US2317091A - Pump controlling mechanism - Google Patents

Description

April 20, 1943. H. E. ADAMS 2,317,091

PUMP CONTROLLING MECHANISM Filed Aug. 2, 1940 3 Sheets-Sheet l In mm for Hfl/FDZD 190,013,

fltornegs April 20, 1943. v ADAMS 2,317,091

PUMP CONTROLLING MECHANISM Filed Aug. 2, 1940 a Sheets-Sheet 2 H In z/entor #19901 D E/YDflM-S fliiorneys April 20, 1943, MS 2,317,091

PUMP CQNTROLLING MECHANISM Filed 2, 1940 s Sheets-Sheet 3 V I w w R 1 I l 4 & ,r H

Inventor M /P010 fl0/7M6,

flttorncy Patented Apr. -20, 1943 PUMP CONTROLLING MECHANISM Harold E. Adams, South Nor-walk, Conn., assignor to Nash Engineering Company, South Norwalk, Conn., a corporation of Connecticut Application August 2, 1940, Serial No. 349,956 7 Claims. (Cl. 103-97) This invention relates to liquid pumping systems and more particularly to a new and improved mechanism for controlling the operation of a centrifugal or other type of liquid pump.

It is well known that a centrifugal pump becomes less eilicient in operation even to the extent of a complete breakdown of its normal operating characteristics, if air or gas becomes entrained in the liquid flow through the pump, or if the pump becomes air bound, and accordingly it is a primary object to prevent uncovering of the eye of the centrifugal impeller, the suction connections, or the inlet to the pump where such uncovering would be objectionable, and thereby prevent inlet of such air or gas to the pump, and hence to the pump discharge.

The efilcient operation'of pumps of this nature requires maintenance of a reasonable pressure in the volute of the pump and it is a further object to so control the discharge of the pump as to maintain the necessary pressures within the pump.

It is important in systems utilizing pumps of this nature that the liquid discharge from the pump be controlled, that is, cut oil at times when otherwisethere might be insufficient liquid supplied to the pump, not only in order to maintain efficient operation, but to prevent flow of air or gas through the liquid discharge connections with resultant deleterious effects to apparatus beyond the pump discharge. As an example of such deleterious results, if the pump discharges to a pipe line, and air is carried along with the liquid,

. this tends to cause corrosion in the pipe. Again,

if the pump is applied to a heating system, as in the case of returning condensate from the returns of a heating system to the boiler, and air is discharged from the pump it will tend not only to corrode the boiler shell and tubes, but also it will put air into a system where steam is to be used.

While the present invention is of general application, and by no means limited to use in a heating system, for purpose of illustration a typical arrangement is herein illustrated which might be readily adapted to use with a vacuum steam heating system, or in any type of a system in which a receiver from which liquid is to be pumped, and discharged back into the system, is utilized.

Specifically it is a feature of the invention to obtain the desired operating results by the use of a valve in the discharge of the centrifugal pump, which is controlled by a pilot valve between the discharge valve and the receiver, whereby the discharge from the pump can be controlled by conditions in advance of the pump.

A further object of the invention isto provide a discharge control which allows the centrifugal pump to discharge liquid at its full normal capacity, or to throttle the discharge of the pump to the rate of inflow into the receiver or to the pump, or to entirely cut oil the discharge, should the inflow to the pump cease.

To the attainment of the foregoing and other objects which will appear as the description proceeds, reference may be made to the accompanying drawings, wherein:

Fig. 1 is an elevation partly in section, diagrammatically showing a typical arrangement of a centrifugal pump and receiver with the control devices;

Fig.2 is a vertical section of one form of piston operated discharge valve;

Fig. 3 is a vertical section partly in elevation of a pilot control valve for the discharge valve, showing a float mechanism for actuating the pilot valve;

Fig. 4 is a vertical section illustrating a variation of a discharge valve, difiering from that in Fig. 2 by the employment of a diaphragm in lieu of the piston, as a controlling means for the valve;

Fig. 5 is a vertical section illustrating a further modification, utilizing a bellows arrangement, functioning similarly to the action of the piston or diaphragm of Figures 2 and 4;

Fig. 6 is a vertical section showing a different type'of discharge valve, operable by any of the forms of actuator shown in Figures 2, 4 or 5; and

Fig. 7 is an elevation partly in section, diagrammatically showing a typical arrangement of a centrifugal pump and receiver with a variation in the control devices from that disclosed in Fi 1.

