What pressure to set in the pressure tank and how to check it

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Why the correct pressure in the pressure tank determines the entire operation of the water system

The pressure tank is not just a passive water reservoir. It is the heart of the entire home water system – and the air (or nitrogen) pressure in the air chamber of the tank directly determines how often the pump turns on, the comfort of water use, and how long the entire system will operate without failure. Adjusting this pressure is one of the few interventions a typical homeowner can do themselves, without special tools. And yet, it is one of the things people most often neglect or do incorrectly.

In practice, we encounter two extremes. First: a customer buys a tank, connects it, and never checks the pressure. After two years, the pump starts every five seconds, the membrane is cracked, and the tank no longer performs any function – it functions only as a metal decoration on the piping. Second: a customer reads that the pressure should be checked, inflates the air to four bar, and wonders why the pump does not reach the desired pressure and why the water flows weakly. Both problems have the same cause – a lack of understanding of what pressure to set and why.

This article will explain the mechanism of how the pressure tank works, the specific values to set, the procedure for checking the pressure, and what happens when the pressure is incorrect. If you are also interested in selecting a tank or comparing types, please also see other topics in our Knowledge Center – for example, Pressure tank with a bladder or without a bladder – what is the difference or What size pressure tank do I need for my home.

How the pressure tank actually works – the basic principle without which nothing makes sense

In order to understand why the air must have a precisely defined pressure, you first need to understand what happens inside the tank. The pressure tank is divided into two chambers – the air chamber and the water chamber. In tanks with a membrane (bladder), these chambers are separated by a flexible membrane or a butyl rubber bladder. In older tanks without a membrane (so-called non-bladder construction, typical for example for galvanized pressure tank HVP 200L), the air is in direct contact with the water.

When the pump is operating, it pumps water into the tank. The water compresses the air in the tank. When the pressure in the system reaches the upper limit (the so-called pump cut-off pressure), the pump turns off. From that moment on, the household is supplied with pressure from the air, which pushes the water out of the tank. When the pressure drops to the lower limit (the so-called pump cut-in pressure), the pump starts again. This amplitude – the difference between the cut-in and cut-off pressure – determines how much water the tank actually delivers in one cycle.

The key principle is simple: the pre-charged air pressure must always be lower than the pump cut-in pressure. If the air pressure were the same or higher than the cut-in pressure, the pump would have to immediately fight an excessively high back pressure at startup, or it would not be able to get water into the tank at all. Conversely, if the air pressure is too low, the water will occupy most of the tank volume and the system will behave as if the tank did not exist.

What specific pressure to set – formula, numbers and examples

The golden rule that applies to tanks with a membrane (bladder) is: pre-charged air pressure = pump cut-in pressure minus 0.2 bar. So if your pump is set to start at 2.0 bar, the air in the tank should be pre-charged to 1.8 bar. If the cut-in pressure is 2.5 bar, the air should be set to 2.3 bar.

For tanks without a bladder (non-bladder construction), a slightly different rule applies – typically the setting is at the level of the pump cut-in pressure, or even lower (depending on the manufacturer and instructions). Always check the manual for the specific tank.

Typical values for common home water systems

Most home water systems have a pressure switch set to a cut-in pressure of 1.5 – 2.5 bar and a cut-off pressure of 3.0 – 4.5 bar. This depends on the height of the building and the requirements of the appliances. For orientation, we provide a few specific examples from practice:

Low-rise family homes (ground floor + 1 floor), pumping from a well up to 20 m depth: cut-in pressure 1.8 bar, cut-off pressure 3.5 bar → pre-charge air to 1.6 bar
Bungalow with floor heating and a shower: cut-in pressure 2.0 bar, cut-off pressure 3.5 bar → pre-charge air to 1.8 bar
House with a hydromassage bath or irrigation system: cut-in pressure 2.5 bar, cut-off pressure 4.5 bar → pre-charge air to 2.3 bar
Garden water system for simple garden irrigation: cut-in pressure 1.5 bar, cut-off pressure 3.0 bar → pre-charge air to 1.3 bar

Important notice: some sources mention the rule "air pressure = cut-in pressure minus 0.5 bar". This applies to older systems or situations where the pressure switch has a larger amplitude. In practice, we recommend a value of 0.2 bar below the cut-in pressure as a safe standard for modern membrane tanks. If you have any doubts, contact the pump or switch manufacturer.

