Safety valve for a water heater: why is it needed, how to install

Not only the life of the equipment, but also the safety of residents depends on the correct piping of an electric storage-type water heater (boiler). That’s how serious things are. And its correct piping is a safety valve for the water heater on the cold water supply. 

What is it needed for

Installing a safety valve prevents the pressure inside the device from rising above the norm. What causes pressure to rise? As you know, when heated, water expands, increasing in volume. Since the boiler is a sealed device, there is nowhere for the excess to go – the taps are closed, there is usually a check valve on the supply. Therefore, heating water leads to an increase in pressure. It may well happen that it exceeds the tensile strength of the device. Then the tank explodes. To prevent this from happening, put a safety valve for the water heater.

This is how the installed valve for relieving pressure in the water heater looks like

Maybe you don’t need to install a safety valve, but just remove the check valve? With a sufficiently high and stable pressure in the water supply, such a system will work for some time. But the decision is fundamentally wrong, and here’s why: the pressure in the water supply is rarely stable. Often there are situations when water barely runs out of the tap. Then the hot water from the boiler is forced out by pressure into the plumbing system. At the same time, the heating elements will be exposed. For some time they will warm the air, and then they will burn out.

But burned out heating elements are not the worst thing. It is much worse if they become hot, and at this time the pressure in the water supply system will rise sharply. The water that has fallen on the hot heaters evaporates, there is a sharp increase in pressure – by a jerk – which leads to a guaranteed rupture of the boiler flask. At the same time, a decent volume of scalding water and steam escapes into the room under high pressure. What it can threaten is understandable.

How does work

It would be more correct to call a safety valve for a water heater a valve system, since there are two of them in the device.

They are located in a brass or nickel-plated case, which looks like an inverted letter “T” (see photo). At the bottom of the housing there is a check valve that prevents the outflow of water from the water heater when the pressure in the system decreases. In the perpendicular branch there is another valve, which, when the pressure is exceeded, allows some of the water to be released through the fitting.

Boiler safety valve device

The mechanism of operation is as follows:

  • As long as the pressure in the boiler is less than that in the water supply (when filling or when the tap is open), the poppet plate of the non-return valve is pressed out by the flow of water. As soon as the pressure equalizes, the spring presses the plate against the protrusions of the body, blocking the flow of water.
  • When the heating is on, there is a gradual increase in the temperature of the water, and with it the pressure also increases. Until it exceeds the limit, nothing happens.
  • When the threshold level is reached, the pressure compresses the safety valve spring, and the outlet to the fitting opens. Some of the water from the boiler is discharged through the nozzle. When the pressure drops to normal, the spring locks the passage, the water stops flowing.

According to the principle of operation, it is clear that water from the fitting will constantly dig in. This happens when the water is heated, when the pressure in the water supply decreases. If you periodically see water on the fitting, then everything is working fine. But the draining liquid must be diverted. To do this, put a tube of suitable diameter on the pipe, be sure to fix it with a clamp. The normal working pressure of the boiler is from 6 bar to 10 bar. Without mechanical fastening, the tube will be torn off in no time, so we select a high-quality clamp, tighten it well. Take the tube to the nearest sewer drain.

One more thing: the tube on the fitting needs a transparent and preferably reinforced (the so-called “herringbone”). Why reinforced is understandable – due to pressure, and transparent – to be able to control the performance of the device.

Types and varieties

If we are talking about conventional safety valves for a water heater, then they look almost the same, only the nuances differ. But it is these small details that are responsible for the convenience and safety of operation.

Safety valve for the boiler with the possibility of forced pressure relief

In the photo above, there are two safety valves with release levers. They are needed for periodic performance checks. The lever flag is lifted up. He pulls the spring behind him, freeing the let to dump water. This check should be done about once a month. You can also empty the boiler tank – raise the flag and wait until everything drains.

Design features

The difference in the presented models is that the model in the photo on the left has a lever fixed with a screw. This eliminates the possibility of accidental opening and complete discharge of water.

Two other differences stand out. This is an arrow on the body, indicating the direction of water movement, and an inscription showing what pressure the device is designed for. Seemed like minor details. But if you can figure out the direction of water movement (look in which direction the poppet valve is deployed), then it’s more difficult with the face value. How to distinguish, for example, at 6 bar or at 10 bar? Only checks. And how will their sellers be distinguished? No way. By boxes. What if they put it in the wrong box? In general, it is better not to take a valve without marking on the body. These are usually the cheapest of the Chinese designs, but the price difference isn’t big enough to make it worth the risk.

