Socket for pipe coupling

A pipe coupling comprises a cylindrical plug having a peripheral groove formed in an outer peripheral surface, and a socket to be connected to the plug. The socket includes a main body having a receiving hole formed in an end portion thereof for receiving the plug, a sleeve having a front end portion axially slidably inserted in the receiving hole, a base portion located outside the receiving hole, an axial through hole for receiving the plug such that it can slide therein, and a plurality of radial through holes formed therein at circumferentially regular intervals and radially inwardly tapered, and a plurality of lock members received in the radial through holes, part of each of the lock members being able to project into the axial through hole. The main body has an escape groove opening to that inner peripheral surface of the body, which defines the receiving hole, the escape groove allowing the lock members to move between a position in which they project from the radial through holes of the sleeve into the axial through hole, and a position in which they are retreated within the radial through holes. The sleeve has a plurality of axially extending slits formed between each pair of adjacent ones of the radial through holes, and a plurality of flexible fingers provided between the slits.

BACKGROUND OF THE INVENTION 
This invention relates to a socket for a pipe coupling adapted to be used 
for fluid, and more particularly to an inexpensive socket of simple 
structure which consists of a small number of components and can be 
assembled easily, and also to a socket having a structure capable of 
automatically maintaining a plug in a locked state (an inseparable state) 
and preventing a connection error. 
Pipe coupling for fluid are well known from, for example, Japanese Patent 
Application KOKAI Publication No. 6-272795 and Japanese Utility Model 
Application KOKOKU Publication No. 56-16448. 
The structure of the pipe coupling disclosed in Japanese Patent Application 
KOKAI Publication No. 6-272795 will be described briefly with reference to 
FIG. 10 which shows a cross section of the pipe coupling. 
In the figure, reference numeral 101 denotes a socket body, in which a seal 
member 106, an elastic member 107, an inner collar 108, and an urging 
member 109 supported by the collar 108 are arranged. An outer collar 110 
extending from the socket body 101 covers those elements. The outer collar 
110 has an inclined surface having a larger diameter at its inner side and 
contacting the urging member 109, while the inner collar 108 can be slid 
from the outside. 
When in this pipe coupling, insertion of a male member such as a plug or a 
pipe, not shown, has been started, the front end of the male member 
contacts the urging member 109, thereby moving the inner collar 108 and 
the male member to the left in the figure, against the urging force of the 
elastic member 107. When the urging member 109 has reached the 
large-diameter portion of the socket body 101, it moves to a radially 
outer space of the large-diameter portion, whereby the male member is 
inserted until its front end contacts a step 104, and positioned there. 
Further, when in this state, a pulling force has been applied to the male 
member, the urging member 109 is urged toward an inclined surface 113 of 
the outer collar 110 by the urging force of the elastic member 107, 
thereby urging the male member against the inclined surface 113. As a 
result, the male member is prevented from being pulled out of the socket. 
The male member can be easily pulled out of the socket body by pushing the 
front end of the inner collar 108 toward the socket body 101 to enable 
movement of the urging member 109 to the large diameter portion of the 
socket body 101. 
The structure of the pipe coupling described in Japanese Utility Model 
Application KOKOKU Publication No. 56-16448 will be described with 
reference to FIG. 11 which illustrates a cross section of the connector. 
The pipe coupling comprises a plug 220 and a socket 230. The plug 220 has 
an insertion rod 223 with a peripheral groove 224 formed in a peripheral 
portion thereof and to be engaged with lock balls. The socket 230 is 
constituted of a main body 231, a sleeve 238, lock balls 241 and a spring 
244. The spring 244 and the sleeve 238 are fitted in a cylindrical end 
chamber 236 formed in an end portion of the main body 231 of the socket 
230. The sleeve 238 has a desired number of tapered radial holes 240 
formed therein, in which the locking balls 241 are slidably inserted such 
that they can project from the inner-diameter portion of the sleeve 238. 
The portion of each lock ball which is opposite to the projecting portion 
is engaged with an escape groove 243, which has a tapered wedge surface 
242 constituted of a peripheral portion of the inner wall of the 
cylindrical end chamber 236 in the main body 231. A groove is formed in 
one of the front end surface 231a of the main body 231 and a front end 
collar 237 incorporated in the sleeve 238, and a pin is provided on the 
other of them. The axial length of each of the groove and the pin is made 
to correspond to a distance over which the sleeve slides. As a result, the 
sleeve 238 is retreated against the elastic force of the spring 244 to 
release the lock balls 241 and enable attachment and detachment of the 
plug 220, only when the sleeve 238 is rotated with respect to the main 
body 231 such that the pin is engaged with the groove. 
