BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a fitting for connecting a plastic pipe, and more particularly to a fitting for a plastic pipe which is capable of maintaining an uniform seal ability regardless of deformation of pipe owing to a temperature change and an aging.

Description of the Prior Art

Generally, a plastic pipe is predominantly used in various machines and tubing because of its low plumbing cost and its easy assembling. As one of the above-mentioned conventional pipes, a fitting for ^' polyethylene pipe is made in accordance with the KS (Korean Standards) B 1564 which comprises a fitting body, a tightening nut and a brass slite olive. However, the fitting has a sealing ability decreasing on using.

More specifically, since the fitting made in accordance with the KS B 1564 is mounted on a pipe in such a manner that the fitting body is inserted into the pipe at its insertion part and the tightening nut is engaged with the fitting body with the brass slite olive interposed therebetween, fluid leakage occurs between the fitting body and the pipe because the pipe expands or contracts owing to a temperature change and an aging.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described problems occurring in the prior art fitting and an object of the invention is to provide a fitting for a plastic pipe which has a plurality of rubber O-rings mounted on an outer ci cumference of an insertion part thereof so that a seal ability between the fitting and pipe

can be improved and a fluid leakage by the temperature change and the aging can be prevented.

In accordance with the present invention, the object mentioned above can be accomplished by providing a fitting for a plastic pipe comprising a fitting body having an outer thread at its end and an insertion part to be inserted into a pipe at the end face, a brass slite olive adapted to be inserted on the insertion part of the fitting body with a pipe with the pipe therebetween and in contact with the end face of the fitting body, and a tightening nut having an inner thread adapted to be engaged with the outer thread of the fitting body with the brass slite olive interposed between, said insertion part of the fitting body being formed with a plurality of annular grooves having rectangular sections at its outer surface and the annular grooves being fitted with rubber O-rings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the invention will become more apparent upon a reading of the following detailed specification and drawings, in which:

Fig. 1 is a partially sectional view of a fitting for a plastic pipe according to the present invention which is exploded;

Fig. 2a is a partially sectional view of the fitting of the invention which is ready to be mounted on a pipe; and

Fig. 2b is a view similar to Fig. 2a which is mounted on the pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fitting for a plastic pipe according to the present invention will now be described by referring to the accompanying drawings.

Referring to Fig. 1 , there is shown a fitting for a plastic pipe according to the present invention. As

illustrated in the drawing, the fitting 1 comprises a fitting body 2 having an insertion part 6 to be inserted into a plastic pipe 11, a brass slite olive 4 adapted to be mounted on the pipe 11 and in contact with the fitting body 2, and a tightening nut 3 adapted to be threadedly engaged with the fitting body 2 with the brass slite olive 4 therebetween.

More specifically, the fitting body 2 is formed with an inner thread 7 at an outer surface of its inner end and with an outer thread 8 at an outer surface of its outer end. Also, the fitting body 2 is formed with a tapered surface 9 at its inner end surface.

The insertion part 6 has the same outer diameter as an inner diameter of a plastic pipe 11 to be connected and is formed at its outer surface with annular grooves 6a. A plurality of rubber O-rings 5 are fitted in the annular grooves 6a. In this case, although the illustrated insertion part 6 is formed with three annular grooves 6a, only two rubber O-rings 5 are fitted in the annular grooves 6a, that is, the innermost and the outermost grooves 6a each is filled with the rubber 0-ring 5 but the middle groove 6a is not fi 1 led.

Therefore, when the fitting 1 has been mounted on the plastic pipe 11, an inner surface portion of the plastic pipe 11, which corresponds to the position of the middle, is embedded in the middle groove 6a by a radial inward compression force of the brass slite olive 4, thereby preventing the plastic pipe 11 from being separated from the insertion part 6. Furthermore, since the annular grooves 6a have rectangular shape in section, the rubber O-rings 5 are deformed and embedded in the annular grooves 6a so as to be conformed to the rectangular shape of the grooves 6a. Accordingly, the rubber O-ring 5 can not be separated from the grooves 6a when the insertion part 6 of the fitting 1 is inserted into and drawn from the pipe 11, and they are not broken even though they are compressed by the radial inward compression force of the brass slite olive 4.

The above-mentioned fitting body 2 of the invention may be applicable to various fitting members, such as a female faucet socket, a union, a tee, a reducer and the like, so that it can be connected to another tubing fitting or a stationary machine.

The brass slite olive 4, which is to be interposed between the fitting body 2 and the tightening nut 3, is formed with tapered surfaces 4a at circumferences of its opposite ends. One of the tapered surfaces 4a corresponds to the tapered surface 9 of the fitting body 2 and the other corresponds to a tapered surface 3b of the tightening nut 3 to be described later. Also, the brass slite olive 4 has inner annular projections 4b at its inner surface.

The tightening nut 3 is formed with an inner thread 3a at its inner surface and with the tapered surface 3b corresponding to the other of the tapered surfaces 4a of the brass slite olive 4 at an inner surface of its outer end.

