Knowledge base
Water pressure fluctuations in buildings — what causes them?
Water pressure drops are a common problem in multi-family residential buildings and industrial facilities. Learn about the causes and the role of buffer tanks in pressure stabilisation.
The problem in numbers
Recommended pressure range for the internal water system of a residential building.
Estimated share of multi-family buildings experiencing water pressure problems.
Potential energy savings achievable by using a buffer tank in a domestic hot water system.
Typical service life of a membrane in a pressure vessel tank under correct operating conditions.
Causes of water pressure fluctuations
Water pressure fluctuations in a building can have many causes — from issues on the water supply network side, through design errors in the installation, to worn system components.
Peak water demand — in multi-family buildings, simultaneous water use by many residents (morning and evening peaks) leads to significant pressure drops. The problem is more pronounced in buildings without a balancing tank.
Undersized installation — pipe diameters that are too small, insufficient pump capacity, or the absence of a buffer tank mean the system cannot meet instantaneous demand.
Water hammer — sudden valve closures (e.g. by dishwashers or washing machines) generate pressure waves that propagate through the system. They cause the characteristic "banging" in pipes and accelerate wear on fittings.
Faulty pressure-reducing valve — a damaged or incorrectly set pressure reducer fails to maintain a constant output pressure, resulting in fluctuations felt by users.
Hydrophore unit problems — a worn pump, a faulty pressure sensor, or a defective pressure vessel tank cause cyclical pressure drops and spikes.
Diagnostics — how to find the source of the problem?
An effective solution requires a correct diagnosis. Here are the steps that help identify the cause of fluctuations:
Pressure measurement at the building inlet — a pressure gauge on the service connection makes it possible to determine whether the problem lies with the water supply network or the internal installation. Pressure at the connection should be 2–6 bar and stable.
Peak demand test — opening several draw-off points simultaneously allows you to assess how the system responds to increased demand. A pressure drop of more than 1 bar indicates insufficient capacity.
Hydrophore unit inspection — checking the pre-charge pressure in the pressure vessel tank (should be 0.2–0.3 bar lower than the pump cut-in pressure), the condition of the membrane, and the pump's operating parameters.
Pressure-reducing valve inspection — measuring pressure before and after the pressure-reducing valve, and checking output stability under load. Pressure-reducing valves have a limited service life and require periodic replacement.
If diagnostics indicate that the system requires increased buffer capacity or replacement of the pressure tank — correct selection of the new unit's parameters is essential.
The role of the buffer tank and diaphragm tank
Diaphragm (expansion) tank acts as a shock absorber in the system — it compensates for momentary pressure spikes and drops, reduces the frequency of pump cycling, and protects the system against water hammer.
In hot water systems, a buffer tank (DHW storage tank) stores heated water and delivers it during peak demand periods. This allows the heat source (boiler, heat pump) to operate more evenly, and users do not experience pressure or temperature drops.
Expansion/equalising tank in a cold water system serves a similar function — it stores a reserve of water and releases it during periods of increased draw-off, stabilising pressure throughout the system.
A correctly sized tank eliminates most pressure problems without the need to replace the entire system. The key parameters are: capacity (matched to peak demand), working pressure (in line with system parameters), and material (stainless steel for drinking water, carbon steel with a protective coating for heating systems).
Selecting tank capacity — what to consider?
An undersized tank will not solve the problem, while an oversized one means unnecessary costs. Correct selection requires taking several factors into account:
Number of draw-off points and users — the basic parameter defining peak water demand. In residential buildings, approximately 30–50 litres of hot water per person per day is assumed.
Output capacity of the water/heat source — the tank must compensate for the difference between instantaneous demand and the output of the boiler or water supply connection.
System working pressure — determines the material and structural requirements of the tank. Tanks operating above 0.5 bar overpressure are subject to UDT supervision.
Available space — the tank dimensions must allow for transport and installation in the target room. Where space is limited, vertical tanks with a smaller diameter may provide a suitable solution.
For large systems (multi-family buildings, hotels, industrial facilities), selection should be supported by design calculations that take the water consumption profile into account.
When is tank replacement necessary?
A pressure tank or buffer tank requires replacement when: the membrane is damaged (a diaphragm tank cannot maintain pre-charge pressure), corrosion has compromised the integrity of the walls, or the tank's parameters no longer match the current system requirements (e.g. following a building extension).
Replacement with a tank of greater capacity or higher pressure ratings is often the most effective solution chronic pressure problems — a more cost-effective and less invasive solution than redesigning the entire installation.
When replacing a tank, it is worth considering a stainless-steel tank — particularly in drinking water and domestic hot water systems. Superior corrosion resistance translates into longer trouble-free service life and better water quality.
A new pressure tank must be approved by UDT before being commissioned. The manufacturer should provide the complete technical documentation required for device registration.
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