US664563A - Unloading means for air-compressors. - Google Patents

Description

No. 664,563. Patented Dec. 25, I900. 6. DE LAVAL & 6; P. ABORN. UNLOADING MEANS FOR AIR COMPRESSORS.

(Application filed Apr. 3, 1900.]

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Patented D 6. 25, I900.

3 Sheets-Sheet 2.

G. DE LAVAL&. G. PJABURN. UNLOADING MEANS FOR A'IB COMPRESSOBS. (Applicati'onfiled Apr. 3, 1990.]

(No Model.)

N0. 664,663. Patented Dec. 25, I900. 6'. us LAVAL & 6. P. ABORN.

UNLOADING MEANS FOR A? COMPRESSOBS.

(Application filed Apr. 3, 1900.)

3 She6ts-Sheet 3.

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UNITED STATES PATENT OFFICE.

GEORGE DE LAVAL, OF CAMBRIDGE, AND GEORGE P. ABORN, OF BOSTON,

MASSACHUSETTS, ASSIGNORS TO GEORGE F. BLAKE MANUFACTUR- ING COMPANY, OF NEW YORK, N.

UNLOADING MEANS FOR AlR-COMPRESSORS.

SPECIFICATION forming part of Letters Patent No. 664,563, dated December 25, 1900.

I Application filed April 3, 1900. Serial No. 11,282. (N model.)

To all whom it may concern.-

Be it known that we, GEORGE DE LAV-AL, a resident of Cambridge, Middlesex county, and GEORGE P. ABORN, a resident of Boston, Suflolk county, State of Massachusetts, citi- Zens of the United States, have invented certain new and useful Improvements inUnloading Means for Air-Compressors or the Like, fully described in the following specification and the accompanying drawings, forming a part of the same.

In the operation of single-stage air-compressors it is common to provide unloading means by which further compression is stopped and the load upon the compressorpiston relieved when the air in the receiver, such as a tank or any pipe system, exceeds the pressure desired, and provision for thus stopping. the compression and relieving the load upon the compressor-piston in case of such excess of pressure and resuming compression or reloading the piston when the receiver-pressure is again reduced has been made in various ways, as by opening and closing a connection between the opposite ends of the cylinder through which the air may circulate without compression, or opening and closing relief-valves for the cylinders to the atmosphere or to an auxiliary receiver, and otherwise.

In another application filed simultaneously herewith we have described and claimed a multiple-stage air-compressor provided with unloading means so arranged that the unloading and loading of the piston or pistons of the lower pressure cylinder or cylinders is controlled by the final-receiver pressure in connection with the pressure from the intermediate receiver or receivers, this result being attained in the preferred construction shown in that application by applying the final-receiver pressure and the pressure for any cylinder in opposition to each other and in such a manner that on the operation of the unloading means for the high-pressure cylinder the final-receiver pressure is immediately cut off or reduced so that the intermediatereceiver pressure operates the unloading means for the lower pressure-cylinder.

The especial object of the present invention is to provide an improved construction of unloading devices for use in carrying out the broad invention of the above-mentioned application, and we aim particularly to provide asimple, cheap, and quick-acting construction by which certainty of action in unloading the pistons at the proper time rela- ,tively to each other shall be assured. It is very desirable with multiple steam compressors, especially compressors working at a very high final pressures, that the high-pressure piston shall not be unloaded before the lower pressure piston or pistons and that the lower pressure piston or pistons shall not be loaded before the high-pressure piston in order to avoid excessive and injurious load upon the lower pressure piston or pistons. The unloading devices of the present invention are especially adapted for such m ultiplestage compressors operating at high final 7o pressures in that the unloading devices for the high and lower pressure cylinders are so combined that the movement of the same valve controls the ports for unloading and loading the difierent cylinders, so that the 5 unloading and loadingof the diiferent pistons must necessarily be timed accurately in relation to each other, so far as the movement of the unloading-valve is concerned. The construction may be such that the normal 86 action of the unloading device is to unload the high and lower pressure pistons at ex: actly the same time; but, as it is always pos sible that there may be some slight diiference in the movement of the cylinder-valves or other parts controlled by the unloading device or in the action of the fluid or other connections through which the movement of the unloading device affects such parts, we prefer to employ such a construction that the 90 high-pressu re piston is normally loaded a little before and unloaded a little after the lower pressure piston or pistons, as We thus secure greater certainty that the lower pressure piston or pistons shall not be loaded 5 when the high-pressure piston is unloaded, and this result may be attained very simply and accurately in the unloading devices of the present invention.

