EP2609332A1

EP2609332A1 - Membrane pump having an inertially controlled leak extension valve

Info

Publication number: EP2609332A1
Application number: EP11745539.4A
Authority: EP
Inventors: Horst Fritsch
Original assignee: Prominent Dosiertechnik GmbH
Current assignee: Prominent GmbH
Priority date: 2010-08-26
Filing date: 2011-08-15
Publication date: 2013-07-03
Also published as: JP5862903B2; WO2012025423A1; RU2013113209A; CA2808388A1; CN103154517B; CA2808388C; BR112013004584A2; US20130209280A1; JP2013536364A; RU2573069C2; CN103154517A; KR20130138194A; DE102010039829A1

Abstract

The invention relates to a membrane pump having a delivery chamber (9) separated from a hydraulic chamber (8) by means of a membrane (1), wherein the delivery chamber (9) is connected to one intake connection and one pressure connection and the hydraulic chamber (8) that can be filled with a working fluid can have a pulsating working fluid pressure applied thereto, wherein the hydraulic chamber (8) is connected to a working fluid reservoir (15) by means of a leak extension valve (6), wherein the leak extension valve comprises a closing body that can be displaced back and forth between a closed position in which the valve passage is closed, and an open position in which the valve passage is opened, said body being held in the closed position with the aid of a pressure element, wherein the pressure element is designed such that, when the pressure in the hydraulic chamber (8) is less than a set pressure p_L, the closing body (16) is displaced in the direction of the open position. In order to provide a membrane pump having a leak extension valve reducing or even eliminating the disadvantages of the state of the art, according to the invention the mass of the closing body (16) is so great that the closing body (16) is displaced by no more than 0.2 mm in the direction of the open position in case of a pressure drop to 0 bar lasting no longer than 1 millisecond due to a pressure surge in the hydraulic chamber (8).

Description

Diaphragm pump with inertia-controlled leak-relief valve

The present invention relates to a diaphragm pump with a leak-relief valve and to a method of sizing a leak-relief valve.

Diaphragm pumps generally have a delivery chamber which is separated from a hydraulic chamber by a membrane, wherein the delivery chamber is in each case connected to a suction connection and a pressure connection. The filled with working fluid hydraulic chamber can then be acted upon with a pulsating working fluid pressure. As a result of the pulsating working fluid pressure, a pulsating movement of the diaphragm is produced, as a result of which the volume of the pumping chamber becomes periodically larger and smaller. This makes it possible, via the suction port, which is connected to a corresponding check valve with the pumping chamber to suck the fluid when the volume of the pumping chamber is increased, and via the pressure port, which is also connected to a corresponding check valve with the pumping chamber, under Relieve pressure when the volume of the pumping chamber is reduced.

As a working fluid usually a hydraulic oil is used. In principle, however, other suitable liquids, such as. B. water can be used with a water-soluble mineral additive.

Through the membrane, the medium to be pumped is separated from the drive, whereby on the one hand the drive is shielded from harmful influences of the pumped medium and on the other hand, the fluid from harmful influences of the drive, eg. As impurities, is shielded.

The pulsating working fluid pressure is often provided by means of a movable piston in contact with the working fluid. The piston is z. B. in a hollow cylindrical member moves back and forth, whereby the volume of the hydraulic space is reduced and increased, which leads to an increase and decrease in the pressure in the hydraulic chamber and in consequence to a movement of the membrane. Despite various measures to prevent flow around the piston with working fluid, can not be ruled out in practice that each stroke a small amount of working fluid is lost through the narrow remaining gap between the piston and hollow cylindrical element, which gradually the working fluid in the hydraulic chamber is reduced. This has the consequence that the pressure stroke is no longer completely filled by the membrane, since not enough working fluid for pressure movement of the membrane is available. Therefore, it has already been proposed, for example, in DE 1034030, the hydraulic space with the interposition of a valve, a so-called leak-supplementing valve to connect to a working fluid reservoir.

