What is a bypass and why do I need it?

What is a bypass and why do I need it?

Bypass – a bypass pipe with a shutoff valve, which allows you to redirect the flow of fluid bypassing a particular plumbing fixture. This pipe node ensures the smooth operation of pipelines in times of repair of equipment, as well as provides an opportunity to control the flow of fluid. In heating, water and many other piping systems, bypass is an important assembly. In this article, let’s deal with the question of what a bypass is, how it works, where it is used and how to make it yourself.

Bypass in the heating system

What is a bypass: its structure and principle of operation

To make it easier to understand how the bypass looks from the outside, as well as to understand its device, consider a simple illustrative example, with which almost all residents of apartment buildings are familiar. Pull back the curtain on any window and look at the radiator, or rather the section of the wall between it and the riser. What do we see? Two horizontal pipes going to the radiator and the bridge between them – in fact this is the bypass, but for sure it is incomplete and there are no shutoff valves. A complete bypass must have at least three valves, without which it cannot work as intended.

1. The first tap must be installed directly on the jumper itself. If it is a new heating system, then on the pipe itself, if old, then at the bottom, at the intersection of the jumper with the return pipe. In the first case there is a regular ball valve, and in the second the so-called three-way valve, which also serves as a tee. But that’s not the point – in either case, such a valve can either completely block the flow of water through the jumper or reduce it to a certain size. At the very least, it gives the possibility of adjustment.
2. The other two valves are mounted on the horizontal lines to the heater already after the jumper – one mounted on the return pipe and the other on the supply pipe. In case of a leak in the heater at any time these cocks can be closed and thus prevent a flood.

Now imagine for a moment that the first tap (installed on the jumper) is missing – so it turns out that by closing the taps on the radiator, you stop the flow of water throughout the riser, thereby depriving the residents of the upper and lower apartments of heat. This is not good – for this reason, by opening the tap on the bypass and closing the taps on the radiator, you get the opportunity to repair the heater, without stopping the work of the whole heating standpipe. That’s the principle of the bypass. Not only that, such a bypass scheme also allows you to regulate the temperature of the heater. About this a little later, but for now let’s understand the scope of application of this node piping.

Why do we need a bypass: its application area

Almost any complex piping system has a bypass – its purpose you have already understood (it boils down to obtaining the ability to send the liquid past a particular device) and it remains only to deal with its main area of application in the home. Let’s get acquainted with this point in more detail.

• Bypass in the water supply system. In most cases, this device is used in two ways: first, when installing any pumping equipment, including those designed to increase the pressure in the system – if the central water supply is mounted pumping station, then bypass is necessary. Secondly, when installing metering devices (water meters). There is a subtlety – when installing a bypass meter in the apartment can cause problems with the utilities. Here the bypass can be seen as an attempt to steal water – it is tacitly forbidden. Assemble a bypass on the home meter, of course, you can, but in the process of sealing may be a problem – in most cases it is replaced by an ordinary insert, which is mounted instead of the meter at the time of inspection or replacement. Bypass is more convenient than a tube, but, alas, it is easier not to do it than to argue with the water companies. In water systems, the bypass has only one function – it is a bypass line and no more.

• Bypass in the heating system. There are also several options here: first, it is the example discussed above with the heating devices; second, any equipment that can be repaired or replaced without stopping the system as a whole. In general, equipment without which the system or part of it can continue its operation. Such devices include circulating pumps in heating systems with natural circulation of coolant, all kinds of metering and control units and even heating boilers in their serial connection. In heating, the bypass function as a bypass pipe is not the only – here it can also be used as a node to regulate the temperature of the coolant, as described in the example with the heating battery. Such a device is not mounted only on risers – some of its variety is used in individual heating systems. Only in this case, the bypass valve is not installed – the temperature of the heater is regulated by the cut-off and control valves of special design.

In principle, there are other options for using the bypass in water systems – there can be many, and here the main thing to understand the purpose of this node, its principle of operation and the device of the bypass. Well, it is not difficult to find a decent use for it.

Installing the bypass: the subtleties of installation with their own hands

By and large, the bypass jumper has a fairly simple design, and it can be assembled even with minimal experience in plumbing work. Once again, I repeat that the principle of operation of this device and its understanding is important here – knowing this, independently make a bypass for a circulation pump or something else is not so difficult. Let’s consider this process in detail.

