US3612406A

US3612406A - Safety blowgun

Info

Publication number: US3612406A
Authority: US
Inventors: John E Bass Jr; George R Ferguson
Original assignee: GW Murphy Industries Inc
Current assignee: GW Murphy Industries Inc
Priority date: 1969-11-03
Filing date: 1969-11-03
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12

Abstract

A safety compressed-air blowgun for protecting a user thereof against exposure to dangerously high pressures and wherein a pressure-responsive valve is arranged in series flow relation with a manually operable valve for precluding delivery of air from the blowgun at dangerously high pressures through movement of a pressure-responsive valve member relative to a valve seat in response to balancing of air pressures and in such a manner that the valve member is seated to preclude passage of air when the pressure of air downstream of the pressure-responsive valve is above a predetermined safe pressure.

Description

United States Patent Inventors John E. Bass, Jr.

Charlotte, N.C.; George R. Ferguson, Clover, S.C. Appl. No. 873,205 Filed Nov. 3, 1969 Patented Oct. 12, 1971 Assignee G. W. Murphy Industries, Inc.

Houston, Tex.

SAFETY BLOWGUN 9 Claims, 7 Drawing Figs.

US. Cl 239/526, 137/613, l37/505.25,137/498, 239/571 Int. Cl B05b 1/32 Field of Search 137/613, 85, 498, 500, 503, 505, 505.13, 505.25; 239/571, 526

References Cited UNITED STATES PATENTS 2,623,331 7 12/1952 (ireening l 37/613 3,074,426 1/1963 Billington 137/505.25 3,075,546 1/1963 Roberts 137/613 3,269,411 8/1966 Teston 137/613 3,454,041 7/1969 Masson l37/505.25

Primary Examiner-Laverne D. Geiger Assistant Examiner-William B. Wright Attorney-Parrott, Bell, Seltzer, Park & Gibson ABSTRACT: A safety compressed-air blowgun for protecting a user thereof against exposure to dangerously high pressures and wherein a pressure-responsive valve is arranged in series flow relation with a manually operable valve for precluding delivery of air from the blowgun at dangerously high pressures through movement of a pressure-responsive valve member relative to a valve seat in response to balancing of air pressures and in such a manner that the valve member is seated to preclude passage of air when the pressure of air downstream of the pressure-responsive valve is above a predetermined safe pressure.

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SHEET 2 OF 3 ATTORNEYS JOHN E BASS 3'2 aha GEORGE RFE-musou nvfiwflffleZJpgbgfls Jw PATENTEU nmmsn 13,612,406 SHEET 3 OF 3 JoHN E. 51x55, Jiaand GEOZGE $2. FERG SON ATTORNEYS INVENTORS:

SAFETY BLOWGUN This invention relates to a safety blowgun and, more particularly to means responsive to the pressure at which compressed air is delivered through a blowgun for protecting a user of the blowgun against exposure to dangerously high pressure.

Compressed-air blowguns are widely used in industrial applications for cleaning tools and workpieces during industrial operations such as machining of metals. With ready availability of compressed-air blowguns, such blowguns have also come to be used by workmen to clean dust and the like from clothing or the workmens bodies. As will be recognized, such use of a compressed-air blowgun exposes a user to danger of significant physical injury where the pressure of air delivered through the blowgun is relatively high. Implementation of recent industrial safety legislation has recognized the dangers inherent in such use of a compressed-air blowgun by requiring limitation of the air pressure delivered through a compressedair blowgun.

In attempting compliance with such industrial safety legislation, two approaches have heretofore been used. The first of these approaches is to limit the pressure at which compressed air is supplied throughout an industrial plant to the pressure specified by the industrial safety legislation. This approach has serious deficiencies in that such pressures are below those at which most pneumatically operated tools function efficiently and thus this approach causes interference with the more important reasons for distributing compressed air within an industrial plant. The second approach is the provision of individual pressure regulators to reduce a more generally distributed relatively high line pressure to a specified lower pressure at locations where a compressed-air blowgun is to be used. This latter approach suffers two deficiencies, one economic and related to the cost of providing a relatively large number of individual pressure regulator devices and the other safety related in that such individual pressure regulators are subject to readjustment by workers more interested in obtaining a high pressure at a compressed-air blowgun than in compliance with safety standards.

