Consigli e ispirazioni

Domestic Water Pressure Booster System: How It Works and How to Size It

In short: a domestic pressure booster system is the set made up of a pump, a diaphragm pressure tank and a pressure switch that keeps your home's water under pressure. The pump starts when the pressure falls below the cut-in threshold and stops at cut-out; the tank reduces the number of starts. For a family of 3-4, a 24-60 litre tank and a pump of about 1 HP are enough. A shower that turns into a trickle as soon as someone opens a tap in the kitchen, a boiler that locks out due to insufficient pressure, a top floor where the water arrives exhausted: if this sounds familiar, the solution has a precise name — a domestic water pressure booster system. In this guide we look at how it really works (spoiler: it is not just the blue tank), how to size the tank and pump with a worked example, and which checks to carry out every year so that it lasts a long time. What a domestic pressure booster is (and what it is not) In everyday language, the booster set means the whole domestic pressurisation system, made up of three elements working together: the pump, which draws the water (from the mains via a break tank, from a storage tank or from a well) and puts it under pressure; the diaphragm pressure tank (also called an expansion or bladder tank): a reservoir containing an elastic bladder of water and a cushion of pre-compressed air; the pressure switch, the switch that turns the pump on and off based on the system pressure. The cycle is simple: you open a tap → the pressure drops to the cut-in threshold (typically 1.4-1.8 bar) → the pressure switch starts the pump → you close the tap → the pressure rises to the cut-out point (typically 2.8-3 bar) → the pump stops. The tank, by giving back the stored water, covers small draw-offs without starting the pump: fewer starts, less wear, lower consumption. In the pressure booster systems and pumps for domestic use collection you will find Varem diaphragm tanks from 2 to 1000 litres, Ebara and Grundfos pumps and complete booster sets. When you really need a pressure booster Insufficient mains pressure (below 1.5-2 bar) or intermittent supply, typical of hilly areas and top floors; supply from a storage tank, mandatory where the water utility delivers at set hours; supply from a well: in this case the pump sizing follows our guide to the well pump; scattered outlets: irrigation, guest house, several units on the same system. Important note: drawing water by direct suction from the public mains is generally not allowed (backflow protection rules such as EN 1717 apply): a break tank (atmospheric storage tank) is installed, from which the booster set pumps onwards. How to size it: tank and pump The pump: flow rate and head The rule of every water system applies: the pump must deliver the household's peak flow rate at the desired pressure. For a family of 3-4 with 2 bathrooms, allow 30-40 l/min; for pressure, aim for 2.5-3 bar at the least favoured tap (1 bar = 10 metres of head, plus lifts and losses). If you start from a tank at pump level, a self-priming pump of about 1 HP is the most common size: you will find full criteria and calculations in the guide to the self-priming pump. The tank: how many litres you need The tank is not a water reserve: it is a shock absorber. Its job is to keep the number of pump starts below 20-30 per hour. Practical rule: the usable capacity (about a third of the nominal volume, between cut-in and cut-out) must cover the short draw-offs. For indicative sizing use the table: Household Peak flow rate Recommended tank Typical pump 1-2 people, 1 bathroom 20-25 l/min 24 litres 0.5-0.75 HP 3-4 people, 2 bathrooms 30-40 l/min 24-60 litres 0.75-1 HP 5-6 people, 2-3 bathrooms + garden 40-60 l/min 80-100 litres 1-1.5 HP Multiple dwellings / intensive use over 60 l/min 200-300 litres or a twin-pump set 2 HP or a booster set Indicative values for single-phase systems with a 1.4/2.8 bar pressure switch. A bigger tank does not increase the pressure: it only lengthens the pump's rest periods (and its life). The air pre-charge: the detail everyone forgets The tank's air cushion must be checked with the system depressurised (pump off, tap open) using a simple tyre pressure gauge on the valve: it must be 0.2-0.3 bar below the cut-in pressure of the pressure switch. Example: cut-in at 1.6 bar → pre-charge at 1.4 bar. A wrong pre-charge is the number one cause of pumps that keep “kicking in and out” continuously. Worked example: family of 4, single-storey house Scenario: single-storey house fed from a storage tank at plant-room level, 2 bathrooms and a kitchen, target of 3 bar in the house. Peak flow rate: shower (10 l/min) + basin (8) + kitchen (10) + margin = 35 l/min ≈ 2.1 m³/h. Head: cut-out at 3 bar = 30 m, + 3 m of lift and losses → the pump must deliver at least 33-35 m at 2.1 m³/h: a 1 HP stainless steel self-priming pump is the right size. Tank: a 60-litre diaphragm tank (usable capacity ~20 litres): the pump starts only for real draw-offs, not at every flush. Pressure switch: set to 1.6/3.0 bar; tank pre-charge at 1.4 bar, to be checked once a year. Modern alternative: inverter-driven booster sets modulate the pump speed and keep the pressure constant with very small tanks. They cost more but are compact and quiet: you will find them in the same collection. Installation, maintenance and safety Location: a dry, ventilated, frost-protected room; leave space to inspect the air valve and the pressure switch. Every year: check the pre-charge, verify that the pump does not exceed 30 starts/hour and listen for “water hammer” (if present, the diaphragm may be damaged). Broken diaphragm? Typical symptom: water comes out of the air valve. In tanks with a replaceable diaphragm you replace only the bladder, without changing the vessel. Hard water: limescale scales up the impeller, pressure switch and diaphragm. If your bathroom fittings tell a story of white streaks, read how to remove limescale from the shower and consider treating the water upstream. SAFETY: a pressure booster combines pressurised water and electricity. The electrical line must be protected by a 30 mA residual current device and any fixed connection made by a qualified installer. Before any work (pre-charge check, cleaning, pressure switch replacement), switch off the power and release the system pressure by opening a tap. Never tamper with the pressure switch setting beyond the rated limits of the pump and the tank. FAQ: frequently asked questions about domestic pressure boosters What is the difference between a booster system and a simple pump?A pump on its own switches on and off at every draw-off and does not maintain pressure when the system is idle. The booster system adds a diaphragm tank and a pressure switch: pressure remains available day and night and the pump starts only when it is really needed. How many litres should the pressure tank of a house have?For 1-2 people, 24 litres are enough; for a family of 3-4, 24-60 litres; from 5 people up, or with a garden, better 80-100 litres. A big tank does not increase the pressure: it reduces the number of pump starts. At how many bar is a domestic pressure booster set?The typical setting is cut-in at 1.4-1.8 bar and cut-out at 2.8-3 bar, with the tank's air pre-charge 0.2-0.3 bar below the cut-in. Higher pressures stress seals and mixer taps with no real benefit. Why does the booster pump keep cutting in and out continuously?Almost always the air pre-charge is insufficient or the diaphragm is broken (check: does water come out of the air valve?). Other causes: a tank too small for the consumption, or a small leak in the system that slowly lowers the pressure. Is a pressure booster noisy? Where is it best installed?A well-sized domestic pump makes about as much noise as a washing machine on spin, for a few seconds at a time. Install it in the garage, cellar or plant room on anti-vibration mounts, away from bedrooms; inverter-driven sets are the quietest. Can I connect the booster pump directly to the water mains?No: regulations prohibit direct suction from the public network, because it would steal pressure from other users. A break tank at atmospheric pressure is installed, from which the booster set pumps towards the house. In conclusion A well-sized pressure booster system makes itself forgotten: constant pressure at every tap, a pump that starts a few times a day, one pre-charge check a year. Start from your family's peak flow rate, choose the tank with the table and verify the pump on its curve. You will find Varem tanks, pumps and complete sets in the pumps and pressure booster systems collection, with fast shipping and instalment payment options.