CA1323891C - Plastic pipe connection - Google Patents

Abstract

ABSTRACT
A coupling sleeve pushed onto the plastic pipe and provided with barbs is drawn over a driving shoulder against the connecting piece by a union nut. The flared pipe end is clamped between a curved end face of the connecting piece and the coupling sleeve. Possible leakages caused by the flow of the pipe material are prevented by a spring, and the pipe is prevented from turning during assembly by a sliding ring. The device used for assembling the pipe connection has grips for fixing the pipe in position with a toggle lock and a press ring, which can be displaced in sliding manner on a stop acting as a centering arbor, and can be actuated by a hand lever. With only a few manipulations, the coupling sleeve can be pushed onto the centrally held plastic pipe. Owing to the omission of the supporting sleeve required hitherto, the through-flow cross-section of the plastic pipe is not reduced by the installation of this pipe connection. Heating up the end of the plastic pipe is no longer necessary during assembly. The pipe connection, which can be made cost effective, is uncomplicated in its construction and absolutely liquid-tight.

Description

~323891 ~

Plastic Pi~e Connection A fact known to every expert in drinking-water installation technology is that the metal pipes previously used almost exclusively have in recent years also been increasingly replaced by plastic pipes for drinking-water installation systems.
There is a good reason for this: on the one hand, the water conduit made of plastic, in particular of crosslinked polyethylene, is not subject to any kind of corrosion nor therefore to the dreaded pitting, whereas on the other hand - to mention only the most outstanding advantages - scarcely any flow noises develop and it has been possible to lay the conduit in a considerably simplified manner owing to the omission of complicated working operations.
It is the object of the present invention to propose a pipe connecting system which:
- does not involve any kind of reduction in the through-flow cross-section~
- does not cause any heating up of the pipe end during ~ assembly and is therefore independent of external¦ 20 energy (power for a heating unit), - because of its design, can be manufactured more cost effectively, installed in the simplest manner and released as often as desired.
This object is achieved by the invention defined in the patent claims, with the invention comprising on the one hand a method of constructing a liquid-tight connection between a plastic pipe and a connecting piece made of metal or plastic, and on the~

i~23~ la 20152-1177 other hand a plpe connectlon made accordlng to thls method and also a device for assembling this pipe connection. Preferred embodiments are given ln the dependent patent claims.
In accordance wlth the present lnventlon, there ls provlded a connector for provlding a substantially llquld-tight seal between a plastic liquid-conveying member and a metalllc liquid-conveylng member, which ls provided with external threads and adapted to be connected to said plastic llquld-conveying member in end-to-end fashion, said connector comprising a sleeve which is circumferentially continuous, said sleeve including a tubular body, attaching means extendin~ radially inwardly from an inner cylindrical surface of said body for flxedly and non-rotatably attaching sald sleeve to said plastic llquld-conveylng member, sald inner cylindrical surface of said sleeve havlng a diameter which is less than an outer diameter of said plastic liquid-conveying member but which ls sufficiently large to permit said sleeve to be applied to sald plastic liquld-conveying member by substantially non-rotatably pushlng said sleeve along said plastic liquid-conveying member in a first axlal dlrection from a non-threaded end of said plastic liquid-conveying member toward an opposite end of said plastic liquid-conveying member, said non-threaded end of said plastic liquid-conveying member being the end which is to be connected to said metallic liquid conveying member, and said attaching means penetrating into said plastic liquid-conveying member a distance sufficient to inherent any movement of said sleeve relative to said plastic liquid-conveying member in a second axial dlrection opposite to said first axial direction, whereby said sleeve ls non-rotatably and non-removably attached to ~ ~ 2 ~ lb sald plastlc liquid-conveying member such that tsaid sleeve and said plastlc llquid-conveying member form a permanent subassembly, and a first coupling member formed integrally wlth said body and extending radially outwardly from an outer cylindrical surface thereof, and a nut mounted substantially coaxially on said sleeve such that sald nut can be applied to sald plastlc llquld-conveylng member together wlth said sleeve, sald nut including a second coupllng member extending radially inwardly adjacent one end of said nut, said second coupllng member terminating ln close proximity to said outer cylindrical surface of said body of said sleeve, and internal threads located ad~acent to an opposite end of said nut, said internal threads being threadedly engageable wlth sald external threads of sald metalllc llquld-conveylng member, and sald nut being rotatably about said sleeve and slideable therealong in said second axial dlrection between a first position in which said internal threads of said nut are not in engagement with said external threads of said metalllc liquid-conveying member and a second position in which said internal threads of said nut are in engagement with said external threads of sald metalllc liquid-conveylng member, whereby after sald sleeve ls applied and attached to said plastic li~uid-conveying member said nut can be slid from said first position to said second position and then rotated so as to thread said nut onto said metallic liquid-conveying member and thereby move said first and second coupling members into an abutting relationship in which they cooperate with each other during the continued rotation of said nut for the purpose of urging said plastic liquid-conveying member into engagement with said metallic liquid-conveying member 'S,j, 't'~
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lc 20152-1177 in such a manner that said plastlc liquid-conveying member and said metallic liquid-conveying member are connected in end-to-end fashion wlth a substantlally llquld-tlght seal therebetween and whereby any undesired rotation of sald sleeve relatlve to said plastic liquid-conveying member as sald nut is threaded onto said metallic liquld-conveying member does not result in any substantlal movement of said sleeve relatlve to sald plastic liquid-conveying member ln said flrst and second axial directlon to thereby promote the formation of the liquid-tight seal between said plastlc llquld-conveylng member and sald metalllc liquid-conveying member.
In accordance with the present lnvention there ls provided a method of constructing a liquid-tight connection between a plastic pipe and a connecting plece made of metal or plastic, whereln a coupling sleeve havlng an outwardly extending coupllng member at one end thereof ls first of all attached to an end portion of the plastic pipe ln such a way that the end of the plastic pipe pro~ects out of the sleeve bore and wherein the coupling sleeve and the plastic pipe fixed thereto, are then drawn against the connecting piece by a union nut gripping the coupling member.
This invention also provides a pipe connection made according to the above-described method comprising a coupling sleeve, the inside bore of which is provided with barb-like anchoring members and grooves running parallel to the coupling sleeve axis, which grooves provide protection against turning, and having an inside diameter smaller than the outside diameter of the plastic plpe; a coupling me=ber lntegrally ior~ed on tùe end iace .