With the above discussion in mind, it is an object of the present invention to ensure that a user of a compressed-air blowgun is protected against the dangers present where excessively high pressure is released through such a blowgun and further to ensure that compliance with industrial safety regulations is achieved and maintained in a most practical and economical manner. In realizing this object, a blowgun structure is provided which may be used in conjunction with any normal air pressure distributed in an industrial plant and yet will protect an employee-user and comply with the requirements set forth in the aforementioned safety regulations. Valve means are incorporated in the blowgun to permit a user manipulating the blowgun to manually control the release of air therethrough and further to preclude delivery of air from the blowgun at dangerously high pressures. In particular, first and second valve means are arranged in series flow for controlling compressed airflow through the safety blowgun under manual control and in response to air pressures.

It is a further object of the present invention to provide for ready adaptation of previously existing compressed-air blowguns to requirements of limiting pressure pursuant to the aforementioned legislation. To this end, the present invention contemplates the combination, with a pneumatic blowgun, of means for protecting the user thereof against exposure to dangerously high pressure. Such protective means preferably takes the fonn of a pressure-responsive valve member mounted and arranged for movement in response to a balancing of compressed-air pressure upstream of the valve means, compressed-air pressure downstream of the valve means, ambient atmospheric air pressure, and a biasing force imposed by a resilient means.

Some of the objects and advantages of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a safety blowgun assembly incorporating the present invention;

FIG. 2 is an elevation view, in section, through the blowgun assembly of FIG. 1;

FIG. 3 is an enlarged elevation view, in section, througha portion of the blowgun assembly of FIG. 2;

FIG. 4 is a reduced respective view, in exploded form, illus' trating certain of the valve means elements incorporated in the blowgun assembly of FIGS. 1-3;

FIG. 5 is a view similar to FIG. 2, showing a modified form of safety blowgun assembly in accordance with the present in vention; FIG. 6 is an exploded perspective view of certain elements incorporated in a valve means useful in a combination constructed in accordance with the present invention; and

FIG. 7 is an enlarged elevation view, partially in section,

through an assembled valve means of FIG. 6. I {g Referring now more particularly to the drawings, it is to noted that the present invention contemplates more than one arrangement of elements in achieving a safety blowgun. assembly and valve accomplishing the objects set forth above. The present discussion will proceed first with reference to a particularly preferred form for a safety blowgun assembly in accordance with this invention, with attention to be turned to alternative arrangements at a later point herein. In this connection, it is to be noted that the safety blowgun assembly generally indicated at 10 in FIGS. 1-3 include a blowgun' body 1 l configured for ready manipulation and having a passage 12 therethrough for the flow of compressed air. Preferably, the blowgun body 11 is constructed by a suitable process of casting and machining metal, as has heretofore been known in the manufacture of such industrial products. Interposed in the passage 12 are first and second valve means for controlling airflow therethrough, with the valve means being arranged in series flow relation such that air passing through the blowgun body 11 passes in succession through the two valve means and closure of either of the two valve means is effective to prevent release of air through the safety blowgun assembly 10.

