US2622533A - Automatic recirculating control for pumps - Google Patents

Description

Dec. 23, 1952 ER 2,622,533

AUTOMATIC RECIRCULATING CONTROL FOR PUMPS Filed Aug. 6, 1948 2 SHEETS-SHEET 1 FIG. I

INVENTOR. HHR OLD f9. 5 CHL IE 05/? BY if. Mm

Dec. 23, 1952 H. A. SCHLIEDER AUTOMATIC RECIRCULATING CONTROL FOR PUMPS Filed Aug. 6, 1948 2 SHEETSSHEET 2 Illillll INVENTOR. HAROLD H. 5cHu0R Patented Dec. 23, 1952 AUTOMATIC RECIRCULATING CONTROL FOR PUMPS Harold Augustus Schlieder, Erie, Pa., assignor to Continental Foundry and Machine Company, East Chicago, Ind., a corporation'of Delaware Application August 6, 1948, Serial No. 42,873

12 Claims.

This invention relates to an automatic recirculating control for centrifugal boiler feed pu p and more particularly to a control of this type adapted to steam turbine driven pumps.

It is well known that the pressure loss through the stages of a steam turbine is substantially directly proportional to the load on the apparatus such as a feed water pump driven by the turbine. At periods of relatively low or no load on centrifugal type feed water pumps for boilers associated with a driving steam turbine in a conventional manner loss of suction and frequently damage to the pump occurs. For example, a centrifugal pump associated with a boiler feed water system may lose suction by vapor binding. Although the centrifugal pump may be intended to pump water the liquid being pumped may be heated above its boiling point under certain conditions. If the discharge line from the pump is throttled or shut off so that only a relatively small quantity or no liquid is being pumped, the liquid trapped in the pump is whirled around in the pump casing and the power developed by the pump driving unit is largely transformed into heat in the pump. This heat is absorbed by the liquid in the pump and when the liquid temperature increases to the boiling point, steam is formed and water will not be thereafter pumped even though the discharge line is opened. The steam must be vented from the pump casing before water will flow into the pump again. Further, it frequently happens that due to the temperature increase, the normal clearance between the relatively movable parts of the pump disappears causing the internal parts of the pump to seize and bind and ruin the pump.

I have devised an arrangement particularly adapted to steam turbine driven centrifugal type boiler feed Water pumps wherein the above mentioned disadvantages of loss of suction in and possible damage to the pump are substantially eliminated.

According to the invention, a connection to a pressure control line is made at a point in the turbine where the steam pressure at maximum load is for example, 125-150 pounds per square inch. Another connection to a pressure line is made at the turbine outlet. Since the pressure through the stages of a turbine is substantially directly proportional to the load on the driven apparatus, the difference in pressure between these two points will vary substantially in proportion to the load on the turbine. At zero load on the turbine there may be a drop of 25-30 p. s. 1. through this section of the turbine to keep the pump turbine unit up to speed at no load. About p. s. i. would be available from the no load to full load range. When the demand on the pump drops to a point such as 10% of the pump output I provide means for automatically recirculating water through the pump. A recirculating line from the outlet side of the pump to the inlet side includes a valve adapted to open and permit recirculating flow back to the inlet side of the pump when the pressure difierential between the pressure control lines connected to the turbine drops below a predetermined value. Any increase in pressure differential between the turbine pressure control lines connected to the turbine will prevent recirculating liquid flow through closing of the valve in the recirculating system.

The principal advantage of this arrangement of measuring the pump discharge is that a considerable amount of valve operating power is made available through the turbine which cannot be obtained as conveniently from any other source. This arrangement enables the movement of the recirculating liquid flow control valve to be extremely positive and accurate.

I also contemplate that a constant pressure type of valve could be used in the recirculating system involving only a high pressure connection from the turbine, the low pressure side of the valve communicating with atmosphere.

A primary object of the invention is to provide automatic means for preventing loss of suction and damage to centrifugal type fluid pumps driven by a steam turbine.

Another object of the invention is to measure and utilize the flow through a steam turbine as determined by the turbine load to control minimum load on apparatus driven by the turbine.

