US2968250A - Pump - Google Patents

Description

Jan. 17, 1961 v. s. LOBANOFF ETAL 2,968,250

PUMP

2 Sheets-Sheet 1 Filed Dec. 5, 1956 INVE/V roRs l/AL s LOBANOFF SYDNEY 3 SMITH EC/61OFF & SLICK ATT RA/EVS A MEMBER OF THE FR PUMP 2 Sheets-Sheet 2 Filed Dec. 5, 1956 5 3 WW M mws was a m vr 5 A v l FM 1 mm mm mm vm mm mm m N N el ECKHOFFfi/g/CK 7 AT 0 N VS BY M 4 v A MEMBER OF THE ilnited States Patent PUlVIP Val S. Lobanolf, Oakland, Calif and Sydney S. Smith, New York, N.Y., assignors to United Centrifugal Pumps, a corporation of California Filed Dec. 5, 1956, Ser. No. 626,379

3 Claims. (Cl. 103-111) This invention relates to centrifugal pumps and particularly to a pump construction wherein the impeller shaft is sealed adequately against fluid leakage. In the handling of fluids with a centrifugal pump, the problem exists of adequately sealing the pump shaft so that the liquid handled does not leak from the pump. It will be appreciated that with inflammable or explosive fluids, such as are provided by various hydrocarbons or organic chemicals, and particularly with radioactive materials, this problem is a very serious one. Further, many materials are abrasive or corrosive to the pump seals and bearings and it is highly desirable to exclude the material being pumped from these parts. For instance, the pump of the present invention is well adapted to handle crude oil which contains sand.

It is in general the broad object of the present invention to provide a novel and improved pump construction wherein the shaft of the pump is effectively sealed against leakage of the fluid being pumped.

Another object of the present invention is to provide a pump seal wherein a sealing liquid is used and wherein the system is adjusted so that any leakage will be a leakage of the sealing liquid into the pump and not a leakage of the pumped material out of the pump.

Still another object of the present invention is to provide a novel balancing system wherein the pressure of the sealing liquid is automatically adjusted to a substantially constant differential pressure across the seals which is adequate to seal the pump over a large range of pump pressures yet will not soar to undesirably high values when the pressure of the liquid being pumped drops to a low value.

A further object of the invention is to provide a novel pressure alarm and control system for a fluid sealed pump, which gives a constant visual check that the pump is operating under safe conditions, which automatically starts a sealant pump when the pressure in the sealing system drops, which automatically shuts down the main pump if the sealant pump is unable to maintain a sat pressure, and which will fail safe.

A still further object of the present invention is to provide a novel pressure equalizing system so that a single sealing system may be used to protect a multiple stage pump.

The invention includes other objects and features of advantage, some of which, together with the foregoing, will appear hereinafter.

In the drawing accompanying and forming a part hereof:

Figure 1 is a side elevation, partly in section, through a centrifugal pump embodying the present invention, together with a schematic showing of a flow control system utilized to effect an absolute seal of the rotary shaft against leakage of the fluid pumped.

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Figure 2 is an enlarged fragmentary view through a seal at one end of the pump shaft.

In the drawings, there is shown a double volute pump including a suitable base 6 upon which the pump structure, generally indicated at 7, is mounted. The pump includes a first stage, generally indicated at 8, and a second stage, generally indicated at 9. Impellers 11 and 12 are mounted upon a shaft 14, the latter being mounted in bearings 16 and 17 provided at each end of the shaft. Bearings 18 are also included to take up the the axial thrust. Shaft 14 is adapted to be driven by suitable means, not shown.

A first stufling box, generally indicated at 21, is pro vided about the shaft at each end of the casing. This stuffing box includes packing 22 provided between the casing and a sleeve 25 mounted on shaft 14. The packing is forced into sealing engagement by a flanged ring 23. Several studs 24 provide a guide for the ring, while springs 28, mounted between a nut 27 on each of the studs and the flange ring 23 to provide a pull upon the flange ring urging the packing into sealing engagement. The casing includes a tubular extension 31 closed by a flange 32, the latter being secured over the tubular extension by suitable means, not shown. The shaft 14 is sealed by a mechanical gland' 33 in the region where it issues from the tubular extension and passes through the flange 32 closing the end of tubular extension 31.

In accordance with this invention, the fluid being handled by the pump is removed from one of the stages and is applied to a device which in turn maintains a pressure in excess of that in the pump stage which must be sealed. For example, referring to the drawing, fluid under pressure is taken from the first stage of the pump through line 36 and is led into the base of cylinder 42 and from the suction or inlet through line 37 and is led into the base of cylinder 43 to provide two fluid streams. A differential cylinder structure 41 is provided including a first cylinder 42 and a second cylinder 43, the latter being a larger cross-sectional diameter than the former. A closely fitting piston is provided in each cylinder, these being indicated respectively at 44 and 46, the two being connected by a piston rod 47.

