in the PQ characteristic. If the rigid valve seat 46 and the valve body are used, the sealing performance in the drawing-in process becomes insufficient and the TQ characteristic is hindered.

  Therefore, an object of the present invention is to provide a constant displacement electromagnetic pump with little change in discharge amount even when there is a change in discharge back pressure or a change in fluid temperature.

  A constant capacity electromagnetic pump according to the present invention includes a cylinder provided between a suction passage provided in a suction joint and a discharge passage provided in a discharge joint, a piston reciprocating in the cylinder, and the piston A discharge valve provided on the discharge joint downstream of the intake valve, an electromagnetic plunger fixed to one end of the piston, and a coil for reciprocating the electromagnetic plunger. An electromagnetic pump that performs a pump action by changing a volume of a pump chamber constituted by the suction valve, the discharge valve, the cylinder, and the piston, and is disposed downstream of the discharge valve in the discharge passage in the discharge joint. The discharge valve is provided with a back pressure valve, the valve body is made of plastic or ceramic, the valve seat is made of an elastic body such as rubber, and the back pressure valve , A plastic or ceramic that valve body and the valve seat, characterized in that to make a hard material such as metal (Claim 1).

  Thereby, the characteristics of the change in the discharge amount with respect to the fluctuation of the load back pressure, that is, the PQ characteristic, and the characteristics of the change in the discharge amount with respect to the change in the fluid temperature and the ambient temperature, that is, the improvement of the TQ characteristic are improved. Figured. The behavior of the check valves of the suction and discharge valves of the fixed displacement electromagnetic pump has a great influence on the PQ characteristics and the TQ characteristics, and it cannot be operated in synchronism with the reciprocating movement of the piston. Of course, it is required to increase the operating speed.

  Regardless of how accurate the piston stroke is, if the check valve operating speed, particularly the valve closing speed, is slow, the change characteristic of the discharge amount is large and the purpose cannot be satisfied.

The piston stroke is restricted by the elastic stopper at the upper part and restricted by the shut-off valve at the lower part, and it should be constant, and the discharge amount should be obtained by multiplying the piston pressure receiving area by the stroke amount. There is a leak from the clearance between the check valve and the reverse flow, which is the leak during the time required to open and close each check valve, and this depends on the value of the load back pressure. This is a factor that the PQ characteristic does not become flat even if it is operated.

  The check valve closing speed has the greatest effect, and the check valve closing speed is expressed by the behavior of the spring / mass system, excluding the viscous damper due to the viscosity of the fluid. , The parameter of the spring constant of the valve spring. It is effective to increase the valve closing speed by reducing the weight of the valve body with a plastic material and increasing the spring constant of the valve spring.

  For this reason, in the discharge valve, the valve body is made of a light material, and is made of an elastic body such as rubber to prevent leakage from the valve seat, increasing the contact surface pressure and increasing the valve closing speed. In order to prevent leakage and prevent backflow, the back pressure valve temporarily receives the back pressure, the valve body is made of a light material, the valve seat is made of a hard material such as metal, and the back pressure is received by the back pressure valve. This reduces the burden on the back pressure of the discharge valve and, as described above, enables the valve closing speed to be increased, so that even if there is a change in the discharge back pressure or a change in the fluid temperature, the change in the discharge amount can be reduced. A small constant displacement electromagnetic pump can be provided.

  The discharge valve is preferably a poppet valve and the back pressure valve is preferably a ball valve (Claim 2), and the valve seat of the discharge valve is preferably provided with a lip portion (Claim 3). Thereby, a contact surface pressure can be raised.

  It is preferable to provide an escape passage that eliminates a closed space generated by the contact of the electromagnetic plunger with a stopper formed of an elastic body for determining the top dead center position of the piston. . As a result, the pressure fluctuation in the closed space caused by the electromagnetic plunger coming into contact with the stopper made of an elastic body is released into the electromagnetic plunger working space through the escape passage, and a stable piston stroke is given.

  The piston that slides in the cylinder has an outer diameter portion with a predetermined outer diameter, and a small diameter portion is formed before and after a portion where a radial through hole is formed, and the small diameter portion and the predetermined outer diameter It is preferable that the part is connected at an obtuse angle. As a result, the small diameter portion and the predetermined outer diameter portion of the portion in the radial direction are connected at an obtuse angle, thus preventing galling of the cylinder.

  Preferably, a filter and a check valve are disposed downstream of the suction passage of the suction joint. This prevents the fluid in the pump chamber mainly composed of the electromagnetic plunger movable material during the suction process from flowing out of the suction passage.