While, however, the especial object of the which is most desirable in this class of constructions. 7

As a full understanding of the invention can best be given by a detailed description of a construction embodying the same, such a description will now be given in connectionwith the accompanying drawings, showing a two-stage compressor embodying the invention in its preferred form as applied in connection with unloading the pistons by connecting the cylinder ends for the circulation of the air without compression and unloading devices for a similar single-stage compressor,

and the features forming the invention will then be specifically pointed out in the claims.

In the drawings, Figure 1 is a plan view of the compressor. Fig. 2 is an end elevation. Fig. 3 is a vertical'section on the line3 of Fig. 2. Fig. 4 is a vertical section on the line 4 of Fig. 3. Fig. 5 is a view similar to Fig. 4, showing the parts in a different position. Fig.

-6 is a section on the line 6 of Fig. 4. Fig. 7 is an outside view, looking in the same direc tion as Fig. 3, of an unloading device for single-stage compressors. Fig. 8 is a section of the unloading device of Fig. 7, this view corresponding to Fig. 4.

Referring to said drawings, A B are respectively the low and high pressure cylinders of 'a twostage compressor, the pistons or plungers of which are power or steam driven in any suitable manner through the piston or plunger rods-my. The compressor-cylinder A has the suction-pipe E and delivery-pipe F, and through the latter delivers to the intermediate receiver or intercooler G, from which the high-pressure cylinder B takes its suction -through suction-pipe H, and this cylinder delivers through pipe I to the final receiver,

such as a tank or any pipe system. The cylinders A B are shown as having top dischargeva'lves, connecting the cylinders with delivery-passages K, leading to delivery-pipes F I. The dischargevalves ct, of which one is shown "in section in Fig. 3, are of a common form,

' with cylindrical extensions, forming pistons 10, moving in cylinders 11, so that the fluidpressure may be applied to these pistons, tending to close the valves, in addition to the light closing springs 12, and these pistons seat tightly against the screw-plugs 13, forming the endsof the cylinders 11 when the valves are open, so as to prevent air leaking past the pistons and to the backs of the valves. All

the delivery-valves of the two cylinders A B, to which pressure is applied in connection with the unloading means, are of the same form, and the construction of each of the two cylinders in respect to these valves and the passages K is the same.

As shown in the drawings, the unloading means acts in conjunction with only one delivery valve at each end of each cylinder, but it will be understood that fluid-pressure may be applied to each or any number of the delivery-valves and controlled so as to form a part of the unloading means in accordance with the size and character of the compressor and the result desired. It will be understood also that the position and form of the deliv cry-valves and delivery-passages may be varied widely, and that the suction valves, which are not shown, may be of any suitable form.

Referring now to the unloading means used in connection with the general features of the compressor above described, there is mounted at one side of the high-pressure cylinder B a double cylinder or barrel Q, in which move two plungersfg, both forming valves, the plunger orvalvef controlling ports by which the fluid-pressure on plunger or valve g is controlled to secure the movement of the latter, and the plunger or valve 9 controlling ports for the unloading and loading of the cylinders A B. The plungerfis connected through a rod 14 and yoke 15 to a lever 16, on which is suspended the weights to, which exert downward pressure upon the rod 14 and plunger f, and thus determine the receiverpressure at which the plungerf will be moved upward against the pressure of the weights or moved downward by the weights against the receiver-pressure and the unloading means operated to unload and load the pistons. The plungerf has a seat 1 at the bottom of the cylinder in which it moves, upon which seat it rests in its normal position, and

