JP5862903B2 - Membrane pump with inertia controlled leakage compensation valve - Google Patents

Description

  The present invention relates to a membrane pump having a leakage compensation valve and to a method for determining the size of a leakage compensation valve.

  A membrane pump generally includes a pump chamber that is separated from a hydraulic chamber by a diaphragm, and the pump chamber is connected to a suction connection portion and a pressure connection portion. A pulsating working fluid pressure can be applied to the hydraulic chamber that can fill the working fluid. As the pulsating working fluid pressure causes the diaphragm to pulsate, the volume of the pump chamber expands and contracts periodically. In this way, when the volume of the pump chamber expands, the pump medium can be sucked in via a suction connection connected to the pump chamber via a separate check valve. When the volume of the pump chamber shrinks, the pump medium receives pressure and is discharged via a pressure connection which is likewise connected to the pump chamber by a corresponding check valve.

  Typically, the working fluid is hydraulic oil. However, in principle, other suitable fluids can be used, for example water containing a water-soluble mineral supplement.

  The diaphragm separates the pumped medium from the drive, so that, on the one hand, the drive is protected from damage caused by the pump medium, and on the other hand, the pump medium is also damaged by the drive, e.g. Protected from contamination,

  The pulsating working fluid pressure is typically generated by a movable piston in contact with the working fluid.

  For this purpose, for example, the piston moves back and forth in a cylindrical hollow element, whereby the volume of the hydraulic chamber is expanded and contracted, causing an increase and decrease of the pressure in the hydraulic chamber, As a result, diaphragm movement occurs.

  Despite the wide variety of measures aimed at preventing the working fluid from flowing around the piston, the fact is that during each stroke, a narrow gap remains between the piston and the cylindrical hollow element. It cannot be prevented that a small amount of working fluid is lost. Therefore, the amount of working fluid in the hydraulic chamber gradually decreases. As a result, there is no longer enough working fluid available to perform the compression movement of the diaphragm, so that the pumping stroke is no longer completed by the diaphragm.

  Thus, for example, German Patent No. 1034030 proposed connecting the hydraulic chamber to a reservoir for working fluid via an intervening valve, a so-called leakage compensation valve.

  When this leakage compensation valve is used, a working fluid can be added to the hydraulic pressure chamber as necessary. However, when doing this, care must be taken not to add too much working fluid to the hydraulic chamber. The reason is that if this is the case, the diaphragm will go too deep into the pump chamber during the pumping stroke, and under certain circumstances may contact the valve or other parts and be damaged. is there.

For this reason, the leakage compensation valve usually comprises a closing body, for example in the form of a closing ball, which can move back and forth between a closed position in which the valve gate is closed and an open position in which the valve gate is open. ing. The closure body is biased to the closed position by a pressure element, for example a spring. The pressure element is only closed body is designed to move in the direction of the open position when the pressure in the hydraulic pressure chamber becomes lower than the set pressure p _L.

Since the pressure in the hydraulic chamber inevitably decreases during the intake stroke, that is, while the piston moves backward, the set pressure p _L is applied to the fluid in the hydraulic chamber via the leakage compensation valve during the intake stroke. Must be set so that it cannot be entered. The leak compensation valve should only contain a deficient amount of working fluid at the end of the suction stroke when the piston is hardly moving.

  In this case, it should be noted that the pressure in the pump chamber is maximized at the end of the pumping stroke. In this case, when the suction stroke starts, the diaphragm will then move in the direction of the hydraulic chamber until the pressure in the pump chamber drops to the static pressure at the suction connection. As the inhalation stroke continues, the inhalation stroke produces a pressure pulse, the so-called Joukovsky pulse. The reason is that in the pump chamber, the pump medium is now supplied via the suction connection, which causes a rapid change in the speed in the suction line. This pressure pulse causes high frequency pressure oscillations in the hydraulic chamber. The pressure in the hydraulic chamber is temporarily greatly reduced.

