How to connect HDPE pipes: types of connections (fittings, couplings, welding) and their features

Modern water pipes are rarely made of metal. It has worthy competitors - polymers, which are gradually replacing it in many areas. One such material is low-density polyethylene. Pipes for pressure pipelines, that is, for water pipelines and even gas pipelines, are made from this material. This type of material is becoming increasingly popular, since connecting polyethylene pipes is easy to do with your own hands. You just need to follow very simple rules.

When organizing private water supply, HDPE pipes are often used

Advantages and features of application

Polyethylene pipes are made from low-density polyethylene. This material is abbreviated as HDPE. It is characterized by increased strength and elasticity, and has good performance properties:

• chemically neutral, can be used for transporting food products;
• smooth walls prevent the formation of plaque inside;
• not subject to corrosion;
• small coefficient of thermal expansion - about 3% at maximum heating (up to +70°C);
• They react normally to the freezing of water inside, due to elasticity they increase in diameter, and after thawing they return to their original dimensions.

One point to remember! If you need pipes that are resistant to freezing (for example, for installing water supply in a country house), when choosing, look at the description or technical specifications. Not all types of copolymers used for pipe production tolerate freezing well. So be careful.

The main disadvantage of polyethylene pipes is the restrictions on the temperature of the transported medium: it should not be higher than +40°C, that is, only cold water supply can be made from HDPE; they cannot be used for hot water and, especially, heating.

Polyethylene water pipes are available in different diameters

Another point: polyethylene does not tolerate UV radiation well. When constantly exposed to the sun, the material loses its elasticity and, after some time, breaks (some manufacturers make HDPE pipes that are UV-resistant, but they are more expensive). Therefore, open laying of water supply pipes from plastic pipes is very undesirable. But it is very possible to run a pipe in a trench from a well or borehole to the house, and distribute cold water throughout the house. This is a fairly economical and convenient solution, since the installation and connection of polyethylene pipes is not very difficult. If we are talking about a detachable connection, then it does not require any equipment. All you need is fittings and hands.

Operating principle of the hydraulic tank

Typically, the inner bulb is located in a container of air at a standard pressure of 1.5 bar. When turned on, water is supplied by an electric pump installed in the well into the tank, filling the rubber bulb - it increases in volume, compressing the air space inside. When the pressure (standard 3 bar) reaches the threshold of the automatic relay, the electric pump turns off and the flow of water into the line stops.

When turned on, water flows to the consumer under pressure created by a rubber membrane compressed by air. Upon reaching the minimum level of 1.7 bar. the relay closes the power supply circuit of the electric pump and the line is filled.

Fig. 3 Example of installing a hydraulic accumulator in a water supply system with a submersible pump

Which polyethylene pipes are better?

For the production of water pipes, two grades of polyethylene are used - PE 80 and PE 100. The hundredth polyethylene is more dense and durable than the eightieth. For water supply systems in a private home, the strength of PE 80 is more than enough - they can withstand pressure up to 8 atm. If you like a large margin of safety, you can take them from PE100. They work normally at 10 atm.

First of all, you need to choose a manufacturer

What you should pay attention to is the country in which the product was produced. The leaders in quality are European manufacturers. High precision execution guarantees high system reliability. Average quality and prices are from Turkish companies, in the cheaper price segment are Chinese manufacturers. Their quality, as usual, is also much lower. It’s difficult to give advice here; everyone chooses at their own discretion (or what is available in the region).

Why do you need a hydraulic tank?

The hydraulic accumulator is always placed in the individual water supply main; it works constantly and performs the following functions:

• Smoothes out the negative consequences of hydraulic shocks. When the electric pump is triggered, the water flow suddenly stops or accelerates, while the liquid acts on the pipeline and its components with physical force. Connecting the hydraulic accumulator to the water supply system allows you to smoothly accumulate and release water due to the plastic rubber membrane located inside.
• Connecting a hydraulic tank reduces the number of cycles of turning on and off a borehole or sump electric pump due to the accumulation of liquid, which is released into the line during use and maintains pressure in it, preventing the electric pump from turning on.
• Hydraulic accumulators create an emergency supply of water in times of power outages or pumping equipment failure.
• The connection diagram of the hydraulic accumulator to the pump and water supply system normalizes the pressure, allowing it to avoid sudden changes in the event of unstable operation of the electric pump.