However, when in the case of the first-mentioned pipe coupling, the outer 
and inner collars 110 and 108 are assembled, the inner collar 108 with the 
urging member 109 is inserted into the outer collar 110 which has a 
uniform diameter as indicated by reference numeral 111, and then the outer 
collar 110 is cramped to form the inclined surface 113. Thus, the 
assemblage requires the cramping step and a cramping machine, which is a 
great obstacle to simplification of the assemblage or reduction of the 
assemblage cost. Further, the pipe coupling does not have a lock 
mechanism, and therefore if a force is applied from the outside to the 
inner collar 108 when the pipe coupling is assembled, it is possible that 
the urging force of the urging member will be released and the pipe will 
come out of the socket. 
On the other hand, when in the case of the latter pipe coupling, the sleeve 
238 is inserted into the socket 230, the lock balls 241 fall from a hole 
(not shown) formed in the socket into the tapered hole of the sleeve 238, 
and thereafter the hole in the socket 230 is blocked. Therefore, a great 
number of assemblage steps are required, which is disadvantageous for 
reducing the assemblage cost. Moreover, although the pipe coupling 
includes a lock mechanism which consists of the groove and the pin for 
preventing the detachment of the plug 220 in the connected state, the 
locking function of this lock mechanism is effected by the operator 
rotating the sleeve 238 after the connection of the socket is completed. 
Therefore, if the lock operation is forgotten, the plug 220 will come out 
of the socket 230 when an unintentional force has been applied to the 
sleeve 238 to push it within the socket 230. 
BRIEF SUMMARY OF THE INVENTION 
The invention has been developed to solve the above-described problems and 
is aimed at providing a socket for pipe coupling in which a sleeve and a 
main body can be assembled instantly, and which has a lock function and 
can avoid erroneous connection of the a plug to be connected thereto. 
According to the present invention, there is provided a socket for pipe 
coupling comprising: a main body member having a receiving hole formed in 
an end portion thereof for receiving a male member; a sleeve having a 
front end portion axially slidably inserted in the receiving hole, a base 
portion located outside the receiving hole, an axial through hole for 
receiving the male member such that it can slide therein, and a plurality 
of radial through holes formed therein at circumferentially regular 
intervals and radially inwardly tapered; and a plurality of lock members 
received in the radial through holes, part of each of the lock members 
being able to project into the axial through hole. The main body member 
has an escape groove opening to that inner peripheral surface of the 
member, which defines the receiving hole, the escape groove allowing the 
lock members to move between a position in which they project from the 
radial through holes of the sleeve into the axial through hole, and a 
position in which they are retreated within the radial through holes; and 
the sleeve has a plurality of axially extending slits formed between each 
pair of adjacent ones of the radial through holes, and a plurality of 
fingers provided between the slits. The fingers can be elastically bent in 
a radial and inward direction of the sleeve by the urging force of the 
main body member which is transmitted via the lock members when the sleeve 
has been inserted into the receiving hole. 
Accordingly, the front end portion of the sleeve can be radially inwardly 
bent simply by pushing the sleeve into the socket, whereby the sleeve and 
the socket can be easily assembled. 
It is preferable that the radial through holes each have a diameter along 
the axis of the sleeve, and a diameter along the circumference of the 
sleeve, which is smaller than the first-mentioned diameter. 
According to another embodiment of the invention, the socket further 
comprises a spring located in the receiving hole for urging the sleeve 
toward the one end portion of the main body member, and a spring seat ring 
slidably mounted on the sleeve for supporting one axial end portion of the 
spring, the spring seat ring being disposed to move toward another axial 
end portion of the spring against the urging force of the spring when the 
each lock member is shifted by the male member toward another end portion 
of the main body element. Preferably, the radial through holes extend up 
to the front end portion of the sleeve. 
When in this embodiment, the plug is connected, the spring seat ring shifts 
together with the lock members, but the sleeve does not move. Accordingly, 
at the time of connecting the plug, the sleeve can be locked to prevent 
disconnection of the plug and socket. 
