US20080213107A1

US20080213107A1 - Reciprocating pump

Info

Publication number: US20080213107A1
Application number: US12/011,317
Authority: US
Inventors: Noboru Yagi
Original assignee: Yagi Seisakusho YK
Current assignee: Yagi Seisakusho YK
Priority date: 2005-08-03
Filing date: 2008-01-25
Publication date: 2008-09-04
Also published as: WO2007015429A1; JPWO2007015429A1; CN101238289A

Abstract

The present invention is aimed to provide a pump which can not only obtain high discharging pressure and large capacity but obtain a substantially non-pulsating flow with a miniaturized configuration and even if the pump is operated with low power. To achieve the object, a pump of the present invention is characterized in including a pump chamber (17), an intake passage (34) for taking liquid into the pump chamber via an intake valve (V1) being opened when liquid is taken into the pump chamber, a discharge passage (43) for discharging liquid to an outside of the pump chamber via a discharge valve (V2) being opened when liquid is discharged from the pump chamber, a cylinder (11) in communication with the pump chamber, a plunger (12) slidably provided within the cylinder and biased toward a bottom dead center side by a spring (16), and a moving element (P) being brought in contact with the plunger and stroking the plunger upward, wherein the moving element moves upward and downward via a motion conversion means (20 a , 20 b , 20 c) for transforming rotary motion of a rotary shaft (21) of an electric motor (22) into upward and downward motion, the plunger in descending motion and moving element are spaced apart.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of PCT international application No. PCT/JP2006/314980 filed on Jul. 28, 2006, incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a reciprocating pump (hereinafter, referred to as “pump”). More particularly, the present invention relates to a pump including a cylinder which is in communication with a pump chamber, a plunger which is slidably provided within the cylinder and is biased toward a bottom dead center side by a spring, and a moving element which is brought in contact with the plunger and strokes the plunger upward. The moving element moves upward and downward via a motion conversion means for transforming rotary motion of a rotary shaft of an electric motor into a vertical motion, and the plunger in descending motion and the moving element are spaced apart. The high speed microvibration of liquid discharged to the outside of the pump chamber thereby becomes substantially a non-pulsating flow.