the final-receiver pressure is applied below the plungerf through pipe 17, connecting with the receiver or pipe system, (not shown,) and the receiver-pressure from pipe 17 in the normal position of the parts when the compressor is working is admitted also through the central and transverse port 2 in the plungerfand port 38 to a chamber 39 above the plunger g, so that the receiver-pressure is normally applied to the top of this plunger g. The plungerf has a marginal port 3 extending longitudinally thereof and connecting with a passage 4 in the casing between the two plungers fg, the port 3 being of sufficient length to connect the ports 38 4 when the plunger fis moved upward for unloading, and thus the chamber 39, connected through ports 38 3 4 and connections presently to be described, with the suction-chamber of the low-pressure cylinder A or the atmosphere.

Turning now to the construction of plunger or Valveg,which controls the unloading-ports, this plunger has a seat 1 at the bottom of the cylinder upon which it rests in its normal position, and the pressure from the intermediate receiver G is applied below the plunger 9 through pipe 24, the pressure from the intermediate receiver on the bottom of the plunger 9 thus being opposed to the pressure of the final receiver upon the top of that plunger in chamber 39. Spring 29 also acts upon the top of said plunger g, tending to force the plunger downward, and thus assures the seating of the plunger and closing of the unloading-ports in starting the compressor, and in any case when the excess of pressure on the lower side of the plunger g, tending to force the valve upward, is decreased or relieved, so as to be less than the pressure of the spring 29. The plunger 9 has a port 5, controlled by a check-valve 40,0pening downward, through which the final-receiver pressure from chamber 39 is normally admitted to a chamber 18 in the casing of the barrel Q, with which connect pipes 19 20, connecting with the topsof the cylinders 11 on the high-pressure cylinder B, and through which the final-receiver pressure is normally applied to pistons in a direction tending to close the valves a of the high-pressure cylinder. The plunger 9 is also provided with a port 6, extending transversely to the plunger and longitudinally thereof, and a longitudinal marginal port 7,

, tion through pipe 22 with the suction-chamber of the low-pressure cylinder A, so that the pressure in the pipes 19 20 and back of the valves a of the high-pressure cylinder is reduced to the suction-pressure of the cylin- "der A or the atmosphere, when the plunger g is raised to bring the port '6 opposite the chamber 18. The plunger 9 also has a central and transverse port 9, through which the pressure of the intermediate receiver from pipe 24 is admitted normally to the chamber 25 in the casing of the barrel Q, with which chamber connect pipes 26. throu h which the pressure from the intermediate receiver is applied to the pistons on the backs of the dis charge-valves of the low-pressure cylinderA in the same manner as previously described in connection with the valves of the highpressure cylinder B and shown in Fig. 3. The marginal port 7 in the plunger g connects this chamber 25 with the port 8 and suction-pressure chamber 21, When the plunger 9 is raised for unloading, so that the pressure on the backs of the valves of the lowpressure cylinder Ais then reduced to the pressure in the suction-chamber of the cylinder A or the atmosphere, as in the case of the valves on the high-pressure cylinder B, in the same position of the plunger g.