Referring now to the drawings wherein like reference numerals designate like parts and particularly with reference to Fig. 1, it will be noted that the apparatus of the present invention comprises generally a receiver ill, a centrifugal pump H having its inlet or suction connection l2 connected to the receiver l0 and a discharge line ii. A discharge valve assembly I 4 is interposed between the line I3 and a main discharge pipe I! leading to any suitable point to which it is desired to pump liquid from the receiver. If this apparatus is interposed in a vacuum steam heating system, the main pipe line I! will run to the supply side of the system and the returns from the system would be connected to the receiver through the receiver inlet IS.

The centrifugal pump may be driven in any conventional manner by a prime mover M which may be a pulley drive, an electric motor, or any desirable equivalent. A pilot valve assembly indicated generally at IT, is connected by a control pipe line l3 to the lower portion of the assembly H, the pilot valve being controlled by a float i9 having a float rod 20 within the receiver l0.

With this set up, and the centrifugal pump in operation, liquid will be drawn from the receiver l3 through the suction connection or inlet l2 to the eye 2| of the impeller 22, and by centrifugal action into the volute 23 and thence into the pump discharge line i3. The main body of flow through the valve assembly I will of course be from the line l3 to the main discharge pipe I6, the flow rate being controlled by the postion of the movable valve 26.

Referring now particularly to Fig. 2, it will be seen that the valve 26 is provided with a depend-.

ing skirt 2! ported'or cut away as indicated at 23. The valve stem 23 terminates at its lower end in a piston 33 operable in a guide cylinder 3|, there being tolerable clearance provided between the piston and its guide cylinder for a purpose which will appear. The valve proper 26 cooperates with a valve seat 32, the diameter of which is less than the diameter of the piston 30. When the valve assembly is in its full down ward position with the valve 26 engaging its: seat 32, it completely closes the connection between the pump discharge line 13 and the main discharge linet l5, by forming a tight seat at 32. As the valve opens, it provides a graduated increase in flow from line [3 to line l5, in proportion to the lift of the valve, due to the gradual uncovering of the ports 28 in the valve skirt 21.

The valve of course is guided by the skirt and the piston 30 operating in the guide cylinder 3|.

The closing and opening of the valve assembly is produced by the hydraulic balance, or unbalance, maintained by the action of a controlling pressure on the bottom or underside of the piston 33, through the operation of the pilotvalve 33 in the assembly I1, and the pressure difference generated by the centrifugal pump itself.

As stated, there is a reasonable or tolerable clearance between the piston 30 and the walls of the piston guide cylinder 3|, and it has also been pointed out that the diameter of the piston is greater than the diameter of the valve seat 32. Coming back'to the pilot valve assembly H, the valve proper 33 is normally held closed on its seat 34 by means of a light spring 35, and the normal differential in pressure, created by the centrifugal pump, between the control line I8 and the interior of the receiver l3. Provision is made for opening the pilot valve 33 by the weight of the float i3 and its rod or stem 23, when operating about a fulcrum 36. The end of the rod 20 is slightly extended to engage an extension or stem 31 on the valve 33 when the float 19 drops due to a lowering of the normal level of liquid within the receiver. I

It is desired to maintain the level of liquid in the receiver above the opening to the suction or inlet l2 of the pump, and thus constantly maintain the eye of the pump submerged or below the level of liquid in the receiver, and accordingly the float assembly is positioned such that it is inoperative to open the valve 33 unless and until the level of liquid in the receiver drops below a predetermined level or point indicated generally at 33, In other words, the weight of the float I3 is only operative to open the valve 33 when the liquid level in the receiver reaches the desired low limiting point 33, and at any higher level, the natural buoyancy of the float removes pressure from the valve stem 31 and the valve is thus maintained in a normally closed position.

Under normal operating conditions, when the centrifugal pump is running, a pressure is maintained in the pump discharge line l3 that is of course greater than the pressure in the suction connection or inlet l2 to the pump, and hence greater than the pressure within the receiver l3. Assuming the pilot valve 33 to be in its normal closed position, with the liquid level in the receiver at or above the arbitrary level 33, there can be no flow in either direction through the control line l3, and consequently the pressure on the bottom or underside of the piston 33 of the discharge valve 26, will be equalized with that on the top or upper side, by the natural transmission of liquid pressure through the clearances provided between the piston and the guide cylinder 3|. Also it is obvious that the pressure on the pump discharge line l3 will be higher than the pressure in the main discharge conduit II when the centrifugal pump is in operation.