Another object of the invention is to measurev and utilize the varying pressure through stages of a steam turbine in response to varying load conditions of apparatus driven by the turbine to control the minimum load on driven apparatus which might be damaged by relatively light loads.

Another object of the invention is to provide in a steam turbine-centrifugal fluid pump unit automatic means for causing a recirculating fluid flow through the pump when the pump load drops below a predetermined value.

Another object of the invention is to provide in a unit comprising a centrifugal type boiler feed water pump driven by a steam turbine, automatic means including a gradual opening valve for causing recirculating flow of feed water through low a predetermined value.

Other objects of the invention and the invention itself will be more clearly understood from a consideration of the following description and drawings wherein:

Fig. 1 is a view, largely diagrammatic, of a boiler feed water pump and turbine unit embodying the invention,

Fig. 2 is a longitudinal sectional view of the recirculating system control valve illustrated in Fig. 1, and

Figure 3 is a fragmentary diagrammatic view generally similar to Figure 1 but wherein the low pressure chamber of the valve illustrated in Figure 2 communicates directly with atmosphere instead of the outlet of the turbine.

Referring now to the drawings, I have indicated at Ill (Fig. 1) a conventional multi-stage steam turbine having a steam inlet at l l and a steam outlet at [2. It is well known that the pressure loss through the stages of a turbine of this type is directly proportional to the load on the turbine. The turbine shaft I3 is drivingly connected to the shaft I l of a centrifugal type liquid pump I6 by a coupling l'l.

Centrifugal type liquid pumps are well known wherein rotating parts within the pump housing subject liquid to a desired pressure due to centrifugal force whereby the liquid may be forced into a boiler against boiler pressure. However, if the load demands on the boiler are relatively light or negligible, the feed water regulating valve responds accordingly and a relatively small amount of water flows to the pump I6. Inasmuch as the pump is designed or chosen to handle the maximum feed water demands of a particular system, continued high speed rotation of the pump under low or negligible feed water supply will not only create a condition in the system which is highly undesirable as previously explained but the pump may be damaged due to continued operation under these conditions.

To overcome the above mentioned disadvantages of operating the pump under negligible load I provide means for automatically recirculating liquid through the pump when the pump output falls to a value such as 10% of rated capacity. In this instance, since the pump is driven by a multi-stage steam turbine I utilize the fact that the pressure loss through the stages of a multi-stage steam turbine is directly proportional to the load on the turbine or the load on the pump directly coupled thereto as a means of controlling flow through the recirculating system. The recirculating system comprises a conduit l8 extending from the outlet side of the pump indicated at is preferably to a point back in the system relative to the pump such that a considerable quantity of liquid is available for recirculation through the pump. In the present instance, the conduit I8 discharges into a water storage tank and a conduit 21 extends from the bottom portion of the tank to the pump inlet. A water supply conduit extending from a suitable source discharges into tank 26 and is adapted, in a conventional manner, to maintain a desired liquid level therein. A fluid pressure operated valve 22 is inserted in conduit 18. Any suitable type of valve operable when a pre-determined pressure differential is attained may be employed but I preferably employ a valve of the type illustrated in Fig. 2. The valve 22 has an inlet 23 connected to the pump outlet conduit l 9 and an outlet 24 connected to the conduit I8. A valve port 26 is controlled by a valve stem 2! fixed to a diaphragm 28. Diaphragm 28 is sealingly connected to the valve yoke to provide chambers 29 and 3|. Chamber 29 is connected by a steam line 32 to an intermediate stage of the turbine l0 and chamber 3| is connected by a steam line 33 to the steam outlet of the turbine. The usual shut-01f valves for the high and low pressure connection are indicated at 34 and 36 with a by-pass control valve being indicated at 31.

It will now be apparent that a valve such as indicated at 22 may be adapted to open or have its port uncovered when a pre-determined lifting force is exerted on the valve stem 21. This will occur when the pressure differential between the chambers 29 and 3| is insufiicient to resist the valve opening tendency or effect of spring 38, the effect of spring 33 being adjusted by manipulation of nut 39 and lock nut 4 I. Since the valve 22 may be adjusted to automatically open and permit recirculating flow through pump Hi When the output of the pump falls to a pre-determined value, it will be recognized that the characteristics of a steam turbine enables the turbine ID to be utilized as a means of measuring the load drop on apparatus driven thereby, whereby damage to the driven apparatus may be avoided. In the present instance effecting recirculation through the pump avoids loss of suction and damage thereto.