In order to prevent the leakage compensation valve from opening during this pressure pulse and thereby allowing the working fluid to flow into the hydraulic chamber, the set pressure p _L must be set correspondingly low. This means that the pressurizing element of the leak compensation valve must be of a relatively large size.

  However, this is a disadvantage for known membrane pumps. This is because it becomes difficult to drop below the set pressure of the leakage compensation valve at the end of the intake stroke. Therefore, if the working fluid in the hydraulic chamber is too low at the end of the suction stroke, appropriate structural measures must be taken to ensure that the leak compensation valve actually opens properly. . This increases the cost of the membrane pump.

  Accordingly, an object of the present invention is to provide a membrane pump having a leakage compensation valve that reduces or even overcomes the above disadvantages, based on the above-described conventional technology. In addition, the present invention aims to provide a method for determining the size of a leakage compensation valve that reduces or even overcomes the above disadvantages.

The purpose is a membrane pump of the type defined above , wherein the pressurizing element is set so that the pressure in the hydraulic chamber (8) is higher than the minimum pressure in the hydraulic chamber (8). When the pressure is lower than p _L , the closure body (16) is designed to move in the direction of the open position , and the pressure pulse in the hydraulic chamber results in a pressure drop lasting up to 1 millisecond. This is achieved by the present invention using a membrane pump, characterized in that the mass of the closure body is sufficiently large so that the closure body moves only 0.2 mm or less in the direction of the open position when it occurs.

  In fact, the pressure pulse that occurs when the pressure in the pump chamber drops to the pressure at the suction connection, the so-called Joukovsky pulse, is a high frequency pulse, i.e. it occurs in a period of less than 1 millisecond. Has been observed. According to the present invention, when such a pressure pulse occurs, the mass of the closure body and its inertia are sufficient so that at that time the inertial body can move only 0.2 mm or less in the direction of the open position. Built to be large. After 1 millisecond, the pressure has already risen again and the movement of the closure body is stopped. Usually, the movement of the closure body, which is less than 0.2 mm, is small enough that for the working fluid the resulting gap is too small to allow a significant amount of working fluid to be pumped into the hydraulic chamber.

  Should this small amount still be inconvenient, in a preferred embodiment, the closure body is zero in the direction of the open position when the pressure pulse in the hydraulic chamber results in a pressure drop lasting up to 1 millisecond. It is designed to move only 1 mm or less.

  Obviously, due to the Joukovsky pulse, the maximum pressure pulse can cause a pressure drop in the hydraulic chamber reaching 0 bar. In the following, an example of calculating the mass of the closure body is shown.

Actually, despite the pressure pulse, the pressure in the hydraulic chamber does not drop to 0 bar, but to the minimum pressure p _min . This minimum pressure p _min depends on, for example, process parameters such as static pressure at the pump suction connection, piston speed and hydraulic chamber and pump chamber volumes.

In the prior art, the set pressure p _L is usually less than p _min , but in a preferred embodiment, p _L is greater than p _min . Therefore, the return spring of the leakage compensation valve can be made smaller, which makes the operation of the pump significantly easier.

With regard to the method for determining the dimension of the leakage compensation valve of the membrane pump, the purpose previously defined is that the closure body (16) is subjected to pressure in the hydraulic chamber (8) in the hydraulic chamber (8). becomes lower than the high set pressure p _L than the minimum pressure, while designed to move in the direction of the open position, a result of the pressure pulses in the hydraulic chamber, when the one millisecond lasting pressure drop occurs in the longest This is achieved if the mass of the closure body is selected such that the closure body moves only 0.2 mm or less in the direction of the open position, preferably only 0.1 mm or less.

  Further advantages, features and possible applications will become apparent from the following description of preferred embodiments and the accompanying drawings.

  FIG. 1 is a partial cross-sectional view of a prior art membrane pump.

  FIG. 2 is a diagram showing a pressure profile in the hydraulic chamber during the suction stroke.