According to a yet another embodiment of the invention, the socket further 
comprises a lock ring mounted on a portion of the sleeve close to the base 
portion, the lock ring preventing movement of the sleeve in a direction in 
which the lock members are retreated within the radial through holes. The 
lock ring can be formed of a C-shaped elastic ring. 
According to another embodiment of the invention, the socket further 
comprises: a spring located in the receiving hole for urging the lock 
members toward the one end portion of the main body member; the escape 
groove having a tapered surface for pressing the lock members urged by the 
spring in a radial and inward direction of the sleeve, and a stepped 
portion formed adjacent to the tapered surface for holding the lock 
members between itself and the outer peripheral surface of the male member 
to thereby interrupt engagement of the lock members with the tapered 
surface. In this case, locking of the plug by the lock members before the 
plug is completely inserted into the socket can be prevented, which 
prevents incomplete connection of the plug and socket. 
More preferably, the main body member has an inwardly tapered surface at 
the one end portion side, and the sleeve has an inwardly tapered surface 
at the base portion side. In this case, the sleeve or the plug can be 
easily inserted into the main body member. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description,. or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out 
hereinafter.

DETAILED DESCRIPTION OF THE INVENTION 
A connector for fluid according to a first embodiment of the invention will 
be described with reference to FIGS. 1-3. 
In FIG. 1, the pipe coupling according to the first embodiment of the 
present invention is comprised of a socket 1 and a plug 2. When the plug 2 
has been inserted in the socket 1, they are connected to each other. 
The plug 2 has a fluid passage 2b formed in a center portion thereof, and a 
wide peripheral groove 2a formed in an outer peripheral portion of an 
insertion portion 2c thereof for receiving lock members 4 (which will be 
described later). When high pressure has been applied within the 
connector, the plug 2 fixedly connected to the socket 1 is urged in its 
disengaging direction, whereby each lock member 4 is put into contact with 
a left-hand (in FIG. 1) step of the peripheral groove 2a. Thus, the 
peripheral groove 2a serves as a stopper for preventing detachment of the 
plug 2 (as indicated by the solid line in FIG. 1), and also has a function 
for moving a sleeve 3 to the right to form a clearance L, in which a lock 
ring 7 (which will be described later) is received when the lock member 4 
has engaged with the peripheral groove in a manner which will be described 
later. 
The socket 1 is assembled from a main body la, the sleeve 3, the lock 
members 4, a spring 5, seal members 6 and the lock ring 7. A fluid passage 
1b is formed in a center portion of the main body 1a. 
A peripheral wall 8 radially inwardly projects from the inner peripheral 
surface of the fluid passage 1b of the main body 1a. A receiving hole 10 
is formed in an end portion of the main body 1a for receiving the plug 2, 
while a connection port 9 to be connected to a fluid pipe (not shown) is 
formed in that end portion of the main body 1a, which is opposed to the 
first-mentioned end portion with the peripheral wall interposed 
therebetween. 
A plurality of recesses 11 which each holds a seal member 6, a spring 
reception recess 12 with a diameter larger than the outer diameter of an 
insertion portion 2c of the male member 2, and an escape groove 13 with a 
diameter larger than the spring reception recess 12 are formed in that 
inner peripheral wall of the main body 1a, which defines the male member 
receiving hole 10. The escape groove 13 has a tapered surface 14 having 
its diameter reduced toward the inlet of the receiving hole 10, and a tip 
engaging stepped portion 15 as an end portion for guiding the outer 
periphery of the sleeve 3. Further, an engagement portion 16 for holding 
the lock ring 7 is formed of the end portion of the main body 1a which 
defines an outer end periphery of the receiving hole 10. The engagement 
portion 16 has a tapered surface 16a to be engaged with the sleeve 3 when 
the sleeve 3 is inserted. The lock ring 7 is formed of a C-shaped 
resilient member which can be opened. 