BACKGROUND

A pump for providing a crank mechanism which is improved in its efficiency by decreasing lateral pressure generated between a sliding element and a sliding portion in the case the sliding element is actuated by a crank or vice versa is disclosed, for example, in Japanese Unexamined Patent Publication No. 303254/1996.
The crank mechanism disclosed in Japanese Unexamined Patent Publication No. 303254/1996 includes a sliding element which axially supports one side of a coupling rod in a swingable manner and is slidably provided at a sliding portion, a parallel passage including two passages which are provided in parallel at an end of the sliding portion on the side of the coupling rod and are spaced apart from each other, a wheel which is axially supported at the other end of the coupling rod and is rotatably positioned within the parallel passage, a connecting rod which is swingably provided at the other end of the coupling rod, and a crank pin of a crankshaft which is rotatably provided at the connecting rod.
A pump for providing a glass electromagnetic-driven pump which is suitable for transporting or circulating a corrosive gas or reactive gas without leakage and has highly uniform gas flow rate is disclosed in Japanese Unexamined Patent Publication No. 106463/2002.
The pump disclosed in Japanese Unexamined Patent Publication No. 106463/2002 includes a glass cylinder having an inlet or outlet at one end and a check valve mechanism, a glass plunger which is provided in the cylinder and has a ventilation hole at its center and which is slidable within the glass cylinder, a glass communicating member which is closely integrated with an inner wall of the glass plunger and which respectively forms an opening at the outlet side or inlet side and a sealing portion at the opposite side or which forms sealing portions including a ventilation hole at both outlet and inlet sides, a glass-covered magnetic driving member which is connected to an end of the glass communicating member and seals a rod magnetic body therein, a glass coupling tube which surrounds the periphery of the glass-covered magnetic driving member at a predetermined interval and is connected with the glass cylinder, and one or a plurality of electromagnetic driving coils which are provided to surround the glass coupling tube in order to drive the glass-covered magnetic driving member located within the glass coupling tube.
Japanese Unexamined Patent Publication No. 64273/1990 discloses an eccentric cam used as a cam for a plunger pump which uses a stepping motor as a drive source.
In the case of a conventional diaphragm pump and plunger pump, the flow of discharged liquid is not a complete non-pulsating flow. For example, in the case of a pump disclosed in Japanese Unexamined Patent Publication No. 232616/2004, in order to operate the pump with non-pulsating flow at all times by automatically compensating pulsating flows changing in accordance with operating conditions, the decrease in discharge quantity at an early stage of discharging period of a diaphragm pump is prevented by reducing the volume of a pump chamber by driving a plunger in the discharge direction right before that period. The reduced volume of the pump chamber is made to be larger than the decreased discharge quantity, and the quantity of the operational flow corresponding to the difference is discharged from a discharging mechanism. A pulsating sensor is provided at a conduit at the discharging side, and a controller detects a pulsating flow based on a signal from the sensor. The controller adjusts the discharge quantity of the discharging mechanism in order to eliminate the pulsating flow.
In the case of a pump disclosed in Japanese Unexamined Patent Publication No. 108188/2004, discharge quantity is decreased at an early stage of a discharging period of a diaphragm pump which constitutes a pump. The volume of a pump chamber is reduced in such a manner that the reduced discharge volume is slightly larger than the decreased quantity by controlling a plunger of the diaphragm pump in a compensating period which is prior to a discharge period and is between an intake period and discharge period. A sub chamber for increasing the volume of the pump chamber is provided during the compensating period, and compensating quantity which is equal to the decreased discharge quantity is obtained by correcting the decreased volume of the pump chamber in accordance with increased volume of the sub chamber. Operating condition changes are thus addressed by the increased volume of the sub chamber to be adjustable.

SUMMARY

In the case of using the cam mechanism disclosed in Japanese Unexamined Patent Publication No. 64273/1990, when a plunger and a moving element of a crank are in contact at all times and the tension of a spring for biasing the plunger toward a bottom dead center is strong, a side wall of the plunger is subjected to wear greatly in accordance with the increase number of motor rotations and the pump life is decreased. Furthermore, since the response of a check valve cannot be rapidly obtained, a valve located at an intake side and a valve located at a discharge side are subjected to open simultaneously. Therefore, there has been a problem that the discharge quantity is decreased.
There are conventional diaphragm pumps and plunger pumps which artificially transform (rectify) a pulsating flow into a non-pulsating flow by providing such as a plurality of pumps or a sub chamber. However, a pump which can obtain a substantially non-pulsating flow has not been proposed. Furthermore, in a gas concentration measurement device which uses absorbing solution, fluctuation is likely to be generated in a measurement value in the case a pulsating flow is present in the transported absorbing solution. In order to prevent this, the response of the measurement indication is made to delay. A pump which is capable of obtaining a substantially non-pulsating flow is desired in order to achieve a measurement device with excellent response property.
Such conventional problems arise due to the facts that a plunger and a moving element of a crank are in contact at all times, the plunger and restoration force of a spring are not optimized, and the response of the intake valve/discharge valve and the number of motor rotations are not optimized. An object of the present invention is to provide a pump which is not only capable of obtaining high discharging pressure and large capacity but also obtaining a substantially non-pulsating flow with a miniaturized configuration and even if the pump is operated with low power.
A pump according to Embodiment 1 of the present invention is characterized in including a pump chamber, an intake passage for taking liquid into the pump chamber via an intake valve being opened when liquid is taken into the pump chamber, a discharge passage for discharging liquid to an outside of the pump chamber via a discharge valve being opened when liquid is discharged from the pump chamber, a cylinder in communication with the pump chamber, a plunger slidably provided within the cylinder and biased toward a bottom dead center side by a spring, and a moving element being brought in contact with the plunger and stroking the plunger upward, wherein the moving element moves upward and downward via a motion conversion means for transforming rotary motion of a rotary shaft of an electric motor into upward and downward motion, the plunger in descending motion and moving element are spaced apart.
It is advantageous that a non-pulsating flow can be obtained when the discharge passage is connected to an elastic resin tube.
The motion conversion means and moving element may be an eccentric cam being coupled with the rotary shaft of the electric motor.
The motion conversion means may include a crank arm of which an end is coupled with the rotary shaft of the electric motor and a connecting rod of which an end is swingably attached to the other end of the crank arm via a crank pin, wherein the moving element is swingably attached to the other end of the connecting rod and is guided to a guide member extending to a vertical direction.
It is preferable when the intake valve and discharge valve are check valves includes a lower passage and upper passage which are in communication with each other and through which liquid flows, a valve seat provided at a connecting portion of the lower passage and upper passage, a valve plug provided within the upper passage, and a movement restricting means for restricting moving distance of the valve plug, wherein the valve plug comprises a body supportably provided on the valve seat and an adjusting means for adjusting opening/closing response of the check valves which is provided at a lower side of the body.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view showing a pump of the present invention.

