Press fittings and presses for metal-plastic pipes: rules for a reliable connection

Recommendation points

• The essence, advantages and disadvantages of technology
• Product range and selection rules
• Crimping tool
• Basic installation rules

Despite the shortcomings of metal-plastic pipes, they remain a fairly popular material for the installation of plumbing systems, largely due to their low cost. The vulnerabilities of such plumbing can be partially eliminated by using press fittings, which we will discuss in detail..

The essence, advantages and disadvantages of technology

Traditionally, the connection of metal-plastic pipes is performed using threaded compression fittings. The disadvantages of such fittings are well known, almost all of them are the result of the poor quality of Chinese products. Poor stamping, low grade alloys, and lack of quality control at the end of the production cycle have resulted in the vast majority of threaded fittings being unstable against corrosion and water hammer. Attempts to find high-quality fittings do not lead to success: this connection technology is already obsolete and is not recommended by leading plumbing manufacturers.

Alternatively press fittings can be offered. In essence, these connections can be considered as a kind of continuation of the line of fittings for pipes made of XLPE. The principle of crimping is similar, however, the material of the press fittings is metal, not plastic. The nickel-plated crimp sleeve, due to the lack of elasticity inherent in plastic, does not slide on the pipe, but is crimped around it using a special tool.

Sliding metal press fittings for metal-plastic pipes also exist, but their scope is a composite pipe made of cross-linked polyethylene, while in the domestic practice of plumbing installation, pipes based on polypropylene and polyvinyl chloride are mainly used. It will not work to connect such pipes with slip fittings: they are designed for a different nominal bore and wall thickness.

The main feature of such connections is that they are one-piece, which means that by the beginning of the installation the configuration of the rough plumbing must be finally approved. Of the advantages of press fittings, the following are most pronounced:

• They do not require tightening during operation.
• Hydrodynamic strength of joints exceeds that of pipes.
• Corrosion resistance of compression fittings is higher than that of threaded ones due to a special anodized coating.
• The highest quality fittings have an alloyed coating for increased resistance to aggressive environments where cement is present, as well as an internal coating that excludes the reaction of brass with water.
• When pressing, there is no need to control the tightening force, it is impossible to squeeze the press fitting.

Product range and selection rules

In the Russian market, the vast majority of compression fittings for multilayer pipes are represented by Valtec. From the point of view of quality, this reinforcement cannot be called a reference, but its assortment is the most complete, therefore it is on this example that it is easier to get acquainted with all the variety of such connections..

If we classify press fittings by purpose, we can distinguish three main groups: connecting and branching, transitional and special. The first category is the most extensive, it includes all fittings intended exclusively for use in that part of the rough plumbing system where only reinforced plastic pipes appear. There are couplings, and tees with crosses, as well as angles at 45 ° and 90 °. Some of the connections have a collapsible threaded connection, but this is rather an exception to the general rule. Connecting fittings are available in several standard sizes for pipes from 16 to 32 mm.

Transitional fittings are designed to connect the wiring with metal-plastic pipes to the inlet lines and all sorts of plumbing equipment. The basis of this group is made up of corners and tees, in which one or two branches are made in the form of a threaded crimp connection, a threaded fitting, a rigid or union nut. Also, the list of transitional connections includes the so-called water sockets – corner fittings with ears for fixing to the wall, designed for installing mixers.

Special fittings are the least numerous category of fittings for reinforced plastic pipes. This mainly includes tees and elbows with chrome-plated tubular outlets for connecting radiators through a Eurocone, ball valves with fittings for crimp connections, lugs for connecting to manifolds, as well as bypass connections for sections with intersecting pipes.

Of course, Valtec is not the only manufacturer of press fittings for multilayer pipes. In addition to these Italian (in fact, relatively high-quality Chinese) products, you can also find original French Comap, Russian Minkor and Altstream fittings, original Italian Prandelli and ICMA. There are really a lot of products on the market, there are also counterfeits, so it would be incorrect to talk about an unambiguous superiority in the quality of any of the brands. You always need to pay attention to the quality of stamping, metal thickness, completeness and, most importantly, the availability of a product certificate. It is also important enough that fittings, pipe and crimping tool are purchased from the same supplier to ensure full compatibility..

Crimping tool

One of the main disadvantages of one-piece plumbing connections is the need to use a special crimping tool. There are several approaches to the acquisition of such equipment..

When installing plumbing fixtures with your own hands in your own apartment, the most correct option is to take a set of tools for temporary use at the manufacturer’s official dealer center. There is one marketing trick here: when contacting a consultant, you should ask to draw up a complete set for installation: pipes, fittings, tools, means for sealing threaded connections, having previously provided a pipe layout diagram. In this case, even if there is a hitch during work due to the lack of materials for installation, you will not have to overpay for the lease extension.

Masters can also recommend two options for the acquisition tool. For those who are decorating bathrooms, simultaneously installing the simplest systems, manual crimping pliers and means for preparing connections are suitable. But, as already mentioned, it is important to immediately determine the brand of plumbing that will be used. If the foreman is aiming to work in a professional manner on subcontracting, the electric tool will be more preferable. Despite the higher cost, the speed of work increases significantly, which will allow you to hand over the object in the shortest possible time and move on to the next one. In addition, the power tool is more versatile: to work with fittings of a certain brand, you just need to purchase a set of crimping jaws.

Basic installation rules

Despite the high manufacturability, the connections on the press fittings are made quite easily even by people who have no experience. The basic set of tools includes:

1. Shears for metal-plastic pipes, preferably with a forward feed of a knife.
2. Rimmer – special scraper for internal chamfering.
3. Pliers with jaws of the corresponding diameter.
4. Expander for pre-flaring.

The crimping mechanism itself is well understood when considering the longitudinal cut of the fitting. The fitting has a pair of O-rings, and the crimp is performed with three belts: exactly in the middle between these rings and on either side of them. This is the key to making high-quality connections: the jaws of the pliers must exactly match the shape of the fitting used, as well as the pipe diameter and wall thickness.

The installation process is extremely simple, for a start it is necessary to cut all the pipe segments that make up the plumbing network according to the appropriate dimensions. It is very important to ensure that the ends of the pipes are cut strictly perpendicularly, for which special scissors are needed. If flakes have formed on the inner coating of the pipes, they must be removed with a rimmer, and, if necessary, flared with an expander. A ferrule must be installed on the fitting in advance and made sure that it fits snugly into the retainer ring lock. After that, a pipe is inserted into the fitting, its edge should appear in the viewing windows. The final stage is crimping the sleeve using electric or manual pliers, the side of the jaws should be located close to the sleeve retainer.