Frequently asked questions about pressure vessels for home water systems

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Frequently asked questions about pressure vessels for home water systems – comprehensive answers from practice

Over the years of practical experience with home water system installations, the same questions keep coming up. A customer comes in with a pump, sometimes even with a pressure switch, and then stops at the selection of the pressure vessel – and that's where the problems start. "How many liters do I actually need? Do I need a bladder, or is that galvanized one without a bladder enough? Why does my pump turn on every minute, even though I have a tank?" This article collects the most frequently asked questions, answers them thoroughly and with sufficient technical depth so that after reading it, you will know what to buy and why – and later be able to identify problems without unnecessary calls to a technician.

If you're new here and don't yet know where to start, I recommend first reading the article How to choose a pressure vessel for a home water system in this Knowledge Center – that one provides the basic framework. Here we go deeper into specific questions that may seem "stupid" to ask in a store, but are actually key to the proper functioning of the entire system.

What does a pressure vessel actually do – and why you can't do without it

This is a question that customers usually don't ask out loud, but from their follow-up questions it is clear that they don't always know the answer. A pressure vessel is not a water reservoir in the usual sense – it is not a tank from which you pump water. It is a pressure tank whose primary function is to maintain pressure in the system even when the pump is not running, and at the same time to prevent the pump from starting every time you draw off ten centiliters of water.

Imagine this: you open a tap in the garden for a moment, about half a liter of water flows out. Without a pressure vessel, this would immediately cause a pressure drop, the switch would start the pump, the pump would run for three seconds, the pressure would reach the upper limit, the switch would stop the pump – and this would repeat dozens of times per hour. Such an operating mode is deadly for the pump: the motor windings overheat, the starting capacitors wear out, and the pump's lifespan is reduced from tens of thousands of hours to a fraction. The pressure vessel absorbs small water withdrawals from its own compressed air (or bladder) supply, the pressure in the system remains within the switching range, and the pump does not start at all.

The second function of the pressure vessel is protection against hydraulic shocks – sudden pressure spikes when a valve or tap is closed quickly. These shocks can damage seals, fittings, and in extreme cases even pipes. The pressure vessel absorbs these shocks.

What is the difference between a bladder tank and a non-bladder tank?

This is probably the most common question and there is an entire separate article in this Knowledge Center on it (Pressure vessel with bladder or without – what is the difference). Here I will give a brief but practically oriented answer.

Non-bladder tank (so-called air chamber tank): Water and air are in direct contact. Air gradually dissolves in water and "escapes" from the system – the tank loses its air cushion and stops performing its function. This is manifested by the pump starting too often (see the question below). Air must therefore be periodically refilled – either manually via a bleed valve or automatically using an automatic air vent. Galvanized non-bladder tanks are cheaper and offer a larger volume at the same price, which is their main advantage. An example is a galvanized pressure vessel HVP 200L with a water mark of 6 bar – vertical, without a bladder, suitable for more productive well systems with planned regular maintenance.

Bladder or membrane tank: Air and water are separated by a rubber membrane (flat) or bladder (balloon shape). Therefore, air does not dissolve in water, the tank maintains its preset pressure for a long time and does not require frequent service interventions. However, the membrane or bladder can rupture after years – this is their weaker point. A horizontal pressure vessel AQUA OLA 24l is a typical example of a compact membrane (membrane) tank for smaller households or as an addition to a pressure station.

Why does my pump start too often?

This is a symptom that customers most often call about after purchase and installation. If the pump starts every minute or even more frequently even with low consumption, the causes are usually the following:

Small tank volume – the tank is undersized for the system and consumption. If you have a house for 4–5 people and you have connected a 24-liter tank to the pump, you will likely have problems with higher simultaneous consumption.
Lack of air cushion – the non-bladder tank has lost its air, is completely filled with water and cannot perform its pressure-balancing function. Solution: drain water from the tank and refill the air to the correct level before refilling again.
Burst membrane or bladder – if you have a bladder tank and it has stopped damping, the bladder has probably burst. You can easily verify this: press the Schrader valve (air valve like on a bicycle) at the top of the tank – if water comes out instead of air, the bladder is punctured.
Incorrectly set pre-charge pressure – the pre-charge pressure (air on the side without water) must be set to 0.2–0.3 bar below the lower limit of the pressure switch. If the pre-charge pressure is too high, the effective water volume in the tank is minimal.
Incorrectly set pressure switch – the difference between the on (p-on) and off (p-off) pressure is too small. Ideally, the range should be at least 1.5 bar, preferably 2 bar.

What air pressure should be set and how to measure it?

Air pressure is the pressure value to which the tank is filled with air from the factory (or after a service intervention), measured when the tank is empty – that is, without water. This value is set and checked via a Schrader air valve, usually located on the top part of the tank.