1~23~91 ld 20152-1177 of the coupllng sleeve faclng toward the connecting piece; and, with a unlon nut on the one hand grlpping over the coupllng member and with lt belng posslble on the other hand for the unlon nut, with lts end portion facing away from the coupling sleeve, to be screwed onto the connecting plece provlded with an external thread.
Thls lnvention also provldes a devlce for assembllng the above described pipe connection comprising~
- a clamplng holding devlce for fixing the plastic plpe ln position in axially non-displaceable manner, - a stop for flxing the end portlon of the plastlc plpe ln position and for locatlng the driving sleeve, and also - a press rlng guided in slidlng manner on the stop and coupled to a drlve member ln such a way that the press ring, when lts drive member is actuated, pushes the coupllng sleeve onto the plastlc plpe end flxed ln positlon.
An exemplary embodiment of the subject matter of the invention is descrlbed below wlth reference to the attached drawings, in which:
Figure 1 shows a sectional representation of the ~'~ 2 ~

end portion of a plast;c pipe after assemb~y of the driving sleeve, Figure 2 shows the associated finished pipe connection, F;gure 3 shows a section along line I-I in Figures 2, 5 and 7, Figure 4 shows a variant of the representation according to Figure 1, Figure S shows the assoc;ated finished pipe connection, Figure 6 sho~s d further variant of Figure 1, Figure 7 shows the associated finished pipe connection, Figure 8 shows a side view, partly in section, of the device used for assembling the pipe connection ~assemb~y phase 1), Figure 9 sho~s a side view of the same device in another operating position (assembly phase 2), Figure 10 shows a further, partly cut aYay v;ew of this device (assembly phase 3), and Figure 11 shows a design detail.
According to Figure 1, an unslotted couT~ling sleeve 3 is located on the periphery of a plastic pipe 1 which is preferably made of crosslinked polyethylene, which coupling sleeve 3 has been pushed axially onto the plastic pipe 1 in a nlanner yet to be described. The coupling sleeve 3, prefer-ably made of brass, has an unslotted cylindrical base body which has a number of inwardly directed, barb-like teeth 3a and also - on its end face facing the pipe end - a radially outwardly projecting integrally formed portion which, on account of its function, is designated as coupling mem~er 3b. The coupling member 3b can be made as either a con*inuous annular flange or in the form of individuaL driving dogs at a distance from one another.