FIG. 2 is an explanatory view showing an example of a buffer tank applied to the pump of FIG. 1.

FIG. 3 is a graph showing a pattern of motions of the pump according to Embodiment.

FIG. 4 is a graph showing a relation between the number of motor rotations of the pump of FIG. 1 and discharge quantity.

FIG. 5( a) is a sectional explanatory view showing one example of a check valve applied to the pump of FIG. 1 and FIG. 5( b) is a sectional explanatory view showing an arrangement of the valve plug.

FIG. 6 is a sectional explanatory view showing a stator of the valve of FIG. 5.

FIG. 7 is an explanatory view showing a pump of another embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, a pump according to the present application is explained in detail by referring to the accompanying drawings. The following description of certain Embodiments is presented to illustrate the present pump and to assist one of ordinary skill in making and using the same. The description of certain Embodiments of the pump is not intended in any way to otherwise limit the scope of the invention.
FIG. 1 is an explanatory view showing a pump of the present invention, FIG. 2 is an explanatory view showing an example of a buffer tank applied to the pump of FIG. 1, FIG. 3 is a graph showing a pattern of driving methods of the pump according to the present invention, FIG. 4 is a graph showing a relation between the number of motor rotations of the pump of FIG. 1 and discharge quantity, FIG. 5( a) is a sectional explanatory view showing one example of a check valve applied to the pump of FIG. 1, FIG. 5( b) is a sectional explanatory view showing an arrangement of the valve plug and FIG. 6 is a sectional explanatory view showing a stator of the valve of FIG. 5.

