US2101960A - Centrifugal pump - Google Patents

Description

Dec. 14, 1937. E. A. A. sJosTROM CENTR IFUGAL PUMP Filed Jan. 21, 1936 M B m Patented Dec. 14, 1937 UNITED STATES PATENT OFFIQE Swed Application January 21, 1936, Serial No. 60,098 In Sweden February 11, 1935 4 Claims.

The present invention relates to improvements in centrifugal pumps, and the purpose of the invention is to enable a high vacuum to be obtained, even if the pump conduits and passages are not entirely filled with liquid. This is desirable in all cases, Where centrifugal pumps are used as suction pumps for the transportation of liquids from one level to another, and particularly when such pumps are driven intermittently,- and also where centrifugal pumps are used for the transportation of water of condensation or liquids containing air from receptacles, in which a high vacuum is desired to be maintained. The inventiomis particularly related to centrifugal pumps, in which-the impeller lies below the inlet and outlet openings of the pump casing, and is principally characterized by this that the impeller has ducts beginning at the inlet opening of the impeller and leading to sealing means between the suction and the pressure side, said ducts being at least along some part of their length so directed that, due to the rotation of the impeller, liquid is thrown from'the suction side through said ducts to said sealing means.

In the annexed drawing an embodiment of the invention is illustrated by way of example. Fig. 1 is a vertical cross section of a single-stage centrifugal pump with vertical axle. Fig. 2 is a side view of the same pump and the pipes connected thereto. Fig. 3 is a fragmentary view of the impeller looking in axial direction, and Fig. 4 is a cross section of the sealing means at the impeller on a larger scale than in Fig. 1.

The centrifugal pump illustrated in the drawing comprises a pump casing divided in two parts and 2 and an impeller 5 secured, to a vertical shaft 3 by means of a nut 4. The pump casing has a supply portion 6 adapted to be connected. to a pipe 28 through which a liquid is to be drawn to the pump, and communicating with the suction chamber 1 of the pump. As illustrated in Fig. l, the suction chamber 1 extends around the volute 8 to the under side of the impeller 5, where a chamber is formed, which contains liquid, even if the supply and delivery pipes are empty. The impeller 5 comprises-two disks 9 and I0 having blades provided between them. The disk 9 in the usual manner forms the impeller hub.

For the purpose of sealing between the suction side and the pressure side of the pump rings I2 are provided at the outer sides of the disks 9 and III, which rings project into grooves |3 in the sealing collars l4 secured in the volute 8. Between the rings I2 and collars'l l a certain play must always be present, and if the pump is not totally filled with liquid, or is supplied with liquid having air mixed therein a considerable air leakage occurs through the space between the rings and the collars during the operation of the transportation of'fuel from bottom tanks in ves-- sels to other tanks situated at a higher level, for

instance day tanks, and also in all cases where a centrifugal pump has to operate with a considerable suction'head and is not running continuously, so that the pipes leading to and from the pump may be empty, when the pump is started,

or if the pump is used for withdrawing a fluid mixed with air from a vessel, such as a condenser, in which a high vacuum is desired to be maintained. It is sometimes possible to eliminate these disadvantages by special arrangements for producingvacuum in the suction pipe, when thepump is to be started, and for this purpose water jet pumps, ejectors or the like are often used. If, for instance, feed water is available, as is'sometimes the case on board of ships, such a quantity of water may also be supplied to the pump that it may gradually produce a sufficient vacuum for filling the suction pipe.

However, in order that the pump should be able to produce and maintain a high vacuum itself, even if the pipes are empty, a good liquid seal is necessary between the rings l2 and the collars M. In order to effect this grooves I5 according to the invention are formed at the inner edge of the disks 9 and ID, from which grooves ducts l6 and I1 lead to the grooves I3 in the collars l4. The portions l6 of these ducts are directed substantially parallel to the passages between the blades of the impeller, and when liquid is supplied to the groove l5 said liquid upon rotation of the impeller is thrown outwards through the ducts l6 and conducted through the ducts I! to the sealing space, which is filled with pressure liquid preventing air passage this way. A stuffing box 8 is provided around the impeller shaft 3 and pressure liquid is supplied to said stufling box from the pressure side of the pump chamber of the pump at the flange 24. The outnected. Thus the flowing velocity of the liquid in the portion 2| is reduced to a considerable extent, and the air entrained therein gets a possibility to rise. The pipe 23 is connected to the outlet portion 2| at a place, where a pocket 26 is formed, which is protected from liquid mixed with air flowing'directly from the volute 8 by a ridge 21. The liquid withdrawn from the pocket 26 through the pipe 23 will therefore be relatively free from air.