  FIG. 3 is a cross-sectional view of a leakage compensation valve according to one embodiment of the present invention.

  FIG. 1 shows the main parts of a membrane pump in partial cross-sectional view. The membrane pump includes a diaphragm 1, which partitions the hydraulic chamber 8 from the pump chamber 9. The pump chamber 9 is connected to the suction connection portion and the pressure connection portion via respective check valves. A working fluid pressure pulsating by the piston 3 can be applied to the hydraulic pressure chamber 8. In the illustrated embodiment, the diaphragm 1 is connected to a spring 10 mounted in the mounting base 13. The spring 10 positively biases the diaphragm in the direction of the hydraulic chamber. As soon as the pulsating pressure of the working fluid moves the diaphragm back and forth between the walls 4 and 7, the volume of the pump chamber expands and contracts. When the volume of the pump chamber shrinks, the pump fluid in the pump chamber is discharged through a check valve at the pressure discharge port. When the volume of the pump chamber expands due to the backward movement of the diaphragm 1, the pump fluid is sucked from the suction connection portion via the check valve. Thus, due to the periodic movement of the diaphragm, the pump fluid is periodically sucked from the suction connection and discharged at a higher pressure through the pressure connection.

  The diaphragm is held between the clamp frames 11 and 12. The presence of the return spring 10 means that the diaphragm can swell as indicated by the dashed line 14.

During operation, under certain circumstances, the working fluid escapes through the gap 5 in the piston 3. In order to ensure that an appropriate amount of working fluid is always present in the hydraulic chamber 8, a leakage compensation valve 6 is provided through which the hydraulic chamber 8 is connected to the working fluid reservoir 15. ing. The leak compensation valve includes a small ball that is biased into the valve seat by a spring. The spring of leakage compensation valve 6 that regulates the setting pressure p _L. When the pressure in the hydraulic chamber 8 drops below the set pressure p _L , the ball of the leakage compensation valve rises from the valve seat, and additional working fluid is typically drawn from the working fluid reservoir 15 below atmospheric pressure (1 bar). It becomes possible to flow into the hydraulic chamber 8. Additional working fluid flows to increased pressure in the hydraulic pressure chamber 8 exceeds the set pressure p _L, then the spring of the leakage compensation valve 6 returns the ball within the valve seat, thereby closing the valve gate To do.

  FIG. 2 shows the pressure in the hydraulic chamber during the suction stroke as a function of time. At the start of the suction stroke, the pressure in the hydraulic chamber is approximately the same as the pressure at which the pump discharges the pump medium from the delivery connection. This pressure is significantly higher than the static pressure in the suction line. It should be understood that the pressure in the hydraulic chamber is also determined by the return spring 10. However, this pressure difference is not relevant to the present invention and will not be considered below.

As the piston 3 moves rearward, i.e., to the right in the embodiment shown in FIG. 1, the suction stroke begins. This means that initially the pressure in the hydraulic chamber decreases slowly, and after the pressure in the pump chamber becomes higher, the diaphragm moves to the right, ie in the direction of the hydraulic chamber. Here, the pressure in the pump chamber slowly drops until it reaches the static pressure _pSO at the suction connection. As the pressure drops further, the individual check valve connecting the pump chamber to the suction connection opens and the pump medium flows in via the suction connection. At the moment when the pressure in the pump chamber reaches the static pressure at the suction connection, a sudden change in the fluid velocity occurs in the suction line. This speed change Δv gives rise to a so-called Joukovsky pulse, Δp _st = ρ × a × ΔV. Where ρ is the density of the pump medium and “a” is the wave propagation velocity in the suction tube filled with fluid.

  Since both chambers are connected via a diaphragm, this Jukovsky pulse in the pump chamber generates a pressure pulse in the hydraulic chamber.