When and how to check the pressure in the pressure tank

The pressure in the pressure tank is checked on an air valve (so-called Schrader valve – the same type you know from bicycle and car tires). The valve is usually located on the top part of the tank, sometimes on the side, covered by a plastic cap.

When to check it at all?

At first installation – the manufacturer usually pre-charges the pressure to 1.5 bar, but not always. Always verify the actual value.
Once a year during regular maintenance – air slowly escapes through the membrane and valve, a drop of 0.2–0.5 bar per year is normal.
When the pump starts too often – if the pump starts every 10–30 seconds instead of every few minutes, the pressure may be low or the membrane may be broken.
After any intervention in the system – for example, after starting the system in spring after winter shutdown.
If water instead of air flows out of the valve during the check – this is a serious sign of a broken membrane.

What you will need

A digital or analog air pressure gauge (so-called manometer) with a range of 0–6 bar – best with a needle for Schrader valves. Cheap models from car shops for a few euros are sufficient, an accuracy of ±0.1 bar is adequate.
A compressor, pump, or pressurized bottle with air/nitrogen for inflation.
A plastic cap for the valve to protect it after the check is completed.

Step-by-step procedure for checking

Step 1 – Pump shutdown: Before any pressure tank inspection, disconnect the pump from the electrical supply. This is not just a formality – the pump can start at any time when the pressure drops, and while working near the tank, this can be dangerous or cause inaccurate measurements.

Step 2 – Releasing water pressure from the system: Open a tap or valve in the house and let the water flow out until the stream stops and the water pressure in the pipes drops to zero. This is a crucial step. While there is water pressure in the tank, it is not possible to correctly measure the air pressure in the chamber – the inflated air must be in balance only with atmospheric pressure, not with water pressure.

Step 3 – Accessing the valve: Unscrew the plastic cap of the Schrader valve. Sometimes it is stuck or blocked by corrosion, carefully loosen it. The valve is spring-loaded – it opens automatically when the pressure gauge pin is applied.

Step 4 – Measuring: Attach the pressure gauge and read the value. If water instead of air flows out of the valve or sprays out, the membrane (bladder) is broken. The pressure tank is then non-functional and the membrane or the entire tank must be replaced. More about this issue can be found in the topic Common pressure tank faults and how to fix them.

Step 5 – Adjusting the pressure: If the measured value is lower than the target, inflate air using a compressor, pump, or from a pressurized bottle (note, never use oxygen or other flammable gases – only air or technical nitrogen). If the value is higher, carefully release air by pressing the central pin of the valve, for example with a pencil. After adjustment, measure again. Put on the cap, turn on the pump, and observe whether the system behaves normally.

What happens if the pressure is set incorrectly – specific consequences

Air pressure that is too low

This is the most common case we encounter in practice. When the air pressure drops significantly below the pump's cut-in pressure (or is zero), the membrane practically shifts entirely to the air chamber side and water occupies almost the entire internal volume of the tank. The tank no longer functions as a pressure buffer. Result:

The pump turns on every few seconds – so-called short cycling (short cycling). The pump's electric motor is not designed for thousands of starts per day and quickly wears out.
Water pressure in the entire house fluctuates dramatically – when you turn on the shower, you may feel vibrations and temperature changes.
Increased wear on the pump, switch, and all seals in the system.
Shortened lifespan of the entire water system by several years.

Air pressure that is too high

Less common, but equally harmful. If the air pressure is higher than the pump's cut-in pressure:

The pump is unable to push water into the tank because air offers too much resistance.
In extreme cases, the pump may still operate, but the water pressure in the system will never reach the required level.
The membrane is permanently pressed toward the water chamber side, and the stress on its material is increased.
In extreme cases (air pressure exceeding the tank's maximum working pressure), there is a safety risk – this is why every tank is equipped with a safety valve and the maximum operating pressure is indicated on the label.

For illustration: in the case of a stainless steel pressure tank CH 300L with a maximum working pressure of 10 bar, there is a large margin for adjustment, but that does not mean you should set the air pressure to 6 bar just because the tank "can handle it." The functional setting is determined by the pressure switch, not the tank's capacity.

Specifications according to tank type

Tanks with a membrane (bladder)

For tanks with a membrane, the rule described above applies: pre-charge pressure = switching-on pressure minus 0.2 bar, with the measurement always taken when the water pressure in the system is at zero. An example of a smaller bladder tank is the pressure tank AQUA OLA 24L horizontal, which is commonly used with smaller household pumps. Its factory pre-charge pressure is usually 1.5 bar – in most cases, this should be checked and possibly adjusted according to the specific pressure switch settings before starting operation.

