WO1994000689A1

WO1994000689A1 - Pump arrangement

Info

Publication number: WO1994000689A1
Application number: PCT/SE1993/000571
Authority: WO
Inventors: Svante Bahrton
Original assignee: Svante Bahrton
Priority date: 1992-06-26
Filing date: 1993-06-24
Publication date: 1994-01-06
Also published as: SE9201981L; SE9201981D0; SE9201981A0

Abstract

The invention relates to a pump arrangement for liquids, which comprises at least one pair of cooperating pump chambers (1, 2), to and from which the pumped liquid flows in and out alternately governed by a pneumatic control system. The object of the invention is to suppress pulsations in the outgoing flow. For that purpose the arrangement is designed so that the suction and pressure strokes in each of the pump chambers occur independently of the suction and pressure strokes in the other pump chamber. In this way an active compression pressure does always reside in at least one of the control chambers of the control system so that a drive pressure is continuously maintained in the outlet line (11) from the pump arrangement.

Description

Pump arrangement

The present invention relates to a pump arrangement for liquids comprising at least one pair of cooperating pump chambers which, when actuated upon by a pneumatic control system, are alternately supplied with or drain¬ ed of the liquid being pumped, each of said chambers being connected, via an inlet branch line having a non¬ return valve, to a tank or the like via an inlet trunk line and, via an outlet branch line, each of which also having a non-return valve, to a common trunk outlet line, a control valve being provided to govern the filling and emptying of pneumatic control chambers related to said pump chambers.

Such arrangements are used for the pumping of liquids within several technical areas, e.g. for the transport of liquids in the food manufacturing industry and in the pharmaceutical industry. In such contexts diaphragm pumps are generally used because they exhibit several operational advantages, primarily the fact that, when the outlet flow is shut off, the pumping pressure is maintained but the drive unit is not operating meaning that no energy is supplied to the liquid. Also as far as mechanical forces are concerned diaphragm pumps are kind to the liquids pumped. Further, such pumps are relatively insensitive to the presence of bigger par¬ ticles, fibres and the like in the liquid. However, on the other hand diaphragm pumps have certain operational limitations or drawbacks, especially that the outgoing flow is not constant timewise but heavily pulsating. Those pulsations generate vibrations which cause mecha¬ nical stresses on the equipment as well as disturbing noise. Another disadvantage of the pulsating character of the flow resides in difficulties in the measuring of flow and pressure. Finally, the pressure and the flow rate of the outlet liquid stream is dependent of the installation level and of the liquid level in the tank from which the liquid is supplied to the pump, i.e. of the static pressure in the conduit from the tank.

The object of the invention is to provide a pump arrangement at which the above-mentioned disadvantages and limitations have been eliminated or in any case essentially reduced. For that purpose the pump arrange¬ ment includes means which start the pressure stroke in the one pump chamber before the pressure stroke in the other pump chamber has ended. To make this possible the two pump chambers must operate independently of each other. The invention is based on the realization that such an individual mode of operation and the corres¬ ponding advantages cannot be attained in prior art pump arrangements where the chambers are dependent of each other. By way of example, in diaphragm pumps the two diaphragms are mechanically interconnected and mechani¬ cally connected with the control valve. According to the present invention there is no such mechanical connection between the pump chambers and the control valve.

Two embodiments of the invention will now be described with reference to the drawing diagrammatically illu¬ strating each of those embodiments.

Fig. 1 illustrates a pump arrangement having two single-acting diaphragm pumps which are not mechani¬ cally interconnected.

Fig. 2 illustrates a pump arrangement having two single-acting pumps with no diaphragm or other mechani- cal partition between the control fluid and the pumped fluid.

The pump arrangement shown in fig. 1 comprises two pump chambers 1 and 2, each having a diaphragm 3 and 4, respectively. The pumped liquid 8 enters through a trunk feed line 5 and continues via branch lines 6, 7 with non-return valves into the space below the dia¬ phragm in the related pump chamber. Liquid 8 exits through two branch lines 9 and 10, respectively, which are connected to a common trunk outlet line 11.

