US3131641A - Dynamic seal improvement - Google Patents

Description

May 5, 1964 .1. E. CYGNOR DYNAMIC SEAL IMPROVEMENT Filed Aug. 17, 1962 //VA ET w 5 M F ATTORNEY United States Patent Filed. Aug. 17,1962, Ser. No. 218,222 1 Claim. (Cl. 103-103) This invention relates to improvements in dynamic seals and has among its objects to provide a seal of this type in which fluid gassing in the vanes of the dynamic seal impeller is overcome even at extremely high impeller speeds; in which a clean interface is maintained at the impeller face; and in which the horsepower requirement for 'the seal is much less than for previous seals.

A further object of this invention is to provide a dynamic seal construction especially adapted for use in high-temperature liquid metal pumps in which the operating characteristics of the seal are little affected by changes in clearance in the dynamic seal impeller.

These and other objects and advantagesof the improved seal construction will be pointed out or will be evident from the following detailed description of a preferred embodiment of the seal shown in the accompanying drawing.

In this drawing FIG. 1 is a diagrammatic, vertical, sectional elevation through a pump provided with the seal of this invention;

FIG. 2 is a transverse sectional view through the pump casing on line 22 showing one half of the seal impeller in plan; and

FIG. 3 is a much enlarged view showing the gas-liquid interface.

As herein shown, a typical liquid metal pump includes a casing having a main pump impeller chamber 12. A shaft 14 extends through a wall 16 of the casing in which it is journalled at 18 and carries an impeller 20 at its free end in chamber 12. A main liquid metal inlet 22 supplies liquid to the impeller 20. The liquid metal is discharged under pressure through a usual outlet 24.

Shaft 14 also carries a dynamic seal impeller 26 which rotates in a chamber 28. As shown most clearly in FIG. 2, this impeller has a plurality of radial vanes 30, herein 24 in number. In accordance with this in vention, impeller 26 has a plurality of concentric grooves 32 which transect the vanes on one side of the impeller. These grooves have outer side walls 34 which are normal to the plane of the impeller and inwardly and upwardly directed oblique inner walls 36. Casing wall 16, which is shown as a separate casing member, has an equal number of concentric ribs, or deflector rings, 38 formed on its vane-confronting face. The cross section of these ribs conforms to the cross section of the grooves 32 and the ribs enter into these grooves, suitable operating clearance being allowed between the walls of the grooves and the ribs.

Casing wall 16 also forms one wall of an outer chamber 40 in which inert gas, which may be helium, is 0 provided under pressure in a Well-known manner in dynamic seals. A recirculating pipe 41 is provided for bleeding off liquid metal from chamber 28 at the tip of impeller 26 and returning it to the low pressure inlet 22.

In operation, high pressure fluid which leaks past the vane tips of impeller 20 passes along shaft 14 at 42 and enters the seal chamber 28 where it is picked up by the vanes 30 of the dynamic seal impeller. This leakage fluid is opposed by the blanket gas which passes from chamber 40 through the journal 18 into the impeller chamber 28 and forms the usual interface with the leakage liquid. This interface is shown in FIG. 3 at A.

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For purposes 'of illustration, the clearances at 42 and 18 have been greatly exaggerated.

By reason of the cooperating grooves 32 and the ribs 38, this dynamic seal has superior operating characteristics as compared to previous seals which lacked'these features. First, it has been found that fluid gassing in the vanes of impeller 26 is eliminated even at pump speeds of 5500 rpm. to 8000 rpm. The seal runs with a good, clean interface even at these high speeds. The ribs 38 give the interface a guide to run on when the interface is in such a position that it coincides with a rib. When the interfaceis between two ribs, the ribs efiectively isolate the slight amount of gassing that takes place at the interface from the rest of the liquid. The gassing is very slight except-for interface positions beyond point B, FIG. 3. From this point on gassing gets progressively worse until the interface gets beyond the last rib 38. At this point the fluid is a foam and remains that way until the interface goes off the seal impeller. If the interface is then brought back up to point A, the fluid will clear up immediately. Clearances of the fluid between the vanes is very important because this affects the cooling flow which is passed by the dynamic seal tip to remove the heat put into the fluid by the vanes and by recirculation. The amount of gas this cooling flow has in it is very important in some instances; for example, when the pump is used with an inpile loop. If the flow is not absolutely clear, it will gas up the loop fluid in a shoirt time.

Even though some blade material is removed to make the grooves 32, an increase in pressure differential between the gas-liquid interface and the dynamic impeller tip is noted. This pressure differential compares very favorably with the theoretical differential which was 109 psi. by test and 112 p.s.i. by calculation at 5500 rpm. and radius of 1.4 in a specific pump tested.

The horsepower requirement for the dynamic seal of this invention is much less than for previous seals. In the pump tested it was found that at 5500 rpm. 6.2 horsepower is needed to drive the seal compared with 7.75 horsepower for previous seals. This is a reduction of 21%. The reason for this horsepower drop can be explained by the reduction of recirculation between the vanes 30 of the seal impeller. This recirculation is virtually eliminated by the deflector rings 38 which effectively block it.

The seal of this invention has been tested at well over 8000 rpm. and its good operating characteristics were not affected at all by this high speed. In fact, it is possible to run the pump at this speed with a gas-liquid interface position nearer the tip of impeller 26 than at lower speeds. The seal has been run at different clearances over a substantial range and it was found that'no change occurred in the operating characteristics, showing that the seal is not sensitive to clearance change.

It will be evident that as a result of this invention a dynamic seal has been provided having improved operating characteristics as regards gassing of the fluid in the vanes, the quality of the interface, the pressure differential between the interface and the dynamic impeller tip, and the horsepower required to operate the seal.

While only one embodiment of this invention has been shown herein, it will be evident that various changes may be made in the construction and arrangement of the parts without departing from the scope of the invention as defined in the following claim:

I claim:

A pump having an impeller casing including a Wall, said casing enclosing a main pump impeller chamber and a seal impeller chamber, a drive shaft extended through the wall of said casing through said seal impeller chamber and into said pump impeller chamber, a main pump impeller on said shaft in said main pump impeller chamher, a liquid inlet and a liquid outlet for said main imeller chamber, a dynamic seal impeller on said shaft in said seal impeller chamber receiving the liquid which leaks past said main impeller tip, said seal impeller having generally radially extended vanes provided with a plurality of radially spaced concentric annular grooves in the face thereof remote from said main pump impeller which transect said vanes, a casing member having an equal number of annular continuous ribs on a face thereof which confronts said grooved vanes, said ribs registering with and entering into said grooves, each of said grooves in said vanes having its outer wall normal to the plane of said seal impeller and having its inner Wall inclined from the bottom of the groove upwardly and away from said normal wall, and each of said annular ribs having a radial cross section which conforms to the cross section of said grooves, and means for effecting a gas-liquid interface between said confronting surfaces including a chamber on the remote side of said casing member from said confronting ribbed surface for supplying inert gas under pressure to seal said chamber.

UNITED STATES PATENTS Wilkinson Oct. 25, Zoelly May 19, Lichtenstein June 18, MacLean Nov. 15, Vaughn Nov. 10, Fletcher Oct. 30, Jurgensen Nov. 23, Boardman et al Nov. 24, Means July 18,

FOREIGN PATENTS Great Britain June 8, Germany May 19, Germany May 14, Italy Oct. 10, Germany Nov. 24, Germany July 24, Germany Jan. 18,

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