The pump above described operates in the following manner: It is assumed that the supply'and delivery pipes, of the pump have no valves of any kind and that the liquid, when the pump is stopped, escapes from the pipes. However, the entire pump casing due to its shape will act as a liquid trap, and when the pipes are emptied liquid will still remain in the pump casing most likely to a level corresponding to the upper edge of the upper collar I4, Fig. l. The supply and delivery pipes and the uppermost parts of the pump casing are then filled with air. When the pump is started the eye or inlet portion of the impeller is emptied as well as the impeller itself, and the liquid level in the volute and the part 2! communicating therewith rises somewhat. Then the pump substantially pumps air or liquid mixed with air. As long as there is so much liquid left in the suction chamber 1 that some liquid flows over the upper edge of the upper collar M the pump will continue to withdraw air. The liquid flowing down along the inner surface of the collar I4 is caught in the groove |5 at the inner edge of the disk In and is thrown from here through the ducts I6 parallel to the passages between the impeller blades and pressed into the space between the ring l2 and the collar I4 and seals said space against the air in the volute. Said air tends to press the sealing liquid back through the space between the sealing rings and collars to the suction side of the pump, where at least some part of the sealing liquid is again caught in the groove and returned to the sealing means through the ducts l6, l1.

However, if the pump after having been operated for some time does not producea sufficient vacuum, the valve 22 may be opened. Due to the pressure at the pressure side of the pump liquid substantially free from air iiows through the pipe 23 to the suction side of the pump. Said liquid serves then as feed liquid and flows down over The pipe l9 illustrated in Fig. 2 supplies pressure liquid to the stufiing box around the pump shaft 3. Said pipe may also advantageously be connected to the pocket 26 of the portion 2| instead of being connected in the manner illustrated in Fig. 2.

The pump above described;and.illustrated in the drawing should, of course, on1y= betconsidered as an example and may be .modified in several ways without departing from theprinciple of the invention. Thus, the invention may be applied to pumps having a vertical shaitas ,well as to pumps having a horizontal shaft and also to pumps with one or more impellers The pressure liquid may also be withdrawn directly from a part of the volute, where liquid is always available.

What I claim is:

l. A centrifugal pump having an impeller comprising disks and a number of blades provided between saiddisks and having passages provided between them, a central inlet opening in one of said disks leading to said passages, ducts in said last mentioned disk beginning at an inner portion of the disk and ending at a part of said disk more remote from the center of the disk than said inner portion, said ducts having at least along some part of their length substantially the same direction as the passages between the impeller blades, and sealing means between the suction side and the pressure side of the impeller, saidducts communicating at their outer ends with said sealing means and at their inner ends with said central inlet opening.

2. A centrifugal pump having an impeller comprising disks and a number of blades provided between said disks and having passages therebetween, 8. central inlet opening in one of said disks leading to said passages, ducts in said last mentioned disk beginning at an inner portion of the disk and ending at a part of the disk more remote from the center of the disk than said inner portion, and sealing means between the suction side and the pressure side of the impeller, said ducts communicating at their outer ends with said sealing means and at their inner ends with said central inlet opening.

3. A centrifugal pump having a vertical shaft, an impeller comprising two disks and a number of blades provided between said disks and forming passages between them, a central inlet opening in the upper disk leading to said passages, an annular groove at the upper side of the inner edge of said upper disk, said groove being positioned at least in part in radial direction inside the inner surface of the impeller eye or inlet opening of the pump casing, so that liquid flowing down said inner surface is caught in said groove, sealing means between the suction side and. the pressure side of the impeller, and ducts in the upper disk extending from said groove and ending at a part of the disk more remote from the center of the disk than said groove, said ducts communicating with said sealing means.

4. A centrifugal pump having an impeller comprising disks and a number of blades provided between said disks, a. central inlet opening in one of said disks leading to passages between the impeller blades, ducts in said last mentioned disk beginning at an inner portion of the disk and ending at a part of said disk more remote from thecenter of the disk than said inner portion, sealing means between the suction side and the pressure side of the pump, said ducts'communieating at their inner ends with the suction side of the pump and at their outer ends with said sealing means, and a pocket formed in the delivery portion of the pump and protected from the direct flow of liquid from the pump by means such as a ridge, said pocket communicating with the suction chamber ofthe pump through a pipe,

ERIK ALBERT ALEXANDER SJ6S'I'R6M.

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