As is shown in FIGS. 2A and 2B, the sleeve 3 to be fitted into the plug 
receiving hole 10 is formed of a cylindrical member which has a collar 3a 
provided as a base portion, and an axial through hole formed therein for 
receiving the plug such that it can slide. The sleeve 3 includes 
cylindrical central outer peripheral surfaces with tapered surfaces 3b and 
stepped portions 3c extending continuously from the opposite ends of the 
tapered surfaces 3b. A plurality of slits 3d are formed axially in the 
sleeve 3 on the opposite side of the collar 3a to allow free end portions 
of the sleeve 3 to be radially inwardly warped. A plurality of tapered 
holes 3f radially extending through the sleeve for holding the lock 
members 4 are each formed in the tapered surface 3b and the stepped 
portion 3c provided on a corresponding finger 3e, which is formed between 
adjacent slits 3d. Each tapered hole 3f has a minor diameter in a 
circumferential direction of the sleeve and a major diameter in an axial 
direction of the sleeve. Tapered surfaces 3g which define each tapered 
hole 3f on the major diameter side have an angle which allows radial 
outward movement of a corresponding one of the lock members 4. Tapered 
surfaces 3h which define each tapered hole 3f on the minor diameter side 
have an angle which allows holding of a corresponding one of the lock 
members 4 so that the lock members 4 will not fall into a space inside the 
sleeve 3. When each lock member 4 is held in the sleeve and the plug 2 is 
inserted in it, the lock member 4 projects to a radially inner level than 
the outer peripheral surface of the plug 2. A stopper portion 3i, with 
which the tip engaging stepped portion 15 of the tapered surface 14 of the 
escape groove 13 formed on the socket side is brought into contact, is 
formed at each stepped portion 3c on the collar 3a side. On the other 
hand, each stepped portion 3c on the free end side of the sleeve 3 is 
provided as a spring seat portion 3j for the spring 5. Although the sleeve 
3 is formed of a synthetic resin, it may be formed of a metal if the free 
end of the sleeve 3 can be resiliently deformed when the slits 3d are 
formed therein. 
The assembly of the socket and the sleeve 3 constructed as above can be 
instantly performed by simply pushing the sleeve with each lock member 4 
into the plug receiving hole 10, with the seal members 6 and the spring 5 
mounted in the female member 1, as is shown in FIG. 1. 
Specifically, when insertion of the sleeve 3 with the lock members 4 into 
the plug receiving hole 10 has been started, the spring seat portion 3j of 
the sleeve 3 contacts the spring 5. The sleeve 3 is further pushed, 
thereby bringing the tapered surfaces 3b between the stepped portions 3c 
into contact with the tapered surface 16a of the receiving hole 10. When 
the sleeve 3 has been further pushed, the fingers 3e are radially inwardly 
flexed by the tip engaging stepped portions 15, and the stepped portions 
3c of the sleeve 3 climbs over the tip engaging stepped portions 15. The 
sleeve is then restored to its original state. Although at this time, the 
sleeve 3 is pushed back to the right (in FIG. 1) by the urging force of 
the spring 5, the stopper portions 3i formed at the stepped portions 3c 
are engaged with the tip engaging stepped portions 15, thereby preventing 
the sleeve 3 from slipping out of the hole 10. When the pushing force 
applied to the sleeve 3 has been released after the above operation, the 
sleeve 3 is instantly engaged with the plug receiving hole 10 as shown in 
FIG. 1. Thus, the sleeve 3 can be assembled in a simple manner. 
Referring then to FIG. 3, the operation of the sleeve 3 at the time of 
connecting the socket 1 to the plug 2 as a male member will be described. 
When insertion of the plug 2 into the socket 1 which assumes a state as 
shown in (a) of FIG. 3 has been started, it first contacts the lock 
members 4 which project to a radially innerer level than the outer 
peripheral surface of the plug 2. After the plug is further inserted, the 
lock members 4 are radially outwardly moved by the major-diameter side 
tapered surfaces 3g of the tapered holes 3f formed in the sleeve 3, and at 
the same time, the sleeve 3 is moved to the left against the urging force 
of the spring 5 ((b) of FIG. 3). The lock members 4 move along the tapered 
surface 14 which constitutes part of the inner wall of the main body 1a, 
and enter the escape groove 13. As a result, the plug 2 can move toward 
the inner portion of the female member 1. When the plug 2 has reached a 
location near the projecting wall 8, the lock members 4 fall into the 
peripheral groove 2a of the plug 2, and at the same time, the sleeve 3 is 
forwarded by the urging force of the spring 5, thereby causing the lock 
members 4 to be held between the tapered surface 14 of the escape groove 
13 and the bottom surface of the peripheral groove 2a of the plug 2. Thus, 
the plug 2 is connected ((c) of FIG. 3). As a result of the forwarding of 
the sleeve 3, a clearance L for fitting the lock ring 7 therein is 
defined. After the sleeve 3 is inserted until the front end of the plug 2 
contacts the peripheral wall 8, the connection of the pipe coupling is 
completed, and the socket and plug 1 and 2 are fixed to each other. When 
high pressure has been applied within the pipe coupling which is in a 
fixedly connected state, the plug is shifted to the right (with respect to 
the orientation depicted in FIG. 3) by the fluid pressure, whereby the 
lock members 4 are held between the tapered surface 14 and the left-hand 
(in the figure) stepped portion of the peripheral groove 2a formed in a 
peripheral portion of the insertion portion 2c of the plug ((d) of FIG. 
