US2397664A - Liquid pump of the centrifugal type - Google Patents

Description

April 6- H. HlLLlER 2,397,664

LIQUID PUMP OF THE CENTRIFUGAL TYPE Filed March 27, 1944 2 Sheets-Sheet 1 5 v 5 '5 I 4 a FIG./..

FIG-3 MJW April 2, 1946; H. HILLIER 2,397,564

I LIQUID PUMP OF THE CENTRIEUGAL TYPE Filed March 27, 1944 2 Sheets-Sheet 2 Patented Apr. 2, 1946 2.39am mourn rum or 'rrm CENTRIFUGAL TYPE Harold Hillier, Cathcart, Scotland, asslgnor to G. 3:. Weir, Limited, a corporation of Great Brit- Applicatlon March 27, 1944, Serial No. 528,199

In Great Britain April 3, 1943* 1 Claim.

This invention relates to means for the prevention of damageto liquid pumps of the centrifugal type when operating against a closed discharge valve or with a very small liquid flow from the discharge of the pump. Y

When a centrifugal pump is in operation, a proportion of the energy supplied to the pump by the driving unit is absorbed in friction, shocks, eddies and churning within the pump. The energy so absorbed is transformed into heat which increases the temperature of the liquid flowing through the pump. liquid through the pump, the temperature rise, due to these causes, is comparatively small and does not involve any serious consequences, but, when the pump is operating against a closed discharge valve or with a very small flow of liquid through the pump, the temperature rise through the pump can be very considerable and may be such that, in a few minutes, the temperature is raised to the boiling point of the liquid within the pump, and a portion of the liquid is evaporated. Such vaporisatlon may prevent the flow of water into the suction of the pump, thereby preventing the pump from discharging liquid, with the result that seizure or damage may occur between the rotating and the stationary parts due to the lack of an adequate supply of liquid for cooling and lubricating purposes.

The operating conditions of a large number of centrifugal pump installations are such that a certain minimum flow through the pump is necessary, in order to avoid such dangerous conditions arising, and provision is usually made to ensure that, whenever there is a danger of the flow through the pump falling below the minimum required to ensure safe operation, an emergency outlet from the discharge of the pump is opened, either by hand or automatically, to allow the pump to discarge a predetermined minimum quantity of liquid back to the source of liquid sup-. ply, such predetermined quantity being fixed as necessary to prevent a dangerous rise in temperature through the pump under any condition of operation The quantity of water passing throu h such emergency outlet is usually known as the bypass discharge.

For many centrifugal pump installations, the operating conditions are such that a hand-operated bypass meets all requirements, but, in other installations, such as centrifugal pumps used for'boiler feed purposes, it is necessary to operate two or more centrifugal pumps discharg- With a considerable flow of as to share proportionally the total quantity of water discharged. With extremely small liquid fiows, it is barely practicable to ensure that each pump discharges its due share of the total, and operating occasions may arise in which the flow is completely stopped. Such conditions arise in a haphazardous fashion, and it is not possible to anticipate them by manual operation of the bypass, so that it is necessary that the bypass should be opened automatically whenever the flow falls below the necessary minimum.

Centrifugal pumps are usually provided on the discharge side with a non-return valve which 25 through the centrifugal pump into the suction ture and the leakage ofhot feed water through the bypass connection results in undesirable heating of the feed supply tank and suction system and a loss of heat potential.

The primary object of the present invention is to provide an improved apparatus for controlling the flow of bypass liquid from a centrifugal pump in such manner as to prevent any flow through the bypass connection when the pump is in normal operation and the bypass is closed, and to eliminate, or reduce to a minimum, the resistance to the closing motion of the non-return valve on the discharge of the pump. For this purpose, the bypass valve-is remotely hydraulically actuated by means of liquid taken from the discharge of the pump, the flow of such actuating liquid being controlled by a small pilot ing in parallel, and such pumps are so designed 86 valve, the primary operating force controlling the bypass discharge being thereby reduced minimum.

