Side-channel pump and method for operating same

Abstract

The invention relates to a side-channel pump and to a method for operating a side-channel pump in which an impeller rotates in a working chamber provided with a side channel. According to the invention, the pump is operated at an overspeed with a gas-filled working chamber in a first step. The speed is then reduced to an operating speed in order to pump a liquid. The pump according to the invention has a high suction power as a result of the overspeed, but only gas is drawn initially.

Claims

1. A method for operating a side-channel pump, said method comprising a. providing a side-channel pump in which an impeller rotates in a working chamber provided with a side channel, the side-channel pump having an operating speed when pumping liquid and a maximum speed at which the side-channel pump can pump liquid, said operating speed being no greater than said maximum speed; b. operating said side-channel pump at an overspeed when said working chamber is filled with a gas, said overspeed being greater than said operating speed; and c. reducing the speed of said side-channel pump to said operating speed when said working chamber is filled with liquid.

2. The method of claim 1, wherein the overspeed of step b. is at least 50% greater than said operating speed.

3. The method of claim 1, applying a first driving power to said side-channel pump in step a. and applying a second driving power to said side-channel pump in step b., said first driving power being less than said second driving power by at least 10%.

4. The method of claim 1, wherein said operating speed is between 1200 rpm and 4000 rpm.

5. The method of claim 1, wherein the overspeed is between 3600 rpm and 7000 rpm.

6. The method of claim 1, wherein said operating speed is in the range of 1200 rpm to 2000 rpm and said overspeed is in the range of 3600 rpm to 5000 rpm.

7. The method of claim 1, wherein said operating speed is in the range of 2000 rpm to 4000 rpm and said overspeed is in the range of 5000 rpm to 7000 rpm.

8. The method of claim 1, wherein the side-channel pump is a sealless side-channel pump where a driven end of a shaft of said side-channel pump is arranged completely within a casing of said side-channel pump.

9. The method of claim 1, wherein the side-channel pump comprises a plurality of working chambers provided with a side channel.

10. The method of claim 1, wherein an inlet stage of said side-channel pump is configured as a centrifugal stage.

11. The method of claim 10, wherein said centrifugal stage comprises a rotor within which a plurality of channels extend from a central region to a peripheral region of said rotor.

12. The method of claim 11, wherein said plurality of channels are distributed uniformly over the circumference of the rotor.

13. The method of claim 1, wherein said side-channel pump is employed to pump liquefied gas out of a tank through a line at least partially filled with evaporated gas in a gaseous state and wherein step b. pumps said evaporated gas to draw said liquefied gas through said line and into said side-channel pump.

14. A side-channel pump comprising: an impeller which rotates in a working chamber provided with a side channel; a motor arranged to apply driving power to said impeller; and a controller arranged to deliver driving power to said motor to rotate said impeller at a an operating speed when pumping liquid, said side-channel pump having a maximum speed at which the side-channel pump can pump liquid, said operating speed being no greater than said maximum speed, wherein said controller is configured to operate said side-channel pump at an overspeed greater than said operating speed when said working chamber is filled with gas and to reduce the rotational speed of said side-channel pump when liquid enters said working chamber.

15. The side-channel pump of claim 14 in combination with a liquefied gas tank connected to an inlet opening of the side-channel pump.

16. The side-channel pump and liquefied gas tank of claim 15, wherein the liquefied gas tank is below the side-channel pump.

17. The side-channel pump of claim 14, comprising an inlet stage configured as a centrifugal stage.

18. The side-channel pump of claim 14, wherein said impeller is carried on a shaft arranged within a casing of said side-channel pump, said shaft being magnetically coupled to said motor.

19. The side-channel pump of claim 14, comprising a plurality of impellers rotating in a plurality of working chambers, said working chambers fluidly connected in series so that gas or liquid being pumped passes through the plurality of working chambers in succession.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described by way of example below by means of advantageous embodiments with reference to the attached drawings, in which:

(2) FIG. 1: shows a schematic illustration of a side-channel pump according to the invention;

(3) FIG. 2: shows an arrangement comprising a side-channel pump according to the invention and a liquefied gas tank; and

(4) FIG. 3: shows a block diagram of the method according to the invention.

DETAILED DESCRIPTION

(5) In the case of a side-channel pump according to the invention in FIG. 1, a shaft 14 is rotatably mounted in a pump casing 15. The pump casing 15 is provided with an inlet opening 16 and an outlet opening 17, wherein the inlet opening 16 is arranged concentrically with the shaft 14. The opposite end of the pump casing 15 from the inlet opening 16 is designed as a split cage 18, within which there are arranged magnet elements 19, which are connected to the shaft 14. Magnet elements 20 are arranged outside the split cage 18, said elements being connected to the output shaft of an electric motor 21. The electric motor 21 is provided with a controller 35.