3). Thus, detachment of the plug 2 is prevented. Moreover, when high 
pressure has been applied within the pipe coupling, the lock member 4 is 
engaged with the tip engaging stepped portion 15 of the tapered surface 
14, thereby more reliably preventing the detachment of the plug 2. 
After that, the lock ring 7 attached to the engagement portion 16 of the 
socket 1 is fitted between the collar 3a of the sleeve 3 and an end of the 
socket 1, with the result that movement of the sleeve 3 can be prevented 
and hence unexpected detachment of the members 1 and 2 can be prevented, 
even when an unintentional force is applied thereto ((d) of FIG. 3). 
Further, since each tapered hole 3f has a major diameter in the axial 
direction of the sleeve 3, no force will act upon the lock members 4 even 
when the sleeve 3 shakes in the axial direction, with the lock ring 7 
fitted. The lock ring 7 may be fitted on the outer periphery of the sleeve 
3 after the state shown in (d) of FIG. 3 is obtained. 
To detach the plug 2 from the socket 1, the lock ring 7 is released at the 
state shown in (d) of FIG. 3, and then the sleeve 3 is axially moved 
against the urging force of the spring 5 as shown in (e) of FIG. 3. As a 
result, the lock members 4 are moved, by the axial tapered surfaces 3g of 
the tapered holes 3f formed in the sleeve 3, radially outwardly and 
simultaneously axially along the tapered surface 14, and reach the escape 
groove 13. In this state, the plug 2 can easily be removed from the socket 
1. 
Referring then to FIGS. 4 and 5, a pipe coupling for fluid according to a 
second embodiment will be described. 
The second embodiment is characterized in that the plug 2 can be connected 
to the socket 1 in a state in which the lock ring 7, used in the first 
embodiment, is beforehand provided in that outer peripheral portion of the 
sleeve 3 which is located between the main body 1 and the collar 3a of the 
sleeve 3, i.e. when the sleeve 3 is in its lock state. The structure of 
the sleeve 3 itself also significantly differs from that employed in the 
first embodiment. In other words, although in the first embodiment, the 
lock ring 7 is shifted to the outer peripheral portion of the sleeve 3 
after the socket and plug are connected to each other, thereby executing 
its locking function, the second embodiment is characterized in that 
immediately after the plug and socket are connected, the pipe coupling 
automatically assumes the locking state, without the operation of the lock 
ring. 
In FIG. 4, the pipe coupling of the second embodiment comprises a socket 1 
and a plug 2, which have the same structures as those in the first 
embodiment. In FIG. 4, similar members to those in the first embodiment 
are denoted by corresponding reference numerals. The sleeve 3 employed in 
the second embodiment and differing from that of the first embodiment will 
be described. 
As is shown in FIGS. 5A and 5B, the sleeve 3 to be fitted in the plug 
receiving hole 10 of the main body la is formed of a substantially 
cylindrical member, which has a collar 3a at one end thereof, and, at the 
other end thereof, a plurality of slits 31 which enable radially inwardly 
flexing of the tip of each finger of the sleeve 3, and radial through 
holes 30 for receiving lock members 4. Accordingly, the radial through 
holes 30 are formed in the shape of slits extending to the free end 
portions of the sleeve 3. Those portions of the sleeve 3 which are close 
to the collar 30a have tapered surfaces 30a for holding the lock members 
4, i.e. the inner portions of the radial through holes 30 (guide slits 30 
for guiding the lock members) are defined by the tapered surfaces 30a. 
Further, the innermost portions of the radial through holes or guide slits 
30 are defined by tapered surfaces 30b for radially outwardly pushing the 
lock members 4. A spring seat ring 32 which also serves as a spring seat 
is slidably attached to that outer peripheral surface of the sleeve 3 in 
which the slits 30 and 31 are formed. The ring 32 is in contact with ring 
receiving portions 3k of the sleeve 3, and receives the urging force of 
the spring 5, thereby urging the sleeve 3 to the right and limiting a lock 
hole 30c which receives the lock member 4 (see FIG. 4). 