The basic rule is: air pressure = lower limit of the pressure switch minus 0.2 bar. For example, if your switch is set to 2.0–4.0 bar (the pump turns on at 2.0 bar and turns off at 4.0 bar), the air pressure should be 1.8 bar. Never more than the lower limit of the switch, because otherwise the pump would have to overcome the air pressure before any water could even enter the tank – and the effective usable volume would be zero.

How to measure and set the air pressure:

Disconnect the system from the pump or close the appropriate valve.
Drain the water from the tank via the drain cock at the bottom or via the nearest water outlet.
When the tank is empty (no water is flowing out), attach a pressure gauge to the Schrader valve and measure the air pressure.
If the pressure is lower than required, add air through the same valve using a regular air pump or compressor.
If the pressure is higher, release air by pressing the core of the valve.
After setting, refill the system and check its function.

A detailed procedure with values for different types of switches can be found in the article What pressure to set in a pressure tank and how to check it.

How many liters of pressure tank do I need for my house?

This is the second most common question, and the answer depends on several factors. For a detailed calculation, I refer you to the article What volume of pressure tank do I need for my house, but here I will give a practical guideline based on real customer cases.

As a rough rule of thumb, the effective (usable) volume of water in the tank should cover at least 1–2 minutes of pump operation at maximum flow. The problem is that the effective volume is only a fraction of the total nominal volume of the tank – with a properly set air pressure and switch range, it is usually about 25–40% of the total volume.

Type of house / use	Recommended total volume	Effective volume (≈30%)
Garden water supply, 1–2 people	20–50 l	6–15 l
Family house, 3–4 people, well	80–150 l	25–50 l
Larger house, 5+ people, irrigation	200–300 l	60–100 l
Agriculture, supply of multiple buildings	300 l and more	90 l+

From practice: a customer with three bathrooms, a garden, and an automatic irrigation system covering 500 m² came with a 50-liter tank and the pump was switching on every minute. After replacing it with a galvanized pressure tank HVP 300L in vertical design, the switching frequency was reduced to several times less – the pump now has a much longer interval between starts and the expected motor lifespan has significantly increased.

Galvanized or stainless steel tank – which is better?

I deal with this topic in detail in the article Galvanized vs. stainless steel pressure tank – which is better. Here I will give the key practical points.

Galvanized tanks are internally coated with a zinc layer, or may have an epoxy coating. They are cheaper for the same volume, available in large capacities (200 l, 300 l and more), and have a long tradition in well systems. Their limitation is that in more aggressive water (low pH, high CO₂ content), gradual corrosion can occur, and customers must expect regular inspection of the internal surface condition.

Stainless steel tanks made of austenitic steel (typically AISI 304 or AISI 316) are significantly more resistant to corrosion, hygienically safe for drinking water, and have a longer lifespan in aggressive water. For a premium price, you get a tank that does not require internal protection and is unrestricted for drinking water. For demanding installations with a requirement for hygienic safety, the stainless steel pressure tank CH 90 L vertical is an excellent choice for medium-sized households, while for larger supply systems the stainless steel pressure tank CH 300 L vertical is available.

Summary from practice: with normal well water with a pH around 7 and without aggressive compounds, galvanized tanks work without problems for decades. For water with lower pH (below 6.5), high sulfur or chloride content, stainless steel is clearly the better choice – long-term replacement costs are higher than the price difference at purchase.

Can I install a pressure tank horizontally, vertically, or in any position?

The orientation of the tank depends on its construction. Tanks without a bladder (air-chambered) have clear requirements: air accumulates in the upper part of the tank, water remains at the bottom. Therefore, they must be installed vertically – water inlet from below, air at the top. If you were to place such a tank on its side, water would occupy the entire volume and there would be no air cushion. Customers sometimes overlook this point and actually have an air-chambered pressure tank installed horizontally – the result: minimal damping function, frequent pump switching.

Tanks with a membrane or bladder are more flexible. The membrane physically separates air and water, so the orientation is less important – these tanks can stand vertically, lie horizontally, or be installed at an angle. Manufacturers usually specify the recommended orientation in the manual; for larger tanks (100 l and more), vertical orientation is generally preferred due to better load distribution and easier maintenance.

If you are dealing with a practical space issue in the boiler room or technical room, read the article Vertical, horizontal or upright pressure tank – which type to choose – there you will find specific recommendations for different layouts.

What accessories are needed for a pressure tank?

