High pressure or low pressure? (What distinguishes the faucets)
Manufacturers of faucets clearly indicate whether it is a high or low pressure model. This is even visually labelled with a flash to make it stand out.
Non-experts, though, are often unaware of important details.
A wrong purchase in this area can have serious consequences, as you will read below.
To ensure that this does not happen to you, we will answer all your questions about high-pressure vs. low-pressure faucets – also known as vented taps or three hose faucets – in this article.
What is a low-pressure faucet?
A low-pressure faucet is a special mixer faucet designed for connection to unpressurized hot water cylinders.
The logical consequence of this definition is that it cannot be used in combination with a central hot water supply or pressure-resistant instantaneous flow heaters – more details will follow in a moment.
Once a low-pressure faucet has been installed, it is virtually impossible to distinguish it optically from a high-pressure faucet – you will learn how to distinguish between them in the next part.
How can I recognize and distinguish between high-pressure and low-pressure faucets?
This important question is often asked and you will find everything you need to know in our article about the difference between high-pressure and low-pressure faucets.
We have dedicated that article to this question because the distinction is so important. You might want to read it right now and then come back to this article.
Being able to distinguish between these faucet types is so important because low-pressure faucets must be used under certain conditions – and also must not under other conditions.
We will take a closer look now at what these requirements are.
Low pressure faucets (three hose faucets)
When do I need a three hose faucets / vented tap?
At the beginning there is often the question why a low pressure faucet is necessary at all. There is a quick answer to this question, because a low-pressure faucet is always suitable when there is:
● generally no central hot water supply, or
● in some rooms only a cold water outlet available
If one of the two points applies to your situation, you only have access to cold water.
Of course, you could also opt for a cold water faucet directly in this case.
However, if you still want to get hot water to gush out of your faucets, you can use decentralized hot water supply via hot water storage tanks – also known as under-sink cylinders or boilers.
Since these devices often operate without pressure, they must under no circumstances be connected directly to the water pipe or operated with high-pressure faucets.
The reason for it is that these hot water reservoirs are not designed for the water pressure of the household supply – in most countries this is between 3 and 6 bar – and could burst.
Incidentally, this would be one of the unpleasant consequences of a mistaken purchase of high-pressure vs. low-pressure faucets mentioned above.
Why a low-pressure faucet is called what it is called
In order to avoid precisely such a fiasco like burst hot water cylinders, there are low-pressure faucets.
As already mentioned, hot water storage tanks are usually not pressure-resistant – i.e. they cannot withstand the pressure of the domestic water supply (there are now also pressure-resistant models that are more expensive and heavier, though).
For this reason, a special faucet must be connected between the water connection of the building’s water supply and the under-table unit (or as a table-top model).
This special faucet is the low-pressure faucet, which reduces the water pressure that flows into the hot water tank.
It is precisely for this reason that these faucets are also called low-pressure faucets, as they reduce the water pressure to a lower level.
How does a low pressure faucet work?
In order to accomplish its task, low-pressure faucets, in contrast to high-pressure faucets, always have 3 connections.
By the way, low-pressure faucets can always be identified with certainty by these three connections. Another characteristic is a schematically depicted flash.
What are these three hoses for?
- The first connection leads from the cold water wall valve to the faucet.
- The second connection feeds the cold water with reduced pressure into the hot water tank
- The third connection is for the warm water, which flows from the
- hot water storage device to the faucet
Due to an elaborate valve control system inside the faucet, it now allows the following two scenarios:
- Only cold water is demanded from the faucet: cold water flows via the first connection directly to the outlet.
- Only hot water is demanded: cold water then flows through the second connection at low pressure into the flow heater and displaces the pre-heated water there, which flows through the third connection into the faucet to the outlet.
In the everyday situation where lukewarm water – a mixture of cold and warm water – is demanded, both scenarios take place simultaneously.
So some cold water flows directly to the outlet, while some of it flows at reduced pressure into the reservoir to displace the warm water there.
This ingenious operating principle with clever valve control is also the reason why low-pressure faucets are more expensive than high-pressure mixer faucets or cold water faucets.
Installation – How to properly connect low-pressure faucets
The correct installation of a vented faucet is fairly easy and should be possible for almost anyone without the help of qualified personnel.
For the installation or exchange of the new faucet you only need the following:
- Suitable tools
- New faucet
- Hot water tank (if not already installed)
In the following short video by Hornbach, we believe that all the essentials of the installation are explained briefly and crisply in a clear and easily understandable way. Even though it’s in German language, if you follow the steps visually, the installation should succeed without problems:
Easy installation of the low-pressure faucet in 10 steps
Here again the most important points from the video, which are to be considered when installing your new low pressure faucet:
- remove the siphon (place the bucket under it)
- switch off the hot water tank and remove the plug (in the case of a planned replacement, remove completely)
- unmount the old faucet and pull it out of the kitchen sink
- install new faucet
- attach the hose for cold water to the wall valve
- connect the other two hoses to the hot water tank (for
hot and cold water)
- do not forget the seals!