Because of this higher pressure on the underside of the valve 26 from the line I3, this pressure diiference will cause the valve 26 to lift and allow a flow to the main dischargeline ii, the amount of flow and the degree of lift depending upon the pressure drop that exists across the valve. Whenever the centrifugal pump is shut down, the pressure in the discharge pipe [3 will immediately drop and go below that existing in the main line IS. The immediate resultant tendency to reversal of flow will cause a closing of the valve 26, seating same tightly on the seal 32. In thisrespect, the action of the valve 26 is quite similar to that of a conventional check valve, except that this action is cushioned and thus improved by the snubbing action of the piston 30 operating in its guide cylinder I. Should the pump continue to operate, and

reduce the liquid level in the receiver l3 to a" point-below the level 33, the float 13, in lowering, will open the pilot valve 33. A flow will immediately start, with the opening of the pilot valve, through the clearance between the piston 33 and its guide cylinder 3|, into the underside of the chamber formed by the guide cylinder below the piston, and thence back through the control line l3 and the valve 33 into the receiver Ill. The size of the opening through the valve seat 33, and past the stem 31 is proportioned suflicientiy great so that when the valve is fully opened by the flow, liquid leaking through the clearance space between the piston 30 and the cylinder walls 3| will flow freely into the receiver I! with a minimum of restriction. In fact. the only restriction of such flow is around the piston 33, within the guide cylinder.

Opening of the valve 33, therefore, provides for the reduction in pressure beneath the piston 30. This reduction in pressure on the underside ofthe piston causes an unbalance in pressure between the underside of the piston, and the top 'or upper side thereof where the full discharge pressure of the centrifugal pump is being applied to the piston through the line l3. This diflerence in pressure produces a downward movement of the valve 26, tending to throttle or close oil. the flow from line l3 to the main discharge line [5.

If the pilot valve 33 is opened wide by the rapid falling of the liquid level in the receiver l it will immediately create a large unbalance of pressure across the piston 39, and because of the greater diameter of the piston with respect to the diameter of the valve seat 32, it will overcome the upward pressure exerted by the flow through the discharge line i3 on the valve 26, and will thus firmly close the valve on the seat 32.

In addition to the difference in area between the valve 26 and the piston 30, there is the additional pressure in the top of the valve assembly, exerted from the main discharge line l5, and also the application of pressure by a seating spring 39, positioned between the top of the valve 26 and the underside of the top wall of the housing of the assembly [4, all of which further tends to maintain the valve tight on its seat 32. With this arrangement, it will be evident that further' pumping of liquid from the receiver to is stopped before the liquid in the receiver can drop materially below the minimum desired level 38, which level is established at an appropriate point effective to prevent a reduction of liquid level to a point where air might be drawn into the suction connection or inlet of the centrifugal pump, thus effecting the advantages and eliminating the objections heretofore mentioned.

Should liquid continue to flow into the receiver in through its inlet l6, at a rate lower than the normal discharge rate of the centrifugal pump, then the arrangements described herein provide for throttling of the discharge from the centrifugal pump by the valve 26, so as to maintain the same rate of discharge past this valve as the incoming rate of flow through the inlet Hi. This is caused by the throttling effect from the float control valve 33, and liquid level in the receiver I0, when the throttling action of the valve 33 stops free flow of liquid around the clearance spaces between the piston 30 and the cylinder 3|, to an extent where suflicient pressure will be built up on the underside of the piston 30 to balance the other pressure forces in the pipe lines l3 and [5, to a point'where a balanced condition is reached, by the throttling action of the ports 28 in the valve skirt 21.

The pressure variation between the normal operating point and the shut-oil or closed discharge point of a conventional centrifugal pump is not a wide enough variationto cause any difliculties such as building up detrimental pressures within the pump. The equalization of the pressure on the under side of the piston 30, with the pressure forces in the lines l3 and I5 prevents the building up of unfavorable pressures in the pump even should the discharge characteristic of the centrifugal pump cover a wider than nonnal range of pressures.

