US1782926A - Method of and apparatus for controlling boiler feed water - Google Patents

Description

No v. 25, 1930. J. L. KIMBALLL: 1,782,925;

METHOD of AND APPARATUS For: CONTROLLING BOILER/"FEED'WATER Filed May 21, 192'? lnven tor @torwe Patented Nov. 25 i930 bra n, sraras JAMES Ewrs \KIMZBALL, or, isnvnarra massacnusnrrs, ,assmme T0 assis armrest/mun Mrs. 00., or ex-mam, massaenusnrrs METHOD orannarranar'ns ro'a con'rnonzsrne BOLILER FEED WATER Application fiIecIMay 21, 1927, Serial No. 193,362.

My invention relates to a methodof and improved apparatus forcontrolling boiler feedpumps, and more specifically, to the control of motor-driven boilerfeed pumps.

;,- a The object of my invention is to maintain a variable pressure between the steam pressure of the boiler and the feed line pressure at the pump, said pump pressure beingincreased on a decrease in boiler pressure and 1o likewise decreased on an increase in boiler pressure. Heretofore differential bo lervfeed pump governors have been so arranged that the diiierence in pressure between the steam generated by the boiler and'the water supplied by pump was either ofaconstant value for varying-steam pressuresor that the difference in pressure would be reduced on increased boiler loads and likewiseincreased on low boiler loads. i v 1 It is readily conceivable that this is the I wrong method of control, and that it is desirable to employ regulating equipment -which will maintain an increased pump pressure when the boiler is generating an in- 5 creased amount of steam, for the simple reason. that the more steam the boiler generates, the more water must be fed tothe boiler, and in order to feed an increased amount of .water on an increase in boiler load, it is necessary J tomaintain a higher pump pressure.

Where a constant pressure 1s maintained,

or where the pressure tends to decrease on increased boiler load, it becomes necessary to either continuously adjust a or adjust the regulator.

' It will be understood that the pressure of a steam boiler varies with the demand or boiler load, usually termed thepressure opteed valve, 1

arr-ET oFFiCE is decreased. This increase and decrease in pressure is of a predetermined value, it being such as may be required to feed an amount of water corresponding to the amount of water beingevaporated by the boiler. It will be understood that in pumping feed water through thefeed line pipe with the various valves, also through the feed waterrheater, that there willbea considerable dropin pressureyand the pressure drop will be in,

creased on increased volume demand; it is,

therefore,- the purpose of my invention 'to so :vary the pressure at the pump as to compensate for these losses, thereby, always insuring a suflicient supply-of water at the required pressure to feed the boilers under varyingload demands. y i

Referringto the drawing,.19 represents asteam boiler, 18 is a pump forsupplying the boilerwith water, 20 is a motor for drivmg the pump, 21 is the feed line to the boiler it, being understood that in this line there will be installed the ordinary boilervstop valve (not shown in thedrawing) and usually a feed water heater for raising the'teinperature of the feed water, 16 represents a jrheostat forcontrollin'g thespeed of the motor 20; 15 is a pilot motor for operating the rheostat16, and 31 is a switch for controlling the operation of the pilot motor 15; 1

Thusyfar Ihave enumerated apparatus which is old in theart, and I will now describe the novel featuresof my invention.

A pressure head 1 has upper and lower pressure chambers 22 and 23; thesecham theupper chamber is pressure connection 24 wherebythe feed line pressure is allowed to exert a forceon the under side of diaphragm 3.- To the lower chamber is a pressure-con- ,ss bers have flexible diaphragins 2 and 3. T0 L nection 25 which permits the steam pressure ofthe boiler to exert a force on the'upper side of diaphragm 2. The feed line pressure ginthe chamber 22 is counteracted by means of coil spring 9 acting through lever] and pressure cap 5, and likewise the steam pressure in chamber 23 is counteracted by means of spring 8 acting through lever 6 .and pressure cap 4, The spring 8 being adjusted for a predetermined boiler pressure, and likewise the spring 9 being adjusted at predetermined feed line pressure, in excess of the boiler pressure, it will be seen that the levers 6 and 7 will float up and down in accordance with variations in the feed line and boiler pressure, the lever 6 being responsive to variations in steam pressure, and lever 7 responsive to variations in feed line or pump pressure.