The cylinder 43 is closed except for an indicator rod 48, which projects beyond the cylinder; by reference of the height of rod 48 relative to an indicating scale 49, one can determine the relative position of the piston 46 in the cylinder 43 and thereby how much fluid is present above the piston 46. The space above piston 46 and cylinder 43 is maintained filled with a supply of a suitable inert liquid, supplied from tank 51 by pump 52 through lines 53 and 54. A check valve 54A is used to prevent fluid from backing through the lines 53 and 54. It will be obvious that the fluid issuing from the cylinder 43 will be under a higher pressure than the fluid admitted through line 37. This fluid is taken ofi through lines 61 and 62, and is supplied to each of the tubular extensions 31 to provide a pressure in excess of the pump inlet or suction. The fluid chosen is one which is compatible with that being pumped so that any fluid which leaks into the pump does not affect adversely the pump operation. In this manner, one can ensure that any leakage which occurs is not from the pump, but into the pump whereby an adequate seal is maintained about the shafts.

It is obvious that the degree of protection, i.e., the difference in the pressure of the sealant and the pressure on the opposite side of the seal, will be controlled by the relative sizes of the pistons 44 and 46. Thus, ifa large degree of protection is necessary, e.g., if the inlet pressure is subject to sudden surges, the two pistons can be made more nearly the same size than is illustrated, while if a smaller degree of protection is thought necessary, the difference in sizes of the pistons may be made greater.

More specifically, it is desirable that the pressure applied through lines 61 and 62 to the exterior of the packing 22 and 68 not be too great for excessive pressure applied tothe packing will either cause inward leakage or unnecessary packing wear. Thus, if pressure were transmitted directly through line 36 to lines 61 and 62, the differential pressure applied to the exterior of the packing'would be far too great. Even if a given fraction of the pressure in line 36 were applied directly to lines 36 and 37, as through a hydraulic pressure reducing system, satisfactory results would still not be achieved as pressures in line 36 might become sufficient at times to cause even the preselected fraction thereof to become excessive when applied to packing 22 and 63.

Thus, itis desirable that a more or less fixed differential pressure be'provided across packing 22 and 68, e.g. about 50 pounds or less, irrespective of the pressure in either lines 36 or 37. This is achieved by the diflerential cylinder structured-1 wherein a larger cylinder is mounted atop a smaller cylinder and in direct communication therewith and a large piston within the top cylinder is joined by means of rod 47 to the smaller piston 44 in the smaller cylinder. Thus, line 37, which provides communication between the suction side of the pump and the volume represented by the interior of cylinder 42 and that portion of the cylinder 43 which is directly beneath the piston 46 supplies what might be termed a reference pressure. That is, in the absence of line 36 and piston 44, it may be seen that the pressures in lines 37 and 62 (or 61) are in a 1 to 1 ratio (neglecting the effect of rod 48). Hence there would be no differential pressure across the packing 22 and 68. But where the smaller piston 44 is connected by means of rod 47 to the larger piston 46 and the first stage output pressure of the pump is transmitted through line 36 to beneath the piston 44, there will be a transmission of pressure to the fluid in cylinder 43 which is above piston 46. This pressure will be dependent upon pressure introduced through line 36. That is, pressure introduced beneath piston 44 will result in a relatively small increase in pressure transmitted through piston 46 to lines 61 and 62. But it is to be further noted that everyincrease in first stage output pressure transmitted through line 36 is directly offset by an equivalent increase in the pressure transmitted through line 37 from the suction side of the pump since the reason for a sudden surge in the first stage output pressure will be a corresponding and equivalent surge of pressure on the suction side. Hence the surges (pressures) will counteract one another to an extent sufficient to provide a constant differential across packings 22 and 68. Expressed differently, the pressure transmitted through lines 61 and 62 will be a relatively constant and fixed amount greater than the pressure in line 37, irrespective of the extent to which the pressure in line 37 may fluctuate. Actually, this differential would be absolutely fixed were it not for the use of control rod 48 which results in a slight increase in the differential pressure in line 61 (or 62) as against that in line 37 due to the fact that the upper surface area of piston 46 is somewhat decreased by indicator rod 48 extending through the top of the cylinder 43. It is this indicator rod which causes a slight variation between the minimum and maximum differential across the packing, as set forth in the table appearing later in the specification.

Obviously, the differential may be increased Whenever desired by the simple expedient of increasing the surface area of piston 44 so that the high pressure from the first stage output of the pump is transmitted more directly to the fluid within cylinder 43.

It will also be obvious that with the system illustrated the sealing pressure will be substantially constant over a a g range of pump inlet pressures. The following nonlimiting example is given to illustrate the operation of the system:

There is, therefore, always a differential pressure of approximately 25 to 30 pounds across the packing 22 on the drawing which prevents any of the pumped liquid from leaking into the stufling box chamber.