It is contemplated that other types of liquid pump than the pure centrifugal type may be used in a system such as that herein described, and that the discharge control mechanism will be equally applicable. In some instances, however, particularly if an impact or scraper type of liquid impeller is utilized, it is within the scope of the invention to use a pilot control valve which would operate the main cut-off valve in the discharge, as a by-pass valve rather than as a shutoff valve, because of the different characteristics of the pump. An impact or scraper type of pump requires increased power and almost unlimited pressure build-up when the discharge is used in exactly the same manner as described heretofore, but instead of closing the discharge, the main valve would open a by-pass which would carry the discharged liquid back to the receiver or suction side of the pump, and the liquid would merely recirculate during the period of time that the pilot valve is opened. This would, therefore, require a main valve similar to the valve organization H, but reverse acting. The by-pass line would merely be a pipe line extending from the discharge to the receiver, substantially paralleling the control line [8, with an appropriate pressure check valve from the pump chamber.

As a variation in structure of the piston type discharge valve, reference may be made to Figure 4 wherein the piston is eliminated in favor of a pressure diaphragm 49, and orifices H-IZ are provided to establish communication between the chambers below and above the diaphragm 49, in lieu of the clearance between the piston 39 and the guide cylinder 3i. It is obvious that the operation of this form of structure is identical with that described in Fig. 2.

As a slight modification of the flat diaphragm idea, a bellows diaphragm is illustrated in Fig. 5. This form of control utilizes the bellows die frame 43 but is in all other respects the same as to operation as the forms illustrated in Figures 2 and 4. The eifective area of either the diaphragm or bellows, is of course, greater than that of the valve 26.

Fig. 6 shows a modification in the valve head portion of the structure, and since any of the control means, i. e., piston, diaphragm or bellows may be utilized, no description thereof is necessary. In this form of discharge valve, the valve head varies from those of Figures 2, 4 and 5 in that it is made in two parts, one a floating valve member 44 which seats directly on the main valve seat 32, and the other a spherical seated, auxiliary valve member 45 attached to the valve stem 29,

which is in turn guided by the control means (not shown) at the base of the stem, and a guide piston 46 operating in the head of the assembly l4.

The floating valve member 44 is guided by a relatively loose fit with the stem 29, and as stated, the stem 29 with the auxiliary member is guided in part by the guide element 46 operating in the head of the assemblage l4. Because of the spherical seating arrangement, the member 45 automatically takes its seat at 41, when the valve closes, to form a tight seal with the floating member 44.

In action, the floating member 44, upon the stopping of the pump, immediately drops in position on the valve seat 32, thus stopping back flow from the pipe line IS. The valve member 45, under the action of the diiferential pressure across it, follows up this closing action more slowly to finally seal oil minor leakage around the guiding surface of the floating member 44, and forms a leakproof seat with the self-aligning spherical arrangement 31.

The floating member 44, of course, previous to this, has adapted itself to its seat on the valve at 32. The two seats are thus both self-aligning and leak proof after the final closing action, and the combination of the two provides a selfaligning valve, and has the further advantage of quick closing upon stoppage of the centrifugal pump regardless of any sluggish action which might follow when the valve stem is controlled by a bellows, diaphragm, or piston.

While the form of invention embodied in Fig. l is preferable because of its simplicity and mechanical action, it may be desirable to control" the pilot electrically, and Fig. 7 is illustrative of one mode of so controlling the apparatus. In this form of the invention, instead of a mechanical pilot valve arrangement, operable directly by the float in the receiver, a float controlled electric snap switch 48 operating a normally been closed. The control line i8 can be tapped into the receiver at any suitable point below the minimum liquid level, as indicated at 54. Except for the electric actuation of the pilot valve 49 the operation of this form of apparatus is exactly the same as that described in connection with Fig. 1.

The advantages and operation of the invention are believed to be obvious. Not only is it possible to completely out off the discharge when the liquid level in the receiver reaches a point at which air would be admitted to the pump, as by cessation of flow into the receiver, but should there be a flow into the receiver less than that normally provided for, the discharge from the centrifugal pump will automatically be throttled to accord with such inflow to the receiver.

At no time will the centrifugal pump become air bound, nor will its efficiency even be impaired as by the entrainment of some air with liquid to the eye of the impeller or other inlet to the pump.

In addition to maintenance of maximum efficiency in the pump, there will be no tendency towards surging caused by the pump losing its supply of liquid and thereafter having to pick up a fresh supply, since the pump itself will in effect be submerged, at least insofar as the impeller eye or the pump inlet are concerned, thus providing for uniform pumping action.

