US3433162A

US3433162A - Centrifugal pump with slip coupling

Info

Publication number: US3433162A
Application number: US624313A
Authority: US
Inventors: Sixten Englesson
Original assignee: Stenberg Flygt AB
Current assignee: Xylem Water Solutions AB
Priority date: 1963-12-16
Filing date: 1967-03-20
Publication date: 1969-03-18
Anticipated expiration: 1986-03-18
Also published as: FR93464E; BE696648A; GB1187043A; NL6704566A

Description

March 18, 1969 s. ENGLESSON CENTRIFUGAL PUMP WITH SLIP COUPLING Sheet Filed March 20, 196'? INVENTOR! S'lnn E17/03901, 37M. Mn-nl,

M3 orney March 18, 1969 s. ENGLEssoN 3,433,162

CNTRIFUGAL PUMP WITH SLIP COUPLING Filed March 2o, 1967 sheet 2 of s March 18, 1969 s, ENGLESSON 3,433,162

CENTRIFUGAL PUMP WITH SLIP COUPLING Filed March 20, 1967 sheet '3 of 5 Figlia Discharge against a constant pressure head in the pipe system irrespective of the discharge from same, the pressure at the suction being variable Pressure at suction side Pressure head in the ipe system Figlib Pressure head in the pipe system Mu Ada/my March 18, 1969 s. ENGLEssoN 3,433,162

CENTRIFUGAL PUMP WITH SLIP COUPLING' Filed March 2o, 19e? sheet 4 of 5 Fig. 5a Discharge against a constant pressure head in the pipe system irrespective of the discharge from same, the pressure at' the suction side being constant.

H Constant level const.

F i g. 5 b H H const.\

n1 I"2 nmax O Q Q Q No discharge from 1 2 max pipe system INVENTOR:

aI/MA M,

March 18, 1969 s. ENGLEssoN 3,433,162

CENTRIFUGAL PUMP WITH SLIP COUPLING Filed March 2o, 1967 sheet 5 of s Reshaping of the pump characteristic and protection of the motor against overload by torque limitation Mv max The motor speed is assumed to be constant IN VEN TOR r S'fxe/J Eng/essen,

United States Patent O 4,865/ 66 U.S. Cl. 103-87 2 Claims Int. Cl. F04d 13/04; F04!) 49/02 ABSTRACT OF THE DISCLOSURE A membrane-actuated throttle valve is provided between the discharge and the suction side of a slip-coupling connecting the impeller of a centrifugal pump to the drive motor shaft.

The present invention refers to a centrifugal pump comprising a slip-coupling connected between the motor and the pump, which device provides the possibility of achieving a certain speed regulation by slippage. The slippage, however, is a loss which is proportional to the difference in revolutions which is converted into heat which must be dissipated by cooling.

The application thus relates to a centrifugal pump comprising an impeller arranged in a fluid chamber for the pumped uid and a driving motor for said impeller arranged outside the pumped duid. The slip-coupling connecting the impeller to the driving motor is located in said tluid chamber.

lt is an object of the present invention to further increase the possibilities of controlling the impeller speed by means of a slip-coupling, the invention being essentially characterized in that a controllable throttle valve is provided between the discharge and the suction side of the coupling.

A centrifugal pump provided with said device makes it for instance possible to maintain a constant pressure in a pipe system irrespective of the discharge from the system and to a certain extent even irrespective of the pressure at the suction side of the pump. This possibility can be provided by a further development of the invention which consists in that the controllable throttle valve is controlled by a liquid pressure at the discharged side of the centrifugal pump.

Another operation possibility when using the pump according to the present invention consists in that it is even possible to provide a constant pressure in the pipe system irrespectve of the discharge from said system, the pressure at the suction side of the pump remaining constant. To that purpose, according to a further modification of the invention, the controllable throttle valve is arranged to be controled by a pressure-sensitive means preferably connected to the discharge side ofthe pump.

A further operation possibility provided by the invention includes the use of the slip-coupling for limiting the capacity in sewage-water pumps, particularly submersible pumps, having a maximum free passage through the pump impeller. According to a further embodiment of the invention an adjustable throttle valve is to that purpose provided between the suction side of the discharge side of the slip-coupling, said throttle valve responding to a spring set for a determined torque of the pump shaft. Said adjustable spring-biased throttle valve may be either connected in parrallel with the controllable throttle valve or be constituted by said controllable throttle valve.

For actuating the controllable valve a diaphragm-actuated stem is provided which is tted in an axial recess in the impeller drive shaft, said valve being preferably constituted by a slide arranged for axial reciprocating movement in said recess.

The invention will be more particularly described hereinafter with reference to the accompanying drawings, in which:

FIG. 1 illustrates a pumping unit comprising a pump impeller wth a built-in slip-coupling,

FIG. 2 is a top plan view of the slip-coupling partly in section,

FIG. 3 is a vertical section through a slip-coupling,

FIGS. 4a and 4b are graphs illustrating the operation when the pump discharges against a constant pressure head in the system and irrespective of the magnitude of the discharge from the system, the pressure on the suction side being variable,

FIGS. 5a and 5b are a diagramm and a graph, respectively, illustrating the operation when pumping against a constant pressure head in the system irrespective of the` discharge from the system, the pressure on the suction side being constant, and

FIG. 6 is a graph illustrating the operation when the pump characteristic is modified and a protection against overload is achieved by limiting the torque in the slipcoupling.