It can be seen that, after a certain time from the start of the suction stroke “s”, the pressure p _H in the hydraulic chamber drops rapidly for a short period (Δp _st ). Immediately thereafter, it rises again sharply, which results in a pressure oscillation that decays rapidly at high frequencies. It can be immediately seen that the pressure pulse drops to a maximum of p = 0. However, the pressure in the hydraulic chamber does not actually drop to zero, but falls to the minimum pressure p _min set by the operating parameters and the structure of the membrane pump.

In order to prevent the leakage compensation valve from opening when a pressure pulse drop reaching p _min occurs, in the prior art, the set pressure p _L of the leakage compensation valve is smaller than p _min .

However, according to the techniques of the present invention, the set pressure p _L is, p _L as long as less than the average pressure p _m in the liquid chamber, can be chosen to be much higher than p _min.

  The present invention is based on the recognition that pressure pulses only occur for very short periods of Δts <1 ms.

  According to the invention, the mass of the closure body is chosen to be sufficiently large so that such a pressure pulse causes an increase of less than 0.2 mm, or preferably less than 0.1 mm.

  FIG. 3 shows a leakage compensation valve according to the present invention.

The leakage compensation valve includes a closing body 16 accommodated in the valve body 18. The closing body 16 comprises a closing element 20 that closes the hole in the valve body 18 in the closed position, so that the line 19 to the working fluid reservoir is separated from the hydraulic chamber 8. As shown in FIG. 3, the closure body is biased to the closed position by a spring element 17. The pressure of the working fluid in the working fluid reservoir and hence the pressure in the conduit 19 remains essentially constant. When the pressure in the hydraulic chamber 8 drops below the set pressure p _L essentially given by the spring 17, the closing body 16 in the position shown in FIG. The connection with the hydraulic chamber 8 is opened. In principle, the clearance between the valve body 18 and the closing element 20 is sufficient to drain a considerable amount of working fluid through the line 19 into the hydraulic chamber, even if the closing body moves only 0.2 millimeters. It is assumed that this is not the case.

ここで、Δｔは圧力パルスの持続時間であり、ｂは圧力パルスに起因する閉鎖本体の加速度である。加速度は次式のように算出される：

ここで、Ｆは閉鎖本体にかかる力であり、ｍは閉鎖本体の質量である。従って、次式が得られる：

または

圧力パルスは１ミリ秒、すなわち、Δｔ_s＝１ミリ秒、よりも長くは持続しないこと、閉鎖本体の運動は最大で０．１ｍｍ、すなわちΔｓ_s＝０．１ｍｍ、であるべきこと、且つ、圧力パルスは圧力を０ｂａｒまで低下させる、すなわち圧力パルスは設定圧力ｐ_L、例えば０．７ｂａｒ、と同じ大きさであることを仮定すれば、このとき、閉鎖要素の直径が８ｍｍ、すなわち対応する表面積が約０．５ｃｍ²の場合：

従って、

示した例では、０．１ｍｍを超える閉鎖本体の運動を防止するために閉鎖本体の質量は少なくとも１７．５ｇでなければならない。 The stroke of the closed body, Δs, is calculated as:

Where Δt is the duration of the pressure pulse and b is the acceleration of the closure body due to the pressure pulse. The acceleration is calculated as:

Here, F is a force applied to the closing body, and m is a mass of the closing body. Thus, the following equation is obtained:

Or

The pressure pulse should not last longer than 1 ms, ie Δt _s = 1 ms, the movement of the closure body should be at most 0.1 mm, ie Δs _s = 0.1 mm, and Assuming that the pressure pulse reduces the pressure to 0 bar, ie the pressure pulse is as large as the set pressure p _L , eg 0.7 bar, then the diameter of the closure element is 8 mm, ie the corresponding surface area Is about 0.5 cm ² :

Therefore,

In the example shown, the mass of the closure body must be at least 17.5 g to prevent movement of the closure body above 0.1 mm.

  If the mass of the closure body is chosen so large, even a pressure pulse reaching 0 bar will not move the closure body so that a significant amount of working fluid is released in the hydraulic chamber.