Accordingly, as the tightening nut 3 is engaged with the fitting body 2 so that the nut 3 and the fitting body 2 are pulled toward each other, the brass slite olive 4 is radially inwardly compressed by slide action between the tapered surfaces 4a of the brass slite olive 4, tapered surface 9 of the fitting body 2 and the tapered surface 3b of the nut 3, so that the plastic pipe 11 is compressed on the insertion part 6 of the fitting body 2. Hence, the pipe 11 is fixedly connected to the fitting 1.

Operation of the fitting according to the present invention will be described hereinafter.

Fig. 2a shows the fitting according to the invention which is ready to connected to the pipe and Fig. 2b shows the fitting completely connected to the pipe.

As shown in the drawings, in order to connect the fitting 1 to the pipe 11, the tightening nut 3 and the brass slite olive 4 are first inserted on an end of the pipe 11 and then the fitting body 2 is inserted in the end of the pipe 11 at its insertion part 6. Subsequently , the tightening nut 3 is engaged with the fitting body 2 by using

two wrench. At this time, the brass slite olive 4 is radially inwardly compressed against the surfaces 9 and 3b of the fitting body 2 and the tightening nut 3, as previously mentioned. Therefore, the inner surface of the pipe 11 is in closely contact with the outer surface of the insertion part 6 with the rubber O-rings 5 interposed therebetween, so that fluid such as air, liquid and the like, which flows through the fitting body 2 and the pipe 11, can not leak therebetween even though a gap occurs between the fitting 1 and pipe 11 due to a temperature change and an aging.

Also, the pipe 11 can not be separated from the fitting body 2 since the inner annular projections 4b of the brass slite olive 4 are stuck in the outer surface of the pipe 11 and a portion of the inner surface of the pipe 11 is embedded in the middle groove 6a of the insertion part 6 due to the inward compression force, .

As apparent from the above description, since the fitting for plastic pipe according to the present invention is constructed such that the insertion part of the fitting body is formed with a plurality of the annular grooves and flexible rubber O-rings are fitted in the annular grooves, the fitting can prevent leakage of fluid caused by a temperature change and an aging by means of the flexibility of the rubber O-rings.

For a better understanding of the present invention, some specific examples and comparative examples will be given hereinbelow by way of illustration of its particular embodiments but these examples should not to be construed to limit the scope of the present invention.

EXAMPLE 1

Twenty fittings capable of connecting pipes having outer diameter of 16 mm, as shown in Fig. 1, were made of brass material in accordance with the present invention.

The fittings were connected to both ends of plastic pipes having length of 30 cm and one side ends of the pipes were

clogged with caps so as to prepare twenty test pieces. The other side ends of the pipes were connected to hydraulic testers, respectively. Ten of the test pieces were applied with ambient temperature water (20 ± 3"C) under hydraulic pressure of 60kgf/crrr for ten minutes and the other ten test piece were applied with high temperature water (80 ± 3°C)under hydraulic pressure of 40kgf/cnr for ten minutes. Then, the test pieces were checked in regard to breakage of the fittings and the pipes and leakage of water. The test results are given in Table 1.

In the present example, metal tubes coated with plastic material (trade mark "YUGONG KITEC PIPE COR 12" manufactured by YUGONG Limited., Korea), which are manufactured by a process described in Europe Patent No. 0024220, were used as the pipes.

EXAMPLE 2

Ten fittings were made in similar manner to EXAMPLE 1 and connected to both ends of five pipes having length of 4 m so as to prepare five test pieces. The test pieces were alternately and repeatedly applied with water of temperature of 95 ± 3°C and water of temperature of 18 ± 3°C under hydraulic pressure of lOkgf/cm ² at a time interval of 15 minutes. Then, the test pieces were checked in regard to breakage of the fittings and the pipes and leakage of water (Thermo cycling Test). The test results are given in Table 2.

COMPARATIVE EXAMPLE 1 Twenty fittings made in accordance with the KS B1564 having the same diameter as that in EXAMPLE 1, which are commercially available, were checked in similar method to EXAMPLE 1. The test results are given in Table 1.

In the present example, the fittings made in accordance with the KS B1564 are fittings (12A) manufactured by NAMSUNG PRECISION INDUSTRY COMPANY, Korea.

COMPARATIVE EXAMPLE 2

The ten fittings used in comparative example 1 were prepared and checked in similar method to example 2. The test results are given in Table 2.

Table 1

EXAMPLE No. 20 ± 3°C 80 ± 3°C

EXAMPLE 1 no leakage in 10 no leakage in 10 samples samples

COM. EXAMPLE 1 no leakage in 10 no leakage in 3 samples samples, leakage in 7 samples

Table 2

EXAMPLE No. repeat cycle time

EXAMPLE 2 no leakage up to 3,000 cycles 1 ,500 hours

COM. EXAMPLE 2 leakage at average 8 cycles 4 hours

Note, repeat cycles: 18 ± 3°C (15 min) - 95 ± 3 ^β C (15 min) - 18 ± 3°C (15 min)

1 cycle (30 min)