At the right hand end of the levers 6 and 7 is connected the pilot motor controlling switch, the lever 6 being connected to the barrel 11 of the switch and lever 7 being connected to the frame 10 of the switch.

I will now describe the operation of the pilot switch: the frame of this switch has insulated contactors and terminal connections 12-13 and 14:, while the barrel of the switch is made up of a cylindrical contacting portion 26 and two portions of insulating material 27 and 28. The switch as shown is in a neutral or open circuit position, but if the barrel should be moved upward, or the frame downward, then terminal 13 would make contact with cylindrical portion 26 and current would flow from one side of the line and from 12 to 13 operating the pilot motor in one direction, and if either the barrel was lowered or the switch frame raised, current would flow from the line and from 12 to 14, thereby operating the motor in the opposite direction. It will be noted that one side of the line is direct to the pilot motor, so all that is necessary to reverse the motor, it being of the split field type, is to alternate the flow in the other two lines.

The operation of the system is as follows assuming a normal steam pressure in chamber 23 of 100 pounds and a feed line pressure in chamber 22 of 130 pounds, and these pressures represent a pressure differential required to feed the boiler under a mean average load condition; and assume that the steam pressure rises, due to a falling load of 101 pounds,then diaphragm 2 will be forced downward compressing counteracting spring 8 and raising the right hand end of the lever 6, which in turn raises contact barrel 11, and the conducting portion 26 will complete a circuit from terminal 12 to terminal 13 on switch frame, thereby operating the pilot motor to install additional resistance in the motor circuit of motor 20 and slow down the pump 18. This slowing down of the pump would reduce the feed line pressure and diaphragm 3 would therefore be compressed by the counteracting spring 9 and the frame 10 of the switch would be raised thereby returning the switch to its neutral or open circuit position and preventing the further operation of the pilot motor. The feed line pressure has now been reduced due to the increase of the boiler pressure.

Now assume that the steam pressure decreases from 100 lbs. to 99 lbs. due to an inthe pilot motor in the opposite direction to cut out resistance and speed up pump motor 20; this in turn will increase the feed line pressure which will force diaphragm 3 upward thereby lowering the switch frame and again returning the switch to a neutral or open circuit position and preventing further operation of the pilot motor. e now have an increase feed line pressure due to a decrease in steam pressure caused by a rising boiler load, and assuming the steam pressure continued to further drop to say 98 lbs. then the operation would be repeated and the feed line pressure proportionally increased. This increase in feed line pressure would continue with the drop in steam pressure until the steam pressure device had operated over its entire pressure-operating range which would be when the left-hand end of the lever 6 engaged the stop screw 29 and no further movement was possible. This pressure-operating range of the steam pressure device would be adjustable by increasing or decreasing the travel of the diaphragm 2.

Now assuming the steam pressure device should be adjusted for a 10 lb. operating range, that is to say, 5 lbs. above and below the mean average steam pressure,-and assuming the water-pressure device should be adjusted for a like pressure-operating range: now if the boiler load should increase to an amount which would cause the pressure to drop from 100 to lbs, then the feed line pressure would be increased from 130 to 135, and the differential would now be 40 lbs. instead of 30, as was the case when the steam pressure was at its mean average value of lbs.

Assuming the boiler load should fall oil to an extent which would cause the steam pressure to rise to lbs.,now the feed line pressure would be reduced to lbs. and the pressure difierential would be 20 lbs. instead of 30, as was the case when the steam pressure was at its mean average.

From the foregoing, it will be seen that I have devised control apparatus which will increase the pressure differential on increased boiler loads and will likewise decrease the pressure differential on decreased boiler loads.