If necessary, working fluid can be added to the hydraulic chamber through this leak-relief valve. However, it is important to ensure that not too much working fluid is brought into the hydraulic chamber, since then the membrane moves in the compression stroke too far into the pumping chamber and may get in contact with valves or other components in contact and damaged. For this purpose, the leak-relief valve generally has a between a closed position in which the valve passage is decided and in an open position in which the valve passage is open, reciprocable closing body, z. B. in the form of a closing ball on. This closing body is by means of a pressure element, for. B. a spring, biased in the closed position. This pressure element is designed such that only when the pressure in the hydraulic chamber is less than a set pressure p _L , the closing body moves in the direction of the open position.

Since there is inevitably a reduction in the pressure in the hydraulic chamber during the suction stroke, ie when the piston is moved back, the set pressure p _L must be set such that no liquid can reach the hydraulic chamber via the leak-relief valve during the suction stroke. Only at the end of the suction stroke, when the piston barely moves, should any refilling fluid be refilled via the leak-relief valve. It should be noted that the maximum pressure prevails at the end of the pressure stroke in the pumping chamber. If the suction stroke is now started, the membrane will move in the direction of the hydraulic chamber until the pressure in the delivery chamber has fallen to the static pressure at the suction connection. If the suction stroke continues, this leads to a pressure surge, the so-called Joukowsky shock, as now conveyed medium is supplied via the suction port in the delivery chamber, resulting in an abrupt change in velocity in the suction line. This pressure surge leads to a high-frequency pressure fluctuation in the hydraulic chamber. For a short time, the pressure in the hydraulic chamber is reduced enormously.

In order to prevent that the leak-relief valve opens during this pressure surge and thus working fluid can flow into the hydraulic chamber, the set pressure p _L must be set correspondingly small, which means that the pressure element of the leak-relief valve must be relatively large.

However, this is disadvantageous in the known diaphragm pumps, since it is now difficult at the end of the suction stroke to fall below the set pressure of the leak-relief valve. Accordingly, constructive measures must be taken to ensure that at the end of the suction stroke, the leak-relief valve actually opens when there is too little working fluid in the hydraulic chamber. This increases the cost of the diaphragm pump.

Starting from the described prior art, it is therefore an object of the present invention to provide a diaphragm pump with a leak-relief valve, which reduces or even overcomes the disadvantages mentioned. In addition, it is an object of the present invention to provide a method for dimensioning a leak-relief valve, which reduces or even eliminates the disadvantages mentioned.

This object is achieved by a membrane pump mentioned above, in which the mass of the closing body is so large that the closing body at a lasting not more than a millisecond surge due to a pressure drop in the hydraulic space by not more than 0.2 mm in the direction of Open position moves.

It has been found that the pressure surge, the so-called Joukowsky shock, which occurs at the moment when the pressure in the delivery chamber to the pressure at the suction port drops, is high-frequency, that occurs during a time interval of less than a millisecond. According to the invention, the closing body is now designed such that its mass and thus its mass inertia is so great that, in the event of such a pressure surge, the closing body can not move more than 0.2 mm in the direction of the open position due to the mass inertia. Since after one millisecond the pressure has already risen again, the movement of the closing body is stopped. Usually, a movement of the closing body is less than 0.2 mm so small that the resulting opening gap for the working fluid is too small to convey a significant amount of working fluid in the hydraulic chamber. If the small amount should nevertheless be disadvantageous, it is provided in a preferred embodiment that the closing body moves by not more than 0.1 mm in the direction of the open position with a pressure surge lasting no more than one millisecond due to a pressure drop in the hydraulic space.

It is understood that due to the Joukowsky shock the pressure surge can lead to a maximum reduction of the pressure in the hydraulic chamber to 0 bar. An example of the calculation of the mass of the closing body is given below.

