claim: 1. In combination with a superchargerh4viiig a discharge duct, a relief valve inounted in the wall of said duct and urged to the closecl position by the air pressure in the duct and opero,@le when open to dis,eliarge into the atmospliere to promote airflow through the supl-rcharger, a check valve preventing a reverse flow througil the duct including a seat in the duct, a door eiigageable with the seat tQ close qff the duct, a braeket on t-lie door, and a hilige coxillecting the. bracket with a wall of said duct so that the door is jaioved toward its closed position against the seat by reverse flow in the duct, a fluid presE;Ure actuated device operatively conliected to the relief v Ive a for moving the relief valve to the open position, a pressure line havilig communication with the duct at the dowpstream side of said seat and leading to said device to supply actuauing pressure thereto, a pilot valve having a casing axed to said duct, said Pilot valve controllin@,y said 1)ressure line and directly enga.@ing said bracket at a, point spaced frorn s4id hingq wqunting to be moved to an opea position to cause opening of the relief valve when the outward airflow in the duct falls below a given value to allow rnoveriaent of the door toward its closed Positioii, and e, 5pring seated in sai.d casing and urging the pilot valve against the bracket and moving the pilot valve to tlie closed position when the door again

9 is moved toward the open position by increased outward air-flow in the duct. 2. In combination with a supercharger having a discharge duct, a relief valve mounted in the v,rall of said duct and urged to the closed position by the air pressvre in the duct iiid operable when open to discharge into the atmosphere to promote airflow thro,,igh the supercharger, a check valve preventing a reverse flow through t'he duct including a seat in the duct, a door engageable with the seat to close off the duct, 9, bi?,cket on the door, and a hinge connecting the bracket with a wall of said duct so that the door is moved toward its closed position against the seat by reverse fiow in the duct, a fluid pressure actliated device oDeratively connected to the relief valve for n-ioving the valve to the open position, e. pressu,-e linc, having communication with the duct at the downstream side of said s,-at and lead;ng to said device to supply actuat-"iig pressure thereto, a pilot valve having a casing fixed to said duct, said pilot valve controlling said pressure line and directly en.-aging said bracket at a point spaced from said hinge mouiltin@,, to be @roved 'uo an open posi-tion to cause opening of the relief valve wh--n the outward airflow in the duct falls below a given value to allow movement of the door toward its closed position, a spring sested in said casing atid urging the pilot valve ogainst the bracket and @movin.- the pilot valve to the closed position when the door again is moved toward the open position by increased outward airflow in the duct, aiid a constant pressure bleed for said pressure actuated device to prevent hunting of the door a-Tid pilot valve. 3. In combination vtith a supercharger hav,@'ng a discharge duct, a relief valve mounted in the wall of said duct to discharge air pressure from the duct to proiilote air flow through the supercharger, the relief valve comprising a valve seat irounted in a wall of said duct facing inwardly relative to the duct, and a valve closure adapted to seal outwardly against the seat and adapted 'uo inove inwardly to open to the atr-qosphere, a check valve in the discharge duct 4@n downstream relation to the relief valve i'Or prevent,"ng the reverse flow of air through the duct including a door hinged in the duct, diaphragm means operatively connected to said relief valve, a pressure line for conveying air pressure from the duct to the diaphragm means to operate the sa@-ne, a pilot valve having a casing fixed to said duct, said pilot valve controlling said pressure line and having an end extending into said duct and engageable with said door to admit pressure to the diaphragm mea.ns to open the relief valve when the outward flow in the duct reaches a given low value, and means for conducting pressure from the duct to 2,648,490 10 the other end of the pilot valve to pressure balance the pilot valve, and a spring seated in said casing and maintaining the pilot valve in engagement with the door and for moving the pilot valve to the closed position when the outward airflow through the duct increases to swing the door open. 4. In combination