Why is the hot water riser rounded: the truth about water hammer and plastic pipes

Residents of new buildings, taking apartments, are surprised to find "bagels" - hinges on plastic risers of hot water under the ceiling. Some simply hide behind a drywall box, others require explanation. Why is the pipe rounded? So the developer is trying to insure residents from pipe breaks. Bagels cannot be removed, but can be replaced with a more aesthetic option.

What is hydroblow and why are they afraid

Water hammer is a sharp and very strong pressure surge in pipes. Able to break the connections and the pipes themselves, to break the valves and arrange a flood. Small hydroblows act gradually, repeatedly squeezing gaskets, slowly but surely deforming and destroying water and heating pipes with microtraumas.

Externally weak hydroblows are recognized as vibration through the pipe, hum, pops, clicks, or other extraneous sounds, which especially irritate residents whose neighbors get up earlier or lie down later.

How does a water hammer occur?

This is a phenomenon when in one section of the pipe the water has already stopped, and the back masses continue to press on it from behind:

• with a sharp overlap of the watercourse;
• when the pump starts abruptly.

In the heating system, water hammer provokes air shock.

Risk factors

What determines the strength of a water hammer:

1. From how sharply there was a constipation or the launch of a watercourse.
2. The volume of water in the pipes and, accordingly, their size.
3. The velocity of the fluid and its pressure.
4. Pipe material.

Formula
Shock wave frequency = 2 pipe lengths / shock propagation velocity in a particular material.

The wave velocity in plastic is 300-500 m / s. For comparison, in steel - 900–1300, and in cast iron 1000–1200 m / s. From this it follows that the impact in the plastic will be stronger, but the cast-iron liners actually extinguish the water hammer.

What happens to the pipe?

Nothing good: it is bursting in breadth, in length it is shortened. Under pressure, the pipe may well burst. More often, mixers and connecting knees suffer: seams diverge, gaskets are displaced or torn, and a leak begins.

From the memories of a locksmith
I’m the third dozen in the plumbing world, but I saw a real water hammer only once (1994) in the elevator unit <...>. Water hammer is when the arrow <...> flies in one second from 8 bar to 60.

The worst thing is the water hammer in the elevator unit, at the pumping station and other communal utilities. To a much lesser extent, pipes in apartments are subject to vibrations, however, it is worthwhile to understand that the cross section of modern risers is narrower (pressure, respectively, higher) than that of Soviet steel pipes, and the material is more mobile and less hardy. First of all, the hot risers are a danger - under heating, the materials expand more.

Protective measures

To avoid breaks, in the basements on all risers, and in apartments on hot put special devices that prevent vibrations from destroying pipes.

Blocking devices, their pros and cons

Shock absorbing eyeliner- these are pipes curved by a wave, loop, or p-shaped from ordinary or special material, for example, reinforced plastic or rubber 20–40 cm long, the easiest and cheapest option.

The shock-absorbing eyeliners are cheap, and at the same time they can withstand the water hammer that in practice you have to experience with plastic communications in the apartment, they do not require special maintenance or periodic replacement of parts.

Bellows shock absorber - corrugated pipe made of ductile metal, capable of compensating for linear expansion, elongation, or both phenomena at once, simpler - single-layer, more advanced - enclosed in a casing, giving additional cushioning.

Bellows shock absorbers in the casing are also unpretentious, while more aesthetic than the previous version.

Important
It is shock absorbers-eyeliners (especially looped bends) and bellows designed to compensate for the extension of the riser, this is their main function, and the repayment of water hammer is more likely secondary. For plastic pipes, especially not very high-quality material, they are just as important as expansion joints.

Shunts - metal pipes, which are inserted into the pipe together through the main valve in the direction of the water flow and bleed off the excess volume of water behind the valve, are ineffective in old pipes clogged with rust and are more suitable for plastic communications.

Shunts are easy to install, do not require opening the pipe, but lose efficiency in proportion to the clogging of the pipe, and in the household circuit this figure can be quite high.

Diaphragm expansion joints (the most common - Valtec) - devices resembling a ball or tank and representing a cavity with an elastic membrane, which is pressed in with a sharp increase in water pressure, and then gradually straightens, returning water to the current, but already without impact force.

Membrane expansion joints hold up to 30 bar, and this is a pretty good indicator. Their weak spot is an elastic membrane, which, over time, deforms, breaks, or hardens due to salts and additives in the water.

Piston or spring (the most popular today is Far) - devices similar to the cap and working on the same principle as the membrane ones, with the difference that the spring replaces the membrane: with an increase in volume, water pushes a plastic disk into the cavity and thereby compresses the spring, then the mechanism returns to its original position, returning water in the circuit.

Piston compensators withstand surges up to 50 bar and ways to protect against real, not weak hydroblow. In addition, they are more resistant to wear than membrane ones, however, they are not insured against leaks at the points of sealing or connection to the pipe, therefore, they need to be checked and replaced periodically.

Control valves - systems that are usually included in comprehensive protection against water hammer and are installed on the controllers of external and common house circuits.

Bypass system - a jumper pipe, which allows you to redirect the current of the water coolant in order to avoid water hammer and breaks in the batteries.

The opinion of experts
Old-school locksmiths consider installing indoor quenchers a waste of effort and money. According to them, a strong water hammer threatens the water treatment canals in the basement, and nothing more. Other masters note that in the past, all taps were closed slowly with a valve, but now they are mainly lever (ball), and household appliances (washing machines, dishwashers) and toilet bowl tanks also shut off the water quite sharply. Therefore, ideally, the absorber should be in front of each such consumer.

Comprehensive prevention measures:

• smooth closing of taps and valves;
• pump power regulator, which slows it down at first revolutions and does not allow to provoke a shock wave.

Actually, “coils” always belonged to hydroshock dampers - a wave-like bend of the riser of hot water, allotted to the bathroom from the toilet. Mistresses used it as a heated towel rail. In fact, the pipe slowed down the flow of water and took off vibrations, reducing the risk of water hammer. However, at the junction of the apartments a leak appeared quite often, especially over the years.

Metal ages faster than high-quality plastic, the installation of ball valves significantly increased the load on the structure, and the difference in materials when plastic was placed on top and metal was left on the bottom or vice versa makes itself felt. Because of this, the "coils" do not work.

How to install

purity.bigbadmole.com/en/ magazine strongly recommends that you entrust any work with pipes, especially risers, to specialists. They will carry out the installation efficiently and quickly.

General rules:

• the shock absorber is installed at a certain length of the pipe (for example, under the ceiling of each odd floor);
• the best option is when the compensator is in front of the valve, tap, valve of household appliances, cranes and other consumers;
• it is also permissible to have a compensator after collector taps (that is, after check valves) in the apartment (see below a photo from S. Savitsky's blog “Ideas for repair”);
• if the gearbox is placed, the compensator follows after it;
• the compensator is necessarily located directly on the pipe or on the corner transition, and not on its dead end tap (see photo below);
• the shunt is installed strictly in the direction of the flow of water;
• a regulator or valve is installed at the controller and connected to it.

Well, sorted out the pipes and risers. And what if the house has an electric storage water heater or a gas "column"? The former are usually equipped with their own safety valves. In the case of a “column” or any other instantaneous water heater, the compensator must be placed after the unit - this will extend the life of its hoses and seals.