The two diaphragm pumps are controlled by means of a pneumatic system. That system comprises a pressure source 12 connected to the inlet port of a fourway two- position valve 13, the valve body of which, shaped e.g. as a slide, is controlled by a unit 14 operating pneu¬ matically or electrically and governed either by a time circuit or by the pump chambers 1, 2. Above each liquid chamber there is a pneumatic compression chamber la, 2a, which via a conduit lb, 2b is connected to the valve 13. Numeral 15 designates a suction unit con¬ trolling the suction movement of the diaphragm in operation at a given moment. The unit has a drive means 16. If the inlet pressure in the feed line 5 is gene¬ rated in some other way, e.g. by a feed pump or by a positive static pressure, means 15 and 16 are not necessary.

The mode of operation of the pump arrangement above de¬ scribed is as follows.

Fig. 1 illustrates a segment of the operational cycle during which pressurized air has been supplied to the left control chamber la from pressure source 12 and through valve 13. In this way there has in this chamber been built up a compression pressure which has forced diaphragm 3 downwards so that liquid is pressed out through branch line 9 having a non-return valve 17. While a portion of the downward movement of diaphragm 3 still remains, valve 13 is switched to its other posi¬ tion. This,starts the creation of a compression in chamber 2a. During the switching phase the air volume, which is locked up in chamber la and which still is subjected to a positive pressure, will continue to press diaphragm 3 downwards. This continues until the compression pressure above diaphragm 4 is greater than that above diaphragm 3 where the pressure is gradually reduced, partly due to the increasing volume and part- ly, somewhat later, due to the fact that this control chamber becomes connected to the outlet port of valve 13. Thanks to this mode of operation there occurs an overlapping between the time intervals during which active compression pressures reside in the chambers so that a drive pressure is continuously maintained in trunk outlet line 11. This in turn means that the flow in that line becomes substantially constant and free of pulsations. In the outlet branch line 10 there is a non-return valve 18.

The components of the arrangement in fig. 2 having a direct counterpart in fig. 1 have been given the same reference numerals. The difference over fig. l is that there are no material partitions (diaphragms or pis- tons) between the pumping and the pumped fluid. Instead there are upper and lower level signal transmitters 19, 20, which prevent liquid from being sucked into the control system and also the complete drainage of a pump chamber. These transmitters can be connected to a logic circuit carrying out the desired function. In order to attain optimal operational conditions it is further necessary that the relation between the inlet and outlet flows is such that the pump chamber under pres¬ sure can never become completely empty. Also, when there is no diaphragm or a corresponding means, liquid must not be sucked into the control valve. This is prevented by means of the upper level signal trans¬ mitters or by other suitable means.

It is to be understood that the terms used to describe the various components of the arrangements according to the two exemplifying embodiments are to be interpreted in a functional and not in a verbal sense. To illu¬ strate this it can be said that the term "non-return valve" is intended to cover any suitable valve capable of carrying out the function of a conventional non¬ return valve, e.g. a valve controlled electrically or mechanically.

Claims

1. A liquid pump arrangement, comprising at least one pair of cooperating pump chambers (1, 2) which, when actuated upon by a pneumatic control system are alter¬ nately supplied with or drained of the liquid being pumped, each of said chambers being connected, via an inlet branch line (6, 7) having a non-return valve, to a tank or the like via an inlet trunk line (5) and, via an outlet branch line (9, 10), each of which also having a non-return valve (17, 18), to a common trunk outlet line (11) , a control valve (13) being provided to govern the filling and emptying of pneumatic control chambers (la, lb) related to said pump chambers (1, 2) , characterized in the arrangement operating so that the suction and pressure strokes in each (1, 2) of said pump chambers take place independently of the suction and pressure strokes in the other (2, 1) of the pump chambers, whereby an active compression pressure is always present in at least one of the control chambers so that a drive pressure is continuously maintained in said trunk outlet line (11) .

2. An arrangement as claimed in claim 1 comprising at lest one pair of diaphragm pumps, characterized in that the control valve (13) switches that quickly from the position in which one (la; 2a) of the control chamber is connected to a suction unit (15) , generating the diaphragm suction movements, to the position in which the other (2a; la) control chamber is so connected, that the compression pressure in said first-mentioned control chamber (la; 2a) is maintained during the switching process.