with a supercharger having a discharge duct, a check valve for preventing a reverse flow throu@ah the duct comprising a hous10 ing counec'Led to the duct having an inlet and outlet, a closure for said inlet pivotally mounted on said housing, an aperture in said housing, a pilot casing mounted on said housing at said aperture, @- pilot valve resiliently mounted in said 15 casing and extending through said aperture for engaging said pivoted closure, a port in said pilot casing opened or closed by said pilot valve for controlling the flow of air from the housing to the pilot casing, a pipe con.,iected at one end to said 20 port, a valve actuating i,-Lechanism comprisin.a an upper and lower section, the other end of sai-d pipe connected to said upper section, a bleed hole in said upper section, a bleed hole in said lower section larger thrn that in said upper sec2.,@l, ti-on, a diaphragm clami3ed between said sections, a stein having one end attached to said diaphragm and passing through said lower section and into said duct, a closure secured to said other end, guides mounted oli said stem and closure, a 6'ij tubular fitting acting as a sleeve for said guides mounted upstream of said check valve in a wall of said duct, spacers connecting said sections with said fitting, a sealing member on said closure to cooperate with said fitting when said door is open to prevent esea-pe of pressure and to disengage fropi said fitting when said door is closed to allow for escape ofpressure. BERNARD L. MESSINGER. I-IOWARD I-1. GRAY. 40 ROBERT R. RICHOLT. References Cited in the file of this patent UNITED STATES PATENTS Numb er Name Date 4 859,34 1 Scheier ------ ------ July 9, 1907 1,052, 172 Rateau ------ ------ Feb. 4, 1913 1,210, 030 Baumann ---------- Dec. 26, 1916 1,222, 352 Banner ----- ------- Apr. 10, 1917 1,267, 880 McBride ---- -------- May 28, 1918 50 1,280, 477 I-lopkins ------ ------ Oct. 1, 1918 2,000, 721 Standerwick -------- May 7, 1935 2,380, 777 Moss ----- --------- July 31, 1945 2,451, 835 Johnson ----- ------- Oct. 19, 1948 55 FORV-IGN PA-LENTS Numb er Country Date 26,987 Great Britain -------------- 1913 344,737 Great Britain ------ Mar. 12, 1931

Patented Aug. I l,, 1993 29648@490 UNITED STATES PATENT OFFICE 2,648,490 SUPERCHARGER DUCT SYSTEM Bernard L. Messinger, Pacific Palisades, Howard H. Gray, San Fernando, and Robert R. Richolt, Tujunga, Calif., assignors to Lockheed Aircraft Corporation, Burbank, Calif. Application October 4, 1947, Serial No. 777,936 4 Claims. (Cl. 230-115) 2 This invention relates to apparatus for supplying air under pressure to enclosures and has more particular reference to the duct systems for conveyin g air under pressure from superchargers to the cabins of airplanes for the purpose of pres- 5 surizing the same. The habitable compartments or cabins of modern high altitude aircraft must be pressurized or supplied with air under pressure during high 10 altitude flight to assure the comfort and well being of the occupants or passengers. It is the general practice to employ superchargers driven by the propulsive engines of the airplane to develop the air pressure required for this purpose. A common duct system usually connects 15 the discharge sides of the superchargers with the compartment or cabin and the latter is equipped with a regulable outflow valve so that there may be a continuous flow of air under' pressure through the compartment to maintain 2C) proper ventilation and the required internal cabin pressure. The discharge ducts of the superch argers are also equipped with check valves for preventing a reverse flow of air in the ducts so that air pressure in the cabin will not escape in the event one or more of the superchargers are not functioning. In certain installation s tt has been found that when the air fi6w from a supercharger falls below a given value, that supercharger overheats due to in- .3 j) sufficient cooling and is liltely to be damaged. Such a decrease in the airflow through any one or all of the superchargers of the system may result from various causes such as blocking or restricting of the duct system, a substantial differ- 35 ence in the speed of operation of the engines driving the superchargers, closing of the eh4eCk valves, etc., and such causes may persist for a suflicient tinie to bring about serious injury to thd affected supercharger or superchargers. 