The operation of the unloading means above described is as follows: All the parts are shown in Figs. 1 to 4 and '6 as in their normal position, with the compressorcylinders working. Assuming now that the pressure in the final receiver, with which pipe 17 connects, reaches the excessive pressure at which the unloading means is to be called into operation to unload the pistons, the first efiect of this excessive pressure, acting through pipe 17 upon the bottom of the plunger f, is to raise this plunger with rod 14 and yoke 15 against the resistance of weights w on lever 16. As this plunger f is thus moved upward and reaches the limit of its movement the port 2, through which the receiver-pressure is admitted to chamber 39, is closed by moving above the lower end of the port 38, and chamber 39 is connected with the suction-pressure chamber 21 and pipe'22 through the port 3, which then connects the port 38 to the port 4, communicating with chamber 21 through ports 7 8. The pressure in chamber 39 thus being reduced to the suction-pressure of the cylinder A, the higher pressure from theintermediate receiver G, admitted through pipe 24 and acting upon the lower end of the plunger 9, raises this plunger immediately against the reduced pressure in chamber 39 and the light pressure of spring 29, and thus moves this plunger g into the unloading position, both plungersfg thus being brought from the normal position (shown in Fig. 4) to the unloading position, (shown in. Fig. 5,) in which chamber 18, with which pipes 19 connect, is open through the unloading-port 6 to the marginal port 7, and thus through port 8 to the suction-pressure chamber'21, and the chamber 25, with which connect pipes 26 to the valves of the low-pressure cylinder A, is connected through ports 7 and 8 to the samesuction-pressurechamber21. The pressure upon the pistons 10 above the dischargevalves Ct of both the low-pressure and highpressure cylinders A B is thus reduced to the suction-pressure of the low-pressure cylinder A or the atmosphere, and these dischargevalves Ct then remain open by reason of the greater pressure on the cylinder sides of the valves, and the air in each of the compressorcylinders A B is thus circulated back and forth through the passages K from one end of the cylinder to the other without any work being done. The load being thus removed from both pistons of the compressor, the compressor runs without doing any work until a drop in the final-receiver pressure and pipe 17 allows the weight w to move the plunger fdownward through the lever 16, yoke 15, and rod 14, when the chamber 39 is again connected through the port 38 with port 2 and the final-receiver pressure again admitted to chamber 39, with the result of moving the plunger g downward against the pressure from the intermediate receiver through the pipe 24, so as to close the connection between chambers 18 and the suction-pressure chamber 21 and bring port 5 into position for the admission of the final-receiver pressure IIO from chamber '89, through chamber 18 and pipes 19 20, to the backs of the valves of the high-pressure cylinder B and bring port 9 into position for the admission of the intermediate-receiver pressure from pipe 24 to chamber 25, pipe 26, and back of the valves of the low-pressure cylinder A, all the parts being thus returned to the position shown in Figs. 1 to 4 and 6 with the discharge-valves operating normally and the compressor-pistons again loaded for work.

It will be seen'from an examination of Figs. 4 and 5 that the ports in plunger g are so p0- sitioned that the unloading-port 7 for the lowpressure cylinder A comes opposite chamber 25 as the plunger g moves upward for unloading before the unloading-port 6for the high-pressure cylinder B comes opposite the chamber 18, so that the pipes 26, leading to the valves of the low-pressure cylinder, are connected with the suction-pressure chamber 21 before the pipes 19 20, leading to the valves of the high-pressure cylinder B, are thus connected, with the result that the low-pressure piston is unloaded slightly before the highpressure piston. It will be seen also that the loading-port 5 for the high-pressure cylinder comes opposite the chamber 18 as the plunger g moves downward for loading before the loading-port 9 for the low-pressure cylinder A comes opposite the chamber 25, so that in loading the final-receiver pressure is applied to the valves of the high-pressure cylinder beforeit is applied to the valves of the lowpressure cylinder, with the result that the high-pressure piston is loaded slightly before the low-pressure piston. We thus secure certainty that an excessive load shall not be brought upon the low-pressure piston, which might result if the low-pressure piston should be unloaded after or loaded before the highpressure piston.

The check-valve is not absolutely essential, but is preferably used in order to avoid all danger of the high-pressure piston being unloaded through port 5 and chamber 39 when the plungerfis moved up to connect chamber 39 with the suction-pressure chamber 21,

which unloading might possibly occur before the plunger g moved to close port 5 to chamber 18. With the check-valve 40 as shown all danger of such unloading of the high-pressure piston is avoided, as the check-valve 40 is closed and prevents any passage of fluid from chamber 18 and pipes 19 20 to chamber 39 when the pressure in chamber 39 is reduced, while upon the admission of the finalreceiver pressure to chamber 39 for loading the check-valve opens against the lower pressure in chamber 18, and thus admits the finalreceiver pressure to the pipes 19 20 and valves a.