The socket 1 and the sleeve 3 constructed as above will be assembled in a 
manner as below. 
In FIG. 4, with the lock member 4 held by the guide slits 30 and the lock 
ring 7 detachably fitted thereon, the sleeve 3 is pushed into the plug 
receiving hole 10 of the socket 1 which has the seal members 6 and the 
spring 5 mounted therein. Thus, the insertion of the sleeve 3 into the 
receiving hole 10 of the socket 1 can be instantly completed as shown in 
FIG. 4. 
More specifically, when the insertion, into the plug receiving hole 10, of 
the sleeve 3 with the lock ring 7, the lock members 4 and the spring seat 
ring 32 mounted thereon has been started, the spring 5 is brought into 
contact with the spring seat ring 32, and tapered surfaces 3b provided at 
stepped portions 3c of outer peripheral center portions of the cylindrical 
sleeve 3 are brought into contact with tapered surface 16a provided at 
inner peripheral end portion of the insertion port 10. When the sleeve 3 
has been further pushed, each finger of the sleeve 3 formed between each 
adjacent slits is radially inwardly flexed by the pushing force, whereby 
the stepped portions 3c of the sleeve 3 climbs over the tip engaging 
stepped portions 15 of the main body 1a. The sleeve is then restored to 
its original state. The stopper portions 3i of the sleeve 3 are engaged 
with the tip engaging stepped portions 15, thereby preventing the sleeve 3 
from slipping out of the hole 10. When the pushing force applied to the 
sleeve 3 has been released after the above operation, the sleeve 3 is 
instantly engaged with the plug receiving hole 10 as shown in FIG. 4. In 
this assembled state, the sleeve 3 is moved to the right (FIG. 4) by the 
urging force of the spring 5 via the spring seat ring 32, thereby forming 
the lock holes 30c between the guide slits 30 and the spring seat ring 32. 
The lock members 4 are held in the lock holes 30c such that they project 
to a radially innerer level than the outer peripheral surface of the plug 
2. 
Referring then to FIG. 6, the operation of the sleeve 3 at the time of 
connecting the socket 1 to the plug 2 as a male member, which are 
constructed as above, will be described. 
When insertion of the plug 2 into the socket 1 which assumes a state as 
shown in (a) of FIG. 6 has been started, it first contacts the lock 
members 4 which project to a radially inner level than the outer 
peripheral surface of the plug 2. The lock members 4 are further moved 
along the guide slits 30 in an axial direction (to the left in FIG. 6). At 
this time, the sleeve 3 does not move. Since the spring seat ring 32 is 
moved to the left by the pushing force of the lock members 4 against the 
urging force of the spring 5, the lock holes 30c gradually axially become 
longer. The lock members 4 are radially outwardly moved, by an end portion 
of the plug 2, along the tapered surface 14 which constitutes part of the 
inner wall of the main body 1a, and enter the escape groove 13. As a 
result, the urging force applied from the lock members 4 to the plug 2 is 
released, and hence the plug 2 can be inserted into the socket 1 ((b) of 
FIG. 6). Since, as described above, the lock holes 30c themselves can be 
enlarged in the axial direction of the sleeve 3 by moving the spring seat 
ring 32 using the lock members 4, the lock ring 7 can be beforehand 
mounted between the main body 1a and the collar 3a of the sleeve 3. When 
the plug 2 has reached a location near the peripheral wall 8, each lock 
member 4 falls into the peripheral groove 2a of the plug 2, and is 
simultaneously forwarded by the urging force of the spring 5 via the 
spring seat ring 32. As a result, the lock holes 3c are shortened along 
the axis of the sleeve 3, thereby holding the lock members 4 between the 
tapered surface 14 of the escape groove 13 and the bottom surface of the 
peripheral groove 2a of the plug 2. Thus, the plug 2 is connected. The 
connection of the pipe coupling is completed when the front end of the 
plug 2 has been inserted until it contacts the peripheral wall 8, thereby 
fixing the socket and plug 1 and 2 to each other ((c) of FIG. 6). 