The importance of a recirculating system including the pump will be appreciated from a brief analysis of the operation of boiler feed apparatus. In boiler feed service the pumps are required to discharge just the right amount of water since there is no storage between the pump and boiler. This is accomplished by installing a valve in the discharge line between the pump and boiler adapted to throttle the flow as required. At periods of light load or no load this valve may nearly close so that there is practically no flow of water from the pump. This is a dangerous period or condition since the pump suction line is always left wide open and the feed water entering the pump suction line is hot (for boiler feeding), usually only a few degrees below the critical temperature for the pressure. This hot water enters the pump and if it cannot pass on through immediately it picks up more heat units due to the work done on it by the pump impeller and flashes into steam. Then the boiler can receive no more water even though in the meantime the load has come on and the valve in the pump discharge line has opened wide. When it is considered that some modern boilers can evaporatev all the water in the drum in a few minues it will be appreciated that the operators must immediately get another pump in operation to avoid a boiler explosion.

Although I preferably employ a valve as disclosed in Fig. 2, I contemplate that the line 33 from low pressure chamber 31 may directly communicate with atmosphere whereby the pressure in chamber 3| will be substantially constant and only a high pressure connection from turbine l0 such as line 32 would control the differential pressure On diaphragm 23. Of course, a leak or failure of diaphragm 28 with this type valve would permit the steam or operating fluid to escape into the room housing the unit until a valve such as 36 was closed. This arrangement is illustrated in Figure 3 wherein valve 35 is normally open to atmosphere thereby continuously subjecting the low pressure chamber 3| to atmospheric pressure. Of course, valve 37 is normally closed since the function of this valve is to balance the pressure on diaphragm 28 when it is desired to adjust the valve 22. This balancing effect is accomplished by closing valves 34 and 36 and opening valve 31.

As previously explained, the conduit l8 preferably extends to a point in the feed water line system back of the pump, since ii' conduit [8 were connected directly with the pump inlet 2i and flow from the pump discharge line stops and valve 22 opens direct-water into inlet 2|, the pump would steam bind in a short time since each time the water goes around the circuit it is heated by the pump. Thus, the water would quickly get as hot as without recirculation. To make the system effective, the water passing through conduit l8 when valve 22 is opened must be carried back in the system to a point such that a considerable quantity of water would have to be brought to the boiling point before the pump can steam bind. For example, if the conduit I 8 extends to the water storage tank and the pump inlet 2| draws water from this large tank all the fluid in the system would have to be brought up to the boiling point before the pump l6 could steam bind.

I have illustrated the steam line 33 as connected to the steam outlet of the multi-stage turbine l and the line 32 as connected to an intermediate stage of the turbine but it is understood that any two points on the turbine giving sufiicient pressure drop can be used, Also, the invention is not limited to a multi-stage steam turbine and a single stage turbine can be used by making the high pressure connection or connecting line 32 just inside the steam throttle valve, and ahead of the steam nozzle. The low pressure connection or line 33 would communicate with the steam outlet or atmosphere. The pressure required at the nozzles is a function of the load. At full load, a unit may require 125 p. s. i. at the nozzle, at half load '75 p. s .i., and at no load p. s. i.

It is understood that the pressme values and percentages hereinbefore referred to are merely arbitrarily chosen for convenience in describing the invention and that the invention is not limited to any specific pressure values and/or percentages.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, since obvious modification will occur to persons skilled in the art.

