US1803660A - Compressor and pump - Google Patents

Description

May 5, 1931. E. w. swARTwoUT 1,803,650

COMPRESSOR AND PUMP l Filed Dec 5, 1928 5 sheets-sheet 1 irzl.

' INVENTOR, EverefU wwarwou,

May 5# 1931. E. w.v swARTwoUT 1,803,660

' COMPRESSOR AND PUMP v Filed Dec. 5, 1928 5 Sheets-Sheet 2 INVENTOR, EverehF SWOYWOUJ,

H ATTORNEY May 5, 1931. E. w. swARTwoUT COMPRESSOR AND PUMP Filed Deo. 5, 1928 5 Sheets-Sheet 3 A'rroRNEY WOU May 5, 1931. E. w. swAR'rwouT 1,803,550

COMPRESSOR AND PUMP Filed Dec. 5. 1928 5 Sheets-Sheet 4 INVENTOR, EvereH' W. Sworfwou,

BY 'lu/L( H ATTORNEY May 5, 1931- E. w. swARTwouT 1,803,660

COMPRESSOR AND PUMP Filed Dec. 5, 1928 5 Sheets-Sheet 5 n l5 e INVENTOR. Evere?? W. warfwoui,

f ATTO N EY Patented May 5, 1931 EVERETT w. sWARTWoUT, or WHITE PLAINS, NEW YORK COMPRESSOR .A N'.D IAUMP Application med December 5, 192s. serial-no. azaeso.

This invention relates to compressorsV and pumps. Y

More particularly, my invention relates to reciprocating compressors, rotary blowers l and pumps having one or more compression or suction compartments, each compartment provided with a piston, or with lobed impellers, or the equivalent for the passage of the medium under compression or otherwise and means for unloading the one or more compartments respectively within pre-determined ranges of unloading pressure.

In my application Ser. No. 219,225, entitledRotary blowers and pumps, led by me on Sept. 13, 1927, I have set forth and claimed the construction of rotary blowers and pumps having one or more compart-V ments vprovided with lobed'impellers, preferably with suitable means for discharging the medium through the discharge outlet of the blower or pump into the discharge line, and means for loading and unloading the blower or pump under the controlrof a pilot valve set to unload and to load up again at any desired maximum unloading pressure.

In my co-pending application Ser. No. 222,455, entitled Rotary blowers, pumps and meters, filed by me on Sept. 28, 1927, I have forth and claimed constructions of rotary blowers, pumps and meters comprising a plurality ofcompartments in each ofwhich is Y disposed lobed impellers or the equivalent for the passage of the medium under com-V pression or otherwise, and means for prol 5 gressively loading and unloading the respective compartments under pilot valve control preset for maximum unloading pressures for the respective compartments. Such plurality of compartments may or may not'have adia- 0 batic means for delivering the respective media into the delivery lines. V

Pursuant to the present invention, the

loading and unloadingmeans with control For the respective one or more compartments, 5 is effective to set the loading and unloading means into operation at a predetermined maximum delivery pressure and when the` capacity is excessive, to malte effective and maintain the 'continuation of the unloading means until the dellvery pressure attains a predetermined minimum pressure, thus positively preventing any hunting action of the controlling means and its coordinative parts in its operation of the loading and unloading means; when unloaded,aand when lthe reduction in delivered capacity in the discharge line results in a drop in pressure to the predetermined minimum-` pressure, loading up again will result. Thus, when delivering into, or exhausting from, systems of substantial capacity, the number of loadings and'unloadings in any given timewill be relatively small' while at the same time, the capacity will be varied to suit the actual .requirements of Ythe distribution system,

maximum saving in power will result, and

Vsmooth operation obtained.