EMBODIMENT 1

By referring to FIG. 1, a pump 1 according to the present Embodiment includes a pump chamber 17, an intake passage 34 extending to a vertical direction which takes liquid into the pump chamber 17 via an intake valve V1 being opened when liquid is taken into the pump chamber 1-7, a discharge passage 43 extending to the vertical direction which discharges liquid to the outside of the pump chamber 17 via a discharge valve V2 being opened when liquid is discharged from the pump chamber 17, a cylinder 11 which is in communication with the pump chamber 17, a plunger 12 which is slidably provided within the cylinder 11 and is biased toward a bottom dead center side by means of a spring 16, and a moving element P which is brought in contact with the plunger 12 and strokes the plunger 12 upward. The moving element P moves upward and downward via a motion conversion means for transforming rotary motion of a rotary shaft 21 of an electric motor 22 into upward and downward motion, and the plunger 12 in descending motion and the moving element P are spaced apart. Since the pump 1 of the present invention performs high speed operation, a liquid flow with high speed vibration is generated outside the pump chamber 17. The liquid flow with high speed vibration becomes a non-pulsating flow (smoothed) by a resin tube which is provided at a piping system connected to the pump 1.
A buffer tank 50 may be provided between an outlet of the discharge valve V2 and the discharge passage 43. By such arrangement (see FIG. 2), a pulsating flow of liquid discharged by the pump 1 is smoothed.
As for the motion conversion means, the means shown in FIG. 1 may be employed. The motion conversion means shown in FIG. 1 includes a crank arm 20 a coupled to the rotary shaft 21 of the motor 22, a connecting rod 20 of which one end is swingably attached to the crank arm 20 a via a crank pin 20 b, and the moving element P of the crank sliding within a cylindrical sleeve S which is swingably attached to the other end of the connecting rod 20 c. However, the motion conversion means of the present invention is not limited to such arrangement. For example, a cam which is eccentrically coupled to the rotary shaft 21 of the motor 22 and other corrections, changes or modifications which are obvious to a person skilled in the art are included in the present invention.
In the following, an operating method of the pump 1 of the present invention is explained with a pattern (see FIG. 4). In the figure, reference numeral W2 is a pattern diagram showing a relation between time and a process flow of the plunger 12, and W1 is a pattern diagram showing a relation between time and a process flow of the moving element P of the crank.
The motor 22 is started by turning a power source of the pump 1 in halting state. The moving element P of the crank is moved upward during a first period T1 between when the moving element P of the crank is spaced apart from the plunger 12 and before the moving element is brought into contact with the plunger 12 (step (a)).
During a second period T2 which is after the first period T1 and before the plunger 12 reaches an top dead center DC2, the moving element P of the crank is brought into contact with the plunger by stroking the same against the bias force of the spring 16 and is moved upward. The intake valve V1 is thus closed and the discharge valve V2 is opened to discharge the liquid in the pump chamber 17 from the discharge valve V2 (step (b)).
During a third period T3 which is after the second period T2 and before the moving element is brought into contact with the plunger 12 after descending to the bottom dead center and moving upward again while the plunger 12 is in a resting state by reaching the bottom dead center DC1 after descending from the top dead center DC2 with slightly delaying the movement of moving element (shown by a dashed line W2 of FIG. 3), the intake valve is opened and the discharge valve is closed so that liquid flows into the pump chamber (step (c)).
Thus, the plunger 12 is allowed for some delaying motion by setting the resting period at the position DC1. The excess force applied to the cylinder 11 is therefore released.
After the third period T3, step (b) and step (c) are repeatedly performed until the power source of the pump 1 is turned off (step (d)).
The upward and downward motion obtained by the operation method of the present Embodiment is performed for 10 to 30 times/second which is high speed as a pump for liquid. The motion appears to be the continuation of microvibration by seen with human eyes. Furthermore, the pulsating flow is absorbed by such as a flexible tube to be connected such that the pulsating flow becomes substantially a non-pulsating flow.
The ratio of the third period T3 to the second period T2 (T3/T2) is preferably in a range of 1<(T3/T2)<1.2 in order to maximize the discharge force of the pump. It is advantageous that the stress applied to the cylinder 11 by the plunger 12 is released when (T3/T2) is 1.
Moreover, the response of the intake valve and discharge valve is optimized when a check valve shown in Embodiment 2 described in the following is employed for the pump 1 of the present Embodiment.
The pump 1 of the present Embodiment can also be operated in the following manner;
The motor 22 is started by turning on the power source of the pump 1 in a halting state. The moving element P of the crank is moved upward during the first period T1 between when the moving element P of the crank is spaced apart from the plunger 12 and before the moving element is brought into contact with the plunger 12 (step (a1)).
During a second period T2 which is after the first period T1 and before the plunger 12 reaches the top dead center DC2, the moving element P of the crank is brought into contact with the plunger by hitting the same against the bias force of the spring 16 and is moved upward. The intake valve V1 is thus closed and the discharge valve V2 is opened to compress the gas within the pump chamber 17 and discharge the compressed gas from the discharge valve V2 (step (b1)).
During the third period T3 which is after the second period T2 and before the moving element is brought into contact with the plunger 12 after descending to the bottom dead center DC1 and moving upward again while the plunger 12 descends from the top dead center DC2 with slightly delaying the movement of moving element and before reaching the bottom dead center DC1, the intake valve V1 is opened and the discharge valve V2 is closed so that liquid flows into the pump chamber (step (c1)).
After the third period T3, step (b1) and step (c1) are repeatedly performed until the power source of the pump 1 is turned off (step (d1)). The period T1 allows time for the plunger which descends by slightly delaying with respect to the crank during the period T3 to release the force.
The ratio of the third period T3 to the second period T2 is a value approximate to 1.2.
The response of the intake valve and discharge valve is optimized when a check valve shown in Embodiment 2 described in the following is employed for the pump of the present Embodiment.
According to the operation method of the pump of the present Embodiment, the flow of liquid discharged to the outside of the pump chamber 17 becomes substantially a non-pulsating flow by means of a flexible tube or the like.