A union nut 4 is located on the periphery of the coupling sleeve 3 shown in Figure 1, which union nut 4 is of such a size that its internal thread 4a can be pushed over the coupllng member 3b, while the radially inwardly projecting annular shoulder 4b can be displaced in sliding manner on .

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-- 3 --the outer per;phery of the coupllng sleeve 3.
Moreover, ;t is important that the coupllng sleeve 3, during its assembly, ;s pushed onto the plastic pipe 1 ùntil its front end face is located at a distance x from the end face of the piPe 1.
The connecting piece 2, which can be seen on the finished pipe connection according to figure 2 and, for example, can be part of a fitting, has an external thread 2a corresponding to the internal thread 4a of the union nut 4 and, moreover, is provided on its end face with a cylin-drical locating bore ô into which the end 9 of the plastic pipe 1 projects.
During the assembly of the pipe connection, the coupling sleeve 3, together with the union nut 4, and pre-ferably uith the interposition of a friction-preventing sliding ring 5, is first of aLl pushed onto the plastic pipe 1 until the distance x is reached. The union nut 4 is then screwed onto the connecting piece 2, with the annular shoulder 4b of the union nut 4 drawing the coupling sleeve 3 via its coupling member 3b against the connecting piece 2. At the same time, the pipe end 9 is drawn into the Locating bore 8 of the-sonnecting piece 2 so that an excellent seal results.
~r~ The sliding ring 5, which is made, for example, of~Teflon or another low-friction materiaL, prevents the pipe 1 from turning when the union nut 4 is tightened.
To prevent the coupling sleeve 3 from turning on the plastic pipe 1, the sleeve is provided with wedge-shaped grooves 7, as shown in the sectional representation accord-ing to Figure 3.
In the variants shown in Figures 4 and 5, and Figures 6 and 7, the reference numerals already introduced for designating the individual parts of the pipe connection have been retained. Differing from the e~bodiment accord-ing to Figures 1 and 2, Figures 4 and 5 show a connecting piece 2 uith a curved end face 2b. In this variant, as Figure 4 shows, the front end of the plastic pipe 1 is slightly flanged (flanging angle B) after the driving sleeve is pushed on, so that, ~hen the union nut 4 is tightened, the pipe end is radially deflected in ~ J~c~ Je ~ k .