Further features and objects of the invention will be more fully understood from the following detail description and the accompanying drawings, in which Fig. 1 shows a side elevation of a compressor, its inlet and discharge pipes equipped with unloading means and a power control therefore. Pursuant to my invention, a portion ofthe unloading means and portions of the control are indicatedin central vertical section;

Fig. 2,is a sectional elevation on line 2f-2, Fig. l; Y f

Fig. 3 is a side elevation showing a modification; a portion of the pilot control appears in central vertical section; y

Fig. t is a side elevation showing my inventionrapplied to a machine having a plurality of compression compartments having a common pilot for controlling the same in which aportion of the pilot is illustrated in central vertical section;

Fig. 5 is a sectional elevation on line 5--5, Fig. 4; l

6 is a horizontal section of a modification ofthe `arrangement shown in Fig. 4; and Fig. 7 shows my invention applied to the vacuum system. Y

Referring to Figs. l and V2, the compressor or blower l0 is illustrated as of the single 'i Vcompartment type. The impelling means is preferably a pair, of lobed impelle'rs, as vis illustrated and described in my aforesaid copending applications Ser. Nos. 219,225 and 222,455. The inlet pipe is shown at 11. The discharge of the unit 10 is indicated at 12 and between the same and the discharge line is provided the check valve 13, preferably disposed within a separate cylindrical pipe casing 14.

Between the discharge 12 and 11 l arrange the unloading passage comprising its inflow piping 15 and its outflow piping 16, the communication of which is controlled by the valve 17, in turn controlled by the pilot means, as appears more fully hereinafter.

In this form of my invention, as illustrated in Figs. 1 and 2, the pilot properV comprises the main valve body 18 in which iso-disposed the pilot valve 19 having at its'opposite ends full diametrically enlarged heads 20, and an intermediate portion 21 of reduced diameter,

thus providing for an annular clearance con# trolling the communication and non-communication of the pipe connections 22, 23 and 24.

The pipe connection 22 communicates with the piping 25 communicating at its inlet 26 with the interior of the housing 14 at a location posterior of the check valve 13 and thus subject to the pressure of the discharge line. The piping 25 has an upper extension 26 communicating with the interior of the casing 27 below its diaphragm 28, and also effective upon the upper face 19a of the pilot valve 19. i

The piping 25 communicates also through its extension 29 with the interior of the mam valve body 18, to its bottom, to be effective upon the lower face 196 of the valve 19.

The pipe 30 communicates at one end with the piping 25, thus subject to the delivery pressure, and at its o-pposite end leads to the interior of the expansible bellows` or other pressure expansion device 31.

The piping 23 leads from the interior of the main valve body 18 at its one end to the interior of the outflow loading passage 16, and thus subject to the inlet pressure. The piping 24 leads at its one end fromthe central interior of the main valve body 13 to its other end to the interior of the casing 32 at the lower or valve side of the diaphragm 33 controlling the loading and unloading Avalve 17. Y

The diaphragm 28 is pre-set in critical pressure operating value by means of the scale beam 34, pendant weights 35 and sliding weight 36, effective by means of the link 37 engaging diaphragm 28 at substantially its center and extending by the rod 38 into rigid connection with the movable pilot valve member 19.

The expansible bellows 31 or equivalent is controlled in its pre-set vertical pressure value position by the weights 39 resting upon the platform 4() supported by arm 41 upon the upper and expansible end oi the bellows 31.

The diaphragm 33 is pre-set by the weights 42 resting upon the platform 43 supported by the rod 44 upon the upper face of the diaphragm Associated with the above stated parts, I have illustrated in the form shown in Figs. 1 and 2, a trigger 45 which co-operates at its end 45a with the maximum and minimum stop member 46, the latter being suitably positioned upon the rod 44 of diaghragm 33. The trigger' 45 is suitably mounted in the reciprocable barrel 47 extending at one side through the upper portion of the casing 32 and biased by the expansion spring 49 lodged within the closed end ot the barrel 47. The barrel 47 is reciprocable within the circular opening of the casing 32. The barrel 47 is provided with a pin 51 received within the opposite, closed ended slot 52 in the trigger 45. The outer arm 50 of the barrel 47 is pivotally connected by a pin at 50a within the slotv of the forked end 53 of the bell crank, pivoted at its center 54, and having an opposite forked end 55, the slot of which receives the pin 56 carried by the arm 41 of the weight 39 and expansible bellows 31. The barrel 47 is provided with an air vent 47A. l

The interior of the casing 32 on the side of the diaphragm 33 opposite to that of the valve 17, communicates with the atmosphere through the opening 32a. And likewise the casing 27 through the air vent 27 a, see Fig. 3.

Pursuant to the specific parts thus described, and the relative positions of the parts as" illustrated in Fig. 1, the pressure of the delivery line effective upon the movable diaphragm 28 at its lower face is less in value corresponding to that exerted by the pendant weights 35 and sliding weights 36, thus causing the movable pilot member 19 to be moved upwardly, bringing its lower enlarged end 20 in closing position relative to the pipe opening 23, and its upper enlarged end 20 free of the pipe opening 22.