Sometimes customers buy only the tank itself and then discover that they need to purchase additional components. A basic set for connecting a pressure tank to a home water supply includes:

Pressure switch – electronic or mechanical, sets the upper and lower pressure limits at which the pump turns on and off. Without a switch, the pump either runs continuously or does not start at all.
Manometer – pressure gauge, which displays the current pressure in the system. Some switches have it integrated, others do not. Without a manometer, you are setting up the system "blindfolded".
Check valve – prevents water from flowing back from the tank into the pump or well when the pump is stopped. For pumps installed directly in the well (submersible), it is usually built-in, but for surface pumps, an external check valve is essential.
Drain valve – for maintenance, pre-pressure checks, and draining the system during winter shutdown.
Reducer coupling (Y-piece or T-piece) – for connecting the tank in parallel to the pipe.
Schrader air valve – for checking and adjusting the pre-pressure of air (most tanks have it from the factory).

For simple connection diagrams including the placement of individual components, I recommend the article Installation of a pressure tank to a home water supply step by step.

How long will a pressure tank last? What shortens its lifespan?

A quality pressure tank, when properly installed and regularly maintained, can last 15–30 years. That is a nice number, but in practice, the lifespan strongly depends on several factors that you can influence:

Water quality: If the water is aggressive (low pH, high sulfate content, free CO₂), galvanized tanks corrode faster. Solution: choose a stainless steel tank or install an appropriate filter / neutralizer before the tank. A water quality analysis in an accredited laboratory (cost around €50–80 for a basic analysis) will pay for itself many times over in saved costs for equipment replacement.

Air pre-pressure: If it is not checked at least once a year, it can drop to zero. The tank then operates in a mode of direct contact between water and the metal wall and the membrane (if present) experiences extreme mechanical stress – it bends to maximum positions with every pump start. This shortens the membrane's lifespan from 10–15 years to 2–5 years.

Number of pump starts: Each start and stop of the pump generates a hydraulic shock that is transferred to the tank. A too small tank causes unnecessary cycles and accelerates wear not only of the pump, but also of the tank's membrane.

Excessive pressure: Operation above the tank's nominal pressure (e.g., a switch set to 6 bar when the tank is certified for 6 bar with no margin) shortens its lifespan and can lead to leaks. Always leave at least 20% margin compared to the maximum working pressure.

UV radiation and frost: A pressure tank should not be exposed to direct sunlight (UV degrades rubber parts) or frost. A tank in an unheated garage or uncovered outside can crack in winter temperatures if water remains inside.

Regular maintenance – about which you can read more in the article Maintenance and servicing of a pressure tank – what and when to check – can double the lifespan of the equipment compared to a neglected installation.

Can I connect multiple pressure tanks in parallel?

Yes, and it makes sense in practice. If you have an existing installation with a small tank and do not want to change the entire system, simply connect another tank in parallel – via a T-piece on the existing pipe. The total effective volume is added. For example, two 100 l tanks have the same effect as one 200 l tank, of course provided both have the same pre-pressure setting.

Conditions for parallel connection:

Both tanks must have the same air pre-pressure.
The connection must have a sufficiently large pipe diameter to allow pressure to equalize smoothly (at least 1" / DN25 for larger tanks).
Each tank should have its own drain valve for independent maintenance.
For tanks with a bladder, it is advantageous to install a ball valve between each tank and the main line – in the case of a burst bladder, you can disconnect the faulty tank without shutting down the entire system.

What to do if water is leaking from the pressure valve on the tank?

The safety relief valve (not the Schrader air valve) is a protective element that opens if the pressure in the system exceeds the set value (typically 6 bar). If water is leaking from it, it may indicate:

The pressure in the system is indeed too high – the pressure switch is set to a too high upper limit, or it is damaged and not functioning properly. Solution: check and reduce the switch setting or replace it.
The relief valve is worn out – after years of operation, the valve may lose its seal even at normal pressure. Solution: replace the relief valve (a relatively cheap and simple intervention).
Water hammer or pressure surge – when the pump is turned on, a short-term pressure surge may occur, which opens the valve. This is a sign that the system lacks sufficient damping volume (too small a tank) or a check valve is missing.

Never turn off or block the relief valve – it is a safety element and its deactivation is dangerous. More detailed solutions for fault situations can be found in the article Common pressure tank faults and how to eliminate them.

Do I need to register, certify or inspect a pressure tank?

This is a question that customers rarely ask, but it is important from both a legal and safety perspective. In Slovakia, pressure vessels for domestic water supply are subject to legislation on reserved technical equipment (Act No. 56/2018 Coll. and related decrees). Most pressure vessels for domestic water supply (pressure up to 6 bar, volume up to 1000 liters) fall into a category that does not require an official inspection before commissioning, but they must have a CE marking and certification according to the Pressure Equipment Directive (PED) 2014/68/EU.

This practically means for you:

Buy only tanks with a CE marking and accompanying documentation (Declaration of Conformity).
Keep the documentation for the tanks – it may be needed in the case of an insurance incident or inspection.
If you have a pressure system as part of a potable water supply, the water supply may be subject to inspection by the regional public health office – it depends on whether you supply only your own household or multiple consumption points.