The first valve means, generally indicated at 20, is a manually operable valve adapted for actuation by a user manipulating the blowgun body 11. The first valve means 20, elements which are shown in greater detail in FIGS. 3 and4, includes a first valve seat 21 which preferably is fonned by"a conical shoulder machined from the body 11 of the blowgun, as described more fully hereinafter, and a first valve member 22 movable relative to the first valve seat 21. The first valve member 22 preferably is a generally conically configured plug member seated upon the extremity of an operating rod 24, which operating rod penetrates the body 11 of the blowgun and is movable relative thereto for controlling displacement of the valve member 22. In order to provide for manipulation of the first valve means by a user of the blowgun 10, an operating trigger member 25 is provided and is mounted to the body 11 of the blowgun for pivotal movement relative thereto. The trigger 25 abuts a lower extremity of the operating rod 24 (FIG. 2) for displacing the same upon the blowgun body being gripped by a user. The trigger member 25 and rod 24 together form an actuation means for displacing the first valve member 22 from a seated position upon the first valve seat 21.

The first valve member 22 is resiliently biased toward a seated position on the first valve seat 21 by a compression spring member 26 received within the blowgun body 11 and engaging the first valve member 22 (FIGS. 3 and 4). The end portion of the spring member 26 remote from the first valve member 22 abuts a ring member 21 which is fixed relative to a generally cylindrical enclosing wall 29. The enclosing wall 29 is formed by an enlarged portion of the passage through the blowgun body 11 (as seen in FIGS. 2 and 3) and serves a number of various functions in the structure of the present invention. While it is convenient for machining and for assembly purposes to form the blowgun body 11 with a configuration illustrated in FIGS. 1 and 2, and fonn generally cylindrical enclosing wall 29 by drilling transversely into the body 11 as there illustrated, it is to be understood that the enclosing wall 29 may be provided in other manners as will be pointed out more fully hereinafter. Similarly, provision may be made for providing a stationary abutment to be engaged by the spring member 26 through means other than the inserted ring member 28.

The enclosing wall 29, in the arrangement to which the present discussion is directed, additionally surrounds elements of a second valve means generally indicated at 30, for cooperation therewith. In particular, the second valve means 30 includes a guiding member 31 having a generally tubular portion of predetermined length with a bore therewith communicating with and forming a portion of the airflow passage 12 through the blowgun body 11 (FIG. 3). The guiding member 31 has a generally cylindrical exterior wall 32 at the tubular portion thereof, for cooperation with other elements of the second valve means 30 as pointed out more fully hereinafter. The arrangement of the guiding member 31 within the enclosing wall 29 is such that the enclosing wall 29 surrounds a termination of the guiding member tubular portion and is arranged concentric with the exterior wall 32 thereof. Thus, the

cylindrical walls

29 and 32 together define a generally annular volume within the body 11 of the blowgun 10.

A generally annular pressure-responsive valve member 35 is interposed between the

cylindrical walls

29 and 32 and occludes the space therebetween (FIG. 3). The valve member 35 has a generally disclike, annular, main body portion 36 having an open space centrally thereof and a flexible skirt portion 38 along the outer circumference thereof. A flow control portion 39 of the valve member 35 is located centrally of the open space and includes a right circular conical surface for seating in the bore through the guiding member 31 at the termination thereof. The inside diameter of the central opening through the valve member 35 is sized for engagement with the generally cylindrical exterior wall of the tubular portion of the guiding member 31, while the circumferential skirt portion 38 has an outside diameter sized for engagement with the generally cylindrical enclosing wall 29. The valve member 35 is guided by this engagement with the

cylindrical walls

29, 32 in linear movement along the guiding member tubular portion and relative to the termination thereof. With such linear movement, the right circular conical surface of the flow control portion of the valve member 35 engages the termination of the guiding member 31 tubular portion and closes the passage 12 against airflow therethrough.

With a particular view toward providing protection for a user of the blowgun against exposure to dangerously high pressures, movement of the valve member 35 results from a balance of a resilient biasing force acting against the valve member 35 and air pressures acting against piston areas thereof. In particular, a spring means such as a compression spring 40 is provided for exerting on the valve member 35 a. force biasing the valve member relative to the termination of the tubular portion of the guiding member 31. Forces which function in cooperation with the spring means biasing force arise from the action of compressed-air pressure upstream of the termination of the bore through the guiding member 31 on an annular piston area of the valve member 35; compressedair pressure downstream of the termination on an annular piston area; and ambient atmospheric air pressure.