EMBODIMENT 2

By referring to FIGS. 5( a), 5(b) and FIG. 1, the check valve V1 suitably used for the pump of the present invention includes a lower passage 34 and upper passage 33 extending to the vertical direction relative to a horizontal surface and which are in communication with each other and through which liquid flows, a valve seat 35 provided at a connecting portion of the lower passage 34 and upper passage 33, a valve plug 36 provided on the valve seat 35 and within the upper passage 33, and a movement restricting means 37 for restricting the moving distance of the valve plug 36.
The valve plug 36 includes a substantially spherical body 36 a supportably provided on the valve seat 35, a spherical body 36 b provided at a lower side of the body 36 a, and an elongate rod body 36 c serving as a coupling portion provided between the body 36 a and spherical body 36 b. The spherical body 36 b and rod body 36 c serve as an adjusting means for adjusting opening/closing response of the check valve V1.
The spherical body 36 b and rod body 36 c give buoyancy to the body 36 a and receive the liquid flow so that high speed motion (10 to 30 times/second) of the pump as well as secure opening/closing operations are achieved. As for the spherical body 36 b, a spherical body formed from glass provided at the lower side of the body 36 a may be employed, however, it is not limited to a spherical body formed from glass. In addition to a glass spherical body, bodies which are suitable for receiving pressure in a form of such as a reverse mushroom body formed from glass or a cowl body formed from glass and are obvious to a person skilled in the art are all included in the present invention. Moreover, the body 36 a, spherical body 36 b and rod body 36 c are not limited to solid bodies of glass, but a weight formed from one or more of metals are preferably embedded depending on the specific gravity of liquid. Furthermore, a hollow body may be used depending on the specific gravity of liquid.
As shown in the figure, the rod body 36 c positions the body 36 a at a center part of the valve seat 35 and prevents rough movement thereof so that smooth and high speed opening/closing operations can be achieved. The shape of the rod body 36 c is not limited to a columnar shape. For example, a prismatic shape, conical shape, pyramid shape, a shape obtained by combining cones, and a shape obtained by combining pyramids which are obvious corrections, changes or modifications to a person skilled in the art are all included in the present invention.
Although it depends on the size of the plunger 12, a free end of the body 36 a and a free end of a stator 37 a are preferably spaced apart for approximately 2 mm when the diameter of the plunger 12 is approximately 12.5 mm and the diameter of the free end of the body 36 a of the check valve is approximately 12 mm under a state where the body 36 a contacts with the valve seat 35. However, it is not limited to such value.
In the present Embodiment, the valve seat 35 has a substantially conical shape. However, the valve seat 35 is not limited to a reverse conical shape and may be an annular shape, for example.
In the present Embodiment, the body 36 a has a substantially semispherical shape, and the free end of the body 36 a is a substantially circular flat surface. A passage for liquid is secured, since a clearance CL2 is provided between the spherical body 36 b/rod body 36 c and the lower passage 34 (although it depends on the size of the plunger 12, the size of the clearance CL2 is between approximately 0.5 and 2 mm when the diameter of the plunger 12 is approximately 12.5 mm and the diameter of the free end of the body 36 a is approximately 12 mm). However, the shape of the body 36 a is not limited to a semispherical shape but may be a shape formed by cutting a surface of a spheroid including a short shaft, for example.
The movement restricting means 37 is the stator 37 a with a substantially semispherical shape which is supported by an inner surface of the upper passage 33. However, the shape of the stator 37 a is not limited to the semispherical shape but may be a shape formed by cutting a surface of a spheroid including a short shaft. The free end of the stator 37 a is a substantially circular flat surface. In specific, the stator 37 a is fixed to the upper passage 33 via an I-shaped support portion 37 b which partially closes the upper passage 33 (see FIG. 5). A passage for liquid is secured, since a clearance CL1 is provided between the upper passage 33 and the stator 37 a (although it depends on the size of the plunger 12, the size of the clearance CL1 is between approximately 0.5 and 2 mm when the diameter of the plunger 12 is approximately 12.5 mm and the diameter of the free end of the body 36 a is approximately 12 mm).
By such arrangement, the check valve V1 is excellent in opening/closing response and is capable of increasing pump head by applying to the pump 1 of the present invention.

