Without a doubt, one of the most common types of polyethylene fittings is threaded polyethylene fittings. Threaded polyethylene fittings refer to connections that do not depend on welding to connect polyethylene pipes to each other, and connection is made through a female fitting.

Currently, manufacturing factories inside Iran produce and market threaded polyethylene fittings up to 125 millimeters in size and at a working pressure of 10 bar. It is worth mentioning that the production of threaded fittings, similar to the production of injected polyethylene fittings, electrofusion fittings, and quick fittings, is achieved through the use of an injection molding machine, pre-prepared steel molds, and raw material granules.

One of the differences between the production process of threaded polyethylene fittings and other types of polyethylene fittings is that, in addition to using polyethylene raw material (for producing the bushing), polypropylene and polyacetal granules (for producing other components) are also utilized.

Considering that polypropylene granules have the largest share in the production of the components of threaded fittings, it might be better to name them polypropylene threaded fittings. However, since these fittings have been commonly referred to as polyethylene threaded fittings from the beginning, they are recognized by this name in the industry as well.

Introduction to the components and various parts of threaded polyethylene fittings

All threaded polyethylene fittings are made up of several components, each requiring different raw materials for their production, and each has its own specific functionalities and characteristics within the structure of the part. These components include:

1- Split: The material of the split in threaded fittings is polyacetal, which is a hard thermoplastic and is resistant and stable against chemical substances as well as physical stresses. The split prevents the polyethylene pipe from coming out of the fitting under high pressure.

2- Bushing: Made of polyethylene, it is located between the split and the O-ring in the structure of threaded fittings. When connecting the part, the bushing exerts extra pressure on the O-ring, sealing the threaded polyethylene fittings.

3- O-ring: Made of rubber, its duty is to seal the threaded fittings that are placed on the polyethylene pipe. Additionally, the O-ring must be flexible and resistant to pressure.

4- Body and nut: The body and nut of threaded fittings are made of polypropylene and are resistant to pressure, physical impact, and chemical changes. Polypropylene materials are more resilient compared to polyethylene raw materials and are more durable against sunlight.

How threaded polyethylene fittings work

As we know, threaded polyethylene fittings consist of the components of the nut, split, bushing, O-ring, and body in that order. To connect pipes to each other using threaded fittings, the following steps are performed:

1- We separate all connection components in the same order they were assembled.

2- We sequentially place the nut, bushing, and O-ring on the pipe while temporarily setting aside the split.

3- The pipe that has the aforementioned three components mounted on it is directed toward the other component, which is the body of the fitting.

4- This process continues until the end of the pipe reaches the edge of the holder located inside the body of the fitting.

5- Then, the O-ring and bushing are moved toward the body of the fitting until they fit inside the body.

6- The nut is brought close to the threaded area on the body of the fitting and tightened with an appropriate wrench.

7- The nut is unscrewed and separated from the other connection components, moving it away in the opposite direction.

8- After that, the split is removed from the groove designed in its structure, placed on the pipe, and finally brought close to the other connection components.

9- At this stage, the threaded fitting is ready for final tightening and sealing.

10- The nut is tightened with the help of an appropriate wrench for sealing the threaded connections. It should be ensured that the tightening continues only to an optimal point; to such an extent that it does not cause the fitting to bulge and distort the appearance of the blades.

Important notes for installing threaded polyethylene fittings

During the installation of threaded fittings, like other polyethylene fittings, certain points must be followed to deliver a flawless installation in the project. These points include:

The ends of the pipes that are to be inserted into the threaded fittings should be completely smoothed with a file, removing any burrs and cleaning them.

Before the connection parts are finally tightened, ensure that each of them is placed in their correct positions.

To ensure complete sealing of the connection, you can use Teflon tape.

The length of the appropriate wrench handle for tightening the connection components should be a maximum of 46 centimeters.

Since threaded fittings cannot withstand the passage of hot water, care should be taken to ensure that fluids with appropriate temperatures flow through the pipes and threaded fittings in the projects.

Applications of threaded polyethylene fittings

For agricultural uses and water distribution networks

For pressurized irrigation uses, including drip and sprinkler irrigation

For water supply systems

For use in small-scale projects

Characteristics of threaded polyethylene fittings

Resistance to corrosion and rust (unlike metal fittings)

Resistance to chemical substances

Resistance to stress and cracking

Resistance to vibrations caused by earthquakes

Resistance to ultraviolet rays

High strength and longevity

High flexibility

Having a smooth and polished internal and external surface

No sedimentation and low pressure drop due to the smooth surface

Advantages of using threaded polyethylene fittings

One of the features that distinguishes threaded polyethylene fittings from other types of fittings is their reusability.

In fact, the welding process during installation can render other fittings (including injected polyethylene fittings, handmade fittings, and brass fittings) unusable, while threaded polyethylene fittings can be reused in other projects after installation.

Furthermore, if one of the threaded polyethylene fittings used in a project becomes defective for any reason, it can be easily replaced.

On the other hand, in small projects, due to the lack of need for transporting or renting a welding machine and subsequently not needing to hire skilled labor to operate it, the use of threaded fittings is recommended over other fittings.

In fact, the high speed of this process stems from this factor.

Additionally, the lack of need for electric power to connect the pipes during installation in the project is another advantage of threaded polyethylene fittings.

Another unique feature of these fittings is that, if any of the components of threaded polyethylene fittings becomes faulty or damaged (such as the split, bushing, nut, and O-ring), they can be purchased separately and easily replaced.

Disadvantages of threaded polyethylene fittings

Despite all the advantages, it should be kept in mind that threaded polyethylene fittings are ultimately available up to a size of 125 millimeters and a pressure of 10 bar, and cannot cover large projects that involve fittings of larger and diverse sizes.

Moreover, since the materials used for the production of the components of threaded polyethylene fittings are different (polyacetal, polypropylene, polyethylene, and rubber), each of them expands and contracts at specific temperatures across different seasons. This may lead to loosening of these fittings and result in leakage.

Additionally, threaded fittings are very expensive.

Manufacturers of threaded polyethylene fittings

It is obvious that using handcrafted polyethylene fittings (Maitri) and brass polyethylene fittings, injection fittings, and electrofusion fittings in projects is marked by a major disadvantage, namely the dependence on the presence of a welding machine and, consequently, the need for a skilled operator.

Knowing this, the production of fittings that can be installed and utilized with greater ease in projects will be valuable.

This makes the efforts of manufacturers of threaded polyethylene fittings, who strive to offer products meeting national and international standards, commendable. However, unfortunately, the drawback of not being able to provide these fittings in sizes larger than 125 millimeters remains unavoidable.

The price of threaded polyethylene fittings

Threaded polyethylene fittings are expensive despite their smaller size, making their purchase for projects comparatively more costly than that of handcrafted or injected polyethylene fittings.

It is worth noting that alongside the high price, the exemption of the employer from purchasing or renting a welding machine and the associated costs of transporting it to the project site help to somewhat balance the cost of purchasing threaded polyethylene fittings.

However, after all these considerations, the price of threaded polyethylene fittings remains staggering.

What kind of connections are threaded polyethylene fittings?

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