More particularly, ambient atmospheric air pressure is admitted to an internal chamber defined within the body 11 of the blowgun 10 by a passageway 45 extending from the exterior of the body 11 to the enclosing cylindrical wall 29 (FIGS. 2 and 3). By provision of the passageway 45, a chamber defined by cooperation of the guiding member 31, the upper annular surface area of the valve member 35 and the enclosing wall 29 is maintained at ambient atmospheric air pressure. Thus, the air pressure acting on an area of the valve member 35 defined between the

cylindrical walls

29, 32 gives rise to a force acting in the same direction as the biasing force developed by the compression spring 40, to resist movement of the valve member 35 toward the seated position. Movement of the valve member 35 toward the seated position is additionally resisted by the application of compressed-air pressure upstream of the termination of the bore through the guiding member 31 to an area of the valve member 35 defined by the flow control portion and equal to the projected area of the flow control portion relative to the bore through the guiding member 31. Finally, compressed-air pressure downstream of the bore termination acts against an annular piston area determined by the inside diameter of the enclosing cylindrical wall 29. It is to be understood that, in the sense used herein, the phrase annular piston areas" refers to both to full circular piston areas as well as piston areas defined between concentric circular limits, so as to encompass the areas of the valve member 35 described immediately above.

It is further to be understood that forces arising from the air pressures acting on the piston areas of the valve members 35 and from the spring means 40 moves the valve member 35 between the seated position on the bore termination when the pressure of air flowing through the passage 12 downstream of the second valve member 35 exceeds a predetermined safe pressure and an unseated position when such pressure is below the predetermined safe pressure. More specifically, should a user of the blowgun 10 manipulate the trigger 25 and open the first valve means 20 for the delivery of air through the passage 12 of the blowgun 10, the balance of forces acting on the second valve member 35 normally is such as to open the passageway to the flow of air and result in delivery of air from the blowgun 10 to whatever end use is desired by the user. However, should the user manipulate the blowgun 10 to position the outlet nozzle therefrom closely adjacent any obstructing surface such as his skin surface, a back pressure builds up within the passage 12 downstream of the first and second valve means 20 and 30. Such a buildup of back pressure within the passage 12 acts to increase the forces tending to seat the second valve member 35 and results in closure of the passage 12. Desirably, the back pressure within the passageway 12 at which this action occurs is set with a view to complying with regulations promulgated under the industrial safety statutes mentioned heretofore. As will be understood, the operation of the safety blowgun assembly described to this point protects a user by entirely precluding the application of dangerously high pressures to the user by means of the blowgun assembly.

In assembling the blowgun assembly described to this point, the guiding member 31 preferably includes means for ensuring sealing of the passageways and chambers defined thereby against undesirable pressure flows. To this end, aryO-ring seal 41 is provided around a portion thereof which separates the bore through the guiding member 31 from the chamber to which ambient air pressure is applied through the passageway 45. Further, a second sealing O-ring 48 (FIGS. 2 and 3) seals the exterior end of the guiding member 31 against possible escape of compressed air thereby. In order to ensure the desired flow of compressed air thereby. In order to ensure the desired flow of compressed air through the passage 12 formed in the body 11 of the blowgun 10, the guiding member 31 is formed with a circumferential grooved portion extending therearound for flow of air into the bores therethrough. Advantage is taken of the presence of the circumferential groove to permit use of a threaded locking pin 49, which enters through the body 11 of the blowgun 10 and secures the guiding member 31 in assembled relation with the body 1 1.