40 It is an object of the present invention to provide a supercharger duct system of the class above referred to embodying practical and thoroughly dependable means for maintaining or reestablishi ng air flonv through the superchargers 45 when the flow throtigh the discharge ducts of the salme falls below a value reciuired for ProPer superch arger cooling, and which maintains a suffir-e t flow through the affected superchargers 1 n each relief valve so constructed and arranged as to open the related relief valve Nvhen the air flow through the respective supercharger discharge duct fglls below a given value. The opening of the relief valve allows a sufficent flow of air through the supercharger to properly cool the same even though the air flow from the discharge duct of the particular supercharger may be greatly restricted or even terminated. Another object of the invention is to provide a system of the character referred to in which the relief valves are controlled or operated by a flow sensitive dev-lce so as to maintain adequate coolino- air flow through the superchargers ir-@ive of the pressure conditions existing in respee - the discharge ducts. Air flow of sufficient value to adequately cool the superchargers must be ma-intained at all tiines regardless of the prevailing pressures in the ducts and in accordance with the invention flow sensing or flow responsive devices substantially unaffected by pressure, control the relief valves. Another object of the invention is to provide a. supercharger duct system of the type described 'm which the check valves in the discharge ducts of the superchargers serve as the flow sensitive devices for controlling the related relief valves. The discharge duct of each supercharger is provided with a check valve to prevent the loss of pressure from the cabin or enclosure when the rolated supercharger is for any reason made idle and the invention utilizes the closures or doors of the check valves as flow sensing devices to control the relief valves which maintain flow through the superchargers even though the check valves are closed. A further object of the invention is to provide, a system of the character mentioned in which the valves do not "hunt" or oscillate but have an"over-center" action so as to assume ihe open bn(I closed positions without oscillating. other objebts @tnd. features of the invention will become apparent from the following detailed description of typical preferred embodiments, thr oughout which description reference is made t o the accompanying I drawings in which@: Figure 1 is a diagrammatic view of a supercharger cabin air supply system embodying one to preserve such cooling so long as the flow 5o form of the present invention; through the ducts remains at such a low value. Figu re 2 is an enlarged fragmentary sebtional. The system of the invention includes an automatica ily operated relief valve or flow mainvie w illustrating one of the relief valves of the tain'mg value for the discharge duct of each syst em illustrated in Figure 1; pilot means for 65 Figu re 3 is a transverse sectional view taken superch arger and a control or

2,648,490 3 substantially as indicated by line 3-3 on Figure 2; F,igure 4 is an enlarged fragmentary sectional view illustrating a portion of one of the check valves and showing the related pilot valve; 5 Figure 5 is a fragmentary sectional view of a check valve and relief valve of another form of the invention; Figure 6 is a transverse sectional view taken as indicated by line 6-6 on Figure 5; and 1:0, Figure 7 is a view similar to Figure 6 illustrating still another form of the inveniion. ln the drawings we have shown the invention associated with a supercharger @system embodying two superchargers 10 for suiapl@ing air un@ i .5 der pressure to a common duct I 1. It is to be understood that the invention may well be incorporated in a system empldyiiig olie @Upe6rcharger, three or more superchargers, @a@nd with the superchargers arranged to individually dis- 20 charge into separate compartment or into a common duct system. The common duct I I may be considered as conveying air under pressure to the cabin of an airplane. The superchargers 10 may be of any selected or required type and are 2,@ adapted to be driven by separate or independent power sources such as aircraft engines 12. Dischar.-e ducts 13 extend from the superchargers 10 to deliver the air under pressure to the common duct II, Each discharge duct 13 in has a check valve V for preventing a reverse flow of air. 