What I claim is as follows:

1. The combination with a'unit comprising a centrifugal liquid pump, a liquid supply system for the pump, and a steam turbine drivingly connected to the pump, of means for automatically recirculating liquid through the pump when the pump output drops to a pre-determined valuecomprising a liquid conduit extending from the outlet side of the pump to a point in the supply system back of the pump, a valve in the conduit, a fluid pressure motor operable by pressure differential between high and low pressure sides thereof operatively connected to the valve, and connections to the motor from points of relatively high and low steam pressure at the turbine, the high pressure connection being arranged to transmit force to the motor tending to move the valve in a closing direction, the low pressure connection being arranged to transmit force to the motor tending to move the valve in an opening direction, and spring means tending to move the valve in an opening direction whereby as the pump output and resultantly the '2. The combination with a unit comprising a centrifugal liquid pump, a liquid supply system for the pump, and a steam turbine drivingly con-' nected to the pump, of means for recirculating liquid through the pump automatically when the pump output drops to a pre-determined value, said means comprising liquid conduit means extending from the outlet of the pump to a point in the liquid supply system back of the pump, normally closed valve means in the conduit means controlling liquid flow therethrough, a fluid pressure motor operable by pressure differential between high and low pressure sides thereof operatively connected to the valve means, a connection extending from a zone of relatively high steam pressure at the turbine to the high pressure side of the motor adapted to transmit force tending to move the motor in a valve means closing direction, a connection extending from the low pressure side of the motor to a zone of relatively lower fluid pressure at the turbine adapted to transmit force tending to move the motor in a valve means opening direction, spring means tending to move the valve means in an opening direction, and the motor being adapted to open the valve means to permit recirculating flow through the conduit means when the pressure differential between the high and low ressure sides of the motor drops to a pre-determined value.

3. The combination with a centrifugal liquid pump having inlet and outlet conduits, and a steam turbine drivingly connected to the pump, of means for recirculating liquid through the pump automatically when the pump output drops to a pre-determined value, said means comprising a liquid recirculating conduit extending from the pump outlet conduit to a point on the inlet conduit remote from the pump, a valve in the recirculating conduit for controlling liquid flow therethrough, a diaphragm type fiuid pressure motor operatively connected to the valve, a steam connection from a point of relatively high fluid pressure at the turbine continuously open to the high pressure side of the diaphragm, a connection from the other side of the diaphragm continuously open to a zone of lower fluid pressure at the turbine, and spring means exerting pressure on the low pressure side of the diaphragm whereby when the steam pressure on the high pressure side of the diaphragm drops to a, predetermined value the valve will be opened permitting recirculating flow of liquid through the pump.

4. The combination as described in claim 3 and wherein the spring means are adjustable to vary the value at which the valve will open.

5. The combination as described in claim 1 and wherein the low pressure side of the motor is connected to the turbine steam outlet.

6. The combination with a unit comprising a centrifugal type feed water pump for boilers, a steam turbine drivingly connected to the pump. and a water supply system for the pump, of means for automatically recirculating water through the pump when the pump output drops to a pre-determined value, said means comprising a water conduit extending from the outlet side of the pump to a point in the supply system back of the pump, a valve in said conduit. a fluid pressure motor operable by pressure differential between high and low pressure sides thereof operatively connected to the valve, a connection extending from a zone of relatively high steam pressure at the turbine to the high pressure side of the motor, a connection extending from the low pressure side of the motor to a zone of relatively lower fluid pressure at the turbine, spring means tending to move the valve in an opening direction, the valve being adapted to partially open and permit recirculation water flow through the pump when the pressure on the high pressure side of the motor drops to a pre-determined value, and the valve being adapted to open more as the pressure on the high pressure side of the motor decreases below said value.

'7. The combination with a centrifugal type feed water pump for boilers, a water supply system for the pump including a storage'tank, and a steam turbine drivingly connected to the pump, of means for automatically recirculating water through the pump when the pump output drops to a pre-determined value, said means comprising a water conduit extending from the outlet side of the pump to the storage tank, a valve in said conduit, a fluid pressure motor operable by pressure differential between high and low pressure sides thereof operatively connected to the valve, a connection extending from a zone of relatively high steam pressure at the turbine to the high pressure side of the motor, a connection extending from the low pressure side of the motor to a zone of relatively lower fluid pressure at the turbine, spring means tending to move the valve in an opening direction and the valve being adapted to open and permit recirculating water flow through the pump when the pressure on the high pressure side of the motor drops to a pre-determined value.