  As described above, according to the first aspect of the present invention, since the back pressure valve on the downstream side of the discharge valve is provided, the load back pressure is divided between the back pressure valve and the discharge valve and the valve body of the back pressure valve is provided. It is light, and the valve seat is made of a hard material, so that the spring constant of the spring is made larger than that of the spring of the discharge valve, the valve body of the discharge valve is light, and the valve seat is made of an elastic body such as rubber. The valve closing speed can be increased from the valve body, and the contact surface pressure can be increased from the valve seat of the elastic body to prevent back flow when the valve is closed.

It is a longitudinal cross-sectional view concerning the Example of this invention. It is sectional drawing of the central part vicinity same as the above. It is a PQ special line figure of the present invention. It is a TQ special line figure of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail.

  1 and 2, a constant volume electromagnetic pump 1 is shown, and a coil 3 to which a pulse current is applied is provided in a case made of a magnetic material such as iron. The coil 3 is connected to a resin bobbin 4 with an electric wire. A guide pipe 6 made of a nonmagnetic metal is inserted into a through hole formed through the center of the bobbin 4 and is connected to the stator upper 8 made of a magnetic material such as iron. And the stator lower 9 are respectively inserted from above and below. Reference numeral 10 denotes an O-ring for airtightness between the guide pipe 6, the stator upper 8 and the stator lower 9. Reference numeral 11 denotes an O-ring that is airtight with the mounting plate 12.

  The stator lower 9 is formed with a hole 13 in the central axial direction and has a screw portion 14 in the middle of the axial direction. A suction joint 17 is inserted into the hole 13 of the stator lower 9, a screw portion 18 is screwed onto the screw portion 14, and airtight is achieved by an O-ring 19. Reference numeral 20 denotes a lock nut for fixing the suction joint 17.

  The suction joint 17 has a suction passage 16 formed in the axial direction thereof, and a strainer 21 is provided upstream of the suction passage 16 and a check valve 22 is provided downstream thereof. This check valve valve 22 is composed of a valve body 23, a valve seat 24, and a spring 25, and is housed in a cylinder that becomes a closing valve seat 27 described below.

  The shut-off valve seat 27 is press-fitted and attached to the suction passage 16 of the suction joint 17 and has a hole 28 in the center, and a shut-off valve 48 described below is seated. When seated, the hole 28 is closed. It is done. The closing valve seat 27 can change its position (vertical direction in the figure) by changing the screwing position of the stator lower 9 of the suction joint 17.

  The cylinder 30 is a cylindrical member, which is manufactured from polyetherketone (PEEK) or the like with little ion elution, and is inserted into the hole 31 of the stator upper 8 made of the magnetic material. The cylinder 30 and the stator upper 8 can be inserted and fixed with O-rings 33 and 33 without being airtight and without causing distortion when the piston is inserted into the cylinder 30.

  The piston 35 is made of a non-magnetic metal, for example, stainless steel, and is a cylindrical body having a through hole 36 in the central axis direction. The piston 35 is slidably inserted into the cylinder 30 and fixed to the upstream end thereof as described below. It is driven by the reciprocating motion of the electromagnetic plunger 43. A suction valve 37 described below is fixed to the downstream end of the piston 35.

  Further, in the middle of the piston 35, a radial radial hole 36a intersecting with the through hole 36 is formed, and a small diameter portion 42 having a smaller diameter than a predetermined outer diameter portion of another portion is formed around the radial hole 36a. The small diameter portion 42 and the predetermined outer diameter portion are connected at an obtuse angle (160 degrees to 165 degrees). Thereby, it becomes favorable to improve the galling of the cylinder by stainless steel.

  Until now, when the through-hole 36 composing the fluid passage and the radial hole 36a communicating with each other are formed, bulging due to processing occurs, so that the diameter is smaller than that part, and the small-diameter portion There is a step between the part of the diameter. When such a piston is hard plated and then centerless polished, nodules are generated due to the concentration of plating current on the level difference during plating, and there is a level difference in the return due to centerless polishing. The amount of discharge may be reduced due to damage. This return was removed using an oil grindstone or the like, but the work was cumbersome and the removal was insufficient, impeding durability. In order to solve this, as described above, the small-diameter portion 42 is connected to another predetermined portion at an obtuse angle of 160 to 165 degrees.

  The suction valve 37 is a conical valve and is composed of a valve body 38 and a valve seat 39. The valve body 38 has a bottom surface 38a facing the pump chamber side, and a rod 38b provided on the top, and a spring receiving member is provided on the rod 38b. 38c is attached. The valve body 38 is seated on the valve seat 39 by a spring 40 interposed between the spring receiver 38 c and the valve seat 39.