EXAMPLE 1

The present invention is further specifically explained on the basis of Examples. However, the present invention is not limited to such Examples.
An experiment was performed by using a plunger with 100 cc (35.5 mm in diameter).
(1) When a distance was 3 mm for a single movement of the plunger, a discharge quantity at 1800 time/min was 9000 cc.
(2) When a distance was 1 mm for a single movement of the plunger, a discharge quantity at 1800 time/min was 5400 cc.
(3) When a distance was 0.5 mm for a single movement of the plunger, a discharge quantity at 1800 time/min was 1800 cc.
Another experiment was performed by using a plunger with 5 cc (12 mm in diameter).
(1) When a distance was 3 mm for a single movement of the plunger, a discharge quantity at 1800 time/min was 1080 cc.
(2) When a distance was 1 mm for a single movement of the plunger, a discharge quantity at 1800 time/min was 720 cc.
(3) When a distance was 0.5 mm for a single movement of the plunger, a discharge quantity at 1800 time/min was 360 cc.
Thereafter, the performance of the pump (discharge quantity) relative to the number of motor rotations (rpm) was measured by using three kinds of springs including a rigid spring (spring constant is 300 kgw/m), a spring with conventional rigidity (spring constant is 140 kgw/m), and a soft spring (spring constant is 100 kgw/m) as the spring 16. The result is shown in FIG. 5. In the figure, reference numeral A indicates a graph showing the performance of the pump using the spring with a spring constant of 100 kgw/m, reference numeral B indicates a graph showing the performance of the pump using the spring with a spring constant of 140 kgw/m and reference numeral C indicates a graph showing the performance of the pump using the spring with a spring constant of 300 kgw/m.

EXAMPLE 2

In FIG. 7, there is shown a variation of Example 1. The same pump as shown in FIG. 1 was employed as two set of pumps of Example 2. The present invention is further specifically explained on the basis of Examples. However, the present invention is not limited to such Examples. The moving elements P and P1 are connected to the rotary shaft 21 via the crank pin CP1 and CP2 respectively, in such a manner that a phase shifting of the upward and downward motion of the moving element P and the moving element P1 is π radian (180 degrees). When a distance was 1 mm for a single movement of the plunger 12, an identical discharge quantity of 5400 cc of two pumps at 1800 time/min was obtained by using a plunger with 100 cc (35.5 mm in diameter).