Under these circumstances the clearance afforded by the reduced portion 21 of the movable pilot valve 19 effects communication between the pipe connections 23, 24, thus subjecting the lower face ot the diaphragm to the inlet or suction pressure ot the blower 10.

Fig. 1 also represents a certain movement of expansion of the expansible bellows 31 under effect of an increase of the delivery line pressure, causing an extent oi" clockwise movement of its bell-crank 153-55, and corresponding motion of the arm 50 and barrel 47 to its full extent to bring its extended 4flange 47a into engagement with the sides of the cylindrical opening in the casing advancing the pin 51 to contact with right hand end of slot 52, and fully compressing the spring 49. Y

Under further increase of the delivery line pressure, such increased delivery line pressure applied to the bottom of diaphragm 23 causes the upward ldisplacement of the valve member 19 to the status when the pipe con-4 ,valve portion 21, at which position the communication of the pipe 23 with such clearance is shut off. Suchconnection of the pipe 24 with the pipe 22 subjects the under t'ace oi the diaphragm 35 to such relatively increased .pressure and overcomes the effective value of the Weights 42, causing the diaphragm 33 to risc and therewith the unloading valve 17 to open communication between the unloader inlet passage 15 with its outlet passage 16.

Upon the rise of the diaphragm 33 the rod 44 and its stop 46 are elevated until the stop 46is moved free of the end 45a of the trigger 45 to project its end 45a under the stop 46.

Under unloading conditions the passage ot' the medium under compression through the blower is effected out ot its discharge port, thence through the unloading passages 15, 16 to return through the inlet of the blower, and thus without effective delivery into the delivery line.

l/Ve will now assume that the pressure in the delivery line has decreased, arising upon withdrawal by consumption or otherwise of the medium.

It will be recalled that upon reaching the maximum pre-set pressure the operation of the pilot valve and associated devices results as above stated, and the delivery line pressure is applied to the lower face ot the diaphragm 33, by communication of the piping 26, 25, thence through 24 to such interior portion of the casing 32 of the diaphragm 33; the delivery lineV pressure is also effective upon eXpansible bellows 31 through the piping 26 and 30. Hence, upon decreased value of pressure in the delivery line, the weights 39 cause the flexible corrugated diaphragm 31 `to contract, moving the arms 41 downwardly, rotating the bell :frank 55-53 counter-clockwise, as viewed in F i g, 1, causing the pin 51 to move to the left, in its slot 52 until it engages the left hand closed end of the slot and eventually forces the end 45a of the trigger 45 trom under the under tace of the stop 46 until the same is free thereof. Upon such withdrawal of the trigger 45 from the stop 46, the weights 42 cause the diaphragm 33 to drop, moving the valve 17 downwards to its shut-oil position, and interrupting communication between the pipe 15 and the pipe 16 of the un# loading means in which status the operation o1 the blower'becomes eliective to pass the medium under compression through theY check valve 13 into the delivery line.

The restored delivery of the medium under compression into the delivery line continues until the pressure of the delivery line again exceeds that pre-set by the weights 35, 36, controlling the movable valve member 19 .by like reference numbers.

and the weights 39 controlling the flexible corrugated diaphragm 31 and the trigger 45, similarly as previously described.

It will be observed that the pipe 26 communicates at one end with the discharge line and connects with the pipe 29 leading to the bottom of the casing 18 of the movable valve member 19, thus subjecting the lower tace 19h of the movable valve member 19 to the discharge line pressure; the pipe 26 also connects with the pipe 25 which communicates with the lower portion of the casing 27 and thus with the upper portion of the casing 18 of the movable valve member 19, and hence subjects the upper tace 19a of the movable valve member 19 also to substantially the same discharge line pressure; accordingly, the opposite faces of the movable member 19 are subjected to substantially equal pressure and are balanced tor all positions of the mov-` able valve member within its casing 18.

