US2672820A - Centrifugal pump - Google Patents

Description

march 23, 1954 H. HILLIER 2,672,820

CENTRIFUGAL PUMP Filed April 22, 1952 3 Sheets-Sheet 1 In ra fir Hm HM March 23, 1954 H, HlLLlER 2,672,820

CENTRIFUGAL PUMP Filed April 22, 1952 3 Sheets-Sheet 2 In yen 7 0!" March 23 1954 H. HILLIER CENTRIFUGAL PUMP Filed April 22, 1952 3 Sheets-Sheet 5 FIG. 3.

Patented Mar. 23, 1954 UNITED STATES PATENT OFFICE Claims priority, application Great Britain April 27, I951 4 Claims. 1 This invention is directed to the prevention of damage to liquid pumps "of the centrifugal type when operating against a closed discharge valve or with a very small liquid flow from the discharge side of the pump.

When a centrifugal pump is in operation, a proportion oftheenergy transmitted to the pump by the driving unit i'sabsorbed in friction, shocks, eddies and churning within the pump. The energy so dissipated is transformed into heat which increases the temperature of the liquid flowing through the pump. With a considerable flow of liquid through the pump, the resultant temperature rise 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 may be considerable and maybe such that, in a few minutes, the temperature of the liquid within the pump is raised tothe boiling point, and a portion of the liquid is evaporated". Such evaporation may prevent the flow of Water into the suction of the pump, thereby preventing the pump from discharging liquid, with the result that seizure may occur between the rotating and the-stationary parts owing to the lack of an adequate supply of liquid for cooling and lubricating purposes.

The operating conditions of centrifugal pump installations are often such that a certain minimum flow through the pump is necessary in order to prevent such dangerous conditions from arising, andprcvision is usually made to ensure that, when there is a danger or the flow through the pump falling below the minimum required to ensure safe operation, an emergency outlet from the discharge or the pump is opened, either by hand or automatically, to allow the pump to discharge a predetermined minimum quantity of liquid back to the source of liquid supply, such predetermined quantity being fixed to prevent a dangerous rise in temperature through the pump under any condition or operation.

The quantity of water passing through such an emergency outlet is usually known as the bypass discharge.

For centrifugal pump installations the operat ing conditions may be such that's hand-operated bypass: meets all requirements, but, in many installations, such as those including centrifugal liquid flows, it is barely practicable to ensure that each pump will discharge its proper share of the total load, and operating conditions may ar se in which the flow is con'ipleiely stopped. Such occasions arise in a haphazardous fashion, and it is not possible to anticipate them by manual operation of the bypass discharge, so that it is necessary that such bypass should be opened automatically whenever the How falls below the necessary minimum.

Centrifugal pump are usually provided on the discharge side with a non-return valve which closes in the event of there being any tendency for liquid to flow back from the discharge line through the pump. It is known to use the 'clo'sing motion of a non-return valve the discharge l ne to open a bypass discharge, either directly or through a relay, a typical example of such an arrangement being disclosed in the prior specification No. 2,397,664.

The closing motion of the non-return valve is usually assisted by means of a spring, and, in some circumstances, the force available is limited to that which can be appl ed by the spring. In largeinstallations, it is of extreme importance that boiler feed pumps should be maintained in operation and any risl'r of damage avoided, and it is desirable, therefore, the operation of the bypass discharge should he sateguarded as tar as possible.

The invention providesan improved apparatus for controlling the flow of bypass liquid from a centrifugal pump in that the opening of the bypass valve is effected in response to :a predetermined rise in temperature of the feed water passing through the pump, such action being supplementary to or substitution for the hydraulic action of apparatus such as described in specificution No. 2,391,664.

With a considerable flow of liquid through the pump; the temperature rise owing to cause already stated is comparatively smalli but the temperature rise increases as the flow through the pumpis reduced. The invention contemplates the use of this increase in temperature at a given low flow through the pump for the purpose of actuating the bypass discharge device whereby the fiowthrough the pum is prevented from falling below the minimum quantity oi water which can be passed through the bypass dischargedevice.

Wi'tl r this purpose view there are provided two thermostats, one in the pumpsuction systern where will be exposed to the temperature of the water entering the pump and the other in the pump discharge system where it will be exposed to the temperature of the water at the discharge of the pump. For convenience, the second thermostat may be arranged in the hydraulic balance discharge line wherein there is a continuous flow of water at a temperature slightly higher than the temperature of water at the discharge of the pump. Each of the two thermostats may be included in a closed system including a Sylphon bellows or the like, the system being filled with an expansive liquid or gas whereby the volume and/or the pressure in the system rises with increase in temperature, the increase in volume being accommodated as desired by the expansion of the bellows.