Safety valves – serviced and not

Also pay attention to the shape of the water outlet. The model on the left has a long, non-linear fitting. A hose fits on it quite easily and the length is enough to install a clamp. The shape of the fitting on the model on the right is different – with an extension towards the end, but more importantly, the fitting is short. You can still pull a hose on it, but the clamp is in question. Unless you crimp it with wire …

In the next photo, safety valves without a forced pressure relief flag. The one on the left has a screw cap at the top. This is a serviced model. If necessary, you can unscrew the lid, remove blockage, scale and other contaminants.

The model on the right is the worst of the options. No markings, forced reset or maintenance. These are usually the cheapest available, but this is their only merit.

For large boilers

All the above models are suitable for water heaters up to 50-60 liters. There are other models for larger boilers, many of which have additional devices built in. Usually this is a ball valve and / or a pressure gauge – to control pressure.

For boilers up to 200 liters

The fitting for water discharge here is with a regular thread, so there will be no problems with the reliability of fastening. Such devices already have a rather high price, but their quality and reliability are much higher.

With pressure gauge and original

Not everyone in appearance likes these devices. For those who attach great importance to aesthetics, very attractive devices are produced. Their price, however, is comparable to the price of an expensive water heater, but it is beautiful.

Can other valves be installed?

Sometimes, instead of a special safety valve for the boiler, they put a subversive one, which is intended for emergency discharge of water for heating. Although their functions are similar, the basic mode of operation is fundamentally different. Demolition should only work in emergency situations. It is designed for salvo discharge of a large volume of liquid. It is not suitable for continuous bleeding of small portions of water. Accordingly, it will not work correctly.

Another case is the installation of only a check valve. It will not allow water to drain when the pressure in the water supply decreases, but it will not save you from increasing pressure in the boiler. So this option doesn’t work either.

How to choose and install

The safety valve for the water heater is selected according to the pressure for which the unit is designed. This number is in the passport. Also, the choice is influenced by the volume of the tank. They produce devices with a response limit of 6, 7, 8, 10 Bar. Basically, all units are designed for such pressure. So everything is simple here.

Installation is simple: linen tow or fum tape is wound on the thread, after which the valve is screwed onto the pipe. It is twisted by hand until it stops, then another one or two turns with the help of keys. It is much more important to choose the right place for its installation. When installing a water heater, this valve is installed directly on the cold water inlet pipe.

Installation example

Next, there may also be a check valve, which is also called a shut-off valve. But this is already reinsurance – the same device is available in the safety, and often after the water meter at the inlet. The installation diagram is shown below. This is one of the normal options.

Boiler safety valve installation diagram

The diagram has a ball valve. It is necessary to empty the tank before conservation for the winter (in summer cottages) or before dismantling for maintenance and repair. But more often they put it on a tee, which is screwed directly onto the inlet pipe of the water heater. A safety valve is screwed onto the tee from below, and a ball valve is placed in the side outlet.

Installation of a safety valve after a tee

Actually, these are all normal options.

Breakdowns, causes, elimination

In principle, the safety valve for a water heater has only two failures: water either often flows from it or does not flow at all.

First of all, it must be said that water bleeding during heating is the norm. This is how the system should work. Water can also be drained when the boiler is turned off, if the pressure in the cold water supply pipes is higher than the valve actuation limit. For example, a 6 bar valve, and 7 bar in the water supply. Until the pressure drops, the water will bleed off. If this situation repeats often, it is necessary to install a reducer, and it is best on the water in an apartment or house, but there are compact models of reducers that can be installed at the entrance to the boiler.

Boiler piping with safety valve and reducer

How to check if the valve is working? If there is an emergency reset lever, this is easy to do. With the boiler switched off, it is necessary to raise the lever several times, releasing the excess pressure. After that, the dripping stops and does not resume until heating starts.

If the water continues to drain, the spring may be clogged. If the model is serviceable, the device is disassembled, cleaned, and then put in place. If the model is not collapsible, you just need to buy a new valve and install it.

This is how the gearbox looks like – to stabilize the pressure on the boiler

Constantly dripping water is unpleasant and “hit” the wallet, but not dangerous. It is much worse if, when heating the water, you never have water in the pipe. The reason is that the valve is clogged or the outlet fitting is clogged. Check both options. If it doesn’t work, change the valve.

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