My invention illustrated in Fig. 3 is similar in many respects to that illustrated in Iigs. 1 and 2, and like parts are designated In the form illustrated in Fig. 3, the expansible bellows is positioned to cO-operate with a stop associated with the diaphragm of the pilot means, in this instance, the stop 46 being positioned upon the link 37 of the pilot means, in lieu of being positioned upon the rod 44 of the diaphragm 33 controlling the shut-off valve 17 of the unloading means. The pipe connections and relative operations of the expansible bellows 31, its bell crank 53-55, its trigger 45 in co-operation with the stop 46 carried by the link 37 of the pilot-diaphragm 28 correspond in a similar manner as in the construction of Figs. 1 and 2. Simi larly, the weights 42 cooperate with the diaphragm 33 and the shut-oli' valve 17 ot the Vunloading means in a like manner.

In this arrangement the pipe 30 leading at one end to the interior of the eXpansible bellows 31 is of relatively short length as compared with the arrangement shown in Figs.

1 and 2; the other end of the pipe 30 communicates` with the pipe 25, and in turn with the pipe 26 leading to the discharge line.

In the form of my invention illustrated in Figs. 4.and 5, a plurality ot' compartments is provided for the blower, compressor or like device; these compartments may be of equal .0r unequal relative capacities. Individual unloading means are provided tor the respec tive compartments, the lshut-off 'valve of which is controlled by individual pre-set weights or equivalent. The blower discharge may communicate with separate discharge lines or a single discharge line, as desired.

In Figs. 4 and' 5, the control of the respective shutoff valves for the individual unloading means follows the constructionfor the single compartment type illustrated in Fig. Band hereinabove described. Like reference numbers designate like parts, the suffix A being applied to the parts of one compartment, its associated unloading means and its controlling device, the suffix 2 to the second group of these associated parts, and the suffix C to the third group of the associated parts.

ln the arrangement indicated in Figs. 4 and 5, the dischargie outlets of respective compartments communicate with a single discharge line, that is to say, the compartments discharge into a common discharge line through individual discharge passages 12 and individual check-valves 13.

Pursuant to this arrangement, the triggers 45A, 45B, 45C co-act with a common stop 46 on the arm 37 of the common pilot means, ind the respective pointed ends 45a, 45?) and 450 are arranged in vertically spaced relation, relative to the common stop 46; the trigger end 45a is shown lower than the trigger end 4to?) and the trigger end 450 shown gher than the trigger end A15b. By such arrangement` upon the upward flexing of the diaphragm 2S occasioned by a predetermined range of rise of pressure in the discharge line, transmitted through the pipe 26, thence through the pipe to the interior of the lower portion of the casing 32, under the conditions hereinabove set forth, the lowermost trigger end a is the first, upon upward dis placement of the diaphragm 28, to be positioned below the stop 46 to thereby lock the stop 4G and effect the opening of the unloading valve to provide for unloading of the blower 10A; in the event of further increase of predetermined range of rise of the delivery line pressure and corresponding further upward flexing ot the diaphragm 28, the interniediate trigger end 15b will next be positioned under the stop 46 for locking engage` ment therewith and effect the unloading of the blower 10B in a similar manner; and iinally upon further pre-determined range of increase of delivery line pressure and correspending further upward flexing of the diaphragm 28, the highest trigger end e150 is brought under the stop 4G in locking relation therewith.

To eiliect such conjointed control of, say, three compressors or compressing compartments and the common pilot means, the movable pilot member 19 is formed in this instance to have three reduced sections 21A., 21"). 2 C for the respective sets of pressure conveying pipes, the set of pipes 221AM 23A and -l-A for the control of the valve 17A of lhe unloading passages 15A, 16A for the blower compartment 10A; such valve 17A. is provided with a diaphragm similar to the above described diaphragm 33 within the casing 32A and pre-set by the weights 42A; ind similarly for the second blower or compressor compartment, and similar for the third blower or compressor compartment.y the last two named having individual unloading passages ot like construction, individual casings 32B, 32C for the respective diaphragm corresponding to the aforesaid diaphragm 33 and pre-set for range, ot variation of pressure by selective weights 39B, 39C, these parts being shown in partial plan view in Fig. 5.

ln a like manner the set of pipes 22B, 231i 24B lead from the region of movement ot the intermediate reduced portion 21B ot the common movable valve 19 for the control of' the diaphragm of the casing 32B to control. its valve 1TB, and similarly for the set of pipes 22C. 23C and 24C for the control of its valve 17C similarly actuated by its diaphragm and controlledl in range of pressure variation by its pre-set weights 39C.