The two bellows operating in conjunction with the two thermostats may be interconnected by a common diaphragm or connecting plate, the said diaphragm being subjected to the pressures on each side which are generated by the liquid within the thermostatic systems. The opposite ends of the two bellows may be rigidly or elastically maintained in position relatively to one another, so that, whenever the pressure in one bellows increases above the pressure in the other bellows, the common diaphragm will move in the direction of the lower pressure. The bel- 'lows at high pressure may be rigidly fixed at one end while the bellows at the lower pressure is supported by an elastic member such as a spring, set to balance a predetermined difference in pressure between the two bellows, the common diaphragm being free to move as the pressure in the high pressure bellows increases.

The movement of the common diaphragm may be arranged to operate a power relay of the pneumatic, hydraulic, or electric type, and, for

- example, in the last mentioned case it may control a flow of electric current to an electro- .magnet or solenoid thrustor or motor operated device, whereby a pilot valve is opened to permit the flow of operating water to a piston which causes the bypass valve to open and permit the discharge. of bypass water to the suction system of the pump. To ensure that there is no leakage from the pump during normal operating conditions, the pilot valve is preferably of the seated type; the bypass valve is also preferably of the seated type.

A spring may be provided to exercise a force holdin the bypass valve on its seat and the spring load plus the discharge pressure of the pump acting on the top of the valve maintains the valve closed and thereby ensures 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 pilot valve which is operated electrically under the control of the common bellows diaphragm. When the 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 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.

The electrically operated pilot valve may be used in parallel with a mechanically operated pilot valve such as is disclosed in the prior specification No. 2,397,664.

The action of the common bellows diaphragm may be used to actuate a switch whereby electrical power is used to operate a motor, electromagnet or thrustor to open directly to bypass discharge valve, or the arrangement may be such that the motor, electromagnet or trustor maintains the bypass valve in the closed position, and the movement of the common diaphragm actuates the switch, whereby the elec tric power is cut off and the discharge pressure of the pump acting alone or in conjunction with a spring causes the bypass discharge valve to open and allow bypass water to be discharged from the delivery of the pump to the suction system of the pump.

The movement of the common bellows diaphragm may be arranged to operate the electric supply for a given temperature rise through the pump, and there may be provided adjustment means whereby the movement of the said diaphragm can be caused to take place with increased or decreased temperature rise as may be found desirable when the pump is in operation.

It may be provided that the movement of the common diaphragm will move the switch across a variable resistance, whereby the opening of the bypass valve can be varied between zero and full open so as to maintain a substantially constant predetermined difierence in temperature across the pump, whereby the quantity of bypass water is increased as the flow through the pump is reduced and vice versa. For this purpose, the motor, electro-magnet or thrustor may be arranged to vary in its movement or stroke in accordance with the position of the switch actuated by the common diaphragm.

The bellows-operated switch may be arranged to actuate a master electrical device, the position of which controls a slave electrical device, so that the position of the slave device is determined by the position of the master device, while the slave device controls the opening of the bypass valve at any desired position between closed and full open.

In order that my invention may be clearly understood, there will now be described in further detail practical embodiments of the invention illustrated in the accompanying drawings in which Fig. 1 illustrates diagrammatically an arrangement of automatic bypass with thermal operation, and Fig. 2 illustrates diagrammatically the arrangement of an automatic bypass with thermal and mechanical operation. Fig. 3 is a fragmentary view showing a modification incorporating a proportionate transmitter and receiver between the thermostats and the bypass valve.

Referring to Fig. 1, a centrifugal pump I is arranged to draw water from a supply tank 2 and discharge past a non-return valve 3 to a boiler (not shown). On the underside of the non-return valve 3 there is provided a branch 4 from which a bypass discharge line 5 is led back to the supply tank 2, and a control valve 6 is arranged in the bypass discharge line to control the flow of bypass water. The pump I is provided with a hydraulic balancing device 1.

A thermostat 8 is arranged in the suction line in that line.

aavaeco 9 to the pump I- so that it is subjected to the temperature of the Water enteringtthe. pump, while another thermostat ill is. arranged in the balarise-leakage discharge line '1 sothat it-is subiected to. the temperature. of the discharge water The thermostatic. is connected to a Sylphon bellows H by a closed system which is filled with a liquid or gas responsive to the temperature of the thermostat 8, while the thermostat it is connected by a closed system to an other Sylphon bellows I 2 filled with a gas or liquid responsive to the temperature of the discharge thermostat Ill.

