US1097297A - Centrifugal compressor. - Google Patents

Description

J. G. GALLAN.

OENTRIFUGAL COMPRESSOR.

APPLIUATION FILED MAR. 16, 1910.

Patented May 19, 1914.

JohZ/Zia/Han Jqbbgs Witnesses UNITED' STATES PATENT OFFICE.

JOHN G. GAIJIAAN, OF BOSTON, MASSACHUSETTS, ASSIG NOB TO GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK.

CENTRIFUGAL COMPRESSOR.

Specification of Letters 1 atent.

- Application filed March 1-6, 1910. Serial No. 549,748.

Patented May 1.9, 1914;.

To all whom it may concern:

Be it known that I, JOHN 'G. German, a citizen of the United States, residin at Boston, county of Suflolk, State of assachusetts, have invented certain new and useful Improvements in Centrifugal Compressors, of which the following is a specification.

The present invention relates to centrifugal compressors for elastic fluids of that type having velocity converting means located between the exit of the impeller vane and the discharge conduit, and has for its object to improve their construction and operation, whereby the surging, pulsatmg or pufling efl'ect therein under certain load conditions is prevented.

A centrifugal compressor is a very eflicient machine for compressing air but it has. certain objections when the volume of air supplied thereby is small, 71. e., under light load conditions. Under these conditions there is a surging, pulsating or pufiing effect caused by the air within the compressor 0r piping or both which gives rise to excessive vibration of the apparatus and the pipe line connected therewith, to loss of energy, and to noise which is highly objectionable. In some instances the pulsations are so serious as to necessitate shutting down the machine and restarting. As will be readily appreciated for many classes of work this is prohibitive. This pulsating eifect is more especially noticeable in operating on what is known as the rising characteristic of a compressor, which compressor has considerable volumetric capacity or discharges into a vessel, piping or other apparatus having such capacity. The term rising characteristic means that an increase in the volumetric output of the compressor is accompanied by an increase in pressure at light loads. The term volumetric capacity has reference to the cubical content of the compressor and to that of the pipe line and other apparatus connected directly therewith and in which air is received and stored. As a result of said capacity, a high fictitious rate of discharge through the compressor is set up while the capacity is being charged. This high discharge rate determines an increase of discharge pressure due to the rising characteristic, and this in turn augments the discharge up to a certain point. When the resultant pressure reaches a certain value, equilibriumjs reestablished, the rate of discharge is reduced and the pressure generated by the impeller falls again due to the rising characteristic. As the pressure begins to fall, the capacity soto-speak begins to unload with the result that there Is a further decrease of volu metric flow. This latter condition tends to' accentuate itself until a low critical value is reached when. the reverse action begins and continues to the high critical value "come irrespective of the load on the compressor and without appreciable loss of efliclency by providing an agent which not only absorbs the energy of the pulsation to a greater or less extent depending upon conditions, but also prevents any considerable amplitude of swing or oscillation being set up.

The simplest embodiment of my inventioncomprises an automatically operating throttle valve placed in the inlet of the compressor which ofl'ers a more or less constant opposition to flow of the fluid, said opposition being preferably as small in amount as Possible consistent with satisfactory operation. To state the matter in another way, the throttle valve operates with a drooping characteristic and the amount of its throttling should be sufficient to change the-rising characteristic of the compressor at light load to a substantially horizontal one. The valve should therefore have an opening of such size that the throttling effect is very small. It is preferable to so construct this valve that it will follow the fluctuations in volume and pressure of the fluid with reasonable freedom and at the same time be restrained from violent motion by a damping device, such as a dash-pot for example. By preference the damping device should be adjustable so that its effect can be varied. In some instances it will be found desirable to arrange the dash-pot so that the valve can move freely toward its seat and will be retarded in its movement away from the seat. As a result of this the valve will tend to close and increase the 40 the scroll pipe.

throttling action when pulsations start to take place, and will gradually open and decrease such throttling action when the pulsations have been damped out. To state the matter another way the valve with its dashpot is so arranged that it tends, under conditions of surging or pulsating flow of the fluid, to pump itself shut,

In the accompanying drawing which illustrates one of the embodiments of the invention, Figure l isa view in side elevation of an air compressor with certain of the parts broken away; Fig. 2 is a sectional view in a plane perpendicular to the shaft; and Fig. 3 is a detail view partly in plan and partly in section showing the damping means for controlling the action of the throttle valve.