The reduced valve portions 21A, 21B and 21C are related to the respective sets of pipes just enumerated to effect operative relation between the coacting parts upon rise of the predetermined range of the delivery line pressure to effect the closure of the pipe 23A relative to the pipe 22A, the pipe 24A for the stage of rise upward movement of the common pilot valve 19 is brought into commuuication with the pipe 23A. For the second stage of rise of' the predetermined range of the common pilot valve 19 similar operations tale place for the pipes 22B, 23B and 24B and similarly for the filial range ot pressure increase ot the delivery line for the pipes 22C. 23C and 24C.

Such successive stages of operation of the respective unloading means effects the opening of the valve and the unloading of the blower compartment 10A, with continued operation of the two remaining blowers or compressor compartments for the stage of first pre-set range of increase of the delivery line pressure; upon occasion ot the second pre-set range of rise of delivery line pressure, the valve ot' its unloading passages is then moved to its open position, thus providing for the unloading of the second blower or compressor compartment together with the unloading of the aforesaid Erst blower or compressor compartment, while the third blower or compressor compartment is continued in discharging communication with the delivery line. ln the event of the third, and in this instance, maximum range ot increase of delivery line pressure, the third blower or compressor compartment is placed in unloading status, namely, by the opening of its valve corresponding to the aforesaid valve 17 of its unloader.

However? in the event that the third range of increase of the delivery line pressure does not take place, the third blower or compressor compartment continues in full operation; in the event that the delivery lin(` pressure decreases below the pre-set second range olE pressure variation, the valve ofthe Aunloading means of the second blower or ment in full delivery status. Upon the drop of the delivery line pressure in excess of the iirst pre-set range of pressure variation, the unloader of the rst blower or compressor compartment is moved to its closedposition, thus placing all blowers or compressorcompartments in full delivery discharge with the delivery line.

sired number of blowers or compressor compartments co-related in a similar manner pursuant to my invention. i V

It will be observed that the respective pipes 30A, 30B and a similar pipefor the third blower or compressor compartment, lead respectively from the second expansible bellows 31A, 31B and similarly for the third expansible bellows 431A, 31 tothe interior of the lower portion of the common casing 27, and thereby communicate through the pipe 25 with the pipe 26 leading to the discharge line, thus subjecting the respective eX- pansible bellows to the delivery line pressure.

My invention asiillustrated in Fig. 6 follows the type of my `invention illustratedv in Figs. 1 and 2, and is applicable for a multiple blower or compressor compartments, in this instance three being indicated. Like parts are designated bylikereference numbers.

In this type of my invention, the triggers 45A co-act with the stop 46141011 the stem 44A of the diaphragm 33A within the casing 32A, similarly, the ltrigger 45B coacts with stop 46B on the stem 44B of thediaphragm 33B in the casing 32B and the trigger 45C co-acts with the stop 46C on the stem 44C of the diaphragm33C in the casing 32C. Pipe 30 communicates through its branch 30A with the interior of the lower portion of the casing 31A through its branch 30B with the interior of the lower portion of the casing 31A, and through its branch 30C to the interior of the lower portion of the casing 32C.

In a similar manner my inventionis Vapplicable for compressors of the reciprocating type, whether single or in multiple, and discharging into `a single discharge line or sepa rate discharge lines.

Also, in a similar manner, my invention is applicable for controlling the vacuum, i. e., suction pressure, of the inlet pressure line of an exhauster of the interlobal or other rotary type, or of a reciprocating vacuum pump, for effecting a desired vacuum within a predeter# mined range of variation.

As an illustration of one form of such embodiment of my invention, I have `shown in Fig. 7 a vacuum pump, say, of the interlobal type and Vassociated unloading means controlled-by an expansible bellows and pilot corresponding to the inter-relation of these associated parts conforming generally to the yhereinabove described arrangement illusparts are designated by valve 13 with the inlet passage 11 of the IeX- hauster or vacuum pump 10; the discharge passage 12 in this instance may connect directlywith the discharge line 14, that is to of the unloading means communicates at its vone end with the discharge passage 12 and the passage 16 communicates at its one end with the inlet passage 11 posteriorly of the check ranged to communicate through the checklsay, without a check valve. The p assage 15. Similar operations take place for any devalve 13. The valve 17 controlling the inter- ,n

communication ofthe adjacent ends of the unloading Vpassages 15, 16, is controlled by the diaphragm 33, disposed inthe casing 32. The diaphragm 28 of the pilot means, in this instance, controlled in its eiiective extent of displacement by the trigger 45a'in coaction with the stop 46 carried by the link 37. The lexpansible bellows 31, as hereinabove set forth, by communication of its piping 30 with with the pipe 26 is rendered subject to varii.

ations of the pressure to be controlled,.name ly, the vacuum or suction pressure by connection with the pipe 26 with the vacuum pressurev line 60 anteriorly of the check valve 13.