So far I have described my invention in connection with a single boiler, and we will now consider a condition in which there are several boilers, all being fed by the same pump and operated atthe same mean avera pressure of 100 lbs. It will be readily conceived that variations in steam pressure of all the boilers, assuming the pressure pipe to be connected to a steam line common to all boilers, will cause corresponding increase and.

' decrease in the differential pressure as before,

but assuming an extra boiler'should be out, into the line, which would'meanfthat additional feed-water must be pumped to supply this extra boiler; orthata boiler should be cut out of the line, which would mean that less feed-water would'be required we now have a COIldltlOl'l' where .a -var1at1on in feed line pressure may take place without any change in steam pressure, and under such conditions, the controlis from the fe'edline pressure only. Assuming 'anextra boiler shouldbe cut into the line, the feed line pressure would drop, whichwould'decrease the pressure in chamber 22 causing the spring 9 to depress the diaphragm 3and thereby raise theright-handend of thelever 'l' and also the switch frame 10, this would complete a circuit from terminal 12 to, terminal 14 which would Operate the pilot motor to cut out resistance 16 and speed up motor 20.

This would cause the pumpto discharge more water and consequently increase the pressure in the feedline 21 and in the chamber 22 to its original. value, at which timethe switch frame 10 would be lowered was neutral or open circuit position and the further operation of the pilot motor stopped.

Likewise, if a boiler should be cut out of the line,then the feed line pressure would increase raisingl diaphragm3 and lowering switch framelO'which would complete a circuit from terminal 12 to terminal 13, which would operate the pilot motor 15 to cutinresistance, thereby reducing the feedline pressure and returning the switch to neutral.

. It will be seen that any invention provides an independentcontrol ofthe feed line pressure and also provides steam-pressure-operated means to correct this control, whereby the feedline pressure is changed in thjeopposite direction to the change in steam pressure. "While I have described mylnvention 111 connection with electric motor-driven pumps, it will be readily conceived that the same method of control is equally applicable to steam-driven pumps, as the controlling device can just as well be a pilot yalve in which the body of the valve isoperated from one pressure device andthe valve stem from the other. In this way, a fluid. pressure motor would be substituted for the pilot motor and this would operate a throttling valve in place of the rheostat, which in turn would control the operation of a steam-driven pump.

Various other modifications might be made in the structure and arrangement of parts of my improved method of controlling boiler feed-water without departing from the scope mined value in excess. of the :steam pressure in the boilerfor a mean average boiler pressure, and automaticallyincreasmg the feed line pressure ona decrease in boiler pressure, and automatlcally decreasing the feed line pressure on anincrease inboilerpressure. 2. "lhemethodof controlling boiler feedt aining theafeedline pressure a predetermined value in excess of the steam pressure in the boilerforvarying demands, so long as the steam pressure remains constant, and

;waterwhich consists in automatically main- 1 automatically increasing the feed line pressure when the boiler pressure falls below its mean average value, and likewise decreasingthe feedcline pressure when the boiler pressure exceeds itsmean average value.

3. Ina regulating system for maintaining I a boiler feed line pressure difli'erential for feeding the boiler with water, governing means for maintaining a predetermined feed line pressure in excess ofthe steam pressure in the boiler for a mean average boiler pressure, and governing means for increasmg the feed line pressure on a decrease in steam pressure, said governing means likewise decreasingthe feedlinepressure on'a-n increase in steam pressure. i i

4. In a differential pressure regulator means for controlling the pressure at-the high pressure source, a motor for controlling the pressure-controlling means, a governing device for the control ofsaid motor, means controlled by the pressure atthe high and low pressure source for jointly controlling'said governing device for maintaining a predetermined pressure ditferentialjfor a mean average pressure value at the lowpressure source, and means forincreasing the pres sure atthe high pressuresource on a decrease 1H pressure at the low pressure source, and means for decreasing the pressure at the high pressure source 1 on an increase in pressure at the low pressure source. i