'the check valves V illustrated, each include a housing or body 14 interposed in the respeciive duct 13. Each valve housing 14 has an end plate I 5 which carries a valve seat I 6 1,@) adapted to be engaged by the closure or door 17 of the valve. The check valve doors 17 are generally disc shaped parts secured to the end plates 15 by hinge conne6tions 18 so as to be freely swingable between the closed positions and 40 operi or -partially open positions under the influerice of air flow through the dudts 13. The valve doors 17 are provided with somewhat resilient bracket members I 9 for suspending them from the hinges I B. The members 19 are adapt- 4.@) ed to flex so tha@t the doors 17 mo@y iavenly soat or engage against the seats 16. the apparatus or systbm of the inverition further includes pilot vlalves P associated with the check valves V to be actuated or controlled 50 ihereby and relief valves R for-the -dudts 13 controlled by the pilot valves. A pilbt valve P is associated with each check Valve V in a nianrier to be actuated by its d6or 17. Each pilot'V@lve P includes an elongate valve body 20 secuted on 55 ihe exterior of the plate 15 6f'the check valve. The valve body 20 has a passage'21 bbiiimuni6ating with an bpening 22 -in the wall of the plate 15. The operiing 22 commtinicates with the intb@ior of the check valve body 14 and thus has 6( corriiiiunication wi@h ihe di@charge duct 13. It will be observed that the bpenitig 22 and passage 21 communicate with the portion of the duct:13 a,t the downstream side of the check valve door 17, assuming the door to be in the closed'posi- 6.5 tion. A lateral or transverse port 23 in the pilot valve b6dy -20 connects @the pa@sage 21 with a pipe or line 24 Which extends to the related reli6f Valve R will be later described. ;Each pilot valve P further includes a pin or 7( valve member 25 shiftable axially in an opening or bore 26 in the body 20. The bore 26 intersects the lateral port 23 so that the member 25 is adapted to control - communication between the downstream portion of the duct 13 and the 75 4 line 24. An annular groove 27 is formed in the member 25 and the member is adapted to be shifted axially between a closed position where it closes off the lateral port 23 and the open position of Figure 4 where its groove 27 registers with the lateral port to allow the flow of air Pressure from thedownstream portion of the duct 13 to the line 24. The valve member 25 extends through the abovernentioned opening 22 in the plate 15 to project into the check valve housing 14. The projecting end of the member 25 is rouiided off or made partially spherical to Cooperate with the check valve door 17. The member -@5 engages the door 17 at a point adjacent but spaced from the hinge connection 18 so that the Diember is shifted axially in one direction when the door moves toward its closed position. A 8pririg 28 is arrqnged under ermpression between the other end of the member 25 and a plug 29 screwthreaded in the outer end of the valve body 20. The spring 28 occupies a chamber 30 in the body 20 and serves to move the valve rnember 25 in the other direction when the door 17 moves toward its open position. The spring 28 also serves to hold the member 25 in the closed position when the door member 19 is out of contact with the valve member '25. A shoulder 9 on the member 25 is engageable with the end wall of the chamber 30 to stop the member 25 in its fully closed position. As illustrated in Figure 4, the groove 27 is Positioned to register Or communicate with the lateral port 23 when the door 17 is in the closed position and is of sufficient axial extent to remain iii communication with the lateral port throughout a considerable movement of the door. Thus the relationship between the lateral port 2 3 and the groove 2 7 is such that air under pressure from the duct 13 at the downstream side of the door 17 is admitted to the line 24 when the door 17 assumes a partially closed positionby reason of limited air flow through the duct in the downgtream direction. In practice, when air flow from the related supercharger IC reaches a low valite where there is instifficient flow to cool the supercharger, gravity acting on the flowsensitive door 17 causes the door to assume a Positioii where the groove 27 of the pilot valve communicates with the lateral port 23 to @allow Air under pressure to flow into the line 24. It is preferred'to balance the pilot valves P so that they readily respond to movement of the dobr 17. The inactive end of the pilot valve members 25 extend into the adjacent chambers 30. The abovementioned passages 21 communico@te with the chambers 30 at 31 so that air,pressures (if substantially equal value are imposed on the opposito