In securing the desired result of a practically instantaneous action of the unloading ally, the use of the two valvesfg is important, as the movement of the valve g in unloading is not retarded by being compelled to lift the weights w, which are operated wholly by the plunger or valve f, so that action of the valve 9 is very quick when the pressure in chamber 39 is relieved, and in loading also the valve g moves instantaneously on the admission of the final-receiver pressure to chamber 39 instead of being moved downward gradually by the weights to as the fina1=re ceiver pressure falls. The seats 1 for the plungersfg aid also in securing the desired resuit by increasing the effective pressure upon these plungers immediately upon their leaving their seats, so that with a gradual start the speed is rapidly increased upon the pl ungers leaving their seats and exposing their full surface to the air-pressure beneath, and thus a rapid movement of the plungers is secured. This increase of pressure after starting the plungerfacts also to overcome the increase in the effect of the weights to, due to the change in angularity of the weight-lever 16 as the lever is moved upward by the plunger. While this feature is not essential to the invention, broadly considered, it is preferably employed as securing a more rapid and efficient action of the unloading devices.

It will be seen that the construction shown in Figs. 1 to 6 may readily be adapted to a single-stage compressor by simply omitting the loading-port 9, chamber 25, and its connections when the low-pressure cylinder is dispensed with and connecting pipe 24 with the final receiver, so as to admit the final-receiver pressure beneath both plungers f g, when the plunger 9 will be raised against the pressure .in chamber 39 and spring 29, when the pressure in chamber 39 is reduced, as before explained, and the unloading device will then operate, in connection with the high-pressure cylinder, exactly as above described in connection with the two-stage compressor. For a single-stage compressor, however, the construction may be simplified and cheapened somewhat, and I have shown in Figs. 7 and 8 the preferred form of unloading devices for a single-stage compressor, which is very simple and compact. In this construction it will be seen that the construction of plunger f is substantially the same as in the construction previously described, and this plunger connects chamber 39 and port 38 either with pipe 17 through port 2 or with suction-pressure pipe 22 through ports 3 4 in the same manner, pipe 22 being brought in, however, between the two pistons f g to secure a compact construction with short ports. Instead of admitting the final-receiver pressure to chamber 18 from chamber 39 above the plunger g, however, the final-receiver pressure from pipe 17 is admitted through port 41 from the space below plungerf to the space below plunger g, so as to act upon the bottom of the latter, and thus through central and transverse loadingport 5 to the chamber 18, the unloading-port 6 being a marginal port in plunger g of such length as to connect chamber with port 8, leading to suction-pressure pipe 22.

The operation of a single-stage compressor with the unloading devices shown in Figs. 7 and 8 will be readily understood from the preceding description of the operation in connection with the high-pressure cylinder of the two-stage compressor.

While we have shown the unloading means as provided with piping through which the unloading connection is made with the suction-chamber of the low-pressure cylinder, it will be understood that this connection may be made directly to the atmosphere instead of through the suction-chamber, as shown; butit is preferable to make the connection to the suction-chamber, as the noise of an open exhaust is thus avoided, as well as the very objectionable feature of the delivery of dirt and oil which accompanies such open exhaust. V

In both multiple-stage and single-stage compressors it will be seen that a break in the final receiver or its connections will immediately result in relieving the pressure on the backs of the discharge-valves of both cylinders, so that both pistons will at once he unloaded, and a break in the intermediate receiver or its connections will at once result in unloading the low-pressure piston. In the two-stage compressor shown also it is evident that an excessive pressure in the intermediate receiver, if such should exist from any cause, will result in moving the plunger g against the final-receiver pressure, so as to unload the pistons.

An important specific feature of the unloading-cylinder and plunger construction shown, although not essential, is the seating of the plungers at the lower ends of the cylinders, and thus reducing the efiective area of the plungers at the beginning of their movement, so that the start is gradual, but the effective area and speed rapidly increased upon the plungers leaving their seats, so as to secure a rapid opening by the valves of the connection between the pressure and exhaust chambers, and this also overcomes the increase in weight effect upon plunger f which must result from change in angularity of the weight-lever. tion of the unloading devices is thus secured.