, 1~'23~91 interaction with the curved surface 10, and the deflected pipe portion, now directed radially outwards, is clamped between the coupling sleeve 3 and the connecting p;ece 2.
owing to the sealing surface increased in this manner, the sealing effect ;s further improved compared with the embodiment of Figures 1 and 2: in addition, any axial extract;on forces which occur are absorbed.
The inner edge 11 of the connecting Piece 2 is preferably rounded off. Instead of the curvature shown, the end face 2b can also have another appropriate form and, for example, run conically.
As endurance tests have shown, the previously des-cribed embodiments of the pipe connection according to the invention generally ~ork satisfactorily. However, leakages can occur in the course of time under alternating loading as a result of the continual transition from cold to hot water and vice versa, so that the pipe connection can start to drip. These leakages are not, as might be expected, to be attributed to slackening of the union nut 4; on the con-trary, the plastic material of the pipe end starts to flow because of the relatively high clamping pressure. In order to compensate for this flowing phenomenon, which leads to leakage, an elastic adjusting member, for example a spring washer 6, ;s additionally inserted, preferably according to Figures 6 and 7, between the annular shoulder 4b of the union nut 4 and the coupling member 3b of the coupling sleeve 3. The leakage possibly associated with the flow of the pipe ma-terial is therefore automatically compensated by the elas-tic adjusting force of the spr;ng washer 6.
The pipe connection explained in-Figures 1 to 7 is expediently assembled by means of a device uhich is specially developed for this purpose and which will now be described on the basis of Figures 8 to 10. In this des-cription, the design features are to be dealt with first and then the function of the device.
Three functional groups, interacting for a common purpose - to mount the driving sleeve correctly onto the plastic pipe - are arranged on a base body which hence-forth, with respect to ;ts function, is designated as 132`3~
holder 12.
Firstly, clamping grips, designated overall as 13, are provided on the front holding portion, vhich grips have afixed leg 14, a moveably mounted leg 15 and, for actuating the latter, a toggle lock 16. The leg 14 of the grip is preferably made in one piece vith the ho~der 12 and therefore forms the front, laterally slightly protruding extension of the latter. The leg 15 of the grips has a prolongation ~hich acts as a guide link 17 and is coupled on the one hand to the holder 12 via a joint 18 and on the other hand to a clamping lever 20 via a joint 19. The clamping lever 20 is in turn connected to the holder 12 by means of a further guide link 21 and two joints 22 and 23. Therefore the leg 15 of the grips, together with the integrally formed guide link 17, the clamping lever 20 and the guide link 21, forms a toggle linkage by means of vhich the moveable leg 15 of the grips, ~hen the clamping lever 20 is actuated, can be blocked in the closing position tFig. 8) indicated in dot-and-dash lines.
At their free end, the two legs 14 and 15 of the grips each have a clamping jaw 23 and 24. The locating opening of the clamping ja~s 23 and 24, ~here in the closing position, is selected such that they securely hold the plastic pipe 1 against any undesirable axial displace-ent.
The second functional group, the function of ~hichis to bring about the pushing of the coupl~g sleeve 3 against the plastic pipe, comprises a stop 25 vhich is eounted in the holder 12 and acts as a centering arbor and vhich has a press ring 26 mounted displaceably on its periphery. The press ring 26 can be displaced via a con-necting rod 27 and an ar- 29 which is connected to the latter by means of a joint 28 and is extended beyond a fixed joint 30 by an actuating lever 31.
The connecting rod 27 and the arm 29 form a thrust crank which is of such a size that, in its extended posi-tion, it pushes the coupl~g sleeve 3 onto the plastic pipe 1 to an excess dimension x tFig. 1 and 9).
The t~ird functional group, ~hich can be seen from 1323~1 Figure 10, is intended to slight~y initia~ly open out (initial f~anging) the pipe end 1a facing to~ard the stop ~S after the coupling sleeve 3 is pushed on. For this pur-pose, the stop Z5 displaceably mounted in the holder 12 at its end facing away from the conical point 25a, is provided ~ith a stop shoulder 32 which on the one hand acts as a spring plate for a compression spring 33 and on the other hand is he~d in constant contact with an eccentric 34 by th;s compression spring 33. The eccentric 34 is in turn rotatably connected to the axis of the joint 30 tFig. 8) and is adapted in form and position in such a ~ay that it displaces the stop 25 against the restoring force of the compression spring 33 only after the press sleeve 3 has been pushed onto the plastic pipe 1.
Figures 8 to 10 illustrate three phases of the assembly operation. According to Figure 8, the clamping grips 13 are opened, the coupllng sleeve 3 is pushed, together with the union nut 4, onto the centering arbor 25 and the plastic pipe 1, ~ith its opening, sits on the conical centering point 25a. In this position of the pipe, the leg 15 of the clamping grips is now pressed against the pipe 1 and locked by means of the toggle lock 16.
The ~ctuating lever 31 is now swung about the axis 30 in the anticlockwise direction until it has reached the position shown in Figure 9, in ~hich it lies practically coaxial to the holder 12. During this swivelling movement of the actuating lever 31, the press ring 26 on the stop 25, as already mentioned, is pushed forward and at the same time pushes in front of it the coupling sleeve 3 together with the union nut 4 until the couplins sleeve 3 has reached the desired position on the pipe 1. This end position of the press ring 26 is shown in Figure 9.
To be noted here on the one hand is that pushing the coupling sleeve 3 onto the pipe 1 is facilitated by a slightly conical chamfering of the press sleeve opening, ~hich is designated as A in Figure 8. On the other hand, although the eccentric 34 has been turned along by the act-uating lever 31, it has so far not yet been able axially to displace the stop 25 o~ing to its position and shaping.