  The valve seat 39 has a valve hole 41 in the center, is fixed to the downstream end of the piston 35, and has a conical surface (valve hole 41) that is wide on the pump chamber side and narrow on the counter pump chamber side. When the valve body 38 is seated on the valve seat 39, the bottom surface 38a thereof is flush with the pump chamber side of the valve seat 39. Since the valve seat 39 is press-fitted, the end of the front piston 35 swells, but has a smaller diameter in advance than other parts, absorbs the swell, and prevents squeezing of the cylinder 30 during reciprocation.

  The electromagnetic plunger 43 is made of a magnetic material such as iron, and the lower end of the piston 35 is fitted into the fitting hole 46 having an opening at the upper end, and is integrated with the piston 35. And this electromagnetic plunger 43 is reciprocated in the drive space 44 of the electromagnetic plunger enclosed by the guide pipe 6 between the said stator upper 8 and the said stator lower 9, The movement range (movement stroke) is as follows. The stroke amount is restricted by the elastic stopper 50 described below at the upper end and the closing valve seat 27 at the lower end.

  A return spring 45 is elastically mounted between the upper end of the electromagnetic plunger 43 and the lower end of the cylinder 30. The return spring 45 is pressed toward the non-cylinder side and is provided at the lower end of the electromagnetic plunger 43 when no current is applied. The closed valve 48 is seated on the closing valve seat 27 and closes the valve hole 28.

  The elastic body stopper 50 is made of an elastic material such as rubber, and is attached to the lower end of the stator upper 8 and the cylinder 30 via the retainer 49 of the return spring 45. The elastic body stopper 50 comes into contact with the upper end of the electromagnetic plunger 43. By this contact, the passage from the electromagnetic plunger 43 to the suction valve 37 becomes a closed space. In order to influence, a relief passage 52 is formed in the radial direction at the upper end of the electromagnetic plunger 43.

  The pump chamber 53 includes the stator upper 8, the cylinder 30, the valve body 38 of the intake valve 37, the valve seat 39, the piston 35, the valve body 59 of the discharge valve 57 and the valve seat 60 described below, A pumping action is performed by the suction valve 37 and the discharge valve 57 by the volume change of the pump chamber 35.

  The discharge joint 55 is a cylindrical body, and is attached to the upper end of the stator upper 8 by crimping with an O-ring 56 interposed therebetween. A discharge passage 54 is formed in the axial direction, and a discharge valve 57 and a back pressure valve 58 are provided in series from the upstream side of the discharge passage 54.

  The discharge valve 57 includes a valve body 59, a valve seat 60, and a spring 61, and is provided in a back pressure valve seat 66 described below. The valve body 59 has a poppet shape and is made of plastic or ceramic lightly. The valve seat 60 has a hole 62 in the center and is made of an elastic material such as rubber, and has a lip 63 to increase the contact surface pressure.

  The back pressure valve 58 includes a valve body 65, a valve seat 66, and a spring 67, and is provided in the discharge passage 54 as described above. The valve body 65 is spherical and is lightly made of plastic or ceramic. The valve seat 66 is made of a hard material such as metal, and measures are taken so as not to be deformed even when a load back pressure is applied. 68 is an O-ring.

  As described above, the back pressure valve 58 is connected in series with the discharge valve 57 to prevent the fluid from flowing backward into the pump due to the load back pressure and reducing the discharge amount. As a result of verification using an experimental method, it is possible to obtain a PQ characteristic of about 5% up to a load back pressure of about 0 to 40 kPa when only a discharge valve is used without a back pressure valve, and the function is also achieved. it can.

However, in the back pressure region beyond that, the discharge amount is greatly reduced, and in some cases, the operation is unstable or the operation is stopped. This phenomenon is caused by the fact that the discharge valve has not yet closed at the start of the piston suction process, so that the fluid instantaneously flows back to the downstream portion (pump chamber) of the intake valve, and the upstream and downstream sides of the intake valve. Since the fluid pressures are equal, the suction valve is closed by the force of the valve spring.
This pre-improvement characteristic is indicated by a dotted line in the PQ characteristic diagram (discharge back pressure-discharge amount characteristic) of FIG.

  As can be seen from this, in the constant displacement electromagnetic pump, the back pressure valve 58 is indispensable, and the valve closing speed must be as fast as possible. In addition, since the back pressure valve 58 receives a high load back pressure, the valve body 65 and the valve seat 66 are made of a hard material such as metal so as not to be deformed by the load back pressure and are manufactured firmly. It is also necessary. On the other hand, since the valve seat 60 is made of an elastic body and the contact surface pressure of the discharge valve 57 is increased, the backflow in the valve closing process is reduced. This improved characteristic is shown by a solid line in the PT characteristic diagram of FIG.