ends of the valve members 25 to balance the valves. The abovementioned spririgs 28 imposed only a very light load on the valve membeis 25 and-therefore do not interfere with or resist movement of the gravity and flow sensitive doors 17 of the check valves V. A flow maintaining or relief valve R is provided for each discharge duct 13 and is arranged at the upstream side of the related pilot valve P. While the relief valves R may be of any suitable type, we prefer to employ valves that are urged closed by the air pressure in the ducts 13 and that ore adapted to be opened by fluid pressure actuated units such as Pistons or diaphragms. Each duct - 1 3 has a fitting 3 2 secured to the duct around an opening @33 therein. Spaced bolts 34, or theequivalent, secure seat members 35 to the fittings 32. Each seat member 35 has an out@

5 wardly extending tubular part 36 and an iriwardly facing annular seat 37. The relief valves R each further include a valve or closeure 38 provided with spaced outwardly extendifig guides 40 which slidably operate in the tubular parts 36 of the seat members. The closures 38 are disc like parts provided at their peripheries with washers 41 for sealing with the seats 37. The valve closures 38 face inwardly or toward the centers of the ducts 13 to be urged outwardly toward their respective seats 37 by the air pressure and outward flow through the tubular guide parts 36. The guide parts 36 may spill or discharge the air under pressure into the atmosphere. A stem 42 extends outwardly from the closure 38 of each relief valve R. In the embodiment of our invention illustrated in Mgures 1 to 4 inclusive, the means for actuating or opening the relief valves R, in response to air under pressure received from the related pilot valves P, are in the nature of diaphragm mechanisms. Each of these diaphragm units includes a diaphragm housing made of two sections 43 and 44 and a flexible diaphragm 45 secured between the peripheral portions of the housing sections. Rods or bolts 46 mount the diaphragm units on the relief valve assemblies and aid in clamping the peripheral portions of the sections together to secure the diaphragms 45 therebetween. In the particular arrangement illustrated the bolts carry spacer tubes 47 and mount the diaphragm units on plates 48 so that the peripheral parts of the housing sections 43 and 44 are clamped between the bolt heads and the ends of the spaced tubes. The stems 42 of the relief valves R pass through openings in the sections 43 and discs 49 secure the diaphragms 45 to the stems. The walls of the lower diaphragm housing sections 43 are perforated as at 50 so that the lower sides of the diaphragms 45 are subjected to atmospheric pressure. The above described lines 24 from the related pilot valves P connect with fittings 51 on the upper housing sections 44 so that the upper sides of the diaphragms 45 are subjected to air pressure admitted by the lines 24. Bleed orifices 52 of limited capacity are provided in the walls of the upper sections 44 to permit the air pressure above the diaphragms to bleed out when the related pilot valves P close. This permits the relief valve closures 38 to move upwardly against their seats 37. In the operation of the system illustrated in Mgures I to 4 inclusive, the superchargers I 0 are normally driven at a sufficient rotative speed and the speed of their driving engines 12 is sufflciently well matched or coordinated to cause ample air flow through the superchargers to insure adequa,te cooling of the same. Ilowever, during actual ground operating or flight conditions the air flow through one or more of the superchargers IC may fall below a value required for their cooling. This may occur by reason of substantial obstruction to air flow through the ducts I I or 13 or may be occasioned where the superchargers have variable speed drives and one driving engine 12 is operated at a considerably slower speed than the other. in the latter case the output of the supercharger I 0 driven by the engine i 2 operating at the higher speed, will be sufficiently greater than the output of the other supercharger IO to cause a back pressure to develop in the discharge duct 13 of the slower supercharger and there will be only a quite limited air flow through the latter. In -any event, whenever the air flow through a discliarge duct i 3 falls below a value sufficient to adequately cool the related supercharger I 0, the door 17 of the check valve V in that duct moves toward the closed position. This movement of the door 17 shifts the