(6) If the electric motor 21 is put into operation, the magnet elements 20 perform a rotary motion around the split cage 18. Through transmission of the magnetic forces, rotation is also imparted to the shaft 14, with the result that it rotates synchronously with the output shaft of the electric motor 21. Since one end of the shaft 14 issues into the inlet opening 16 and the other end of the shaft 14 is accommodated in the split cage 18, the pump is sealless in the sense that there is no point at which the interior and exterior of the pump are separated solely by a shaft seal. This has the advantage that the pumped medium can be reliably prevented from escaping.

(7) The pump according to the invention comprises four stages, in each of which an impeller 21 rotates in a working chamber 23. The impellers 22 have vanes arranged in a star shape with open vane interspaces, which are closely surrounded by the casing 15. Axially adjacent to the impeller 22, the casing 15 forms a side channel 24, which is open toward the impeller 22 and in which the pumping medium is pumped through exchange of momentum with the impeller 22. The inlet end of the side channel 24 lies opposite an inlet opening, formed in the casing, of the working chamber 23, which is not visible in FIG. 1. The medium entering through the inlet opening passes through the interspaces of the vanes to the side channel 24. A channel 25, indicated only schematically in FIG. 1, in each case extends from the outlet opening of the preceding working chamber 23, through the pump casing 15, as far as the inlet opening of the following working chamber 23. The pumped medium thus passes through the four stages of the pump in succession.

(8) The inlet stage 26 of the pump is configured as a centrifugal stage. A rotor 27 connected to the shaft 14 is provided with channels 40, which extend from a central region to a peripheral region of the rotor 27. The medium entering the channels 14 in the central region is moved outward by the centrifugal force. A channel extends from the outer end of the rotor 27, through the pump casing 15, to the inlet opening of the first working chamber 23.

(9) The pump is designed to pump liquids. For this purpose, the pump is operated at a speed of 3000 rpm, for example, and the liquid is pumped with a volume flow of 35 m.sup.3/h, for example.

(10) In the example of use shown in FIG. 2, the pump 28 according to the invention is connected to a liquefied gas tank 29. A riser line 31 extends from the lower part of the tank 29 toward the inlet opening 16 of the pump 28. A line 34 is connected to the outlet opening 17 of the pump 28 and leads to a vehicle 32 which is to be refueled with liquefied gas 30. The volume flow of the pump is sufficiently great to ensure that it cannot be completely absorbed by the car 32. Gas bubbles are separated from the volume flow in a separator 33 and returned to the tank 29.

(11) The tank 29 is about one third full of liquefied gas 30. The remaining space in the tank 29 and in the riser line 31 is filled with evaporated liquefied gas, and the pressure consequently corresponds to the vapor pressure of the liquefied gas. If the pump 28 is put into operation, starting from this state, the liquefied gas initially enters the pump 28 in the gaseous state. Since liquefied gas continues to evaporate with the application of reduced pressure in the tank 29, the suction power of the pump in this phase must be sufficiently large in order nevertheless to draw in liquefied gas in the liquid state through the riser line 31. According to the invention, this is achieved by virtue of the fact that, in this phase, the pump is operated with an overspeed which is significantly above the operating speed. The overspeed with which the pump is operated, as it were as a blower, can be 7000 rpm, for example. This speed is significantly above the maximum speed at which the pump can be operated when liquid is being pumped.

(12) Despite the higher speed, the power of the pump when it is being operated as a blower is lower than in normal operation, in which liquid is being pumped. If, therefore, a low power is sufficient to accelerate the pump to the overspeed, it follows that the working chambers 23 of the pump are filled with gas. Consequently, the controller 35 is designed to operate the electric motor 21 at low power in the case of the overspeed.

(13) As soon as liquid enters the pump, the resistance increases abruptly and the pump is braked. The controller 35 is designed in such a way that it increases the power of the electric motor 21 as soon as the pump 28 is braked to the operating speed in order to keep the pump at this speed. This operating state is maintained until the car 32 has been fully refueled. As soon as this is the case, the pump 28 is switched off.

(14) When the pump is stationary, liquefied gas which is still in the pump evaporates continuously, with the result that the working chambers 23 return to the initial state, in which they are filled with gas, after a sufficiently long waiting time. If another car is to be refueled, the pump can be accelerated again at low power to the overspeed. On the other hand, if the next refueling operation takes place before the liquid has evaporated from the pump, the resistance is significantly higher, and the pump is operated with a high power at the operating speed from the outset, thus allowing liquid to be pumped.

(15) In FIG. 3, the method according to the invention is shown in schematic form. At the beginning of the method, a car 32 to be refueled is connected to a line 34 of the arrangement according to the invention in step 100. In step 110, the pump 28 is accelerated at low power to a speed of 7000 rpm. As soon as liquid enters the pump, the pump is braked and the controller 35 is designed to set the power of the electric motor 21 in such a way in step 120 that the speed of the pump 28 is held constant at the operating speed of 3000 rpm. Once the car 32 has been fully refueled, the pump 28 is switched off in step 130. In step 140, the line 34 is separated from the car 32, and the refueling process is ended.