Certainly the deleterious results caused by pumping of air through the discharge of the pump, to other parts of a system to which the apparatus may be applied are completely avoided.

It will also be understood that the particular types of pilot valve, discharge control valve, controls for the pilot valve, and the like, are included as illustrative and not as limiting, except as hereinafter claimed, as many variations will ocour to those skilled in the art.

While a centrifugal pump has been described herein as the type of pump to which the control arrangement of the invention is applied, this of course is also to be regarded as illustrative rather than limiting, a centrifugal pump of the type having a central eye or inlet, having been picked as that type of pump most susceptible to impairment in efl'iciency upon the introduction of air into its supply. It is obvious, however, that the control arrangement may be applied to any type of liquid pump, not only to maintain efficient operation in the pump, but to prevent the transmission of air or gas beyond the pump where such air or gas might impair other portions of a system.

Having thus described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

1. In pump controlling mechanism including a pump having a source of liquid supply and a liquid discharge, comprising means to throttle the discharge of the pump in accordance with the level of liquid at the source of supply, the improvement which comprises liquid level controlled means associated with the source of supply and operatively connected to said throttling means for efiecting the throttling action, said controlled means being constructed and arranged to utilize liquid by-passed from the discharge of the pump to its own suction to effect the control of .the throttling means.

2. In pump controlling mechanism of the type including a pump having a source of liquid supply and a liquid discharge, and means to throttle the discharge of the pump in accordance with the level of liquid at the source of supply, the improvement which comprises means to utilize a recirculated portion of the liquid pumped to actuate the throttle means by controlling the flow of liquid recirculated by liquid level means-at the source of supply.

3. In pumping mechanism of the type having a pump, a source of liquid supply, and means for admitting liquid from the said source to the pump, discharge means for the pump including a pressure controlled throttle valve, the improvement which comprises a controlled by-pass connecting the pressure control chamber of the throttle valve to said discharge means and to said source of liquid supply and liquid level controlled means associated with the source of liquid supply and controlling the flow of pumped liquid through said by-pass to cause variation in the unbalance of the pump differential pressure on the pressure controlled throttle valve to control the discharge means in accordance with variations in the level of the liquid in the source of supply.

4. In pumping mechanism of the type having a pump, a source of liquid supply, and means for admitting liquid from the said source to the pump, discharge means for the pump including a pressure controlled throttle valve, the improvement which comprises a controlled by-pass connecting the pressure chamber of the throttle valve to said discharge means and to said source of liquid supply and liquid level controlled means associated with the source of liquid supply and controlling the flow of pumped liquid through said by-pass to cause variation in the unbalance of the pump differential pressure on the pressure controlled throttle valve to cause said throttle valve to close when the level of the liquid in the source of supply descends to a predetermined elevation.

5. In pumping mechanism of the type having a. pump, a source of liquid supply, and means for admitting liquid from the said source to the pump, discharge means for the pump including a pressure controlled throttle valve, the improvement which comprises a liquid by-pass line connecting the pressure control chamber of the throttle valve to said discharge means through a restriction and to said source of supply through a valve controlling flow of liquid therethrough but normally closing said by-pass, and liquid level controlled means associated with the source of liquid supply and connected to said valve for opening the latter and cause the resulting unbalanced pump differential pressure to close the throttle means when the liquid level at said source descends to a predetermined elevation.

6. In a pump mechanism of the type having a pump, a source of liquid supply, means for admitting liquid from said source to the pump, discharge means for the pump, including throttle means, said throttle means including a movable partition separating the pump discharge means from a liquid control by-pass line connected to the discharge means through a restricted orifice and connected to the source of liquid supply through liquid level controlled means associated with the source of liquid supply, said liquid level controlled means causing the application of the pump diflerential pressure to the movable partition to close the throttle means when the level of the liquid in the source or supply descends to a predetermined elevation.

7. In pumping mechanism of the type having a pump, a source of liquid supply, and means for admitting liquid from the said source to the pump, discharge means for the pump including a pressure controlled throttle valve, the improvement which comprises a liquid by-pass line connecting the pressure control chamber of the throttle valve to said discharge means through a restriction and to said source of supply through a valve controlling the flow of liquid therethrough, electrically operated means for controlling the valve and liquid level controlled means to cause opening of said valve and thus to apply the resulting unbalanced pump dillferential pressure to close the throttle means when the liquid level at said source descends to a predetermined elevation.

HAROLD E. ADAMS.

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