The rod 48 not only serves as a quick visual check but is also utilized to actuate a series of micro switches designated 48a, b and c. As the rod 43 rises, switch 43a is first actuated which starts the pump 52, and which may also actuate a pilot light, not illustrated. If the leakage from the main pump is so great that the fillin pump 52 is inadequate to cope with the leakage, the rod 43 will continue to rise and actuate switch 431) which will set off an audible warning. If the warning is ignored, or if the difficulty cannot be rectified, the rod 48 will rise still further and actuate switch 48c which will cut off the driving motor to the main pump and thus shut down the Whole system. Of course, in normal on eration, only switch 48a would come into play, turning the sealant pump 52 on and off to maintain normal pressure in the sealing system.

If desired, suitable cooling coils can be provided as at 71 about each of the seals, while the bearings can be cooled as by circulating a suitable fluid through coils 72 adjacent the several bearings.

it will be noted that in the embodiment shown, only a single differential cylinder 41 is utilized, despite the fact that a two stage pump is employed and the second stage operates at a pressure much elevated above the first stage. This is made possible by a pressure equalizing line. Thus, the small amount of liquid which escapes through the seal 65 bleeds into the annular space 67, thence through the pressure equilazing line 69 and into the suction side of the first stage pump at 73. In this manner the pressure on the seal 68 at the right hand side of the drawing (the second stage) is no higher than the pressure on the seal 22 at the left hand side (the first stage). Of course, if a single stage pump is being protected, no such equalizing system is necessary. Further, in many applications the sealing system may be duplicated, i.e., a separate differential cylinder system is used on the second stage rather than employing the equalizing system and the single differential cylinder system illustrated, in which case no equalizing line is used.

Although the invention has been described in its preferred embodiment as applied to a two stage volute pump, it is obvious that the invention is applicable to any centrifugal pump having any number of stages.

From the foregoing, we believe it wil be apparent that we have provided a novel, simple and improved seal for a centrifugal pump shaft.

We claim:

1. In a centrifugal pump having inlet and outlet sides for pumping a fluid, a pump casing, a shaft mounted for rotation within said casing, packing on said shaft to confine fluid within said casing, a substantially closed charaber adjacent said packing into'which fluid leaking said packing may enter, means for applying a fluid pres' sure within said chamber from a system substantially separate from that of said fluid within said casing, said separate system comprising; a differential cylinder assembly comprising two adjacent internally connected cylinders of different diameters, pistons in each of said cylinders connected by a rod whereby said two pistons move together, a confined space above the larger of the two pistons, a first line leading from the inlet side of the pump to the larger of the said cylinders and connected thereto at a point on that end of the larger cylinder adjacent the smaller cylinder to apply pressure to the bottom of the larger of the two pistons, a second line leading from the outlet side of the pump to the smaller of the said cylinders and connected thereto at a point on that end of said smaller cylinder farthest removed from the said larger cylinder to apply pressure to the bottom of the smaller piston, and a line leading from said confined space to said chamber whereby there is applied to said chamber a fluid pressure which is maintained at a substantially constant excess over the inlet pressure of said pump.

2. In a centrifugal pump having inlet and outlet sides for pumping a fluid, a pump casing, a shaft mounted for rotation within said casing, packing on said shaft to confine fluid within said casing, a substantially closed chamber adjacent said packing into which fluid leaking past said packing may enter, means for applying a fluid pressure to the interior of said chamber from a system substantially separate from that of said fluid within said casing, said fluid pressure being higher than and directly responsive to the pressure of the fluid being pumped at the inlet of the pump, said fluid pressure being maintained at a substantially constant excess over the inlet pressure of said pump, said means comprising a differential cylinder assembly comprising two adjacent internally connected cylinders of diflerent diameters, pistons in each of said cylinders connected by a rod whereby said two pistons move together, a confined space above the larger of the two pistons, a first line leading from the inlet side of the pump to the larger of the said cylinders and connected thereto at a point on that end of the larger cylinder adjacent the smaller cylinder to apply pressure to the bottom of the larger of the two pistons, a second line leading from the outlet side of the pump to the smaller of the said cylinders and connected thereto at a point on that end of said smaller cylinder farthest removed from the said larger cylinder to apply pressure to the bottom of the smaller piston, a fluid reservoir having a line providing fluid communication between said reservoir and said confined space above the larger of the two pistons and a sealant pump in said last mentioned line adapted to draw fluid from said reservoir and apply pressure to the confined space above the larger piston, and a line leading from said confined space to said chamber whereby there is applied to said chamber a fluid pressure higher than the pressure of the fluid being pumped at the inlet side of the pump.

3. The structure of claim 2 wherein a rod extends upwardly from the larger piston and through the confined space, a switch mounted adjacent said rod, said rod being operatively associated with said switch whereby to provide means to actuate said switch, said switch being operatively associated with said sealant pump, whereby said switch may be caused to start the sealant pump when the pressure within said confined space drops below a predetermined value and to stop said pump when the pressure drops below a second and lower predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 879,484 Morterud Feb. 18, 1908 1,759,074 Van Rijswijk May 20, 1930 1,910,811 Peterson May 23, 1933 2,501,304 Bandry et al Mar. 21, 1950 2,649,318 Skillman Aug. 18, 1953 2,730,954 Hornschuch Jan. 17, 1956 2,750,894 Thomas et a1 June 19, 1956

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