When high pressure has been applied within the pipe coupling which is in a 
fixedly connected state, the plug is shifted to the right (FIG. 6) by the 
fluid pressure, whereby the lock members 4 are held between the tapered 
surface 14 and the left-hand stepped portion of the peripheral groove 2a 
formed in a peripheral portion of the insertion portion 2c of the plug 
((d) of FIG. 6). Thus, detachment of the plug 2 is prevented. Moreover, 
when high pressure has been applied within the pipe coupling, the lock 
members 4 are engaged with the tip engaging stepped portion 15 of the 
tapered surface 14, thereby more. reliably preventing the detachment of 
the plug 2. Since in this state, the lock ring 7 is beforehand interposed 
between the socket 1 side end and the collar of the sleeve 3, the sleeve 
is prevented from moving even when an unintentional force is exerted upon 
the sleeve, thereby preventing detachment of the plug from the socket. 
Further, since the lock holes 30c formed between the spring seat guide ring 
32 and the guide slits 30 are axially enlarged when the sleeve 3 is pushed 
to the right (FIG. 6) by the urging force of the spring 5, a clearance is 
formed between the main body 1a and the lock ring 7. This means that the 
lock members 4 are not urged by the tapered surfaces 30b of the guide 
slits 30 even when the sleeve 3 is moved by an amount corresponding to the 
clearance. As a result, the socket and plug 1 and 2 are not disengaged 
from each other. 
To detach the plug 2 from the socket 1, the lock ring 7 is removed from the 
sleeve 3 (the lock ring 7 is formed of a C-shaped resilient ring and can 
be easily removed), and moved to the left against the urging force of the 
spring 5 as shown in (e) of FIG. 6. At this time, the lock members 4 are 
moved, by the tapered surfaces 30b of the guide slits 30 formed in the 
sleeve 3, radially outwardly and simultaneously axially along the tapered 
surface 14, and reach the escape groove 13. In this state, the plug 2 can 
easily be removed from the socket 1. 
Since in the second embodiment, the lock holes 30c defined by the guide 
slits 30 formed in the sleeve 3 and the spring seat ring 32 is 
contractible and expandable along the axis of the sleeve 3, the plug 2 can 
be connected to the socket 1 simply by inserting the plug 2 into the 
socket 1 as in the conventional case, with the lock ring 7 fitted on the 
outer peripheral surface of the sleeve 3. Accordingly, forgetting of 
locking after connection of the pipe coupling can be reliably prevented. 
In other words, since the lock ring 7 is already mounted on the outer 
peripheral surface of the sleeve before the pipe coupling is connected, 
movement of the sleeve 3 can be prevented even when an unintentional force 
is applied to the sleeve 3 after the pipe coupling is connected. This 
means that the detachment of the plug and socket from each other can be 
reliably prevented. 
When in the above-described first and second embodiments, the plug 2 is 
inserted into the socket 1, if the insertion operation is stopped and the 
socket 2 is pulled, before the peripheral groove 2a formed in the outer 
peripheral surface of the plug 2 for the lock members 4 reaches the lock 
members 4, the lock members urged by the spring 5 against the tapered 
surface 14 of the socket 1 is radially outwardly pressed by the plug 2. 
Accordingly, the plug 2 assumes a state in which it cannot be pulled out 
of the socket 1, even when the lock members 4 do not fall into the 
peripheral groove 2a. From this, it is possible that the operator will 
misunderstand that the connection is completely performed, and hence that 
the socket and plug 1 and 2 will be incompletely connected, resulting in 
leakage of a fluid. 
To avoid the above, a third embodiment is proposed. 
Referring to FIGS. 7-9, a pipe coupling for fluid according to the third 
embodiment will be described. 
The third embodiment is characterized in that an engagement portion 20 is 
formed at an end of the escape groove 13 formed in the main body 1a in the 
second embodiment. Because of the engagement portion 20, the socket and 
plug 1 and 2 cannot be connected unless the lock members 4 are completely 
engaged with the peripheral groove formed in the plug 2. In other words, 
the third embodiment differs from the second embodiment only in the shape 
of the escape groove 13. The other components of the socket and plug 1 and 
2 are similar to those of the second embodiment, and description will be 
given using corresponding reference numerals to denote the similar 
components. 