~2c3~ 7 ~
As shown by Figure 1û, if the lever 31 is now moved beyond its coaxial position according to Figure 9, the ec-centric 34 pushes the stop 25 forward by a small extent in-to the plastic pipe 1 and thereby initially opens out the pipe opening, as desired.
~ n the final moVement phase of the actuating lever 31, wh;ch is shown in Figure 10, the arm 29 also strikes a releise ~in 35 arranged on the toggle lock 16, as a re-sult of which the toggle lock is released and the plastic pipe 1 falls out of the clamping grips 13.
According to the exemplary embodiments described, the coupling sleeve 3 is provided on its inner side with inwardly projecting, annular barbs 3a which have the task of reliably anchoring the coupllng sleeve 3 on the plastic pipe 1. At the same time, the coupling sleeve 3, under the effect of a tensile force engaging in axial action, is to drive along the plastic pipe 1 and on the other hand is to be secured if possible against turning on the plastic Pipe.
It ought to be clear to the specialist that anchor-ing the driving sleeve on the plastic pipe can be achieved in the most varied manner. Thus it would be possible for example, inter alia, to make the annular barbs 3a in a threaded for-, and in fact preferably in the form of an angular thread shown in Figure 11. The profile of this thread, designated overall as 36, has a flank F1 which is practically at right angles to the sleeve axis A, and also a flank F2 inclined towird the axis A. The angle ~ of in-clination of the flank F2 relative to the ax;s A can, for example, be between 30 and 70; a preferred anguLar range is between 50 and 60.
As sho~n in Figure 11, the thread 36 is made as a sharply angular thread. To achieve the intended protection against turning, the pitch direction of the thread 36 should be opposite to that of the union nut 4. Therefore if the thread of the union nut 4 is right hand, the thread 36 of the coupling sleeve 3 is selected as left hand.
This embodiment of the coupling sieeve 3, is shown in Figure 11, ought to be especially suitable, for example, ~2~'3~1 for large nominal diameters. At the same time, it ought to be possible in many cases to screw the sleeve onto the end portion of the plastic pipe with a simple plier-like auxi-liary tool - or even by hand - on which end portion it is then reliably anchored both in the axial direction and against turning.
A further type of attachment of the couplin~ sleeve 3 on the plastic pipe 1 cou(d also consist in inwardly projecting resilient barbs being arranged on the ;nner side of the coupling sleeve 3. The sleeve could then be pushed by hand onto the end port;on of the plast;c pipe and would be secured by the resil;ent barbs.
Merely from the description of the function of the device according to the invention, it ought to have be-. come clear - and this has been confirmed by numerous prac-tical tests conducted under the most varied conditions -that, owing to the device according to the invention, the pipe connection can be realized in an uncomplicated manner within the shortest time without prior heating up of the Pipe .
The bore of the coupling sleeve 3 may in the region of its free end also be beveled, so that the plastic tube protrudes out of the sleeve bore, but not beyond the end face of the sleeve.

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Claims (42)

1. A connector for providing a substantially liquid-tight seal between a plastic liquid-conveying member and a metallic liquid-conveying member, which is provided with external threads and adapted to be connected to said plastic liquid-conveying member in end-to-end fashion, said connector comprising a sleeve which is circumferentially continuous, said sleeve including a tubular body, attaching means extending radially inwardly from an inner cylindrical surface of said body for fixedly-and non-rotatably attaching said sleeve to said plastic liquid-conveying member, said inner cylindrical surface of said sleeve having a diameter which is less than an outer diameter of said plastic liquid-conveying member but which is sufficiently large to permit said sleeve to be applied to said plastic liquid-conveying member by substantially non-rotatably pushing said sleeve along said plastic liquid-conveying member in a first axial direction from a non-threaded end of said plastic liquid-conveying member toward an opposite end of said plastic liquid-conveying member, said non-threaded end of said plastic liquid-conveying member being the end which is to be connected to said metallic liquid conveying member, and said attaching means penetrating into said plastic liquid-conveying member a distance sufficient to inherent any movement of said sleeve relative to said plastic liquid-conveying member in a second axial direction opposite to said first axial direction, whereby said sleeve is non-rotatably and non-removably attached to said plastic liquid-conveying member such that said sleeve and said plastic liquid-conveying member form a permanent subassembly, and a first coupling member formed integrally with said body and extending radially outwardly from an outer cylindrical surface thereof, and a nut mounted substantially coaxially on said sleeve such that said nut can be applied to said plastic liquid-conveying member together with said sleeve, said nut including a second coupling member extending radially inwardly adjacent one end of said nut, said second coupling member terminating in close proximity to said outer cylindrical surface of said body of said sleeve, and internal threads located adjacent to an opposite end of said nut, said internal threads being threadedly engageable with said external threads of said metallic liquid-conveying member, and said nut being rotatably about said sleeve and slideable therealong in said second axial direction between a first position in which said internal threads of said nut are not in engagement with said external threads of said metallic liquid-conveying member and a second position in which said internal threads of said nut are in engagement with said external threads of said metallic liquid-conveying member, whereby after said sleeve is applied and attached to said plastic liquid-conveying member said nut can be slid from said first position to said second position and then rotated so as to thread said nut onto said metallic liquid-conveying member and thereby move said first and second coupling members into an abutting relationship in which they cooperate with each other during the continued rotation of said nut for the purpose of urging said plastic liquid-conveying member into engagement with said metallic liquid-conveying member in such a manner that said plastic liquid-conveying member and said metallic liquid-conveying member are connected in end-to-end fashion with a substantially liquid-tight seal therebetween and whereby any undesired rotation of said sleeve relative to said plastic liquid-conveying member as said nut is threaded onto said metallic liquid-conveying member does not result in any substantial movement of said sleeve relative to said plastic liquid-conveying member in said first and second axial direction to thereby promote the formation of the liquid-tight seal between said plastic liquid-conveying member and said metallic liquid-conveying member.