The above method may be further improved by considering that the pressure pulse generally does not cause a pressure drop reaching 0 bar, but only a pressure drop to the minimum pressure p _min. . In this case, the above equation (5), can be used in place of the set pressure p _L, and the set pressure p _L, the difference p _L -p _min the minimum pressure p _min due to the pressure pulse, As a result, the mass can be further reduced. Alternatively, it is possible to increase the set pressure p _L, as a result, the spring 17 can be made lighter, operation of the pump is simplified.

DESCRIPTION OF SYMBOLS 1 Diaphragm 3 Piston 4 Wall 5 Crevice 6 Leak compensation valve 7 Wall 8 Hydraulic chamber 9 Pump chamber 10 Return spring 11 Clamp frame 12 Clamp frame 13 Mounting base 14 Schematic display of the swelled diaphragm 15 Working fluid reservoir 16 Closing body 17 Spring 18 Valve body 19 Pipe line 20 Closing element

Claims (4)

A membrane pump having a hydraulic chamber (8) partitioned from a pump chamber (9) by a diaphragm (1), wherein the pump chamber (9) is connected to a suction connection portion and a pressure connection portion, respectively. A pulsating working fluid pressure can be applied to the hydraulic chamber (8) that can fill the working fluid, and the hydraulic chamber (8) is connected to the working fluid reservoir (15) via a leakage compensation valve (6). The leakage compensation valve (6) is held in a closed position by a pressurizing element and moves back and forth between a closed position in which the valve gate is closed and an open position in which the valve gate is open comprising a closing body which can be, the pressure element, the pressure of the liquid in the pressure chamber (8) becomes lower than the high set pressure p _L than the minimum pressure of the liquid in the pressure chamber (8), The closure body (16) is designed to move in the direction of the open position. In a membrane pump, when the pressure pulse in the hydraulic chamber (8) results in a pressure drop to 0 bar lasting up to 1 millisecond, the closure body (16) moves in the direction of the open position. Membrane pump, characterized in that the mass of the closure body (16) is large enough to move only by 0.2 mm or less.   When the pressure pulse in the hydraulic chamber (8) results in a pressure drop lasting up to 1 millisecond, the closure body (16) moves only 0.1 mm or less in the direction of the open position The membrane pump according to claim 1, characterized in that the mass of the closure body (16) is selected. When the pressure pulse in the hydraulic chamber (8) results in a pressure drop to a minimum pressure p _min lasting up to 1 millisecond, the closure body (16) is moved in the direction of the open position by 0. It is characterized in that it moves only by 2 mm or less, preferably by 0.1 mm or less, where p _min is the velocity of the fluid passing through the suction connection during the suction stroke when a pressure pulse is generated. 3. A membrane pump according to claim 1 or claim 2, wherein the minimum pressure in the hydraulic chamber resulting from a change. It has a hydraulic chamber (8) separated from the pump chamber (9) by the diaphragm (1), and the pump chamber (9) is connected to the suction connection portion and the pressure connection portion, respectively, and fills the working fluid. The pulsating working fluid pressure can be applied to the hydraulic pressure chamber (8), and the hydraulic pressure chamber (8) is connected to the working fluid reservoir (15) via a leakage compensation valve (6). And the leakage compensation valve (6) comprises a closing body (16) that can be moved back and forth between a closed position in which the valve gate is closed and an open position in which the valve gate is open. In the method of determining the dimension of the pump leakage compensation valve (6) , the pressure in the hydraulic chamber (8) of the closing body (16) is higher than the minimum pressure in the hydraulic chamber (8). When the setting is lower than the pressure p _L, it is designed to move in the direction of the open position Together with the liquid pressure chamber (8) As a result of the pressure pulses in the, when 1 millisecond lasting pressure drop occurs in up, only the closure body (16) only below 0.2mm in the direction of the open position Method for determining the dimensions of a membrane pump, characterized in that the mass of the closure body (16) is selected so that it does not move, preferably only by 0.1 mm or less.

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