pilot valve member 25 to a position where its groove 27 communicates with the lateral port 23. The parts are related so that the pilot valve P does not open until the air flow outwardly through the duct 13 has reached such 10 a low value that there is danger of the related supercharger 10 overheating because of insufficient air flow. Opening of the pilot valve P allows air under pressure from the downstream side of the check valve V to flow through the line 24 to 15 the diaphragm housing section 44 to act on the upper side of the diaphragm 45. The diaphragm 45 has an effective area considerably larger thon the effective area of the closure 38 of the relief valve R and pressure on the upper or outer side 20 of the diaphragm opeiis the relief vglve. This allows air under pressure from the duct 13 to escape through the seat member 36 to the atmosphere and a sufficient flow of air is thus established in the duct 13 and fhe supereliarger 10 to 25 properly cool the supercharger. The relief valve R remains open so long as the door II of the check valve V remains in the position where the pilot valve P is open. When a normal flow or a flow adequate for cooling of the 30 related supercharger I 0 is reestablished through the supercharger, the door 17 of the check valve V may remain in the position where the pilot valve P is at lea-st partially open. This is because a certain proportion of the air i9ow from the 35 supercharger I 0 escapes to the atmosphere through the relief valve R and full air flow from the supercharger is not imposed on the door 17 of the check valve V. Ilowever, when the air fiow from the related supercharger IO is somewhat in 40 excess of that required for its proper cooling, the major proportion of the aggregate flow reaching the door 17 is sufficient to move the door to a position where the pilot valve P is closed. Upon closing of the pilot valve P the air under pressure 4 above the diaphragm 45 slowly leaks out through the bleed 52 and the relief valve closure 38 closes against its seat 37 by the action of the internal flow and air pressure in the duct 13. The somewhat delayed closing of the pilot valve P and the 5( delayed closin.@ of the relief valve R prevent "hunting" of the system and oscillation of the door 17 when flow through the duct 13 approaches and reaches that required for cooling of the related supercharger I 0. Thus the valve and 55 duct system has what may be termed an "overcenter action" for preventing "hunting" of the valves. The operation of the valve systems in the various ducts 13 is the same as above described and the valve systems may opc@rate individually 60 or simultaneously, depending upon the nature of the fault in the duct system. Figures 5 and 6 illustrate a form of the invention characterized by a relief valve for a duct 13 operated directly by the flow sensing check valve. (;5 In the simplified drawing of bhis form of the invention, the check valve 60 has a suitable housing 6 I connected in the supercharger discharge duct 13. The interior of the housing 61 carries an annular valve seat 62 which faces down70 stream in relation to the air flow from the supercharger. The closure or dooi, 59 of the check valve 60 is hinged or pivoted in the housing 61 at 63 so as to be movable between the open full line position and the closed broken line position of 75 ngure 5 in response to air flow through the ducts,

9,646,49.0 7 relief valve 64 of Figur,s 5 pnd 6 ineltides a housing or shell 65 projecting radially f roin. the cbeek valvo housing GI or the duct I$. The s@hell 65 lias. its inner end open to tti@e interiqr of the dupt 13 adjacelit the hin e mo-antin 63 2@nd its ti I 9 11 9 O.Uter end is closed by a. threacled cap @6. A series of eircumferentially spaced pqrts 61 is provicled iia the iiiner wall portioii of the shell and the pqrts are open to the at.mosphere. The relief valve 64 further includes a valve mernber 68 10 m,ov"le Pxially in t@he shell 65 and adp,,pted to coiitrql the pqrts 57. The member GO raay be a cup-shaped element closed at its inner elid and having an annular outwardly projecting rin-I 69 on its outer end. The rim 69 i,s engageable with 15 a shoulaer 74 on the iriterior of the shell 65 to iimit inward travel of the meniber 68. A ligbt spring 72 is arranged unde corlpressioii between ,r the cap 66 and the inner end wall of the c,4psliaped meniber 68 to urge the inembqr to the 20 closed position where the ports 67 are clos,-d. In accordance with the invention, the door 59. of the check valve 60 serves to move the member 68 