The bellows II and I2 are coupled together at a common sensitive member E3 in the form of a diaphragm or plate. One end of the bellows I2 is held in position at I2, while the other end acts on the member It. One end of the bellows II is held firmly at l I, while the other end acts on the member It. A spring I l acts on the member I3 in opposition to the bellows l2,'the stress of the spring 24 being variable by adjustment of a nut member 54'. The movement of the member i3 may be amplified, as shown, by a simple lever device I3. The position of the member I 3 is determined by the difference between the suction temperature and the discharge temperature of the water passing through the pump I and by the loading of the spring 14 which can be pre-set to balance any desired temperature difference. The member is will move to one side or the other of its equilibrium position, as the temperature difference rises or falls. The movement of the member I3 caused by a rise in the temperature difference is arranged to move a mercury switch I5 controlling the supply of electric current to an electric thrustor it which, in normal operation, maintains the bypass valve 6 in the closed position, but, on the temperature difierence rising to a predetermined figure, the

movement opens the switch I5, thereby interrupting the current to the thrustor It, so that the pump pressure opens the bypass valve 5 and bypass water is discharged to the supply tank 2.

The switch I5 is so arranged that the member i3 must move through a substantial reverse stroke before it moves the switch it into the closed position and so causes the thrustor It to close the bypass valve 6. As will be understood,

by adjustment of the nut member I 4' the load the switch is operated.

Referring to Fig. 2, the thermostatic control may be used, as shown, to control a hydraulic pilot valve and bypass valve of the type described in the prior specification No. 2,397,664. The bypass valve 5' is of the seated type with a spring I! between the valve 6' and a cover It to assist in closin the valve 6. The discharge pressure of the pump I acts on top of the valve 5' in conjunction with the spring H. The bypass valve 6' is provided with a spindle extension I9 which passes through the bypass valve seat and makes contact with a piston which moves freely in a chamber 2! provided on the outlet side of the bypass valve seat. The chamber 2! has a cover 22 which is connected by a pipe 23 to the discharge of the pump and the flow through this pipe is controlled by a pilot valve 24, the open-- ing and closing of which is efiected through a 6 relay mechanism by the movements of a common member I3 of the thermostatic systems, win the Fig. 1 construction.

The area of the piston 20 is considerably greater than the area of the valve 6 so that, when the valve Ii is opened, water at the discharge pressure of the pump applied to the underside of the piston 28 overcomes the forceof the water applied on'top of the valve 6 plus the spring, so that the valve ii moves into the open position and allows the pump to discharge past the valve 6' to the supply tank 2. When the valve 6 closes, the water in the piston chamber 2| leaks through the clearance between the piston 20 and the chamber walls 2| to the bypass outlet until the pressures on the two sides of the piston are equalised. The pump discharge pressure plus the spring then causes the valve 6' to close and cut on" all flow through the bypass connection.

Owing to the fact that it controls only a small quantity of water to actuate the bypass valve opening piston 2b, the valve 24 may be very small so that the force necessary to operate the valve M is reduced to a minimum. The action of the solenoid I6 is effected under the control of a mercury switch I5 which is opened and closed by the movements of the member I3 of the thermostatic systems, so that the valve 24, and, therefore, the valve 5, are opened when a predetermined difference in temperature between the suction and discharge temperature is reached and closed when another predetermined lower difference in temperature is reached, so that hunting in the opening of the bypass valve is avoided.

As shown, there is provided an additional pilot valve 25 operated mechanically by the closing motion of the pump discharge non-return valve 3 as described in the prior specification No. 2,397,664, so that the bypass may be operated by either or both of these systems.

In the modification shown in Fig. 3 the movement of the thermostat lever I3 is transmitted through a torque amplifier 26 to a transmitter 21 and receiver 28, which latter is operatively connected to the bypass valve 6 whereby the valve 6 is operated proportionately to the resultant movement of the thermostatic devices.

It will be understood that the constructional details and applications may be varied without departure from the invention.

What is claimed is:

1. Means for controlling the discharge of bypass liquid from a centrifugal pump, including a discharge line leading from the centrifugal pump, a bypass line connected into the discharge line, a bypass valve in the bypass line, a sensitive member, two thermostatic devices arranged to act on and move said sensitive member, said thermostatic devices being responsive respectively to changes in the suction and the discharge temperatures of the liquid flowing through the pump, and power means responsive to the movement of said sensitive member for opening or closing said bypass valve in dependence on the resultant movement of said sensitive member by said thermostatic devices.

2. Means as claimed in claim 1, including an electrically operable means for opening and closing the bypass valve, and an electric switch actuatable by said sensitive member for in turn controlling the supply of current to said electrically operable means.

3. Means as claimed in claim 1, including a pilot valve actuatable by the sensitive member References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Mayo June 18, 1935 Filzsimmons Sept. 15, 1942 Hillier Apr. 2, 1946

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