FlG. l shows a pumping unit comprising a pump with a pump casing 1, an impeller 2 and an end plate 3. The stator casing 4 of the motor is flanged onto the

end plate

3, 5 being the hollow pump shaft. A stem 6 shown in dashed lines is titted inside the hollow shaft for axial displacement upwards and downwards, said stem being actuated by a membrane 7 against the action of a spring 8. The membrane is arranged in a pressure chamber 9 to which pressure liquid from the discharge side 11 of the pump can be conveyed Via a duct 10.

ln the fluid chamber 12 of the pump casing is provided a slip-coupling with a casing 13 tted to the impeller 2 and a rotor 14 secured to the motor shaft 5. The rotor 14 of the slip-coupling is provided with blades 15 arranged for sliding radially outwards preferably under spring action, which blades transmit the rotational movement of the impeller to the transmission medium, preferably oil, contained in the slip-coupling casing 13.

The slip-coupling casing is also provided with suction channels 16 and discharge channels 17 which via

ports

13 and 19, respectively, provided in spaced relationship along the pump shaft periphery are communicating with the inside of the pump shaft and corresponding recesses provided in the control slide 20 of the valve, said slide moving axially together with the stem 6.

FIGS. 2 and 3 are detail views of the slip-coupling. FIG. 3 is a section along the lines A-A in FIG. 2. The same reference numerals as in FIG. 1 have been used. The casing of the slip-coupling has been shown with a somewhat exaggerated elliptic shape, it being understood that in reality the ellipse is to be more circular since the oil volume between two adjacent blades 15 may not vary during the passage of the blades from the suction side to the discharge side, if leaks 4between the blades and the casing are to be avoided. The blades 15 are thrust outwards against the slip-coupling casing by springs 21.

Ports

18, 19 are provided along the periphery of the pump shaft 5 4in order to ensure communication between the

channels

16, 17 and the inside of the pump shaft.

The slip-coupling operates as follows: The slip coupling rotor 14 rotates together with a shaft 5 and the blades 15 convey the pressure fluid ahead of them from the suction channel 16 to the discharged channel 17. If the stem 6 and consequently the slide 20 are in the uppermost position, the throttle valve is entirely closed and no communication exists between the suction and the discharged side of the slip-coupling. The motor shaft is in that case firmly coupled to the impeller. As soon as the pressure at the discharged side 11 of the pump becomes too high, the pumped fluid is forced upwardly through the duct 10 into the pressure chamber l9 in the pressure controller on top of the membrane 7 and thrusts the stem 6 downward against the action of the spring 8 so that the valve slide 20 is moved to its lower position, whereby the throttle valve is open so that oil may pass from the discharge side to the suction side of the slip-coupling. Depending upon how large section of said channel is opened by the motion of the slide 20, a larger or smaller part of the work supplied to the slip-coupling rotor is used for pumping oil through the channels of the slip-coupling. Slippage occurs in the slip-coupling and the impeller will thus rotate at a lower speed than the rotor shaft.

Various applications of the invention will be described below, reference Ibeing made to the graphs 4-6.

FIGS. 4a and 4b are graphs illustrating operating conditions where the pressure at the suction side is supposed to be variable but 'where in spite of that the pressure in the pipe system at the discharge side is to be kept constant irrespective of the discharge from the system. FIG. 4a illustrates a boarder-line case where the available water pressure at the suction side is equal to the pressure which is to be maintained in the pipe system. In this case the pressure feeding pipe system is sufliciently high and a pressure controller of the kind shown in FIG. l will therefor adjust the slip-coupling so that slippage occurs; the -impeller is only to follow the liquid stream resulting from the water pressure at the suction side without retarding it.

Should on the other hand the pressure at the suction side drop below the pressure head in the discharge pipe system, as illustrated in FIG. 4b, the pump will have to provide an additional pressure to the pressure of the 'water at the suction side in order to provide the required pressure head in the discharge system. In that case the pressure head in the pipe system will drop at lirst. As a result thereof the channels in the slip-coupling are closed by the slide 20 moving upward. The slippage in the slipcoupling is thus reduced and a firmer coupling is achieved between the motor shaft and the impeller, whereby the pump is thus able to provide the additional pressure head required. Depending upon the How rate Q, Q1, Q2 or Qmax, respectively, discharged from the pipe system, the speed of the impeller will be adjusted to requirement by the slip coupling.

FIGS. a and 5bV illustrate an applicat-ion example of the invention under operating conditions where a constant pressure is to 'be maintained in the pipe system irrespective of the discharge from same, the pressure from the suction side remaining constant.