While the invention has been shown as applied to a two-stage compressor-that is, one in which only two cylinders are employed, so as to secure two compressions-it will be understood that the invention is not to be limited to two-stage compressors, but may be employed in constructions in which a greater number of cylinders and compressions are used, the pressure from the intermediate receiver for each cylinder being applied in opposition to the final-receiver pressure upon an unloading-valve for such cylinder and the final -receiver pressure on such valve controlled by valve f in the same manner as in A very sensitive and rapid acconnection with cylinder A in the two-stage compressor shown.

While the term air-compressor has been used throughout this specification and the term air applied to the fluid acted on, it will be understood that these terms are intended to apply also to compressors for any elastic fluid other than air.

What we claim is 1. In a multiple-stage compressor, the combination with cylinders operating at different pressures, of means for unloading the pistons including an unloading-valvecontrolled by the final-receiver pressure and cpntrolling nnloading ports for the different cylinders, substantially as described.

2. In a multiple-stage compressor, the c0mbination with cylinders operating at difierent pressures, of means for unloading the pistons including an unloading-valve controlling unloading-ports for the different cylinders and under pressure tending to move it into unloading position, connections for applying fluid-pressure to said valve tending to move it into loading position, and means controlled by the final-receiver pressure for applying and releasing said fluid pressure on said valve for loading and unloading the pistons, substantially as described.

3. In a multiple-stage com pressor, the combination with cylinders operating at different pressures, of means for unloading the pistons including an unloading-valve controlling unloading-ports for the difierent cylinders and under pressure tending to move it into unloading position, connections for applying final-receiver pressure to said valve tending to move it into loading position and means controlled by the final-receiver pressure for applyin g and releasing the final-receiver pressure on said valve for loading and unloading the pistons, substantially as described.

4. In a multiple-stage compressor, the combination with cylinders operating at difierent pressures, of means for unloading the pistons including an unloading-valve controlling unloading-ports for the dilferent cylinders, connections for applying final and intermediate receiver pressure to said valve tending to move it in opposite directions, and means controlled by the final-receiver pressure for applying and releasing the final receiver pressure on said valve forloading and unloading the pistons, substantially as described.

5. In a multiple-stage compressor, the combination with cylinders operating at different pressures, of means for unloading the pistons including an unloading-valve controlling unloading-ports for the different cylinders, connections for applying final and intermediate receiver pressure to said valve tending to move it in opposite directions, and a valve moved by and against the final-receiver pressure and controlling ports for applying and releasing the final-receiver pressure on said unloading-valve for loading and unloading the pistons, substantially as described.

IIO

ders when said fluid-pressure is relieved, of

a valve controlled by the final-receiver pressure and controlling ports for applying and releasing the fluid-pressure on the backs of the discharge-valves of both cylinders for loading and unloading the pistons, substantially as described.

7. In a multiple-stage compressor, the combination with high and low pressure cylinders having discharge-valves subjected to fluid-pressure tending to close the valves and arranged to remain open for the circulation offluid between opposite ends of the cylinders when said fluid-pressure is relieved, of a .valve controlling ports for applying and releasing the fluid-pressure on the backs of the discharge-valves of both cylinders for loading and unloading the pistons and under pressure tending to move it into unloading position, connections for applying fluid-pressure to said valve tending to move it into loading position, and means controlled by the finalreceiver pressure for applying and releasing said fluid-pressure on said valve for loading and unloading the pistons, substantially as described.

8. In a multiple-stage compressor, the combination with high and low pressure cylinders having discharge-valves subjected to fluid-pressure tending to close the valves and arranged to remain open for the circulation of fluid between opposite ends of the cylinders when said fluid-pressure is relieved, of a valve controlling ports for applying and releasing the fluid-pressure on thebacks of the discharge-valves of both cylinders for load ing and unloading the pistons, connections for applying final and intermediate receiver pressure to said valve tending to move it in opposite directions, and means controlled by the final-receiver pressure for applying and releasing the final-receiver pressure on said valve for loading and unloading the pistons, substantially as described.