In fact, despite the pressure surge, the pressure in the hydraulic chamber does not drop to 0 bar, but to a minimum pressure p _min . This minimum pressure p _min depends on the selected process parameters, such. B. the static pressure at the pump suction port, the speed of the piston and the volumes of the hydraulic chamber and the delivery chamber from.

While in the prior art usually the set pressure p _{L is} less than p _min , in a preferred embodiment now p _{L may be} greater than p _min . The return spring of the leak-relief valve can therefore be smaller in size, which greatly simplifies the handling of the pump.

With regard to the method for dimensioning a leak-relief valve of a diaphragm pump, the object mentioned at the outset is achieved in that the mass of the closing body is selected such that the closing body does not become more than 0 when the pressure surge persists for no more than one millisecond due to a pressure drop in the hydraulic space. 2 mm, preferably not moved by more than 0.1 mm in the direction of the open position.

Further advantages, features and possible applications of the present invention will become apparent from the following description of a preferred embodiment and the accompanying figures. Show it:

1 shows a partial sectional view of a diaphragm pump of the prior art,

Figure 2 shows the pressure curve in the hydraulic chamber during the suction stroke and

Figure 3 is a sectional view of a leak-relief valve according to an embodiment of the invention.

In Figure 1, the essential parts of a diaphragm pump are shown in a partial sectional view. The membrane pump has a membrane 1, which separates the hydraulic chamber 8 from the delivery chamber 9. The delivery chamber 9 is connected via corresponding check valves with a Saugan- connected and a pressure connection. The hydraulic chamber 8 can be acted upon by means of the piston 3 with a pulsating working fluid pressure. In the embodiment shown, the membrane 1 is connected to a mounted in an installation space 13 spring 10, which ensures that the membrane is biased in the direction of the hydraulic chamber. Due to the pulsating pressure of the working fluid, the membrane is also moved back and forth between the walls 4 and 7, whereby the volume of the delivery chamber is increased and decreased. When the volume of the delivery chamber is reduced, the delivery fluid in the delivery chamber is discharged via the check valve at the pressure outlet. If the volume of the delivery chamber increases due to a return movement of the diaphragm 1, delivery fluid is drawn in via the check valve from the suction connection. As a result of the periodic movement of the membrane, delivery fluid is periodically sucked from the suction connection and discharged via the pressure connection at higher pressure.

The membrane is held between the clamping edges 1 1, 12. Due to the return spring 10 may cause a bulging of the membrane 1, which is represented by the dashed lines 14.

During operation, working fluid may possibly escape via the gap 5 on the piston 3. To ensure that the sufficient amount of working fluid is always present in the hydraulic space 8, a leak-relief valve 6 is provided, via which the hydraulic space 8 is connected to a working fluid reservoir 15. This leak relief valve has a small ball which is pressed in a valve seat by means of a spring. About the spring of the leak-relief valve 6, the set pressure p _{L is} set. If the pressure in the hydraulic chamber 8 falls below the set pressure p _L , the ball of the leak relief valve lifts off the valve set and additional working fluid can flow into the hydraulic chamber 8 from the working fluid reservoir 15, which is generally below atmospheric pressure (1 bar) the pressure in the hydraulic chamber 8 has risen above the set pressure p _L , since then the spring of the leak-relief valve 6 pushes the ball back into the valve seat and thus closes the valve passage.