I may use the closing motion of the non-return valve in the discharge line of the pump to open the bypass pilot valve which may be provided with a spring operative to close the bypass pilot valve during the opening motion of the non-return valve, or I may arrange that the opening movement of the non-return valve will close the bypass pilot valve through a flexible link connection whereby the opening motion of the non-return valve can continue after the bypass pilot valve is closed. I may provide the non-return valve on the pump discharge with a spring to assist in closing the non-return valve and to ensure that sumcient force is available to ensure the opening of the bypass pilot valve and the complete closure of the non-return valve. I may obtain the force for the operation of the pilot valve from a diaphragm one side of which is subject to the discharge pressure of the pump on the underside of the discharge non-return valve, while the other side of the diaphragm is sub- .iect to the discharge pressure in the discharge line on the outlet side of the said non-return valve, in conjunction with the load of a spring. I may provide the non-return valve on the pump discharge with a spring to assist the closing movement of the non-return valve, with the object of providing a definite pressure drop across the valve, such pressure drop bearing a predetermined relation to the quantity of liquid flowing through the valve, so that the same predetermined pressure drop is available across the diaphragm for the movement of the diaphragm in operating and opening the pilot valve for the bypass discharge valve.

To ensure that there is no leakage across the bypass discharge valve under normal operating conditions, the bypass valve is of the seated type. A spring may be provided to exercise a force holding the valve on its seat, the spring load plus the discharge pressure of the pump acting on the top of the valve maintaining the valve closed and thereby ensuring absence of leakage through the bypass valve under normal operating conditions of the pump. On the underside of the bypass valve there may be provided a piston having an area considerably in excess of the bypass valve area. The underside of the piston is in communication with the bypass pilot valve, so that, when the bypass pilot valve opens, the discharge pressure of the pump is applied to the remote side of the piston, causing the piston to move upwards and lift the bypass valve from its seat, thereby permitting the bypass discharge liquid to pass through the bypass valve to the source of liquid supply. When the bypass pilot valve is closed, the water in the chamber under the piston leaks through the clearance between the piston and the chamber to the source of liquid supply, so that the piston is balanced and the spring load, plus the pump discharge pressure, acting on the top of the bypass valve, causes the bypass valve to return to the closed position.

I shall now proceed to describe in detail practical embodiments of the invention as illustrated in the accompanying drawings in which the same reference numerals denote similar parts in the several views.

Fig. 1 shows diagrammatically the arrangement of two centrifugal liquid pumps with automatic bypass valves in accordance with the invention.

Fi 2 is a sectional elevation of the discharge spa-mu to a non-return valve and a bypa s pilot valve in accordance with theinvention.

Fig. 3 is a. sectional elevation of a pilot-operrated bypass valve in accordance with the inven- Fig. 4 is a sectional elevation through a dia- I phragm-operated bypass pilot valve.

Referring to Fig. 1, each centrifugal pump l draws liquid from a tank 2 through suction piping 3 and discharges the liquid through a nonreturn discharge valve 4, and an isolating valve 5, to a common discharge line 6. The two pumps are required to operate in parallel and to share the total liquid flow, but it is difllcult so to manufacture and arrange the pumps that each pump handles its proper share of liquid at very small liquid flows, so that it is always possible at small flows for one pump-to discharge the whole flow and prevent any flow of liquid passing through the other pump. The non-return valve 4 prevents any possible back discharge through the said pump but it is essential to ensure a flow through the pump under such conditions as to prevent overheating of the pump and possible damage to the rotating and the stationary parts of the pump. a

For this purpose, I provide a branch 6a on the non-return valve 4 for a bypass pilot valve which controls the supply of operating water through a pipe 9 to a bypass valve 8 which controls the flow of bypass liquid from the branch I on the nonreturn valve 4 to the liquid tank 2 by way of the pipe l0.

Referring to Fig. 2, the non-return valve 4 has a valve element II which is provided with a central extension spindle l2 which is guided below the valve in a bush l3 formed in the valve seat [4. The extension spindle 12 above the valve is guided in a bush formed in the valve box cover IS.

A spring I6 is provided between the valve I l and the cover l5, so that the bias of the sprin exercises a force to close the valve II. On the underside of the non-return valve seat l4, there is provided a branch 61; into which is inserted a cover I! containing a seat for the bypass pilot valve l8.

An extension of the cover plate I! forms a guide l9 for the pilot valve l8 and centres the pilot valve It in relation to its seat in the cover plate l1.

The guide I9 is provided with a fulcrum 20 on which is mounted a bell-crank lever 2!, the end of one arm of which passes into a slot 22 formed in the pilot valve l8. The other arm of the bellcrank lever 2| is extended so that its extremity lies immediately under the spindle extension l2 of the non-return valve il. The guide IQ for the bypass pilot valve l8 forms housing for a spring 23 which is retained in position by a cap 24 threaded on the guide iii. The spring 23 exercises a force to close the bypass pilot valve' [8 against its seat in the cover I]. The liquid discharge pressure of the pump assists the spring 23 in closing the pilot valve Ill.