- reinstall the siphon
- before switching on the heater it has to be vented. To do this:
a. open the wall valve
b. let cold water run until it runs smooth
c. let warm water run until there is no more air or splashes
- now switch on the heater again
By the way: The video explains the process with the kitchen sink, but the procedure is basically the same in other rooms (e.g. at the vanity in the bathroom or guest toilet).
How can I connect a low-pressure faucet with a pull-out spout?
Good news: It doesn’t matter whether your new faucet has a pull-out spout or not.
You can carry out the assembly and installation in the same way as in the 10 steps just mentioned or shown in the video.
This is because the steps and elements that are important for assembly are located below the faucet. Which type of spout you use is irrelevant.
My low pressure faucet is dripping – is it leaking?
The low-pressure faucet also acts as a pressure relief valve. It is therefore perfectly normal for it to drip a little when the water in the storage tank is heated.
This is because heating causes it to expand, which increases the pressure in the storage tank. In order not to damage the device, the overpressure escapes through the faucet (occasionally accompanied by a light whistle).
It is just as normal, by the way, that the low-pressure faucet keeps running for a brief moment after closing it. This is due to the water circuit being set in motion by the water reservoir. So you don’t have to worry if the faucet doesn’t seem to turn off instantly.
However, the water should not keep running constantly and permanently – at least not beyond the normal drip already mentioned – this could be a hint of a sealing problem.
Can I use a low pressure faucet as a high pressure faucet?
Another frequently asked question is whether an existing low pressure faucet can simply be “converted” and connected directly to the central hot water supply – and can thus be converted into a high pressure faucet without further ado.
This is clearly not recommended.
As already described above, cold water would flow into the boiler on the basis of the 3 line principle in order to push hot water upwards out of the heater when hot water is to demanded.
But since there would be no heater in this scenario, the cold water would simply run into the kitchen cupboard (or under the sink in the bathroom).
Low pressure faucets are solely intended for operation with hot water storage tanks and should only be operated with them.
And what’s more, there are simple high pressure mixer faucets available at very low prices, as we have already analyzed in detail in this article here.
An alternative to low pressure faucets – flow heaters
Instead of managing your decentralized water supply with unpressurized storage tanks, which require a low pressure faucet, there is another alternative.
If you want to keep your hot water supply decentralized, continuous-flow water heaters are often an energy-saving and environmentally friendly alternative.
Unlike hot water tanks, flow heaters do not require expensive low pressure faucets, as they can be operated with conventional mixer faucets or optionally with even simpler pillar faucets.
In contrast to storage heaters, flow heaters do not store any warm water, being permanently heated and thus constantly wasting energy, even if there is no hot water demand at all.
And if there is actually a higher warm water demand, flow heaters supply endlessly warm water, as they do not require any storage tanks.
Hot water tanks, in contrast, only supply cold water once they have run out of water – which is the case with small under-sink units (as with countertop tanks) after just a few liters.
You can find out more about this alternative in our article on flow heaters.
In certain cases, faucets with integrated flow heaters could also be an option.
High pressure faucets
High pressure faucets are the ultimate standard and can be found in a large number of households.
If you have a central hot water supply and thus two water connections, i.e. hot and cold water, then a high pressure faucet is the right choice. This is the case in most homes and you can therefore choose the high pressure faucet without hesitation.
With these models, the high pressure of 3 to 6 bar, which is common in most households and has already been mentioned above, is applied directly to the faucet. Hence the name “high pressure” faucet.
High pressure faucets are available in the widely used version as a mixer faucet with 2 connections, where cold and hot water are mixed directly in the faucet to obtain the desired water temperature at the outlet.
In addition, there are also cold water faucets – also called pillar faucets – which have only one connection. Although they get their name because they are directly connected to the cold water line and therefore only supply cold water, this does not always have to be the case.
There are also pillar faucets that can be connected directly behind a flow heater and thus supply water at the temperature set on the flow heater.
Which mixer faucet for flow heaters – do I need a special faucet?
No, all pressure-resistant flow heaters can be connected to all conventional high pressure faucets.
This also includes cold water faucets, which are the simplest and cheapest type of high pressure faucets.
Especially in connection with electronic flow heaters, where the water temperature can be adjusted individually, cold water faucets can even be used for hot water supply.
However, if you have a hydraulic flow heater, or sometimes just want to get cold water, a normal high pressure faucet is the better choice.
Because this has two standard connections, one for the warm water from the flow heater and a cold water connection from the wall valve.
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