1. For example, the heating line, on which the circulating pump is mounted. The first thing you should do to install the bypass is to remove it and slightly modify the line – in particular, you will need to increase the distance between the threaded ends, on which the pump was screwed. The best way to determine this distance is in the field – I mean, assemble the pump and the assembly around it properly.
2. To do this, immediately behind the pump, on one and the other side, screw on the ball valves – this can be done immediately overhauled. We have split connections on the pump, so it’s no problem to quickly disassemble the assembly and mount it on the pipeline.
3. After the cocks (also on both sides of the meter) are installed tees of exactly the same diameter as the pipeline itself. Here we should make a caveat – the type of tee depends on the pipeline itself. In most cases, are used tees made of the same material as the pipe – if polypropylene or metal-plastic, then first screwed into the cocks threaded terminals and then soldered or screwed to them tees.
4. The size is set and now try on the assembled unit in place, cut the pipeline at the marked marks and put the assembled unit. For convenience in the work it can be dismantled on the american – simply put, remove the pump, and then you have two parts of the pipeline, which will need to connect to the mains. Once this section of the bypass is assembled, the pump is installed in place (overhauled) – only after that can you focus on the bypass pipe itself. Bypass for the circulation pump
5. Here also all is not complicated – to begin with from the tees up the pipeline so that it does not interfere with the pump. Further turns reduce the two nipples coming from the two tees, with each other – at least give them the right direction to each other. And then comes the jumper and faucet, for which installation, again, you need a detachable connection and a pair of threaded ends.

As for the circulation pump, exactly the same principle is mounted and the bypass for other plumbing fixtures. Bypass piping can be positioned both vertically and horizontally – from this point its functionality and quality of work does not change.

Now you know what bypass is and how it works, now it will not be difficult to make this node yourself. If you understand the principle of its operation, then to collect the bypass with your own hands will not be difficult.

What is a bypass and why do we need to install it in the heating system?

Bypass is called a jumper, installed on the heat line parallel to the main line. This uncomplicated detail in the form of a piece of pipe helps to solve a variety of problems, and therefore is considered an important element of any scheme. For what you need a bypass in the heating system of the apartment and private house, is described in detail in our material.

Bypass installation options

When we have determined what a bypass line is, let’s consider the question of why it is needed and where it is installed. Depending on the problem to be solved, the element takes the form of a bypass pipeline or a straight section that connects the supply line with the return line.

Synopsis. The English word bypass literally means “bypass”, “bypass”.

There are several options for installing bypasses in heating systems:

1. On radiators of closed and open single-pipe systems.
2. Parallel to the circulation pump, operating in gravity (otherwise – gravity) heating system.
3. The jumper between the supply and return, forming a small circulation circuit for heating a solid fuel boiler.
4. In various mixing assemblies.

In apartment buildings, where towel heaters are connected to the general hot water riser, the bypass line is also used, acting similarly to the radiator line (item 1 of the list). For what it is necessary there, we will tell further.

Pipes of towel dryers have a large diameter and flow capacity, the jumper is needed only for easy removal of the coil

The first two options are familiar to owners of private homes and apartments. Unfortunately, some owners, who consider themselves big specialists, “improve” bypasses or put jumpers where they interfere with the normal operation of the heating system. Accidental and intentional mistakes we will also look at.

Radiator jumpers of the single-pipe scheme

In most multi-storey buildings of Soviet construction, heating is organized with the help of one-pipe vertical risers, passing through all apartments. The principle of the scheme is to distribute the coolant to the radiators on floors 5-16 at the expense of high flow rate and increased pressure.

For reference. The old cast-iron batteries and steel ribbed convectors had large diameters of internal channels, whose connection to the riser was designed without any bypasses. We are talking about the new generation of devices with high heat output and less flow capacity.

Options for single-pipe heating schemes in multi-storey apartment buildings

Note that the radiators are connected to a single mains by both pipes, between which the bypass is cut in. Pipe bridge is intentionally shifted away from the riser axis, otherwise the water will not flow into the battery, and it will go straight down or up, depending on the direction of the flow. Ideally the circuit functions as follows:

1. Reaching the fork of the first heater, the flow of hot coolant is divided approximately in half – one part flows into the radiator, the second rushes into the bypass.
2. Having cooled down by 1-2 ° C, the first flow is mixed with the bypass flow and returns to the main line. The temperature of the resulting mixture becomes 0.5-1 ° C below the initial one.
3. The process is repeated similarly at the next heaters. To ensure enough heat for all consumers, district heating pumps pump a large amount of coolant through the lines, reducing the temperature drop between the first and the last battery.