In the diagram shown in FIG. 2, the pressure in the hydraulic chamber during the suction stroke is plotted over time. At the beginning of the suction stroke, the pressure in the hydraulic chamber corresponds approximately to the pressure with which the pump discharges the delivery fluid from the pressure connection. This pressure is significantly higher than the static pressure of the suction line. It is understood that the pressure in the hydraulic chamber is additionally determined by the return spring 10. However, this pressure difference is not considered below because it is not relevant to the invention. The suction stroke begins when the piston 3 is moved back, that is, in the embodiment shown in Figure 1 is moved to the right. This initially leads to the fact that the pressure in the hydraulic chamber slowly reduced and since the pressure in the pumping chamber is greater, the membrane will move to the right, ie in the direction of the hydraulic chamber. The pressure in the delivery chamber will slowly drop until it reaches the static pressure at the suction port p _S o. When the pressure drops further, the corresponding non-return valve, which connects the delivery chamber to the suction port, will open and delivery fluid will flow via the suction port. At the moment in which the pressure in the pumping chamber thus reaches the static pressure suction connection, an abrupt change in the velocity of the fluid takes place in the suction line. This speed change Δν leads to the so-called Joukowsky collision Ap _st = p ^■ a ^■ Δν, where p is the density of the pumped medium and a is the wave propagation velocity in the liquid-filled suction pipe.

This Joukowsky collision in the pumping room leads to a pressure surge in the hydraulic room, as the two rooms are connected via the membrane.

It can be seen that after a certain time from the beginning of the suction stroke s, the pressure p _H in the hydraulic chamber abruptly drops for a short time interval (Ap _st ). Shortly thereafter, it rises sharply again, resulting in a high-frequency, rapidly decaying pressure oscillation. It can be seen immediately that the pressure surge can lead to a maximum reduction to p = 0. In fact, however, the pressure in the hydraulic chamber will not drop to 0, but to a minimum pressure p _min , which is predetermined by the operating parameters and the structure of the diaphragm pump.

In order to prevent opening of the leak-relief valve at the pressure surge falling down to p _min , it is provided in the prior art that the setting pressure of the leak-relief valve p _{L be} small

Through the inventive measure the set pressure p _L, but can be significantly larger than p _min be selected as long as p _L is smaller than an average pressure P _m in the hydraulic chamber.

The invention is based on the finding that the pressure surge occurs only during a very short time interval Ats <1 millisecond.

The mass of the closing body is inventively chosen so large that such a pressure surge only leads to a stroke of less than 0.2 mm or preferably less than 0, 1 mm.

An inventive leak-relief valve is shown in FIG. This leak-relief valve has a closing body 16 accommodated in a valve body 18, which has a closing element 20 which, in the closed position, closes a bore in the valve body 18, so that the line to the working-fluid reservoir 19 is separated from the hydraulic space 8. The closing body is biased by means of a spring element 17 in the closed position, which is shown in Figure 3. The pressure of the working fluid in the working fluid reservoir and thus the pressure in the conduit 19 remains substantially constant. When the pressure in the hydraulic chamber 8 drops below the setting pressure p _L , which is essentially predetermined by the spring 17, the closing body 16 is moved upward in the position shown in FIG. 3, so that a connection between the line 19 and the hydraulic chamber 8 is opened. Basically, it is assumed that when the closing body moves only by 0.2 millimeters, that the gap between the valve body 18 and closing element 20 is not sufficient to deliver a significant amount of working fluid through the line 19 in the hydraulic chamber.

The stroke of the closing body As is calculated as:

At ²

As = b. (1)

2 At is At the duration of the pressure surge and b the acceleration, which underlies the closing body due to the pressure surge. The acceleration is calculated as b = F / m, (2) where F is the force on the closing body and m is the mass of the closing body. It follows thus:

F At ²

As = - ^■ - (3)

m 2

respectively.

(4) Assuming that the surge does not last longer than 1 millisecond, ie At _s = 1 millisecond, the movement of the closing body should be at most 0, 1 mm, ie As _s = 0, 1 mm, and that the pressure surge pressure reduction effected to 0 bar, ie the pressure surge has the size of the set pressure p _L , z. B. 0.7 bar, so results in a diameter of the closing element of 8 mm, ie a corresponding area of about 0.5 cm ² :

F = p _L - A = 0.7 - 10 ^■ 0.5 = 3.5 N (5) and thus

10 ^{~ 4}

= 1, 75 - 10 ^"2 kg = 17.5g

In the example shown, therefore, the mass of the closing body must be at least 17.5 g to prevent movement of the closing body by more than 0.1 mm.