The extremity of the lever 2i under the nonreturn valve spindle I2 is so arranged in relation to the non-return valve spindle l2 that closing motion of the non-return valve. ll causes contact to be made between the non-return valve spindle l2 and the extremity of the bell-crank lever 2! at a predetermined position before the v non-return valve ll reaches its seat l4. After contact is made between the spindle l2 and the bell-crank lever 2|, further motion of the non-- return valve ll towards its seat I4 opens the pilot valve l8. The non-return valve H is provided with a skirt 25 and contact is made between the spindle I2 and the bell-crank lever 2| at the position in the travel of the non-return valve II when the skirt 25 enters the seat I 4. It will be seen that, when the flow of liquid past the non-return valve ll falls to a small amount, the skirt 25 will be entering the seat l4 and the bypass pilot valve l8 will be commencing to open. Further movement of the non-return valve H to the completely closed position will ensure that the bypass pilot valve is moved to the full open position. When the centrifugal pump discharges an appreciable quantity of liquid into the discharge line, the non-return valve I I will lift until its skirt 25 leaves the valve seat l4, at which point the pilot valve spring 28 will cause, the pilot valve l8 to seat on'the cover I! and cut off the flow of liquid through the cover l1. As all further liquid fiows through the centrifugal pump up to the maximum, the pilot valve I8 is maintained in the closed position by the spring 23 and the discharge pressure of the pump.

Fig. 3 shows the bypass valve chest 8 which is provided with an inlet branch 28 and an outlet branch 21. The branch 28 joins the branch 1 on the pump non-return discharge valve below its seat. The bypass valve 28 co-operates with a seat 84 to control the flow of liquid from the centrifugal pump discharge through the branch 28 to the outlet 21, whence it can flow to the liquid tank. A spring 29 is provided between the bypass valve 28 and the cover 88, the spring exercising a force to close the bypass valve 28 in conjunction with the discharge pressure of the pump, which passes to the top of the valve 28 by way of the hole 88 in the valve. The upper end of the valve 28 is provided with a. piston 82 guided in the valve body 8 to maintain alignment of the valve 28 relative to its seat .84. A spindle extension 8i on the valve 28 passes through the valve seat and makes contact with a piston 85 which moves freely in a chamber 88 provided on the outlet side of the bypass valve seat. The chamber 88 is provided with a cover 81 from which a pipe 8 connects the bypass valve chest to the pilot valve outlet in the cover l1.

The area of the piston 85 is considerably in excess of the area of the bypass valve 28 so that, when the pilot valve l8 opens, liquid at the discharge pressure of the pump is applied to the under face of the piston 85 in the chamber 88. The force applied to the piston 85 considerably exceeds the force of the spring 28 and the discharge pressure of the pump applied to the top of the valve 28, so that the resultant force available causes the bypass valve 28 to move into the openposition and permit the pump to discharge liquid through the bypass valve 28 tothe liquid supply tank 2.

When the pilot valve l8 closes, the liquid present in the chamber 88 leaks through the clearance between the chamber 88 and the piston 85 to the outlet 21 until the pressures on both sides of the piston 85 are equalised. The resultant force on the bypass valve 28 is then composed of the load of the spring 28 and the discharge pressure of the pump applied to the valve 28 with the result that the bypass valve 28 moves into closed position and all flow through the'bypass is cut oil. a 5

It will berecognised that, since both the bypass valve 28 and the pilot valve l8 are of the seated typ all leakage from the pump discharge through the bypass arrangement is. completely prevented when the pilot valve i8 is closed.

The bypass valve 28 may be of any desired size, and the pilot valve [8, due to the fact that it controls only a small quantity of water to actuate the bypass valve operating piston 85, can be made small, so that the force necessary to operate on the underside of the non-return valve II, the

cover plate 11 forming the closing member of that branch.

To ensure that the pilot valve l8 will close, under all operating conditions, even in the event of the pressure difference across the non-return valve l I being negligible, a condition which may occur when two or more centrifugal pumps are operating in parallel at very light loads, the load of the spring i8 on top of the non-return valve II is made sufficient to ensure, the opening of the pilot valve l8. Referring to Fig. 4, the lower end of the pilot valve 88 is guided in a bush 88 which is screwed into a stirrup 48, the upper end of which passes through a lower diaphragm cover plate 4i and an upper diaphragm cover-plate 42 between which is secured a diaphragm 43, the cover plates and diaphragm being held together by the nut 44 on the end of the spindle 45 formed at the upper end of the stirrup 48. The diaphragm is trapped between a branched cover 48 and a body 41 which contains the inlet branch 48 for the flow of the hydraulic operating liquid controlled by the pilot valve 88, such liquid entering by the branch 48,

' ing by the outlet branch 58.