2. A connector according to claim 1, wherein said sleeve includes inhibiting means for inhibiting said nut from being slid off of said sleeve when said nut is moved from said second position toward said first position.

3. A connector according to claim 2, wherein said sleeve is positioned adjacent said non-threaded end of said plastic liquid-conveying member and said first coupling member is located adjacent one end of said sleeve.

4. A connector according to claim 3, wherein said one end of said sleeve is spaced a predetermined distance from said non-threaded end of said plastic liquid-conveying member.

5. A connector according to claim 4, wherein said non-threaded end of said plastic liquid-conveying member abuts one end of said metallic liquid-conveying member.

6. A connector according to claim 5, wherein said one end of said metallic liquid-conveying member includes a recess which is sized and shaped so as to receive said non-threaded end of said plastic-conveying member.

7. A connector according to claim 6, wherein said recess has a surface which is curved so as to curl said non-threaded end of said plastic liquid-conveying member when said plastic liquid-conveying member and said metallic liquid-conveying member are arranged in end-to-end fashion.

8. A connector according to claim 7, wherein said non-threaded end of said plastic liquid-conveying member is clamped between said one end of said sleeve and said one end of said metallic liquid-conveying member.

9. A connector according to claim 6, wherein said one end of said sleeve engages said one end of said metallic liquid-conveying member.

10. A connector according to claim 3, wherein said inhibiting means includes a flared rim located adjacent an end of said sleeve opposite said one end thereof.

11. A connector according to claim 1, wherein said attaching means includes inhibiting means for inhibiting the rotation of said sleeve relative to said plastic liquid-conveying member.

12. A connector according to claim 11, wherein said inhibiting means includes a plurality of grooves provided in said inner cylindrical surface of said body of said sleeve, each of said grooves extending in an axial direction.

13. A connector according to claim 1, further comprising inhibiting means for inhibiting the rotation of said sleeve and said plastic liquid-conveying member in response to the rotation of said nut.

14. A connector according to claim 13, wherein said inhibiting means includes an anti-friction element interposed between said first and second coupling members.

15. A connector according to claim 14, wherein said anti-friction element includes a plastic lining attached to said first coupling member.

16. A connector according to claim 14 or 15, wherein said anti-friction element includes a plastic lining attached to said second coupling member.

17. A connector according to claim 14, wherein said anti-friction element includes a plastic ring which extends loosely and coaxially around said outer cylindrical surface of said body of said sleeve.

18. A connector according to claim 1, further comprising sealing means for sealing against the leakage of liquid between said first and second coupling members.

19. A connector according to claim 18, wherein said sealing means is a deformable member interposed between said first and second coupling members.

20. A connector according to claim 19, wherein said deformable member is ring-shaped and extends around said body of said sleeve.

21. A connector according to claim 1, wherein said attaching means includes a plurality of barbs, each of said barbs being sized and shaped so as to permit said sleeve to be pushed onto said first liquid-conveying member and then to penetrate and grip said plastic liquid-conveying member.

22. A connector according to claim 1, wherein said attaching means includes an angular screw thread having a pitch which is opposite to that of said internal threads of said nut to thereby inhibit said sleeve from rotating relative to said plastic liquid-conveying member.

23. A connector according to claim 22, wherein said screw thread has, in profile, a first flank lying in a plane which is substantially perpendicular to a central longitudinal axis of said sleeve and a second flank lying in a plane which is arranged at an inclined angle relative to said central longitudinal axis of said sleeve.

24. A connector according to claim 1, wherein said first coupling member includes a continuous circular flange.

25. A connector according to claim 1, wherein said first coupling member includes a plurality of circumferentially spaced-apart dogs.