outwardly when the check valve door 59 mpves toward the closed ' positioii. A lug 70 Proiects 25 froin the inner end of the valve member 68 and iE@ engaged by an arm 71 on the cloor 59. These parts are related sG that when the door 59 is in th ' e open full line position of F-igure 5 the spring 72 liolds the member 68 inwardly to close the 30 ports .67. When the door 59 moves from this full line position towards the closed pqsition, the valve member 68 is shifted out-A@,ordly to uncover the ports 67, It is preferred t.0 pressure balance the relief valve member 68. A port 73 extends '@ 5 radially outward through th,e wall of the shell 65 to the abovementioned shoulder 74. The port 73 maintains the space above the member 68 in communicat".on with the interior of the duct 13 so that the pressures on the opposite sides of the 40 valve member are substantially.balanced. In the operation of the structure shown ixi Figures 5 and 6, the air flow from the related superchanger 10 normally holds the check valve door 59 in the open or partially open position 45 where the valve meniber 68 closes the ports 67. When the air flow through the superchorger a)acl the duct 13 is reduced to a value insufficient to adequately cool the supercharger, the door 59 of the check valve automatically moves toward its 0 seat 62. This movemeiit of the door 59 moves a the valve meinber 68 outwardly to uncover the ports 67. This loermits air under pre.,,sure to e,scape through the ports, G'i to the atmospl@ere increasing tlie air flow through the duc@t (3 and '55 supercharger to a value sufficieiit 'tlo properly cool the supercharger. When the air flo,.w through the supereliarger aiid duct i 3 returns to normal or reaches a value sufficient to cool, the supercharger the door member 59 is moved tow@,rd the 6o open position or away from its seat 62 by the increased air flow. Vlhen this occurs the spring 72 returns the valve member 68 to the positioii where it closes off the ports 67. Figure 7 illustrates another embodiment of the 6,5 invention wherein the check valve is directly associated with the relief valve. In fact, in this comtruction, the check valve al'id the relief valve are integral or intimately related. The check valve includes a housing 30 co-,mected in the duct 70 13 of the related supercharger 10 and provided with an annular seat 8 1. A tangentially disposed bore 82 is formed in tlie wall of the housing 80 and is radially off set f rom the seat 8 I - A gerierally cylindrical closure mel.iber 83 is suported 7r, 8 in the bore 82 for free angular or turning trio.V6.ment. A shaft or axle 87 may s:upport the mernber 83 in the bore 02 for free angular movement. The door 84 of tlxe check valve is secured to this merp-ber 83. The member 83 forms the, fulcrum or pivot olement for the door allowing the door ta move between the open and closed positions under the action of air flow in the duct 13. :The relief valve means includes a port 85 intersecting the bore 82 and having its inner end in communication with the duet 13. at the upstream side of the seat 81 and its outer end open to the atmosphere. The abovemelitioned member 03 comtitutes the closure element of the relief valve and serves to control the port $5. A side portion of the mernber 83 is relieved or cuL, away to have an open sector 86. The parts are related so that the member 6.3 closes the port 85 when the door 84 is held in the open position by air flow through the duct 13 suff!L,,ient to adeciuo@tely cool the related supercharger. When the check valve door 84 moves toward the closed position the open sector of the member 83 comes into register with the port 85 to allow the escape of air under pressure from the duct 13. This provides oldditional air flow through the supercharger IQ suzr cient to in!5ure proper cooling. When the flow through the duct 13 returns to nqrmal or is su@Mcient to provide adequate cooling for the related -upercharger I 0, the check valve door 84 is, moved away from the seat 8 I by the increased air flow. This movement of the door 84 moves or turns the member 83 to the position where it closes the relief port 85. It is believed that it will be readily understood how the structures of Figures 5 and 6 and Figure 7 n-iay be incorporated in a duct system such as shown in Figure 1. Having described only typical preferred embodiments of our ixivention we do nab wish to be limited to the particular details set forth, but wish to reserve to ourselves any features or modifications that may fall within the scope Gf the following claims. We