While the discussion to this point with reference to a safety blowgun assembly 10 in which the pressure-responsive valve means 30 is positioned upstream of the manually operable valve means 20, the present invention further contemplates that the series flow arrangement of the valve means may be reversed. Such a combination is illustrated in FIG. 5, wherein a pneumatic blowgun 50 is illustrated. Where structural elements of the pneumatic blowgun 50 are identical or substantially similar to structural elements of the safety blowgun assembly 10 described heretofore, the reference characters applied are the same with the addition of prime notation. For example, the body 11' of the pneumatic blowgun 50 is generally similar to the body 11 of, the safety blowgun assembly described heretofore.

Points of distinction between the safety blowgun assembly 10 and the pneumatic blowgun 50 include the provision, in the first valve means of means for limiting the stroke or scope of movement of the first valve member 22'. By such limitation, control ,over the volume of the air delivered through the manually operable first valve means 20' may be exercised, providing advantages under some circumstances of use for the pneumatic blowgun 50. Such limitation is obtained by an up wardly extending pin member 51 which moves relative to an adjustable threaded stop member 52.

Other points of distinction as'to the pneumatic blowgun 50 are found in the construction and arrangement of the second valve means 20'. In that valve means, the generally cylindrical enclosing wall 29' is provided by a threaded barrel member 55. One end of the threaded barrel member 55 engages an external thread provided on the body 1 I of the pneumatic blowgun 50, so that the generally cylindrical interior wall 29' of the barrel member 55 surrounds an end portion of the body 11' formed to provide the guiding member 31'. The opposite end of the barrel member 55 is internally threaded to receive a flow-directing nozzle portion such as is illustrated in the safety blowgun assembly of FIGS. 1 and 2. Due to this construction, the spring 40' used in the combination of FIG. 5 may be constructed somewhat differently from the spring 40 shown in FIGS. 3 and 4, while the valve member 35' may be constructed precisely identically to the valve member 35 used in assembly described heretofore.

In the combination of FIG. 5, the operation of the pressureresponsive valve is the same as the function described above with reference to the valve 30 and the assembly of FIGS. 1-4. That is, the valve member moves to a seated position in response to a rise in back pressure downstream of the valve, to preclude the application of dangerous pressures to a user of the pneumatic blowgun 50.

The present invention further contemplates that the pressure-regulating valve means discussed above with reference to the valves 30 and30' in the safety blowgun l0 and pneumatic blowgun combination may additionally be constructed for addition to preexisting blowguns presently in use or for other pressure-regulating applications. As so constructed, the pressure-regulating valve means permits ready modification of existing equipment in order to comply with safety regulations promulgated pursuant to the legislation mentioned heretofore. Such a pressure-regulating valve means 30" is illustrated in FIGS. 6 and 7, where elements identical or generally similar to elements described heretofore have been identified by double prime notation. It will be noted that the pressure-regulating valve means 30" includes a barrel member 50" and a guiding member 31" which cooperate substantially in the manner described above with reference to FIG. 5. In this instance, the guiding member 31 is provided with external threads on both ends, with one set' of threads being engaged by the barrel member and with the other set of threads being sized to replace a discharge nozzle element normally secured in the" body of a preexisting blowgun. In order to modify a preexisting blowgun and obtain the advantages of the present invention, it is only necessary to remove a preexisting nozzle member and insert the pressure-regulating valve means 30" of FIGS. 6 and 7.

In the drawings and specification, there have been set forth preferred embodiments of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

What is claimed is: p

1. A safety blowgun for protecting a user against exposure to dangerously high pressure comprising:

a blowgun body includinga nozzle portion for directing a blowing stream of air, a handle portion configured for ready gripping in the hand of a user and manipulation thereby, and a passage extending from said handle portion to said nozzle portion for compressed airflow through said blowgun body,

first valve means in said passage for controlling airflow therethrough,

manually operable trigger means mounted on said blowgun body for manual actuation by a user gripping said handle portion, said trigger means being operatively connected to said first valve means for opening and closing said first valve means upon manipulation of said trigger means, and