In FIG. 7, the escape groove 13 of the main body 1a has an engagement 
portion 20 consisting of a predetermined stepped portion at which the lock 
members 4 guided along the tapered surface 14 escape from the peripheral 
groove. As a result, unless the lock members 4 completely fall into the 
peripheral groove 2a of the plug 2, the socket and plug 1 and 2 cannot be 
connected to each other since no wedge force acts between the tapered 
surface 14 and the outer peripheral surface of the plug 2. 
Referring to FIGS. 8 and 9, the operation of the pipe coupling at the time 
of connecting the socket 1 to the plug 2 as a to-be-connected member will 
be described. 
When insertion of the plug 2 into the socket 1 which assumes a state as 
shown in (a) of FIG. 8 has been started, it first contacts the lock 
members 4 which project to a radially inner level than the outer 
peripheral surface of the plug 2, as is shown in (b) of FIG. 8. The lock 
members 4 are further moved along the guide slits 30 in an axial direction 
(to the left in FIG. 8). At this time, the sleeve 3 does not move. The 
spring seat ring 32 is also moved to the left by the pushing force of the 
lock members 4 against the urging force of the spring 5. The lock members 
4 are radially outwardly moved, by an end portion of the plug 2, along the 
tapered surface 14 which constitutes part of the inner wall of the main 
body 1a, and enter the escape groove 13 with the engagement portion 20. As 
a result, the urging force applied from the lock members 4 to the plug 2 
is released, and hence the plug 2 can be inserted into the socket 1 ((c) 
of FIG. 8). When the plug 2 has reached a location near the peripheral 
wall 8, the lock members 4 fall into the peripheral groove 2a of the plug 
2 (the state of the connector shifts from one shown in (d) of FIG. 8 to 
one shown in (e) of FIG. 8), and are simultaneously forwarded by the 
urging force of the spring 5 via the spring seat ring 32. As a result, the 
lock members 4 are held between the tapered surface 14 of the escape 
groove 13 and the bottom surface of the peripheral groove 2a of the plug 
2. Thus, the socket and plug 1 and 2 are connected as shown in (e) of FIG. 
8. 
When high pressure has been applied within the pipe coupling which is in a 
fixedly connected state, the plug 2 assumes a state as shown in (a) of 
FIG. 9, in which the lock members 4 are held between the tapered surface 
14 and the left-hand (in the FIG. 9) stepped portion of the peripheral 
groove 2a formed in a peripheral portion of the insertion portion 2c of 
the plug. Thus, detachment of the plug 2 is prevented. 
To detach the plug 2 from the socket 1, the lock ring 7 is removed from the 
sleeve 3 as in the second embodiment, and the sleeve 3 is shifted to a 
state as shown in (b) of FIG. 9. At this time, the lock members 4 are 
moved, by the tapered surfaces 30b of the guide slits 30 formed in the 
sleeve 3, radially outwardly and simultaneously axially along the tapered 
surface 14, and reach the escape groove 13. In this state, the plug 2 can 
easily be removed from the socket 1 (see (c) and (d) of FIG. 9). 
In the third embodiment, the plug 2 can be connected to the socket 1 simply 
by inserting the plug 2 into the socket 1 as in the conventional case, 
with the lock ring 7 fitted on the outer peripheral surface of the sleeve 
3. Accordingly, forgetting of locking after connection of the plug and 
socket can be reliably prevented. 
Moreover, if in the third embodiment, the insertion of the plug 2 is not 
completed (as shown in (c) of FIG. 8), the lock members 4 are received in 
the engagement portion 20 of the escape groove 13. Accordingly, the 
tapered surface 14 does not apply a radially inwardly urging force to the 
lock members 4 irrespective of the urging force of the spring 5. This 
means that the plug and socket 1 and 2 are in a separable state, and hence 
insufficiently fixed connection of the plug 2 to the socket can be 
prevented. 
The engagement portion 20 can also be provided in the first embodiment. In 
this case, the same-advantage as in the third embodiment can be obtained. 
In addition, although in each embodiment, a conventional plug is assumed, a 
pipe can be used as the plug member and directly connected to the socket. 
The pipe to be used as the plug in the third embodiment, however, must 
have a peripheral groove as employed in the above-described plug member. 
It is a matter of course that the invention can be modified in various 
manners without departing from its spirit and scope, and that the 
above-described embodiments are just examples in every respect, to which 
the invention is not limited. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details and representative embodiments shown and described 
herein. Accordingly, various modifications may be made without departing 
from the spirit or scope of the general inventive concept as defined by 
the appended claims and their equivalents.