The pipe`26, as heretofore, communicates with Y the pipe 25, which in" turn communicates with the pipe 22 leading to the interior of the casing 18 of the pilot valve, similarly as hereinabove set forth.

' `The pipe 23, in this instance, communicates at one end with the delivery line 14 and at its opposite end with theinterior of the pilot valve casing 18, and the pipe 24 in 'this instance communicates at one end with the interior of the pilot casing 18 and at the opposite end with the sealed interior of the casing 32. i U f p .In such embodimentsr of my Vinvention wherein vacuum, i. e., inverse7 pressures yare to' be controlled, `the respective variable weights 35, 36 Yof the diaphragm 2 8` of the pilot means are-arranged with `respect to the fulcrum to exert a pressure on the diaphragm 28 through the link 37 in inverse4 direction togthat of my modifications as hereinabove set `forth. The link 37,1in this instance, following the modification of Fig. 3, carries the stop 46-{01 the trigger 45;' p i Also, similarly, the variable weights 39 of the eXpansible `bellows 31 is vapplied in inverse direction through the lever 41,- in lieu of the standard 41 in Fig. 3. The bell crank 55, 53 tends to move the housing 47 and therewith. the trigger 45 inwardly tothe casing 32 upon the downward, i. e., in the inverse direction upon expansion of the expansible bellows 31.

Also, similarly, the variable weights 42 applies its pressure through the rod 44 upon the diaphragm 33 downwardly, that is to say,

in the inverse direction as compared with the corresponding arrangement of Fig. 3.

For convenience the mechanical connection i between the diaphragm 33 and the unloading It will be observed that the valve 17, its stem 17a, the bell crank 61, 63, and the diaphragm rod 44a are located in the casing 32 on the side of the diaphragm to which the pipe 24 is connected, and accordingly the casing 32 on such side is constructed to seal against the outer or atmospheric pressure, thus avoiding the use of gaskets, packing or the like, for the unloader valve 17, the rod 44a. and the immediately associated parts.

The position of the movable valve member 19 within its casing 18 corresponds to that shown in Fig. 3.

Corresponding vinterrelations and objects attained of the controlling and associated parts are present in the forni of my invention shown in Fig. 7 as in that of Fig. 3. invention is similarly applicable for a single vacuum pump pursuant to the arrangement of the controlling and associated parts corresponding to that of Figs. 1 and 2, and for multiple vacuum pumps or compartments corresponding to the forms shown in Figs. 4 and 5, and in Fig. 6.

The operations of the respective parts of the various forms of my invention will be understood from the foregoing.

In these illustrated various forms of my invention Ihave appended the arrows 66 to indicate theiiow of the medium through the inlet passage and the compressor or vacuum pump 10, as the case may be; the arrows 67 indicate the liow of the medium inthe pressure line whose pressure is to be controlled, to wit, thatof the discharge line in the forms illustrated in Figs. 1 to 6 and of the'inlet line illustrated in Fig. 7. The arrows'68, in dot-and-dash outline indicate the direction of flow of the medium during the stage of unloading. Y

In the claims I have employed theeXpansion pressure device to include blowers of the rotary type such as interlobal compressors, also reciprocating pumps and other compressors, and further to include suction or vacuum exhaust/ers of the rotary, reciproeating and other types, the aforesaid being of .single or multiple compartments or units applicable orras designated otherwise in the re- Spective claims.

lWhereas I have described my invention by reference to speciiic forms thereof, it will be understood that many changes and modiiications may be made without departing from the spirit of the invention.

I claim.