5. In a difierenti'alpressure controlsystem lie.

for boiler feed pumps, amotor for driving said pump a speed controlling device for said motor, a reversible motor forcontrolling the operation of the speed-controlling device, a

governing device for the control of there versible motor, a pressure-responsive device controlled from the pump pressure for actuating the governing device to maintain a mean averagepressure difierential for mean average steam pressure, and means wherebythe pump pressure is increased on'a decrease in. steam pressure" below the mean averagevalue and likewise decreased when the steam pressure increases above its mean average value.

p 6. In a difierential pressure regulator, a motor and means controlled by said motor forreg'ulating the pressure at the high pressure source, a governing device for controlling the operatlon of said motor, sald governing device comprising two independently operated co-operating elements, means whereby the operation of either element will affect the operation of said motor, means to control the operation of one of said elements from variations in pressure at the high pressure source, and means to control the operation of the other element from variations in pressure at the low pressure source, all as specified and for the purposeset forth.

7. In a differential pressure regulator, a reversible motor and means controlled by said motor for regulating the pressure at the high pressure source, a governing device for said motor, said governing device comprising two co-operating elements, means whereby the operation of either element will control the starting, stopping and reversal of operation of said motor, means to control the operation of one of said elements from variations in pressure at the high pressure source, and means to control the operation or the other element from variations in pressure at the low pressure source, all as specified and for the purpose set forth.

8. In a differential pressure-control system for boiler feed pumps, a motor for driving said pump, a speed-controlling device for said motor, a pilot motor for controlling the operation of the speed-controlling device, a governing device for the control of the pilot motor, means whereby said governing device is jointly controlled by the pump pressure and by the pressure of the steam in the boiler, and means whereby an increase in steam pressure would cause a decrease in pump pressure, and likewise a decrease in steam pressure would cause an increase in pump pressure.

9. In a difierential pressure control system for boiler feed pumps, a motor for driving said pump, a speed-controlling device for said motor, a reversible pilot motor for controlling the operation of the speed-controlling device, a governing device for controlling the operation of the reversible motor, said governing device being arranged to start, stop and reverse the operation of the pilot motor, means whereby said governing device is jointly cont-rolled by the pump pressure and by the steam pressure of the boiler, and means whereby an increase in steam pressure will operate the governing device to decrease the pump pressure and likewise a decrease in steam pressure will operate the governing device to increase the pump pressure.

10. In a boiler feed-water regulator comprising means for supplying the boiler with water, a governing device for regulating the water-supplying means, said governing device having two co-operating elements, said elements having a relative neutral position and two relative effective positions forregulating the water-supplying means, a pressure device operated from the steam pressure of the boiler for actuating one of said ele ments to either of its elfective positions, and a pressure device operated by the feed line pressure for actuating the other element to a relative neutral positlon, all as specified and for the purpose set forth.

11. In a boiler feed regulator, a motor and means controlled by said motor for regulat ing the feed line pressure, a governing device comprising two independently operated co-operating elements, means to control one of said elements from variations in the feed line pressure, and means to control the other element from variation in the boiler steam pressure, and means, whereby, the combined operation of the said two elements controls the operation of the motor to maintain an increased feed line pressure on an increase in steam demand.

12. In a boiler feed regulator a reversible motor and means controlled by said motor for regulating the feed line pressure, a governing device comprising two independently operated co-operating elements, said elements having a relatively neutral position at which the operation of the motor is not efiective, and two relatively elfectivo positions in which the motor is operated in either of two directions, means to control one of said elements from variations in the feed line pressure, andmeans to control the other element from variations in boiler steam pressure, and means, whereby, the combined operation of the said two elements controls the operation of the motor to maintain an increased feed line pressure on an increase in steam demand.

13. In a boiler feed regulator, a pump for supplying the boiler with water, a motor for controlling the speed of the pump, a governing device for operating the motor, said governing device comprising two independently operated co-operating elements, means to control one of said elements from variations in feed line pressure, and means to con trol the other element from variations in boiler steam pressure, and means, whereby, the combined operation of the said two elements controls the operation of the motor to maintain an increased feed line pressure on an increase in steam demand.

JAMES LEWIS KIMBALL.

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