9; In a multiple-stage compressor, the combination with high and low pressure cylinders having discharge-valves subjected to fluid-pressure tending to close the valves and arranged to remain open for the circulation of fluid between opposite ends of the cylinders when said fluid-pressure is relieved, of a valve controlling ports for applying and releasing the fluid-pressure on the backs of the discharge-valves of both cylinders for loading and unloading the pistons, connections for applying final and intermediate receiver pressure to said valve tending to move it in opposite directions, and a valve moved by and against the final-receiver pressure and controlling ports for applying and releasing the final-receiver pressure on said unloadingvalve for'loading and unloading the pistons, substantially as described.

1O. In a multiple-stage compresser, the combination with high and low pressure cylinders, ofmeans for unloading the pistons including an unloading-valve controlling unloading and loading ports for both cylinders, substantially as described.

11. In a multiple-stage compressor, the combination with high and low pressure cylinders, of means for unloading the pistons including an unloading-valve controlling unloading-ports for both cylinders, said valve and ports being arranged to normally unload the low-pressure cylinder before the highpressure cylinder, substantially as described.

12. In a multiple stage compressor, the combination with high and low pressure cylinders, of means for unloading and loading the pistons including a valve controlling unloading and loading ports for both cylinders, said valve and ports being arranged to normally unload the lowpressure cylinder before the high-pressure cylinder and to normally load the high-pressure cylinder before the low-pressure cylinder, substantially as described.

13. In a multiple -stage compressor, the

inders, of means for unloading the pistons including a valve subjected on opposite sides to final-receiver pressure and the receiver-pressure of the low-pressure cylinder tending to move the valve into its loading and unloading positions, unloading and loading ports for both cylinders controlled by said' valve, and means for controlling the pressure on said valve by the final-receiver pressure, substantially as described.

14. The com bination with a compressor-cylinder, of a plunger-valve controlling unloading-ports for said cylinder and subjected to fluid-pressures tending to move the valve in opposite directions, and a plunger-valve controlled by the receiver-pressure and controlling the pressure on the first-mentioned valve for loading and unloading the piston, substantially as described.

15. The combination with a com pressor-cylinder, of a plunger-valve controlling unloading-ports for said cylinder and subjected to fluid-pressures tending to move the valve in opposite directions, said valve having a seat by which the effective area of the valve is reduced in its normal position and increased at the beginning of its unloading movement and a plunger-valve controlled by the receiverpressure and controlling the pressure on the first-mentioned valve for loading and unloading the piston, substantially as described.

16. The combination with a com pressor-cylinder, of a plunger-valve controlling unloading-ports for said cylinder and subjected to fluid-pressures tending to move the valve in opposite directions, and a plunger-valve concombination with high and low pressure cyl- IIS trolled by the receiver-pressure and controlling the pressure on the first-mentioned valve for loading and unloading the piston, each of said valves having a seat by which the eifective area of the valve is reduced in its normal position and increased at the beginning of the unloading movement, substantially as described.

17. The combination with a compressor-cylinder, of valve g having loading and unloading ports 5, 6, connections for applying re ceiver-pressure to said valve and port 5, port 38 for applying fluid-pressure to the opposite end of said valve, and valve f controlled by the receiver-pressure and acting to connect port 38 with a source of fluid-pressure or with an exhaust, substantiallyv as described.

18. The combination with a compressor-cylinder, of valve g having loading and unloading ports 5, 6, connections for applying receiver-pressure to said valve and port 5, port 38 for applying receiver-pressure to the opposite end of said valve, and valve f controlled by the receiver-pressure and having ports 2, 3 acting to connect port 38 with a source of receiver-pressure or with an eX- haust, substantially as described.

19. The combination with a compressor-cylinder, of valve g having loading and unloading ports 5, 6, connections for applying receiver-pressure to said valve and port 5, port 38 for applying receiver-pressure to the opposite end of said valve, valve f controlled by the receiver-pressure and having ports 2, 3 acting to connect port 38 with a source of receiver-pressu re or with an exhaust,and spring 29 acting on said valve with the pressure from port 38, substantially as described.