second valve means in said passage in'series flow arrangement with said first valve means and for limiting the pressure at which said blowing stream'of air passes through said nozzle portion, said second valve means comprising a second valve seat, a second valve member movable relative to said second valve seat and having piston areas thereof exposed to compressed-air pressure upstream of said second valve seat and to compressed-air pressure downstream of said second valve seat, and resilient means exerting a force biasing said second valve member relative to said second valve seat, the resilient means force functioning with forces arising from said air pressures acting on said piston areas of said second valve member for moving said second valve member between an unseated, flow-continuing position when the pressure of air within said passage downstream of said second valve means is below a predetermined safe pressure and a seated, flow} interrupting position on said second valve seat when the pressure of air within said passage downstream of said second valve means is above said predetermined safe pressure.

2. An assembly according to claim 1 \vhereinsaid second valve means is positioned upstream of said first valve means.

3. An assembly according to claim 1 wherein said second valve means is positioned downstream of said first valve means. 1

4. An assembly according to claim 1 wherein said second valve seat, said second valve member and said resilient means are so arranged and cooperate that said resilient means biases said second valve member toward said unseated position and force arising from air pressure downstream of said second valve means acts to urge said second valve member toward said seated position and in opposition to force arising from air pressure upstream of said second valve means.

5. An assembly according to claim 4 wherein said resilient means biasing said second valve member comprises a compression spring having one end engaging said body and the other end engaging said second valve member.

6. An assembly according to claim 4 wherein said second valve means further comprises means defining a pair of concentric, spaced-apart generally right circular cylindrical walls and further wherein said second valve member has a generally annular body occluding the space between said concentric cylindrical walls and is guided by engagement therewith in linear movement relative to said second valve seat, said second valve member further having a centrally located generally conical projection for valving engagement with said second valve seat on movement of said second valve member relative thereto and in continued engagement with said concentric cylindrical walls.

7. A safety blowgun for protecting a user against exposure to dangerously high pressure comprising:

a blowgun body including a nozzle portion for directing a blowing stream of air, a handle portion configured for ready gripping in the hand of a user and manipulation thereby, and a passage extending from said handle portion to said nozzle portion for compressed airflow through said blowgun body,

first valve means in said passage for controlling airflow therethrough,

manually operable trigger means mounted on said blowgun body for manual actuation by a user gripping said handle portion, said trigger means being operatively connected to said first valve means for opening and closing said first valve upon manipulation of said trigger means,

a guiding member having a generally tubular portion of predetermined length with a bore therethrough forming a portion of said passage and terminating in a second valve seat and having a generally cylindrical exterior wall,

a generally cylindrical enclosing wall surrounding said termination of said guiding member tubular portion and arranged concentric with said exterior wall thereof and having means defining a passageway for communication of the volume defined between said cylindrical walls with the ambient atmosphere,

a generally annular pressure-responsive second valve member interposed between said cylindrical walls and occluding the space therebetween, said second valve member being guided by engagement with said cylindrical walls in linear movement along said guiding member tubular portion and relative to said termination thereof and having a flow control portion for seating in said bore at said termination and for closing said passage against airflow therethrough, said second valve member having annular piston areas thereof exposed to compressed-air pressure upstream of said termination, to compressed-air pressure downstream of said tennination and to ambient atmospheric air pressure, and

spring means for exerting on said second valve member a force biasing said second valve member relative to said termination, said spring means force functioning with forces arising from said air pressures acting on said piston areas of said second valve member for moving said second valve member between a seated position on said termination when the pressure of air flowing through said passage downstream of said second valve member exceeds a predetermined safe pressure and an unseated position when the pressure of such air is below said predetermined safe pressure.

8. The combination of claim 7 wherein said piston area of 9. The combination of claim 8 wherein said spring means comprises a coiled compression spring positioned encircling said guiding member tubular portion and engaging said valve member for urging the same away from the passage-closing position thereof.