1 indicates the casing of the compressor which may be made in any suitable manner. As shown it is composed of parts 2 and 3. Located within a chamber 4 in the casing is a bladed impeller 5 that receives air or other elastic fluid to be compressed from the chambers 6 and 7 located on opposite sides. The impeller compresses the air to a certain extent and also imparts velocity to it. Fluid is admitted to chambers 6 and 7 by the conduit 8. The fluid discharged by the impeller passes through a nozzle or equivalent evice '9, wherein the velocity is converted into pressure, and thence into the scroll pipe 10. The nozzle is annular and is provided with partitions 11 to properly direct the fluid and to assist in converting its velocity into pressure. The impeller is mounted on a shaft 12 that may be driven by a steam turbine, electric or other motor. Fluid is discharged from the compressor by the discharge or outlet conduit 13 that forms a continuation of Mounted on the inlet conduit of the compressor is a casing 14. for the throttle valve 15, the latter being mounted on a stem 16 and suitably guided, as for example by guides 17 I have shown the casing for the valve as being separate from the casing of the compressor but obviously it can be formed integral therewith if desired. On top of the valve casing and leading into it,

-' is an inlet pipe 18, the end of which may, if

desired, form the seat for the valve. The relation of the valve and seat should be such that the fluid to be compressed can enter the valve casing without undue opposition. In other words the valve should have only a slight throttling effect on the incomingfluid. Extending across the casing is a rock-shaft 20 and mounted thereon is an arm 21 that passes through a slot in the spindle 16 of the valve. The relation of the arm'and spindle is such that they both move together without undue friction.

Located outside of the valve casing and mounted on the rock-shaft is an arm 22 which is provided with an adjustable weight or equivalent means 23 whereby the res1stance or opposition to flow of the entering fluid can be varied. Connected to the arm 22 is a rod 24 so arranged that it can have a right line movement, while the arm 22 moves about the axis of the rock-shaft 20. On the upper end of the rod is a piston 25 that is located in a cylinder 26 containin oil or other fluid to damp the movement 0 the piston. The lower end of the cylinder where the rod passes through it is provided with a packing of usual construction to prevent leakage. The upper end of the piston is provided with a gravity or spring actuated valve 27 that is normally seated, as shown, and which is capable of being separated from its seat when the piston is moved downwardly by the action of the valve 15. The valve 27 is or may be provided with leakage ports 28 through which the fluid can slowly escape from one side of the valve to the other. Connected to the cylinder above and below the piston is a by-pass 29 containing a hand-operated valve 30 by means of which the effective action of the dashpot can be regulated by opening or closing the by-pass to a greater or less extent The parts are so arranged that the throttle valve 15 always has a slight tendency to close. This tendency is normally opposed by the fluid entering the compressor from the inlet pipe 18. It will be seen that the dash-pot which is free to move in one direction and is retarded in the other, acts somewhat after the manner of a ratchet and works the valve 15 toward a throttling position whenever there is pulsation, and this regardless of whether the pulsation involves a complete cessation of flow or merely a variation in amount. In other words the valve gradually opens until practically no throttling takes place when the flow is steady, but ust as soon as there is any pumping up and down of the valve, it tends to move up more than it does down, and hence so-tospeak to penalize such action. From the foregoing statement it will be seen that there is an increase in the throttling effect by pulsation and that such action is desirable for the reason that more throttling is required to stop pulsation .than is required to .keep it from starting. Under normal conditions the throttle valve 15 is opened by an amount suflicient to cause only a slight throttling of fluid undergoing compression in the compressor. In the event that fluid tends to pass by reason of any pulsating action from some point beyond the inlet ends of the blades of the impeller back into the inlet conduit 8 and thence into the inlet pipe 18, said action causes the fluid .to temporarily close the valve and by so doing prevent any further surging impulses. The valve 15 may open and close one or more times in order to stop the sur 'ng, or said surgin may be stopped by t e valve closing an opening once. Under other conditions the valve may not close entirely but may merely follow up and down a variable discharge which never reaches zero. These actions are dependent to a large extent upon the load on the compressor and on the construction and arrangement of-the compressor and of the piping connected therewith.

By actual test I have demonstrated the fact that the arrangement shown will ef-- fectively prevent the objectionable surging in compressors.

My improved arrangement has the advantage that the compressor can operate under any condition from no-load to maximum, and this in an economical manner. In other words a compressor of the character described when equipped with my invention has its range of effective action materially increased. The main thlng 1s to locate the valve somewhere bet-ween the point where the fluid enters the system and leaves it to enter the air consuming apparatus. I consider it desirable to locate it near the compressor, but this is not absolutely necessary in all cases. I have shown the throttle valve located on the inlet side of the impeller, but under certain conditions it may be desirable to locate it on the outlet side thereof.

In accordance with the provisions of the patent statutes, I have described the pr1nciple of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof; but I desire to have it understood that the apparatus shown is only illustrative, and that the invention can be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In combination, a centrifugal compressor which operates on a rising characteristic at light loads, a receptacle into which said compressor discharges that has considerable volumetric capacity, and a means which imposes a restriction on the passage of fluid through the compressor at light loads sufiicient to change said rising characteristic of the compressor to an approximately horizontal one.