26. A connector according to claim 24 or 25, wherein said second coupling member is a continuous circular shoulder.

27. A connector according to claim 1, wherein said first coupling member has an inner face which contacts an inner face of said second coupling member when said first and second coupling members cooperate to urge said plastic liquid-conveying member into engagement with said metallic liquid-conveying member, said inner face of said first coupling member lying in a first plane which is normal to a longitudinal axis of said sleeve and said inner face of said second coupling member lying in a second plane which is normal to a longitudinal axis of said sleeve, whereby said first and second planes are parallel to each other.

28. A method of constructing a liquid-tight connection between a plastic pipe and a connecting piece made of metal or plastic, wherein a coupling sleeve having an outwardly extending coupling member at one end thereof is first of all attached to an end portion of the plastic pipe in such a way that the end of the plastic pipe projects out of the sleeve bore and wherein the coupling sleeve and the plastic pipe fixed thereto, are then drawn against the connecting piece by a union nut gripping the coupling member.

29. A method as claimed in claim 28, wherein the end portion of the plastic pipe is initially flared outwardly by a metal arbor and is then finish-formed and is pressed into contact with an end face of the coupling sleeve by a curved or conical pressure surface integrally formed on the connecting piece.

30. Apparatus for applying a coupling connector, which includes a tubular sleeve, to a plastic liquid-conveying member, comprising holding means for holding said connector such that said sleeve extends around said holding means, aligning means on an end of said holding means for automatically aligning one end of said plastic liquid-conveying member with said connector in such a manner that said one end of said plastic liquid-conveying member and said sleeve are arranged substantially coaxially, clamping means for clamping said plastic liquid-conveying member against substantial movement in an axial direction, first moving means for moving said aligning means into engagement or further engagement with said one end of said plastic liquid-conveying member and pushing means for pushing said connector off of said holding means and onto said plastic liquid-conveying member in such a manner that said sleeve is spaced inwardly a predetermined distance from said one end of said plastic liquid-conveying member.

31. Apparatus according to claim 30, wherein said clamping means includes a stationary leg having first gripping means for gripping said plastic liquid-conveying member on one side thereof and a movable leg having second gripping means for gripping said plastic liquid-conveying member on an opposite side thereof.

32. Apparatus according to claim 31, further comprising moving means for second moving said movable leg toward and away from said stationary leg.

33. Apparatus according to claim 32, wherein said second moving means pivots said movable leg toward and away from said stationary leg.

34. Apparatus according to claim 33, wherein said second moving means includes a toggle lock.

35. Apparatus according to claim 34, wherein said holding means includes a centering arbor having a first end which is remote from said one end of said plastic liquid-conveying member and a second end which is proximate to said one end of said plastic liquid-conveying member.

36. Apparatus according to claim 35, wherein said aligning means includes a tapered element provided at said second end of said arbor.

37. Apparatus according to claim 34, wherein said pushing means includes a press ring slidably and reciprocally mounted on said arbor such that said press ring slides back and forth on said arbor.

38. Apparatus according to claim 37, further comprising actuating means for actuating the movement of said press ring, said actuating means including a pivotally mounted lever which is connected to said press ring by a thrust crank such that upon the pivotal movement of said lever said thrust crank moves from a non-extended position to an extended position to thereby move said press ring toward said second end of said arbor, whereby as said thrust crank is moved from said non-extended position to said extended position said connector is pushed by said press ring onto said plastic liquid-conveying member to such an extent that said sleeve is spaced said predetermined distance from said one end of said plastic liquid-coveying member.

39. Apparatus according to claim 38, further comprising opening means for automatically opening said clamping means after said connector has been pushed onto said plastic liquid-conveying member.

40. Apparatus according to claim 39, wherein said operating means includes a stop which is positioned on said toggle lock such that said thrust crank contacts said stop after said thrust crank reaches said extended position to thereby open said toggle lock and release said plastic liquid-conveying member from said clamping means.

41. Apparatus according to claim 40, wherein said lever includes a pivot which is coupled to an eccentric and wherein said first end of said arbor is urged toward said eccentric by a spring.

42. Apparatus according to claim 41, wherein said eccentric is sized and shaped such that after said connector is pushed onto said plastic liquid-coveying member but before said plastic liquid-conveying member is released from said clamping means said eccentric pushes said arbor into said one end of said plastic liquid-conveying member to such an extent that said one end of said plastic liquid-conveying member is flared by said tapered element.