  Also, the temperature rises from the temperature of the fluid and the surrounding temperature, so that the discharge volume decreases due to the decrease in the viscosity of the valve seat, or the valve seat of the discharge valve is made of an elastic body to increase the contact surface pressure. In addition, since the back pressure valve is provided, back flow is prevented and the TQ characteristic diagram (temperature-discharge amount characteristic) is improved as shown in FIG.

  In the above configuration, when a pulse current of, for example, 5 Hz is passed through the electromagnetic coil 3, the coil 3 is excited when it is turned on, the stator upper 8, the stator lower 9, and the electromagnetic plunger 43 are magnetized, and the electromagnetic plunger 43 is moved against the return spring 45. It moves upward, abuts against the cushion 50, and the upward movement is stopped. The movement of the electromagnetic plunger 43 is transmitted to the piston 35, the piston 35 is driven upward, and the pump chamber 53 is reduced from the state shown in FIG. 1 to a dead space. As a result, the internal pressure of the pump chamber 35 rises, and from the pressure difference, the discharge valve 57 is opened and the fluid flows out into the discharge passage 54 and is discharged to the outside.

  When the pulse current is off, the coil 3 is de-energized, the stator upper 8, the stator lower 9, and the electromagnetic plunger 43 are demagnetized. The electromagnetic plunger 43 is moved downward by the return spring 45, and the closing valve 48 contacts the valve seat 27. Stopped. At that time, the volume in the pump chamber 53 increases. As a result, the pressure in the pump chamber 53 decreases, the suction valve 37 is opened from the pressure difference, and the fluid is sucked from the plunger drive space 44. Of course, the pressure in the plunger drive space 44 also decreases, so that fluid is sucked from the outside through the suction passage 16.

  When the pulse current is turned on again, the electromagnetic plunger 43 and the piston 35 move upward, and the pressurizing action is started. Such an action is repeated, a pump action is performed, and the constant volume is discharged because the pump is moved up and down with a predetermined stroke. Therefore, for example, at 5 Hz, a discharge amount per minute obtained by multiplying the bottom area of the pump chamber 53 by the stroke size and 5 times is discharged. And the discharge amount can be changed linearly by changing the frequency of the pulse current to the coil 3.

DESCRIPTION OF SYMBOLS 1 Electromagnetic pump 2 Coil 8 Stator upper 9 Stator lower 16 Suction passage 17 Suction joint 21 Strainer 22 Check valve 27 Closure valve seat 30 Cylinder 37 Suction valve 43 Electromagnetic plunger 44 Electromagnetic plunger drive space 45 Return spring 48 Closure valve 50 Elastic body stopper 52 Relief passage 53 Pump chamber 54 Discharge passage 55 Discharge joint 57 Discharge valve 58 Back pressure valve

Claims (6)

  A cylinder provided between a suction passage provided in the suction joint and a discharge passage provided in the discharge joint, a piston reciprocating in the cylinder, a suction valve provided in the piston, and the suction valve A discharge valve provided on the discharge joint, an electromagnetic plunger fixed to one end of the piston, and a coil for reciprocating the electromagnetic plunger, the suction valve, the discharge valve, and the In an electromagnetic pump that performs pumping operation by changing the volume of a pump chamber composed of a cylinder and the piston, a back pressure valve is provided downstream of the discharge valve in the discharge passage in the discharge joint, and the discharge valve The valve body is made of plastic or ceramic, the valve seat is made of an elastic body such as rubber, and the valve body is made of plastic or ceramic in the back pressure valve. Accordingly, the constant-displacement electromagnetic pump, characterized in that to make the valve seat of a hard material such as a metal.   The constant displacement electromagnetic pump according to claim 1, wherein the discharge valve is a poppet valve, and the back pressure valve is a ball valve.   The constant displacement electromagnetic pump according to claim 1 or 2, wherein a lip portion is provided in a valve seat of the discharge valve.   The electromagnetic plunger is provided with a relief passage that eliminates a closed space that is generated when the electromagnetic plunger comes into contact with a stopper that is made of an elastic body for determining the top dead center position of the piston. 1. The constant displacement electromagnetic pump according to 1. The piston that slides in the cylinder has an outer diameter portion having a predetermined outer diameter, and the axial front and rear of the portion where the radial hole is formed in the radial direction is formed as a small diameter portion, and the small diameter portion and the predetermined diameter The constant displacement electromagnetic pump according to claim 1, wherein the outer diameter portion of each is connected at an obtuse angle.
A constant displacement electromagnetic pump characterized in that a filter and a check valve are arranged downstream of the suction passage of the suction joint.

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