Rice. 1 Hydraulic accumulators for water mains

Types of HDPE pipe connections

There are several types of connections for polyethylene pipes:

• detachable (on fittings or couplings);
• one-piece - by welding: using a special welding machine;
• electric couplings - a heater is built into such couplings; when electric current is applied to it, the polyethylene heats up and fuses.

Welding is used more often on large diameters.
Weld mainly pipes of large diameters, which are used to create main pipelines. Pipes of small diameters - up to 110 mm, used in private construction, are mostly connected using fittings. Couplings are used more often during repair work, since their installation takes longer.

Fittings for polyethylene pipes are shaped parts (tees, crosses, angles, adapters, couplings) with the help of which the required system configuration is created. Since independent connection of polyethylene pipes is carried out more often with the help of fittings, let’s talk about them in more detail.

An approximate set of fittings for polyethylene water pipes

Butt welding

This method is used to assemble systems from pipes with a diameter of 50 mm or more.

To do this, you need a soldering iron for welding HDPE. Such equipment is inexpensive and is sold in almost any hardware store, so there should be no problems with the purchase. The process goes like this:

The ends of the pipes are fixed in the apparatus, after which a heated plate is brought to them. When the polyethylene begins to melt, the plate is removed and the pipes are connected to each other under slight pressure. After the seam has cooled, the clamps are removed and the pipes are removed.

Technological features of the method:

Used to connect elements of the same diameter. You cannot weld parts with a wall thickness of less than 5 mm. Welding can only be done at temperatures from +15° to +45° C.

Assembly on compression (crimp) fittings

An entire system is installed on one or two sides of the fitting (sometimes on three) to ensure the connection. The fitting itself consists of:

• housings;
• clamping nut;
• collets - a plastic ring with an oblique cut that provides a tight fit around the pipe;
• thrust ring;
• gaskets, which are responsible for tightness.

  
  What does a compression fitting for polyethylene pipes consist of?

How reliable is the connection?

Despite the apparent unreliability, the connection of polyethylene pipes with compression fittings is reliable. Properly made, it can withstand operating pressures of up to 10 atm and higher (if these are products from a normal manufacturer). Watch the video for proof.

This system is good because it is easy to install yourself. You probably already appreciated this from the video. Simply insert the pipe and tighten the thread.

Summer residents, in addition to the opportunity to do everything with their own lessons, like it because, if necessary, everything can be disassembled, hidden for the winter, and put back together again in the spring. This is in case the wiring is made for irrigation. The dismountable system is also good because you can always tighten the undercut fitting or replace it with a new one. The disadvantage is that the fittings are bulky and internal wiring in a house or apartment is rarely made from them - the appearance is not the most pleasant. But for the water supply section - from the well to the house - it is difficult to find better material.

Assembly order

The pipe is cut strictly at 90°. The cut should be smooth, without burrs. There should also be no dirt, oil or other contaminants present. Before assembly, the sections of the joined sections are chamfered. This is necessary so that the sharp edge of the polyethylene does not damage the rubber sealing ring.

During installation, the connection of polyethylene pipes on the compression fittings is tightened by hand

The spare parts are put on the prepared pipe in this order: the crimp nut is tightened, then the collet, then the thrust ring. We install the rubber gasket into the fitting body. Now we connect the body and the pipe with the parts put on it, applying force - you need to insert it all the way. We pull all the spare parts to the body and connect them using a crimp nut. Tighten the resulting connection of polyethylene pipes with force by hand. For reliability, you can tighten it with a special mounting key. It is not advisable to use other tools for tightening: the plastic may be damaged.

Setting up the hydraulic accumulator when connecting

Before using a water supply system with a hydraulic accumulator in a private house, you need to know what the pressure in the hydraulic accumulator should be for its optimal operation; take a portable pressure gauge to take readings. A typical water line with a standard pressure switch has response thresholds from 1.4 to 2.8 bar, the factory setting of the pressure in the hydraulic tank is 1.5 bar. To ensure that the hydraulic accumulator operates efficiently and is completely filled, the lower threshold for switching on the electric pump is selected at 0.2 bar for a given factory setting. more - a threshold of 1.7 bar is set on the relay.