As appears from the figures pipe friction losses have been disregarded and for a constant pressure head in the pipe system, Hconst, one obtains along a horizontal line the design points corresponding to a certain discharge Q2 or Qmax from the pipe system, which design points are indicated -by edges. An impeller speed n2 corresponds for instance to a discharge Q2 from the pipe system and an impeller speed nmax corresponds to a discharge Qmax from the pipe system. The control of the slippage of the slipcoupling is also in this case assumed to be achieved by a pressure from the discharge side of the impeller which pressure, as described above, adjusts the slide in the slip-coupling as required in order to obtain the desired slippage.

With reference to the graph in FIG. 6, operation conditions will be described in the case where one desires to reshape the pump characteristic whereby a protection against motor overload is obtained by limiting the torque transmitted by the slip-coupling. This type of operation is particularly appropriate when the power requirement of sewage-water pumps having a maximized free passage through the impeller is to be limited.

1n centrifugal (pumps for sewageand waste-water the aim is to achieve a maximized free passage through the impeller and the casing volute. Ideal conditions are achieved when the pump inlet and the impeller channels have the same size so that all what comes in through the pump inlet also may pass through the whole pump. In other words, there is a free passage for a ball, the diameter of which is equal to that of the lpump inlet. The pressure and iiow rate curve of the pump is then quite flat; the ow rate increases rapidly and therewith also the driving power required on the pump shaft when the counter-pressure decreases. This is inconvenient for two reasons.

One of them is that a huge and expensive motor is required for driving the pump unit if the motor is to be sutiicient along the whole characteristic curve of the pump. The power consumption is high. The other reason is that a very lar-ge quantity of water is discharged into the pipe system, a quantity which may exceed the system capacity and there is a risk for water rising up in the nearby draining gutters and the like.

As shown in FIG. 6 the invention provides the possibility to limit the Aflat part of the characteristic by limiting the impeller speed. By a progressive reduction of the impeller speed it is thus possible to give the characteristic a steaper or atter shape as desired.

A sewage-water pump usually exhausts water from a pit or collecting well, in which the Water is allowed to rise up to a level of 1 meter for instance. The pumps are then started automatically, usually one at a time, and exhaust the water until it reaches the lower level. As the water level in the collecting well drops, the static head increases and the flow rate decreases accordingly. With a very flat characteristic like the one obtained with an impeller having a large free passage, the difference between flow rate at the beginning and at the end of the pumping can be considerable. This leads also to a greater power requirement at the beginning of the pumping.

The speed control according to the invention provides the possibilities to make the characteristic within said area entirely vertical so that the flow rate discharged to the pipe system is uniform irrespective of the head variation.

The control impulses can be obtained from the power supplied to the motor, possibly from the motor current. The speed control can also be achieved by means of a slip-coupling whereby the latter is adjusted for a certain maximum torque. The invention may suitably be used also in connection with purification plants having biologic strata or the like. In such plants it is important that sewage-water is supplied at a constant ow rate. In this case the control impulses are provided by a suitable flow-rate meter.

Heavy concussions occuring in the pipes in connection with the stoppage of the pumps are also a problem which can be solved by means of the invention. If the refluxvalve does not close entirely at the instant the water velocity has dropped to zero after stopping the pump the liquid column will mn backwards gaining in velocity and when the reflux-valve nally closes there occurs a Iwater hammer resulting in severe stresses on the piping and even noise. The invention provides a possibility to reduce the speed of the pump until the flow has stopped. i.e. until the manomatric head of the pump is equal to or somewhat lower than the static head and the pump is not stopped until this condition is reached.

The pump can also be started in the same way whereby a more progressive start with a lower starting current is achieved.

The -graph in FIG. v6 illustrates how the slip coupling operates in order to avoid motor overload. At the speed nm,X the pump discharges at a Iiiow rate QmaX whereby the motor consumes a power of n-max HP which corresponds to a maximum MV max. The slip coupling now starts operating in that the spring-biased Valve in the coupling opens. Slippage occurs and the pump shaft speed drops to n1 which corresponds to a discharged ow rate Q1. The motor output simultaneously drops to N1. At the instant when the slippage occurs the pump characteristie thus gets steeper in that the characteristic is bent downward at a point corresponding to Nmax.

Although the invention has been described in connection with the embodiment shown in the drawings, it is obvious that many alterations or modications may be made within the scope of the appending claims.

What I claim is:

1. A centrifugal pump including a fluid pumping chamber, an impeller arranged in said fluid pumping chamber, a shaft in driving connection with said impeller, a motor driving said impeller by means of said shaft, said motor being arranged outside the pumped fluid, and a hydrostatic slip-coupling arranged in said uid pumping chamber, said slip-coupling being provided with a throttle valve between the discharge and the suction side of the coupling, which valve is controlled by the liquid pressure at the discharge side of the centrifugal pump.

2. A centrifugal pump as claimed in claim 1, a nonrotat able stem being tted in an axial recess in the impeller drive shaft, said valve being actuated by means of said non-rotatable stem operated by said pressure.

References Cited UNITED STATES PATENTS 2,009,001 7/ 1935 Peterson. 2,933,129 4/1960 Wright 103-35 XR 3,155,040 11/1964 Shurts et al. 103-35 ROBERT M. WALKER, Primary Examiner.

U.S. Cl. X.R. 230-15