Note. Such schemes are found in two-storey private houses. And although the vertical riser supplies only a couple of radiators, it is desirable to put a bypass on the top heater, since the performance of the domestic circulation pump is much lower than the industrial “counterpart”.

If you remove the direct bypass line, the entire volume of water will flow through the heater and cool by 1-3 ° C. Because of the large temperature difference, each subsequent apartment will receive much less heat. The room with the last radiator will become as cold as a dog house.

That’s why in a vertical one-pipe circuit, an uncomplicated piece of pipe on the radiator plays an important role. In two-pipe layouts, the hot and cooled coolant goes in different lines, so the bypass is not required.

Here the role of the bypass line plays the distributing pipeline itself

In country houses the small circulation pump capacity is compensated by increasing the diameter and capacity of the pipelines. This is done in the horizontal one-pipe system shown in the photo. Bypass acts the main line, where about 2/3 of the coolant flows and the third part goes to the batteries.

Circulation pump bypass line

In most modern water heating systems the pump unit is inserted directly into the supply or return pipe, which is described in detail in another publication. It is not necessary to install a bypass in this case:

• In case of power failure and the pump is stopped, the coolant will still not be able to circulate independently because of the small diameters of the pipes;
• To remove the pumping unit for repair or replacement, it is sufficient to turn off two taps and unscrew two flare nuts, provided that the unit is correctly assembled;
• Since water is unable to move through the lines without a forced inducement, a bypass jumper will not help keep the system running while the pump is being serviced.

The only case where you need to make a bypass branch for a circulating pump is in a gravity-flow heating system. Firstly, the unit with connections DN 25-32 cannot be cut into the pipe Ø50 mm used in the gravity heat network of private residences. Such a narrowing of the diameter will stop any gravity.

Secondly, the heat supply must work on a universal scheme. The main mode – forced from the pump, in case of power outage – the transition to the natural gravity flow of the coolant by convection. To organize this heating operation, the pump unit must be installed on the bypass.

Practiced two ways to install this node:

1. Ball valve is cut into the direct line, and the heating pump is taken to the bypass line with a mesh filter – strainer and shut-off valves.
2. In the gap of the line is placed ready-made bypass unit with pumping unit and check valve.

In the first option, the transition to gravity mode is done manually. When the power supply is interrupted, someone from the household must go to the boiler room and open a large faucet on the direct section. Otherwise, without water circulation, the boiler will stop heating, the building will freeze and you will freeze.

In the second case, after the power outage will open the automatic check valve, which is in the closed position while the pump is running. But not everything is as rosy as it seems at first glance:

1. The design of some ball valve models does not provide for disassembly. If the element gets dirty, rusted and jammed, you will have to throw out the entire assembly (except the pumping unit and filter).
2. The U-shaped hinge, shown in the photo, serves as an additional air collector. They are equipped with a manual air release valve that must be used periodically. In addition, the strainer is upright, it is not correct.

Hence the conclusion: do not install ready-made automatic bypasses with valve and pump. Better with your own hands build a unit with a shutoff valve. Considerable cooling of the house will begin in 30-40 minutes after turning off, which is quite enough to open the main line.

A rubber ball freely rolls around inside the chamber and closes the passage under the pressure of water

Option two: install bypass node of separate parts, using a brass check valve with a free rubber ball, not pressed by a spring. See photo and video for how such an element looks:

Mixing Assemblies

These elements of heating systems consist of a three-way thermostatic valve and a bypass that connects the return pipe to the supply. The bottom line is this: the bypass line helps to collect the coolant from the two lines in the valve chamber, and at the output to get the water of the desired temperature.

The principle of rushing with the use of the jumper and 3-way valve is used in different parts of the heating network:

• small circulation circuit of the wood boiler;
• piping buffer tank or a heat accumulator; on the heating circuits of water underfloor heating.