INDUSTRIAL APPLICABILITY

According to the pump of the present invention, the pump includes a pump chamber, an intake passage for taking liquid into the pump chamber via an intake valve being opened when liquid is taken into the pump chamber, a discharge passage for discharging liquid to an outside of the pump chamber via a discharge valve being opened when liquid is discharged from the pump chamber, a cylinder in communication with the pump chamber, a plunger slidably provided within the cylinder and biased toward a bottom dead center side by a spring, and a moving element being brought in contact with the plunger and stroking the plunger upward, wherein the moving element moves upward and downward via a motion conversion means for transforming rotary motion of a rotary shaft of an electric motor into upward and downward motion, the plunger in descending motion and moving element are spaced apart. Therefore, it is possible to provide a pump which is not only capable of obtaining high discharging pressure and large capacity but also obtaining a substantially non-pulsating flow with a miniaturized configuration and even if the pump is operated with low power. Furthermore, the pump according to Claim 5, the response performance of the intake valve and discharge valve is remarkably improved since the valve plug includes a check valve including a body supportably provided on the valve seat and an adjusting means for adjusting opening/closing response which is provided at a lower side of the body.
At such as an incineration facility, an agent corresponding to the concentration of hydrogen chloride is inputted for the purpose of removing hydrogen chloride contained in an exhaust gas. However, immediate control cannot be performed since the response performance of a measuring apparatus is poor. Thus, excess amount of agent is inputted and waste agent causes secondary environmental hazard. Consequently, by applying the pump of the present invention to the apparatus for measuring hydrogen chloride, the response performance of the apparatus is improved. The input quantity of the agent is thus optimized and the increase in secondary environmental hazard is prevented.
The pump of the present invention (non-pulsating pump) is also applicable to continuous mixing injection of various materials in the chemical/food industry, coating material transferring system in a coating line, mixing and transferring of ink in printing processes, continuous quantitative injection of chemical ingredients, or uniform mixing of various additives.

Claims

1. A pump comprising:

a pump chamber;

an intake passage for taking liquid into the pump chamber via an intake valve being opened when liquid is taken into the pump chamber;

a discharge passage for discharging liquid to an outside of the pump chamber via a discharge valve being opened when liquid is discharged from the pump chamber;

a cylinder in communication with the pump chamber;

a plunger slidably provided within the cylinder and biased toward a bottom dead center side by a spring; and

a moving element being brought in contact with the plunger and stroking the plunger upward;

wherein the moving element moves upward and downward via a motion conversion means for transforming rotary motion of a rotary shaft of an electric motor into upward and downward motion;

the plunger in descending motion and moving element are spaced apart.

2. The pump according to claim 1, wherein the discharge passage is connected to an elastic resin tube.

3. The pump according to claim 1, wherein the motion conversion means and moving element are an eccentric cam being coupled with the rotary shaft of the electric motor.

4. The pump according to claim 1, wherein the motion conversion means comprises a crank arm of which an end is coupled with the rotary shaft of the electric motor and a connecting rod of which an end is swingably attached to the other end of the crank arm via a crank pin, wherein the moving element is swingably attached to the other end of the connecting rod and is guided to a guide member extending to a vertical direction.

5. The pump according to claim 1, wherein the intake valve and discharge valve are check valves comprising:

a lower passage and upper passage which are in communication with each other and through which liquid flows;

a valve seat provided at a connecting portion of the lower passage and upper passage;

a valve plug provided within the upper passage; and

a movement restricting means for restricting moving distance of the valve plug;

wherein the valve plug comprises a body supportably provided on the valve seat and an adjusting means for adjusting opening/closing response of the check valves which is provided at a lower side of the body.

6. The pump according to claim 2, wherein the motion conversion means and moving element are an eccentric cam being coupled with the rotary shaft of the electric motor.

7. The pump according to claim 2, wherein the motion conversion means comprises a crank arm of which an end is coupled with the rotary shaft of the electric motor and a connecting rod of which an end is swingably attached to the other end of the crank arm via a crank pin, wherein the moving element is swingably attached to the other end of the connecting rod and is guided to a guide member extending to a vertical direction.

8. The pump according to claim 2, wherein the intake valve and discharge valve are check valves comprising:

a valve plug provided within the upper passage; and

a movement restricting means for restricting moving distance of the valve plug;

9. The pump according to claim 3, wherein the intake valve and discharge valve are check valves comprising:

a valve plug provided within the upper passage; and

a movement restricting means for restricting moving distance of the valve plug;

10. The pump according to claim 4, wherein the intake valve and discharge valve are check valves comprising:

a valve plug provided within the upper passage; and

a movement restricting means for restricting moving distance of the valve plug;