If during operation or due to a long storage period it is determined that the pressure in the hydraulic tank is insufficient when measured with a pressure gauge, proceed as follows:

1. Disconnect the electric pump from the power supply.
2. Remove the protective cover and press the hydraulic tank valve in the form of a nipple head at the outlet of the device - if liquid comes from there, then the rubber membrane has been damaged and needs to be replaced. If air comes from the hydraulic tank, its pressure is measured using a car pressure gauge.
3. Drain the water from the main by opening the tap closest to the expansion tank.
4. Using a hand pump or compressor, pump air into the battery tank until the pressure gauge reads 1.5 bar. If, after automation, the water rises to a certain height (high-rise buildings), the total pressure and operating range of the system are increased based on the fact that 1 bar. equated to 10 meters of vertical water column.

When calculating the required pressure in the hydraulic tank for any range, select its value 10% less than the lower threshold of the relay operation. Selecting this value ensures that the built-in membrane will expand and contract within a small range and accordingly increase the service life of it and the entire expansion tank.

Fig.5 Setting up the hydraulic accumulator

Saddles and their scope

In addition to fittings, there is another interesting device that allows you to make branches from a ready-made pipeline. These saddles are specially designed couplings. This coupling has one or more threaded holes. A tap is usually installed in them, and a new branch of the water supply is connected to it.

Saddles for polyethylene water pipes

The sedeks are put on the pipe and secured with screws. After that, a hole is drilled in the pipe surface with a drill and a thick drill in the branch. When it is ready, a crane is installed and the branch is assembled further. This is how the system is improved with minimal effort and cost.

How to choose a hydraulic accumulator

When choosing a hydraulic accumulator, it is better to give preference to models with a rubber bulb - in membrane types, the liquid comes into contact with the metal body, which can cause corrosion.

The main working element of a balloon hydraulic tank is a pear-shaped membrane, the quality of which determines its service life, while the body material plays a less important role, since it does not come into contact with water. The usual material for making a pear is isobutated food rubber; when choosing a model for external installation, special attention should be paid to the flange to which the rubber membrane is attached. Preference should be given to models whose flange is made of thick stainless steel or galvanized steel - such a product will last 10-15 years without losing its tightness.

Another advantage of a balloon tank is the ease of replacing the rubber membrane. To do this, unscrew several hex bolts securing the flange and remove it along with the shell.

Rice. 9 Vertical hydraulic tanks in the water line

Flange connections and transition to metal

System elements that have a flange rather than a threaded connection can be installed in the water supply system. Usually these are taps or other shut-off or control valves. To connect to such elements there is a special fitting for HDPE. On one side there is a standard compression version, on the other there is a flange version. Installation is standard - using a crimp nut on one side, gaskets and bolts on the flange side.

Fitting for HDPE flange connection

When installing a water supply system from polyethylene pipes, questions may also arise about the connection between polyethylene and metal. For these cases, fittings are used, on one side of which there is a thread. It can be external or internal, depending on the type of device or transition being installed. Such fittings are either straight or in the form of a 90° angle.

Fittings for transition from HDPE to metal

The installation is standard - a thread (with careful winding) on ​​one side and a compression nut on the other.

average cost

When purchasing products, you should pay attention to the price tag. If the cost of pipes is below the market average, their quality is unlikely to be up to par.

After all, no enterprise will operate at a loss.

The service life of plastic products largely depends on the composition of the raw materials and is on average 50 years. When using waste ("recycled") - bottles, polyethylene boxes and even disposable syringes - even a properly installed water supply or sewer system will fail within a year and a half. Tap water passing through such pipes will have a strong chemical smell. As a rule, such products do not have any markings and are made of plastic that is not uniform in color.

Table 2 - Average price of HDPE pipes of different diameters

Installing a hydraulic accumulator

After purchasing a suitable model of electric pump for a well or well and connecting it to the pipeline, calculating the volume and purchasing the required hydraulic tank, you need to install it correctly. If the model has a large volume and is installed on vertical legs, you should use the following recommendations:

• It is better to install a volumetric storage tank at the highest point of the house (attic, second floor) - this will create maximum pressure in the water line.
• The floor in the room must be level, humidity must not exceed established standards in order to avoid corrosion of the galvanized flange and surface of the tank.
• It is better to connect the device using a flexible pressure hose in a stainless steel braid and one-inch diameter union nuts made of brass. Avoid supply hoses with aluminum braiding and mounting couplings made from cheap silumin, a brittle alloy of aluminum and silicon.

Rice. 10 Connection diagram of the hydraulic accumulator to the pump and water supply system