The seat 48 is provided with a cylindrical bore 51 which forms a guide for the pilot valve 88, and is provided with holes 52 for the passage of the liquid through the valve seat. A cover 58 provides access to the pilot valve 88 and the stirrup mechanism. An upper stopper ring 54 is trapped between the body 41 and the top cover 48, the body 41 and the stopper ring 54 being provided with stops to limit the movement of the diaphragm and the lower and upper diaphragm plates 4| and 42. In the extreme positions of the diaphragm, the diaphragm is fully supported by the corresponding diaphragm plate and the body 41 or the stopper ring 54.

The branch 48 is connected to the branch 1 on the non-return discharge valve body 4 so that liquid passing through the branch 48 is taken from the discharge of the centrifugal pump on the. underside of thenon-return valve H. A branch 55 is provided above thenon-return valve II and is connected to a branch 58 in communication with the space 51 on 'top of the diaphragm 48 so that the pressure of'the feed main on top of the non-return valve ii is at all times applied to the top of the diaphragm 48. The pressure on the underside of the non-return valve l I is at all times applied to the space 58 on the underside of the diaphragm 43. The diaphragm is therefore subjected to the difference in pressure between the inlet and outlet sides of the non-return valve II. In addition, a spring 58 is arranged between the cover 48 and the-upper diaphragm plate 42, exercising a=1oad in conjunction with the pressure. on the top of the non-return valve ll, so

that the pressure diflerence across the diaphragm 43 is substantially the same as the pressure difference across the non-return valve I.

When the non-return valve H is moved into the open position by the discharge pressure of the centrifugal pump exceeding the pressure inv the discharge main, the pressure difference available across the valve II is exercised across the diaphragm 43 and causes the pilot valve 38 to seat on the valve seat 49, thereby stopping the flow of liquid through the pilot valve. A spring 60 is provided between the pilot valve 38 and the bush 39, so that, as the diaphragm 43 moves the stirrup 48 in the upward direction, immediately the pilot valve 38 seats itself, any further movement of the diaphragm compresses the spring 60 so that the load applied-to the pilot valve 38 is limited to the compression load of the spring 60, until the diaphragm 43 reaches the stop provided by the ring 54 and the upper diaphragm plate 42. The arrangement is such that, when the pilot valve is closed by the movement of the diaphragm, further movement of the diaphragm is permitted by the spring 60 until it reaches the stop, in which position the diaphragm is fully supported so that possible rupture or damage to the diaphragm is thereby prevented.

Before the non-return valve H can open, the pressure on the underside must exceed the pressure on the top side as necessary to lift the nOnreturn valve ll against the spring I! This pressure difference will also 'be exercised across the diaphragm 43', so that the diaphragm 43 will move at the same time and in the same direction as the'non-return valve ll. Opening movement of the non-return valve II is therefore accomasoaou panied by closing movement of the pilot valve 38 and vice versa. I so arrange the loads of the springs l6 and 58 that, when the skirt 25 of the non-return valve ll enters the seat I4, the resultant load acting on the diaphragm 43 causes the diaphragm to move downwards and open the pilot valve 38 so that liquid can flow through the branch 48, past the pilot valve 38, through the pilot valve seat 49 to the outlet branch 50, whence it passes to the bottom of the piston chamber 36, the liquid pressure being applied to the underside of the piston 35 so as to cause the necessary movement to open the bypass valve 28, thereby permitting the centrifugal pump to discharge liquid through the bypass connection to the liquid tank from which the centrifugal pump draws the supply of liquid.

I claim:

The combination with a non-return valve in the discharge line of a centrifugal pump, of a spring-urged by-pass valve of the seated type permitting when open the discharge by. the pump of a predetermined minimum quantity of liquid for eventual return to the suction side of the pump,'a pilot valve of the seated type ,serving to efiect hydraulically the operation of said bypass valve, a spring urging said pilot valve in closing direction, and a lever device having one arm engaged with said pilot valve, the other arm of said lever being free and in the path of motion of said non-return valve whereby said lever is valve.

HAROLD HILLIER.

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