2. A centrifugal compressor which discharges into a receptacle having considerable volumetric capacity and comprises a casing, an impeller therein for imparting velocity to the fluid, means receiving fluid from the impeller and converting velocity thereof into pressure, said impeller and means operating on a rising characteristic, an inlet, and an outlet that receives fluid from the means and freely discharges it into the receptacle, in combination with a valve that at light loads resists the flow of fluid through the. compressor by an amount suflicient to modify said characteristic, and means acting on the valve to cause it to offer a substantially constant opposition to said flow, said valve and means cooperating to 3. A centrifugal compressor which dis-lv charges into a receptacle having considerable volumetric capacity -and comprises a casing, an impeller therein for imparting velocity to the fluid, means receiving fluid from the impeller and converting velocity thereof into pressure, an inlet, and an outlet that receives fluid from the means and discharges it into the receptacle, in combina-' tion with a valve that resists the flow of fluid through the compressor, an adjustable means that acts on the valve to cause it to offer a substantially constant opposition to said flow, said valve and means cooperating to preventpulsations of the fluid by reducing the inlet area when fluid tends to flow backward from the receptacle and through said velocity converting means and.

impeller, and a device for damping movements of the valve.

4. A centrifugal compressor which discharges into a receiving means having considerable volumetric capacity, and comprises a casing, a rotary impeller therein which discharges fluid under relatively high velocity, a means that receives said fluid and converts velocity thereof into pressure, an inlet for the fluid that communicates with the impeller, and an outlet that conveys all of the fluid received from the velocity converting means to the receiving means, in combination wit-h a single valve capable of assuming intermediate position that throttles all of the fluid flowing through the compressor at light loads to v prevent pulsations within the compressor by stopping backward flow of fluid from the receiving means through the velocity converting means and impeller.

5. A centrifugal compressor which dis charges into a receiving means having considerable volumetric capacity, and comprises a casing, a rotary impeller therein which discharges fluid under relatively high velocity, a means that receives said fluid and converts velocity thereof into pressure, an inlet for the fluid that communicates with the im peller, and an outlet that conveys all of the fluid received from the velocity converting means to the receiving means, in combination with a. valve to reduce the amount of fluid entering the compressor at light loads and also to prevent pulsations therein by stopping backward flow of fluid from the receiving means through the velocity converting means and impeller, and means actwhen the fluid tends to flow backward from the region beyond the discharge devices and through them and the impeller, and a damping device for retarding the movements of the a ent.

7. centrifugal compressor comprising an impeller, discharge vanes that receive fluid from the impeller and convert its velocity intopressure, an inlet and an outlet in combination with a valve which throttles the fluid flowing through the compressor and pumps itself shut when surging takes place within the compressor, and a means external to the compressor and acting on the valve to prevent violent movements thereof.

8. A centrifugal compressor comprising an impeller, discharge vanes that receive fluid from the impeller and convert its velocity into pressure, an inlet and an outlet, in combination with a valve that acts on the fluid flowing through the compressor and is sensitive to a condition thereof, said valve pumping itself shut when surging takes place within the compressor, a fluid dash-pot for the valve, and means for regulating the effective action of the dash-pot on the valve.

9. In combination with a centrifugal compressor operating on a rising characteristic at light loads and having a considerable volumetric capacity, a conduit conveying fluid thereto, a conduit conveying fluid therefrom also having considerable volumet, ric capacity, a valve through which all of and having an orifice, a conduit conveying fluid from the compressor and having considerable volumetric capacity, a valve for said orifice through which all of said fluid passes, said valve being biased to close and acting to pump itself shut, a dash-pot which Works freely in one direction only to permit said valve to move toward its seat to increase the throttling action of the valve whenever surging takes place.

11. A centrifugal compressor comprising a compressor, an inlet conduit, a valve movably mounted in the conduit, said valve being adapted to shut ofl and also to vary the flow through the conduit and to be moved by the fluid flowing therethrough, a lever pivoted on the Wall of the conduit, a connection between the valve and the lever, a dashpot connected to the valve which permits a free closing movement of the valve but opposes its opening movement, and means acting on the lever that causes the valve to normally have a slight tendency to close.

12. A centrifugal compressor comprising an impeller and a discharge device that receives fluid from the impeller and converts its velocity into pressure, an inlet and an outlet, in combination with a throttle valve which acts on the fluid admitted to the compressor, means for automatically varying the action of the valve as the flow varies, said means including a device for damping the movements of the valve.

In witness whereof, I have hereunto set my hand this 14th day of March, 1910.

JOHN G. CALLAN.

Witnesses:

Amen A. KRETSCIIMAR, ARTHUR D. Ln'rLE.

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