Claims

1. A safety blowgun for protecting a user against exposure to dangerously high pressure comprising: a blowgun body including a nozzle portion for directing a blowing stream of air, a handle portion configured for ready gripping in the hand of a user and manipulation thereby, and a passage extending from said handle portion to said nozzle portion for compressed airflow through said blowgun body, first valve means in said passage for controlling airflow therethrough, manually operable trigger means mounted on said blowgun body for manual actuation by a user gripping said handle portion, said trigger means being operatively connected to said first valve means for opening and closing said first valve means upon manipulation of said trigger means, and second valve means in said passage in series flow arrangement with said first valve means and for limiting the pressure at which said blowing stream of air passes through said nozzle portion, said second valve means comprising a second valve seat, a second valve member movable relative to said second valve seat and having piston areas thereof exposed to compressed-air pressure upstream of said second valve seat and to compressed-air pressure downstream of said second valve seat, and resilient means exerting a force biasing said second valve member relative to said second valve seat, the resilient means force functioning with forces arising from said air pressures acting on said piston areas of said second valve member for moving said second valve member between an unseated, flow-continuing position when the pressure of air within said passage downstream of said second valve means is below a predetermined safe pressure and a seated, flow-interrupting positiOn on said second valve seat when the pressure of air within said passage downstream of said second valve means is above said predetermined safe pressure.

2. An assembly according to claim 1 wherein said second valve means is positioned upstream of said first valve means.

3. An assembly according to claim 1 wherein said second valve means is positioned downstream of said first valve means.

7. A safety blowgun for protecting a user against exposure to dangerously high pressure comprising: a blowgun body including a nozzle portion for directing a blowing stream of air, a handle portion configured for ready gripping in the hand of a user and manipulation thereby, and a passage extending from said handle portion to said nozzle portion for compressed airflow through said blowgun body, first valve means in said passage for controlling airflow therethrough, manually operable trigger means mounted on said blowgun body for manual actuation by a user gripping said handle portion, said trigger means being operatively connected to said first valve means for opening and closing said first valve upon manipulation of said trigger means, a guiding member having a generally tubular portion of predetermined length with a bore therethrough forming a portion of said passage and terminating in a second valve seat and having a generally cylindrical exterior wall, a generally cylindrical enclosing wall surrounding said termination of said guiding member tubular portion and arranged concentric with said exterior wall thereof and having means defining a passageway for communication of the volume defined between said cylindrical walls with the ambient atmosphere, a generally annular pressure-responsive second valve member interposed between said cylindrical walls and occluding the space therebetween, said second valve member being guided by engagement with said cylindrical walls in linear movement along said guiding member tubular portion and relative to said termination thereof and having a flow control portion for seating in said bore at said termination and for closing said passage against airflow therethrough, said second valve member having annular piston areas thereof exposed to compressed-air pressure upstream of said termination, to compressed-air pressure downstream of said termination and to ambient atmospheric air pressure, and spring means for exerting on said second valve member a force biasing said second valve member relative to said termination, said spring means force functioning with forces arising from said air pressures acting on said piston areas of said second valve member for moving Said second valve member between a seated position on said termination when the pressure of air flowing through said passage downstream of said second valve member exceeds a predetermined safe pressure and an unseated position when the pressure of such air is below said predetermined safe pressure.

8. The combination of claim 7 wherein said piston area of said valve member which is exposed to ambient atmospheric air pressure is defined by the area bounded by the inside diameter of said enclosing wall and the outside diameter of said guiding member tubular portion; said piston area exposed to compressed-air pressure upstream of said termination is defined by the area bounded by the inside diameter of said bore through said guiding member; and said piston area exposed to compressed-air pressure downstream of said termination is substantially as defined by the area bounded by the inside diameter of said enclosing wall.

9. The combination of claim 8 wherein said spring means comprises a coiled compression spring positioned encircling said guiding member tubular portion and engaging said valve member for urging the same away from the passage-closing position thereof.