Tanks without a bladder (non-bladder construction)

In the case of non-bladder tanks, where air is in direct contact with water, the situation is a bit different. Air is slowly absorbed into the water, and the tank requires more regular "airing" rituals. Some older models had an automatic air valve at the top that opens only when the pump is turned off. Modern non-bladder tanks, such as the galvanized pressure tank HVP 300L, have a precisely defined volume of the air and water compartments, with the air pressure maintained at the level recommended by the manufacturer – typically in the range of 1.5–2.5 bar depending on the specific installation.

Important: with non-bladder construction, you should drain the water only to a minimum (not completely), because if you were to drain all the water and then add air using a compressor, you might introduce an excessive air layer, which would disrupt normal operation. Always follow the indicated water level and the manufacturer's instructions.

Air or nitrogen – what really matters

Technical standards for pressure tanks with a membrane mention the possibility of using either air or nitrogen. In practice, most household water systems use regular air from a compressor, which is fully sufficient. Nitrogen is only relevant in specific cases – for example, with very hard water containing high levels of CO₂, where air may accelerate corrosion inside the tank, or in industrial installations.

At the same time, it is important to note: never use oxygen or any other gas besides air or nitrogen. Oxygen in combination with moisture and metal causes rapid corrosion and also poses a safety risk at higher pressures.

Pressure and tank size – an unexpected connection

The pre-charge air pressure together with the tank volume determines the so-called usable volume – that is, how many liters of water the tank can actually deliver in one pump cycle. This calculation is based on Boyle's law (pV = constant).

As an example: for a tank with a total volume of 200 liters, a pre-charge pressure of 1.8 bar, a switching-on pressure of 2.0 bar, and a switching-off pressure of 3.5 bar, the usable volume is between 50 and 70 liters. This means that in one pump cycle, you can withdraw up to 50–70 liters without restarting the pump. In a smaller tank (e.g., 24 liters), this volume will be only 5–10 liters – which is very little for a larger household. Therefore, choosing the correct tank size is just as important as setting the correct pressure. We discuss this topic in detail in the article What pressure tank size do I need for my home?.

For larger households with higher water consumption, where a sufficient tank and long operation without pump activation are important, larger tanks such as the stainless steel pressure tank CH 90L, or even larger volumes made of galvanized or stainless steel, are suitable. Proper pressure setting is especially important for these tanks, as incorrect settings on a large tank mean a significant loss of usable volume.

Recommended inspection and maintenance schedule

Based on practical experience, we recommend the following schedule:

Before the first start-up: always check the pre-charged air pressure and compare it with the pump pressure switch. Adjust if necessary.
Every 6 months (spring and autumn): visual inspection of the entire system, checking seals and connections.
Once a year: measuring air pressure and refilling if necessary. Check the pressure switch.
Every 3–5 years: membrane (bladder) replacement in bladder tanks as a preventive maintenance (depends on water quality and frequency of operation).
Immediately when a problem is detected: short cycling of the pump, water from the valve during inspection, visible corrosion or mechanical damage to the tank.

For more information on what and when to check, see the topic Maintenance and service of pressure tanks – what and when to check.

Practical examples from customer practice

Case 1 – customer with short cycling: The customer purchased a 24L horizontal pressure tank for their home water system three years ago and noticed in early winter that the pump started every 8–10 seconds. During inspection, we measured the air pressure – it turned out to be only 0.3 bar instead of the required 1.8 bar. The membrane was in good condition, but air was slowly escaping through a valve with a corroded seal. It was enough to replace the valve with a new Schraeder valve (cost up to 2 €) and inflate the air to 1.8 bar. The problem was immediately resolved.

Case 2 – burst membrane: The customer had an HVP 200L tank connected to a deep well pump. During the annual inspection, water instead of air sprayed out of the valve. We confirmed that the membrane had burst – or in this case, it was a non-bladder tank, where air was being absorbed into the water faster than usual due to the high CO₂ content in the well water. We recommended regular annual inspections and refilling the air layer according to the water level.