20. The combination with cylinders Q and valves f, g, of chamber 18 and pipes 19, 20 controlled by said valve g, connections for applying fluid-pressure to both ends of valve g and receiver-pressure to one end of valve f, exhaust-pipe 22, ports controlled by valve f for connecting one end of valve 9 with a source of'fluid-pressure or with exhaust-pipe 22, and ports controlled by valve g for connecting chamber 18 With a source of fluidpressure or with exhaust-pipe 22, substantially as described.

21. The combination with cylinders Q and valves f, g, of chambers 18, 25 and pipes 19, 20, 26, controlled by said valve g, connections for applying fluid-pressure to both ends of valve 9 and receiver-pressure to one end of valvef, exhaust-pipe 22, ports controlled by valve ffor connecting one end of valve 9 with a source of fluid-pressure or with exhaustpipe 22, and ports controlled by valve g for connecting chambers 18, 25 with sources of fluid-pressure or with exhaust-pipe 22, substantially as described.

22. The combination With low and high pressure cylinders A, B, of a cylinder having unloading and loading ports for said cylinders A, B, valve 9 controlling said ports, pipe 24 and port 38 for admitting final-receiver and intermediate-receiver pressure to opposite ends of said valves and a valve controlled by the final-receiver pressure and acting to connect port 38 with the final receiver or the exhaust for loading and unloading the pistons, substantially as described.

23. The combination with low and high pressure cylinders A, B, of a cylinder having unloading and loading ports for said cylinders A, B, valve 9 controlling said ports, pipe 24 and port 38 for admitting final-receiver and intermediate-receiver pressure to opposite ends of said valve, spring 29 acting on said valve with the final-receiver pressure, and a valve controlled by the final-receiver pressure and acting to connect port 38 with the final receiver or the exhaust for loading and unloading the pistons, substantially as described.

' 24. The combination with low and high pressure cylinders A, B, of a cylinder having chambers 25, 18 for the respective cylinders and exhaust-chamber 21, connections for admitting the final and intermediate receiver pressures to opposite ends of said cylinder, and valve 9 having loading-port 5 for admitting final-receiver pressure to chamber 18 and unloading-port 6 for connecting chamber 18 with exhaust-chamber 21, loading-port 9 for admitting intermediate-receiver pressure to chamber 25, and unloading-port '7 for connecting chamber 25 with exhaust-chamber 21, and a valve controlled by the final-receiver pressure and acting to connect one end of the cylinder with the final receiver or the exhaustfor loading and unloading the pistons, substantially as described.

25. The combination with low and high pressure cylinders A, B, of a cylinder having chambers 25, 18 for the respective cylinders and exhaust-chamber 21, connections for admitting the final and intermediate receiver pressures to opposite ends of said cylinder, and valve g having loading-port 5 for admitting final-receiver pressure to chamber 18 and unloading-port 6 for connecting chamber 18 with exhaust-chamber 21, loading-port 9 for admitting intermediate-receiver pressure to chamber 25 and unloading-port 7 for connectin g chamber 25 with exhaust-chamber 21, check-valve -10 controlling port 5 to prevent unloading through said port, and a valve controlled by the final-receiver pressure and acting to connect one end of the cylinder with the final receiver or the exhaust for loading and unloading the pistons, substantially as described.

26. In compressor unloading means the combination with a valve controlling unloading and loading ports, of a check-valve opening to admit the loading pressure through the loading-port and closing to prevent unloading through the loading-port, substantially as described.

27. In compressorunloading means the combination with avalve controlling unload? our hands in the presence of two subscribing ing and loading ports for high and low pre'switnesses. I sure cylinders, of a check-valve openingto 'admit the loading pressure through the high- V v i B pressure loading-port and closing to prevent 1 unloading the high-pressure piston through Witnesses: the loading-port, substantially as described. JOHN J FINLEY,

In testimony whereof we have hereunto set i ALVAH F. DOLE.

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