For reference. Scope of application of sub-balance nodes is quite wide. Regulated reduction of water temperature by mixing is used in air heating units (calorifiers) and other climatic installations.

Scheme with boiler circuit protecting the heat generator against condensate

The three-way valve bypass shown in the diagram, which forms a small circulation circuit, protects the solid fuel boiler from condensation during the heating phase. The algorithm of the process is as follows:

1. When the wood is ignited and the pump is turned on, the valve remains closed on the heating system side. Exiting the heat generator jacket, the water turns into the bypass line and returns to the boiler.
2. As it heats up, the temperature of the looped coolant rises. When it reaches the threshold of 50-60 ° C (depending on setting), triggered thermocouple valve, gradually opening the flow from the radiators.
3. The hotter the water in the boiler circuit, the wider the opening of the passage to the cold water from the system. Mixing occurs in the valve chamber, but the flow temperature at the outlet does not drop below the set threshold until the fuel is burned.

In the wiring of TT boilers with a cast iron heat exchanger, the bypass mixing unit plays the role of a safety element. The situation: the heating is working at full throttle, the wood is burning, and suddenly the light goes out. If there is no backup in the form of UPS or electric generator, and the power supply is resumed after 30 minutes, the water in the batteries has time to cool down.

A relief line with a relief valve is not always found on factory manifolds, but it prolongs the life of the pump

Note that within half an hour, the boiler does not have time to cool – the furnace is full of heat and wood. As soon as the pump starts, the cold heat carrier is pumped into the boiler jacket and the cast iron section breaks due to the temperature shock. This is why a bypass is essential in this case.

The same principle of mixing by means of a jumper and valve is used in the distribution header of the underfloor heating. When the temperature in the heating circuits reached normal (35-45 ° C) 3-way valve closes the supply side of the boiler, and the pump drives the coolant through the bypass on the inner ring.

Note. In case the automatically controlled circuits close automatically, the comb is equipped with an unloading bypass. It allows the pump to “twist” the water through the two manifolds and not mix it inside itself, which reduces the life of the unit.

The use of a jumper in the buffer tank piping is identical to the previous variants and is shown in the diagram.

When bundling a buffer cylinder with a solid fuel boiler 2 bypasses are applied

Installation mistakes

Some domestic, or rather, apartment craftsmen when replacing the old cast iron radiators on the new aluminum ones deliberately make two stupid mistakes:

• They mount a ball valve on a straight bypass pipe in order to direct all the coolant into their own radiator;
• Having heard the advice of “smart” people, assemble a mixing unit with a three-way valve, in order to regulate the heat output of the heater.

We should say at once that such installation in a private house is not considered a mistake: there you live alone and you are responsible for the heating. In a “multi-storey” such actions are detrimental to the neighbors, because you unbalance the system and take away more heat. So adjacent apartments get less. As this happens, see the video:

Instead of listing further mistakes, we suggest reading the recommendations on how to properly install a bypass on your own:

1. The jumper on the radiator of an apartment building is a pipe without any shut-off valves and valves. The maximum that is allowed is to reduce the diameter by 1 size (riser DN 20 – connector DN 15);
2. If you want to regulate the heat output of your radiators, please use manual or automatic thermostats. There are special full flow models for centralized networks.

Point #3 requires clarification. With 3-way cocks one branch is always open – the one where the resulting mixture comes out. The same side is where the pump is placed. If the unit is placed on either inlet pipe, then further events will go one of two scenarios: stop circulation or coolant will go through the bypass, closed in the boiler circuit and will not get into the radiators.

In conclusion, briefly about DHW.

Since all of the main conclusions we have made during the description, let’s complete the information picture with the installation of a bypass on the towel radiator. This is the only case where a piece of pipe is placed only for the convenience of service or replacement of the heater. The element has almost no effect on the heat output due to the flow rate and pressure in the water supply. The principle of operation is similar to the bypass on the radiator, only here we distribute hot water.

2 Replies to “What is a bypass and why install it in the heating system”

Why in the picture at the beginning of the article there is an example of a towel radiator, shorted bypass on the riser axis? Water, with this implementation, will never go into the towel radiator itself.

Why would you think that? In apartment buildings with riser heating system, the batteries are connected in a similar way, but the coolant flows into them. Here the diameter of the pipe of the towel radiator is not less than the riser, so about 1/3 of the flow will go there.