Case 3 – too high air pressure: A technician set the air pressure in the new water system to 3.5 bar, while the pump's cut-in pressure was only 2.0 bar. The pump ran, but never reached the required cut-out pressure – it ran continuously. The customer called, saying the "pump doesn't reach the desired pressure". It was enough to release air from the tank to the correct value of 1.8 bar and the system immediately started working normally.

Case 4 – garden water system with changing demands: The customer added an automatic irrigation system to their existing water system, which increased water consumption and required adjusting the pressure switch from 1.5/3.0 bar to 2.0/3.5 bar. However, they forgot to adjust the pre-charged air pressure in the tank. The old value of 1.3 bar was now only 0.7 bar below the new cut-in pressure – not fatal, but unnecessarily limiting the usable volume of the tank. After inflating to 1.8 bar, the system was optimized.

Common questions (FAQ)

What is the factory air pressure in a pressure tank and should it be changed?

Most manufacturers pre-charge tanks to 1.5 bar. This may not match your specific pressure switch settings. Always check the actual air pressure in the tank (with zero water pressure in the system) before the first start-up and compare it with your pump's cut-in pressure. If they do not match (correct value = cut-in pressure minus 0.2 bar), adjust the air pressure using a compressor or by releasing air.

Can I inflate a pressure tank with a regular bicycle pump?

Yes, for small tanks (up to 24–50 liters) with low required pressure (up to 1.5–2.0 bar), it is technically possible, since the Schraeder valve is the same as on bicycle tires with an American valve. In practice, however, it can be quite laborious. For larger tanks or higher pressure, a foot or electric compressor is much more convenient. A pressure of 1.5–2.5 bar is within the range of a standard bicycle pump with a pressure gauge.

How do I know if the problem is with the air pressure or a burst membrane?

Turn off the pump, release the water pressure from the entire system (open a tap), then attach a pressure gauge to the tank's air valve. If air is coming out of the valve and the gauge shows a value – the membrane is likely intact and you only need to inflate it. If water sprays out of the valve or you hear characteristic water under pressure – the membrane is burst. In this case, the bladder (if replaceable) or the entire tank must be replaced.

How often should I check the air pressure in a pressure tank?

We recommend once a year, ideally in spring before the main pumping season (irrigation, higher water consumption). A drop of 0.1–0.3 bar per year is normal. If you notice that the pump is starting significantly more frequently than before, check the pressure immediately – there is no need to wait for scheduled maintenance.

What does it mean when the system "short cycles" and is it always a problem with the pressure tank?

Short cycling (the pump starts every few seconds) is a very characteristic symptom. In most cases (about 70–80 % of cases we handle), the cause is the pressure tank – low air pressure, a burst membrane, or an undersized tank. The remaining 20–30 % of cases have other causes: a leaky pipe in the system (water leak reduces pressure), an incorrectly set pressure switch, or an undersized pump. Always start by checking the pressure tank – it is the fastest and cheapest diagnostic step.

Can a pressure tank be dangerous if the air pressure is too high?

Every pressure tank has a maximum working pressure (PN – Pressure Nominal) listed on the label and in the documentation, typically 6, 8 or 10 bar. Typical home water systems operate at 3–5 bar, which is well below the maximum. If you accidentally inflate the air, for example, to 8–10 bar with a compressor on a tank rated for 6 bar, or if the pressure relief valve on the water side is not working, it could be dangerous. In practice, a typical customer at home using a manual pump will not create such values, but when using a compressor with an adjustable output, you should be careful and limit the compressor output to a maximum of 3–4 bar when inflating a tank for a home water system.

Conclusion – a few minutes once a year that save thousands

Setting and checking the pressure in a pressure tank is one of those things that may seem trivial, but neglecting it has real and measurable financial consequences. A properly set pre-charge air pressure – that is, the pump's cut-in pressure minus 0.2 bar – is the foundation that ensures the tank performs its function as a pressure shock absorber and energy storage. A regular annual inspection with a simple pressure gauge, which you can buy for a few euros, will protect the pump from premature wear and the entire system from failures.

If you are unsure about choosing the right tank for your system or are considering replacing an old tank with a new model, take a look at our other topics in the Knowledge Center – for example How to choose a pressure tank for a home water system, Galvanized vs. stainless steel pressure tank – which is better, or Installation of a pressure tank to a home water system step by step. A complete range of pressure tanks can be found in our category at atria.sk/tlakove-nadoby-3/.

Do you have a question about this topic?

Not sure how to proceed or dealing with a specific situation in your home? Write to us – we are happy to help.