8. The combination with-a. unit comprising a centrifugal type feed water pump for boilers, a water supply system for the pump, and a multistage steam turbine drivingly connected to the pump, of means for automatically recirculating water through the pump when the pump output drops to a pre-determined value, said means comprising a water conduit extending from the outlet side of the pump to a point in the supply system back of the pump, a valve in said conduit, a fluid pressure motor operable by pressure difierential between high and low pressure sides thereof operatively connected to the valve, a connection extending from an intermediate stage of the turbine to the high pressure side of the motor, a connection extending from the low pressure side of the motor to a zone of relatively lower fluid pressure at the turbine, spring means tending to move the valve in an opening direction, the valve being adapted to open and permit recirculating water flow through the pump when the pressure on the high pressure side of the motor drops to a pre-determined value, and the valve being adapted to open more as the pressure on the high pressure side of the motor decreases below said value.

9. The combination as described in claim 8 and wherein the connection from the low pressure side of the motor extends to the steam outlet of the turbine.

10. The combination with a unit comprising a centrifugal type feed water pump for boilers, a water supply system for the pump, and a steam turbine drivingly connected to the pump, of means for automatically recirculating water through the pump when the pump outlet drops to a, pre-determined value, said means comprising a water conduit extending from the outlet side of the pump to a point in the supply system back of the pump, a valve in said conduit, a fluid pressure motor operable by pressure differential between high and low pressure sides thereof operatively connected to the valve, a connection extending from a point on the turbine inside the steam throttle valve and ahead of the steam nozzle to the high pressure side of the motor, a connection extending from the low pressure side of the motor to a zone of lower fluid pressure at the turbine relative to the high pressure connection at the turbine, spring means tending to move the valve in an opening direction, the valve being adapted to open and permit recirculating water now through the pump when the pressure on the high pressure side of the motor dropsto a pre-determined value, and the valve being adapted to open more as the pressure on the high pressure side of the motor decreases below said value. v

11. The combination with a centrifugal type feed water pump for boilers having a given maximum load capacity through an outlet conduit, a water supply system for the pump, and a steam turbine drivingly connected to the pump whereby the pressure drop across points in the turbine will substantially correspond with pump load, of means for automatically recirculating water through the pump when the pump load drops to a pre-determined per-cent of maximum capacity, said means comprising a water conduit extending from the pump outlet conduit to a point in the supply system back of the pump, a valve in the water conduit having a capacity when wide open less than the said pre-determined per-cent of maximum pump capacity, a fluid pressure motor operable by pressure differential between high and low pressure sides thereof operatively connected to the valve, a connection extending from a point of relatively high steam pressure on the turbine to the high pressure side of the motor adapted to transmit force to the motor tending to move the valve in a closing direction, the low pressure side of the motor communicating with a zone of lower fluid pressure at the turbine relative to the turbine high pressure connection to transmit force tending to move the motor in a valve opening direction, spring means tending to move the valve in an opening direction, the valve being adapted to start to open when the pump load falls to said pre-determined per-cent, and the valve gradually opening at a slower rate than the pump load falls below said pre-determined per-cent to open wide at zero pump load.

12. The combination with a unit comprising a centrifugal liquid pump, a liquid supply system for the pump, and a steam turbine drivingly connected to the pump, of means for automatically recirculating liquid through the pump when the pump output drops to a pre-determined value, comprising liquid conduit means extending from the outlet side of the pump to a point in the supply system back of the pump, a valve in the conduit means, a fluid pressure motor operable by pressure diiferential between high and low pressure sides thereof operatively connected to the valve, a connection to the motor high pressure side from a point of relatively high steam pressure at the turbine adapted to transmit force tending to move the motor in a valve closing direction, a connection to the motor from a point of substantially constant relatively low pressure adapted to transmit force tending to move the motor in a valve opening direction, and spring means tending to move the valve in an opening direction whereby as the pump output and resultantly the pressure loss through the turbine drops to a pre-determined value the valve will be opened bythe motor to permit recirculating flow through the pump.

HAROLD AUGUSTUS SCI-ILIEDER.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED ST 'I ES PATENTS Name Date Laufier et al. July 16, 1940 FOREIGN PATENTS Country Date Great Britain Dec. 29, 1915

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