- About threaded plumbing connections
- What are the types of sealants
- Correct winding of FUM and tow
- Packing for hardening and anaerobic sealants
There are several gradations of the reliability of threaded connections in plumbing. Depending on the sealing media used, the estimated life of threaded fittings can vary greatly, so you need to know how Teflon tape, anaerobic paste, flax, and other thread sealants work. will tell you about it in detail.
About threaded plumbing connections
Sealing of detachable joints is ensured by gaskets, which, when tightening the union nut, are tightly clamped between the ends of the pipes or in special grooves of the fittings. In one-piece joints, everything works according to a different principle, to understand which you need to know the main differences between pipe threads and ordinary metric threads..
The first difference is the measurement system: the pipe thread is inch, that is, its two main indicators are the outer diameter of the pipe and the number of threads per inch of length. This does not affect the tightness of the threaded connection, but another parameter matters – the thread profile. If metric threads are sharp, inch threads are flat. Moreover, if you look at the section of the threaded connection, you can see that the platforms at the vertices are not located closely.
This profile allows you to leave a little space in the threaded connection, which is filled with sealant. When the thread is twisted, friction forces arise only between one pair of faces. In this case, the turns of the external thread are slightly pushed out of the internal thread, thus the gap between the flanges of the vertices increases. To compensate for this, the sealant must be capable of expanding without shrinking throughout its life..
What are the types of sealants
Three types of sealing means are used in plumbing connections: winding, plastic hardening and anaerobic. It is impossible to unequivocally single out the best type of sealant, each is represented by a fairly wide range of materials of various qualities. It’s just that certain products are optimal for their purposes..
The most popular type of winding is FUM tape. There is tap water (0.07-0.2 mm thick) and gas (0.1-0.25 mm). The tape is made of Teflon (fluoroplastic), this material is very plastic, under the pressure arising from tightening the thread, the layers of the winding are soldered together. In addition, FUM provides a smooth surface, facilitating easier thread turning..
The second type of winding is linen tow. It is applied with wetting with oil paint or special sealant. The peculiarity of tow is that linen fibers swell on contact with water, sealing the threaded joint. Lack of organic tow, which causes the likelihood of rotting and loss of tightness.
Hardening sealants are gels or pastes with complex chemical formulas. The curing process can be initiated by heat generated by friction between the threads or by forced temperature rise. There are also chemical curing agents that catalyze contact with metal. Sealants have two advantages: positive shrinkage and fast connection times. Some of them are recommended to be used in combination with flax fiber.
Anaerobic seals are a separate category of hardening sealants. Their advantage is that no contact with oxygen is required for polymerization, while the leaked glue remains for a long time in a liquid state and can be used to seal other joints. Anaerobic pastes are of two types: some are designed for normal conditions, others are able to withstand significant mechanical stress and high temperatures.
Correct winding of FUM and tow
Winding is always done on the male thread starting from the back. Ensure that all threads are clean before making the connection. To do this, carefully wipe them off with a metal brush and rinse with a solvent, for example, technical acetone or white spirit. After degreasing, the threads must be wiped dry with a clean cloth..
As it was said, the fluoroplastic has a low coefficient of friction, but this property can lead to the twisting of the winding on the turns of the external thread, which is unacceptable. Nearly all modern fitting systems have external thread notches to prevent slipping of the tape. If they are not there, you will need to scratch the tops of the threads with a file in the axial direction..
Tape is wound from 4-6 layers for 1/2 ” threads to 12-14 layers for 1 + 1/4 ” threads. Winding must be carried out strictly in the direction of rotation of the threaded sleeve, that is, clockwise when looking at the open end of the fitting. If the reinforcement is being packaged, for which the spatial position is important, you must first calculate the number of turns per dry in order to stop at the last incomplete turn. FUM tape does not tolerate reverse rotation of the connection, even a loosening of the tightening can lead to a loss of tightness.
One of the varieties of Teflon winding is plumbing thread. It is made of the same material, but somewhat easier to use. The thread should also be wound from the root of the thread to the edge, but at the same time the last layer of winding must necessarily be carried out strictly along the turns in the opposite direction so that lead grooves are formed.
The principles of working with tow are not very different. It is necessary to select a thin strand from the shock and, when winding, lay it exactly along the turns until the fiber covers the tops of the thread. To reduce twisting friction and seal the joint, the layers of winding are interspersed with hardening sealant such as Unipak or thick paint. One of the features of the seal on the tow is that it is allowed to turn the thread up to 45 ° in the opposite direction.
Hemp packing is considered the most reliable and durable type of connection, but only if the correct lubricant is used. The solvent in the paint and the additives in the sealant have an antiseptic effect, preventing the development of decay processes. Dismantling such connections is more difficult than using FUM tape: it will be possible to untwist the thread only after heating and alternating mechanical action.
Packing for hardening and anaerobic sealants
As with winding, you will need to thoroughly clean and degrease both sides of the threads. In addition, it is recommended to work with disposable gloves, as most sealants are quite sticky and difficult to wipe off the skin..
Using sealing pastes is extremely simple, the only problem is that there are many varieties of such products. They should be selected by thread diameter, type of fluid and its temperature, set fixing time. All conditions under which it is allowed to use a certain sealant are indicated in the instructions.
For example, plain white or gray paste is considered the most versatile option. These sealants are suitable for joining pipes up to 2 ” in diameter, but threads larger than 3/4 ” may require additional linen fiber rewinding. Carefully study the instructions: the drying time for ordinary sealants can reach a day, before that, you cannot supply liquid to the system.
Anaerobic sealants are usually blue, green, or red in color. There is no single dependence of properties on color, but in most cases there is a difference between cold and warm shades of the sealant:
- Blue and green gels are standard anaerobic sealants. Their main property is the ability not to harden in air, polymerization occurs only in an airless space upon contact with metal.
- Red and orange anaerobic sealants are considered to be quick fixes for high strength joints. They harden in just a few minutes, which allows them to be used to quickly repair leaks and to start up the system almost immediately after packaging. However, this may require preheating the threads..