If the mass of the closing body chosen so large, so even a pressure surge to 0 bar, the closing body does not move so far that a significant amount of working fluid leaking into the hydraulic chamber. The described method can be improved even if one considers that the pressure surge generally does not lead to a pressure reduction to 0 bar, but only to a minimum pressure p _min . In the above equation (5), instead of the set pressure p _L, the difference p _L - p _m between the set pressure p _L and the minimum pressure p _min due to the surge can be used, whereby the mass can be further reduced. Alternatively, the set pressure p _{L can be} increased, whereby the spring 17 can be made weaker, which simplifies the handling of the pump.

LIST OF REFERENCE NUMBERS

1 membrane

3 pistons

4 wall

5 gap

6 leak-relief valve

7 wall

8 hydraulic room

9 delivery room

10 return spring

1 1 clamping edge

12 clamping edge

13 installation space

14 schematic representation of a baggy membrane

15 working fluid supply

16 closing bodies

17 spring

18 valve body

19 line

20 closing element

Claims

P a n t a n s p r e c h e

Membrane pump with a via a membrane (1) of a hydraulic chamber (8) separate delivery chamber (9), wherein the delivery chamber (9) is connected to a suction port and a pressure port and the filled with a working fluid hydraulic chamber (8) with a pulsating working fluid pressure can be acted upon, wherein the hydraulic chamber (8) via a leak-supplementing valve (6) keitsvorrat (15) is connected, wherein the leak-supplementing valve (6) one between a closed position, in which the valve passage is closed, and an open position, in which the valve passage is open, reciprocally movable closing body which is held by means of a pressure element in the closed position, wherein the pressure element is designed such that when the pressure in the hydraulic chamber (8) is less than a set pressure p _L , the Closing body (16) moves in the direction of the open position, characterized gekennzeichn et that the mass of the closing body (16) is so large that the closing body (16) at not more than 1 millisecond pressure drop to 0 bar due to a pressure surge in the hydraulic chamber (8) by not more than 0.2 mm in Direction of the open position moves.

Diaphragm pump according to claim 1, characterized Porsche Style nzeich net that the mass of the closing body (16) is selected so that the closing body (16) at a not lasting more than 1 millisecond pressure drop due to a pressure surge in the hydraulic chamber (8) by not more than 0.1 mm moves in the direction of the open position

Diaphragm pump according to claim 1 or 2, characterized in that the closing body (16) at a lasting not less than 1 millisecond pressure drop to a minimum pressure p _min due to a pressure surge in the hydraulic chamber (8) by not more than 0.2 mm preferably is moved no more than 0.1 mm in the direction of the open position, wherein p _{min is} the minimum pressure occurring in the hydraulic chamber due to a pressure surge by a change in velocity of the fluid through the suction port during the suction stroke.

Diaphragm pump according to one of claims 1 to 3, characterized in that p _{L is} greater than the minimum pressure in the hydraulic chamber (8).

Method for dimensioning a leak-relief valve (6) of a membrane pump with a delivery chamber (9) separated from a hydraulic chamber (8) by a membrane (1), wherein the delivery chamber (9) is connected to a suction port and a pressure port and to a working fluid Fillable hydraulic chamber (8) with a pulsating working fluid pressure can be acted upon, the hydraulic chamber (8) being connected to a working fluid reservoir (15) via a leak-relief valve (6), the leak-relief valve (6) being connected between a closed position in which the valve passage is closed and an open position, in which the valve passage is open, reciprocally movable closing body (16), characterized in that the mass of the closing body (16) is selected such that the closing body (16) at a lasting no longer than 1 millisecond pressure surge a pressure drop in the hydraulic chamber (8) by not more than 0.2mm, preferably not moved by more than 0.1 mm in the direction of the open position.