Can I use a pressure tank with a solar or photovoltaic pump?

Yes, pressure tanks are compatible with solar-powered pumps, but you should take into account the specific characteristics of such systems. Solar pumps have variable performance depending on the intensity of radiation – they can therefore deliver variable flow and pressure. A conventional pressure switch, designed for systems with a constant pump output, may not work optimally.

For solar systems, it is therefore recommended:

To use an electronic pressure regulator / frequency converter (inverter), which adjusts the pump speed according to the current panel output and pressure demand.
To choose a larger pressure tank – it acts as a buffer against fluctuations when the intensity of radiation changes (clouds, passing shadows).
To install a backup water tank (accumulation tank) as the primary reservoir and connect the pressure tank after a hydrofor pump, which pushes water from the tank into the distribution system.

Frequently asked questions and short answers (FAQ)

Can I install a pressure tank outdoors?

Technically yes, if it is protected from frost and direct UV radiation. Frost is the biggest enemy – water in the tank expands when frozen and can crack the tank. If outdoor installation is unavoidable, do not forget to insulate the tank, install a drain valve for winter shutdown, and possibly electric heating tapes on the pipes. In practice, we prefer installation in an unheated but frost-free area – boiler room, basement, garage with a minimum temperature above 0 °C.

Can I replace only the bladder/membrane in a pressure tank, or do I need to buy a completely new tank?

It depends on the tank design. Most larger tanks (80 l and above) have a replaceable bladder – it is a standard spare part available from the manufacturer or distributor. Smaller tanks (up to 50 l) are often constructed with a permanently built-in membrane that is not designed for replacement – in the case of a rupture, it is more economical to replace the entire tank. Always check before purchase whether the bladder/membrane for your model is available as a spare part and what its price is – sometimes the price difference between a new tank and a bladder is minimal and it is worth investing in a new one with full warranty.

Why is air shooting out of the tap when I turn on the water?

This is a classic sign of an air-filled tank without a bladder, which is filled with air at too high a pre-pressure, or is entirely air-filled – the water has been drained and the air was not released to the correct level before refilling. The air has entered the pipes and when the tap is opened, it pushes out before the water. Solution: check the pre-pressure, or bleed the system through air vents at the highest points of the distribution. If this happens regularly, consider switching to a tank with a membrane – air does not dissolve into the water from it and therefore does not enter the pipes.

What pre-pressure should I set if I don't know what switch I have?

First, identify the switch – it is usually engraved or painted on it, or you can find it in the pump documentation. If you don't have the documentation, use a pressure gauge: turn on the pump and let it work until it stops on its own (this is the upper limit), and record the value. Then let the water drain from the tap until the pump starts on its own (this is the lower limit). Set the air pressure in the empty tank to a value 0.2 bar lower than the lower limit of switching.

What is the difference between a pressure switch and a pressure regulator?

A pressure switch is a simple electromechanical device that turns the pump on and off when the set pressure limits are reached – it is an "on/off" control. A pressure regulator (pressure reducing valve), on the other hand, reduces and stabilizes pressure from a higher value to a lower one – for example, from 5 bar to 2.5 bar at the house entrance, to protect the fixtures. These are two different devices with different functions; in a well-designed system, both can be present at the same time.

Can I use a pressure tank in a system with a water heater / storage water heater?

Yes, a pressure tank is commonly installed in systems with storage water heaters – in this case, it serves as an expansion tank for hot water. Water expands in volume when heated, and this excess pressure is absorbed by the pressure tank. This is a different use than in a domestic water supply system, but the principle is similar. Note: for hot water systems, the tank should be certified for the appropriate temperature (typically up to 99 °C) and have a membrane made of EPDM rubber resistant to higher temperatures – not every tank for cold water is suitable for hot water. Always check the manufacturer's technical specifications.

Conclusion – what not to forget when buying and installing

A pressure tank may seem like a simple thing at first glance – just a tank full of air. But behind this simplicity lies several critical parameters, the neglect of which can complicate the operation of your entire domestic water supply system. When buying, always check: the volume in relation to your actual consumption and pump performance, the material in relation to the water quality in your source, the presence or absence of a bladder in relation to your willingness to spend time on regular maintenance, and the availability of spare parts for the model.

If you are unsure about the selection, our offer in the category pressure tanks includes solutions from compact horizontal tanks for smaller systems up to large-capacity vertical tanks for demanding supply systems – and with each product, technical documentation is available to help you verify that the tank meets your conditions.

A properly dimensioned, properly installed, and regularly checked pressure tank is an investment for decades. On the other hand, an underestimated or neglected tank can damage the pump, which is much more expensive – and this is an experience we unfortunately see repeatedly among our customers.

Do you have a question on this topic?

Can't decide or are you dealing with a specific situation in your household? Write to us – we are happy to help.