1. The combination of a pressure producing device having aninlet passage and a discharge passage, a pressure line communicat ing with one of said passages, unloading means for said device including passage means for interconnecting said discharge passage with said inlet passage of said device, a valve for said unloading means, and means preset for a deiinite and substantial range of variation of the pressure of the pressure line formoving said valve to and `from its closing and opening positions.

2. rlhe combination of a pressure producing device having an inlet passage and a discharge passage, a pressure line communicat- 'ing .with one oi' said passages, unloading means for said device including passage means for interconnecting said discharge passage with said inlet passage of said device, a valve for said unloading means, and means .including a pilot valve preset for a definite `range of variation of the pressure of the 4pressure line for moving said valve to and from its closing and opening positions.

3. The combination of a pressure producing device having an inlet passage and a discharge passage, apressure line communicating with one of said passages, unloading means for said device including passage means *for interconnecting said discharge passage with said inlet passa-ge o'f said device, a valve for said unloading means, a member ,controlling said valve, means for subjecting said member to the pressure line pressure, means for presetting said member toa predetermined pressure value, and a preset pilot responsive to the pressure line pressure co-acting with said valve controlling member.

4. The combination of a pressure producing device having an inlet passage and a discharge passage, a pressure line communicating with one of said passages, unloading means for said device including passage means for interconnecting said discharge passage with said inlet passage of said device, a .valve for said unloading means, a member controlling said valve, means for subjecting said member to the pressure line pressure, means for presetting said member to a predetermined pressure value, pilot means subject to the pressure line pressure and co-acting with said valve controlling member, and means for presetting said pilot means for a predetermined pressure value.

.5. The combination of al pressure produc- .ing device having an inlet passage and a disa. valve for said unloading means, and means i preset for a deiinite range oi variation of the pressure of the pressure line for moving said valve to and from its closing and opening positions, said pressure range presetting means including a pressure responsive eX- pa-nsible bellows.

6. The combination of a pressure producing device having an inlet passage and a discharge passage, a pressure linecommunicating with one of said passages, unloading `means for said device including passage means for interconnecting said discharge passage with said inlet passage of said device, a valve for said unloading means, and means preset for a definite range of variation of the pressureof the pressure line for movingsaid valve to and from its closing and opening positions, said pressure range presetting means including a diaphragm subject to the -pressure line pressure.

7. The combination of a pressure producing device having an inlet passage and a discharge passage, a pressure line communicating with one oit said passages, unloading means for said pressure device including passage means for interconnecting said discharge passage with said inlet passage for said device, a valve for said unloading means, and means preset for a definite range of variation of the pressure of the pressure line for movin@ said valve to and from its closing and opening positions.

8. The combination of a pressure producing device having an inlet passage and a discharge passage, a pressure line communieating with one of said passages, unloading means for said device including passage means for interconnecting said discharge passage with said inlet passage for said device, a valve for said unloading means, and means preset for a deiinite range of variation of the pressure of the pressure line for moving said valve to and -from its closing and opening positions, a pressure responsive diaphragm and means controlled by an eXpansible bellows for controlling` the displacement of said diaphragm.

9. rEhe combination of a .pressure producing device having an inlet passage and a discharge passage, a pressure line communieating with one of said passages, unloading means for said device including passage means for interconnecting said discharge passage with said inlet passage for said device, a valve for said unloading means, and means preset for a definite range oi variation of the pressure of the pressure line for moving said valve to and from its closing and opening positions, a pressure responsive diaphragm, a stop element displaced upon the displacement of said diaphragmand a co-acting stop element controlled by an expansible bellows.

l0. The combination of a pressure pro-` ducing device having an inlet passage and a discharge passage, a pressure line communicating with one, of said passages, unloading means for said device including passage means for interconnecting said discharge passage with said inlet passage for said device, a valve for said unloading means, and means preset for a derinite range of variation of the .pressure of the pressure line for moving said valve to and from its closing and opening positions, and variable means for controlling the eiective expansion of an expansible bellows.

11. The combination of a pressure produciing device having an inlet passage .and a discharge passage, a pressure line communicating with one of said passages, unloading means for said device including passage means for interconnecting said discharge passage with said inlet passage for said device, a valve for said unloading means, and means preset ior a deiinite range of variation of the pressure of the pressure line for moving said valve to and from its closing and opening positions, variable means for controlling the effective expansion of an expansi- `ble bellows, a pressure responsive diaphragm andpvariable means for controlling the displacement of said diaphragm.

12. The combination of a pressure producing device having an inlet passage and a discharge passage, a pressure line communicating with one of said passages, unloading means for said device including passage mean-s for interconnecting said discharge passage with said inlet passage of said device,

a valve for said unloading means, and means preset for a definite range of variation of the pressure of the pressure line for moving said valve to and from its closing and opening positions', said pressure range presetting means including an eXpansible bellows, weights for variably controlling said eX- pansible bellows, a stop element controlled by the effective expansion of said expansible bellows, a pressure responsive diaphragm, a stop element subject to the displacement of said diaphragm and coacting with said iirstnamed stop element, weights for variably controlling the displacement of said diaphragm, pilot valve means for alternately subjecting said diaphragm to the inlet pressure of said device and the pressure line pres- -sure and weights for predetermining the movement of said pilot valve means.

13. The combination of a pressure producing device having an' inlet passage and a discharge passage, a pressure lineJ arranged to communicate with one of said passages, unloading means for said device including a valve, and means responsive to a predetermined substantial range of pressure variation of the pressure line for moving said valve to effect unloading and loading of said device relative to said pressure line.

14. rl'lie combination of a pressure producing device having an inlet passage and a discharge passage, a pressure line arranged to communicate with one of said passages, a check valve disposed between said one passage and said pressure line, unloading means for said device including a valve, and means responsive to a predetermined and substantial range of pressure variation of the pressure line for moving said valve to eiiiect unloading and loading of said device relative to said pressure line.

15. The combination of a pressure producing device having a plurality of pressure units, inlet and discharge means respective-ly for said pressure units, a pressure line arranged to communicate With one or' said means, unloading means for said pressure units respectively including a. valve for said respective unloading means, and means responsive to the pressure line pressure for Acontrolling said valves respectively for predetermined ranges of variation o'l the pressure line pressure to eliect unloading and loading of said pressure units.

16. The combination of a pressure producing device having a plurality el pressure units, inlet and discharge means 'for said pressure units, a pressure line arranged to commimicate` with one oit said means, said one means being provided with check valves, unloading means for said pressure units respectively including a valve for said respective unloading means, and means responsive to the pressure line pressure `for controlling said valves respectively7 for predetermined ranges of variation of the pressure line pres sure to eiiect unloading and loading of said pressure units.

17. The combination of a pressure producing device having a plurality of pressure units, inlet and discharge means for said pressure units, a pressure line arranged to communicate With one of said means, each of said one means beingprovided With a check valve, unloading means for said pressure units respectively including a valve for said respective. unloading means, and means respensive to the pressure line pressure for controlling said valves respectively for predeter mined ranges of variation of the pressure line pressure to effect unloading and loading of said pressure units.

18. The combination of a pressure producing device having a plurality of pressure units, inlet and discharge means lor said pressure units, a pressure line arranged to communicate with one. of said means, unload ing means for said pressure units respectively including a valve for said respective unloading means, and means responsive to the pressure line pressure for controlling said valves respectively for predetermined ranges of va ri ation of the pressure line pressure to effect unloading and loading of said pressure units, said pressure responsive means including a diaphragm controlling said valve.

19. The combination of a pressure producing device having a plurality of pressure units, inlet and discharge means for said pressure units, a pressure line arranged to communicate with one of said means, unloadingmeans for said pressure units respectively including a valve for said respective unloading means, and means responsive to the pressure line pressure i'or controlling said Valves respectively for predetermined ranges of variation of the pressure line pressure to effect unloading and loading of said pressure units, said pressure responsive means including a pliot valve responsive to the pressure line pressure.

20. rl`he combination of a pressure producing` device having a plurality of pressure units, inlet and discharge means for said pressure units, a pressure line arranged to communicate With one of said means, unloading means for said pressure units respectively including a valve for said respective unloading means, and means responsive to the pres sure line pressure for controlling said valves respectively for predetermined ranges of va riation of the pressure line pressure to effect unloading and loading of said pressure units, said pressure responsive means including diaphragm means controlling said valves respectively, and further including a common pilot valve responsive to the pressure line pressure and controlling the pressures effective upon said diaphragm means respectively.

1n testimony whereof l have signed this specification this 2nd day of Oct., 1928.

EVERETT 1V. SVARTVVOUT.

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