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A booster set gives water pressure to a house, a building or a farm when the mains or the tank does not provide enough. Fixed or variable speed, one pump or several, with or without a tank: the choice is based on the flow to serve, the pressure you want and the use. Here is how to size it without mistakes.
How does a water booster set work?
A booster set takes water where it is (mains, tank, well or rainwater reserve), pressurises it and delivers it on demand.
- A pump draws the water and gives it pressure.
- A bladder tank stores a little pressurised water: it supplies small draw-offs without restarting the pump.
- A pressure switch (or a drive, on a variable-speed model) measures the pressure: the pump starts when it falls below the low threshold and stops when it reaches the high one.
How the pressure is regulated (fixed or variable) makes the difference day to day. Here are the two ways.
Fixed or variable: two ways to regulate pressure
A booster set combines a pump, a regulation system and, most often, a tank. The difference lies in how the pump follows the demand for water.
| Criterion | Fixed speed | Variable speed |
|---|---|---|
| Principle | The pump starts at a low pressure and stops at a high pressure (pressure switch) | A drive adjusts the motor speed to hold a steady pressure |
| Pressure at the tap | It swings between the start and stop thresholds | It stays close to the set value |
| Tank | Essential to limit the number of starts | A small tank is generally enough, depending on the model |
| Budget and use | Lower purchase price; watering, ordinary domestic use | Higher price; comfort, highly variable demand, buildings |
| Range | Fixed-speed booster sets | Variable-speed booster sets |
Already have a pump and only want to improve its regulation? Look at the variable speed drives and the pump automation, checking compatibility with the motor (single-phase 230 V or three-phase 400 V).
On a fixed-speed booster set, the bladder tank stores a little pressurised water and prevents the pump from starting at every small draw-off. A tank that is too small causes too-frequent starts and premature wear. Its pre-charge pressure, measured when empty, should be about 0.2 bar below the pump’s start pressure. Details are in the guide choosing a bladder tank.
Sizing: peak flow and pressure
The booster set must cover the peak flow, that is, the water points open at the same time, and deliver the pressure you want at the least favourable point (the highest or the farthest). The calculation is made in metres of water column: desired pressure + height to climb + friction losses in the pipes. For conversions: 1 bar ≈ 10 mWC and 1 m³/h ≈ 16.7 l/min.
Worked example
Calculation assumption: three water points open at the same time, each at about 12 l/min, that is 36 l/min ≈ 2.2 m³/h. You want 3 bar at the highest tap, located 6 m above the booster set (≈ 0.6 bar), with about 0.4 bar of friction losses. Pressure to deliver: 3 + 0.6 + 0.4 = 4 bar, about 40 mWC. Look for a pump that gives 2.2 m³/h at 40 mWC on its curve, with a margin. These values are assumptions: adapt them to your installation.
The mistake to avoid
Sizing on the pump’s maximum flow quoted “at zero head” or on the number of taps alone. An oversized booster set starts hard, costs more and can exceed the pressure the installation withstands. Work from the flow / pressure point you actually need.
To refine, see the indicative flow rate / pressure table and the guide determining water pressure.
One, two or three pumps: the safe choice
A multi-pump booster set shares the demand and ensures continuity of service. If one pump fails or is being serviced, the others keep the supply going. With variable speed, the pumps start according to need and alternate to share the wear.
- 1 pump: house, garden, small farm. See the booster sets.
- 2 pumps: shared housing, business premises. See the fixed-speed 2-pump booster sets.
- 2 or 3 variable-speed pumps: highly variable demand or a service that must never stop. See the 2 or 3-pump variable-speed booster sets.
The selection method in 5 steps
- Define the use: house, watering, shared building, farm.
- Estimate the peak flow: number of water points open at the same time.
- Calculate the pressure to deliver: desired pressure + height + friction losses.
- Choose fixed or variable according to the comfort expected, how much demand varies and the budget.
- Plan the extras: tank, pressure gauge, check valve, dry-run protection, number of pumps.
The booster set is fed from a tank or the mains: check that suction is sound (airtight pipe, primed pump), because in practice a surface pump cannot draw water from much more than 6 to 8 m.
Frequently asked questions
Is a variable-speed booster set always better?
It gives steadier pressure and suits highly variable demand, but it costs more. For simple use, such as watering or a house, a fixed-speed model with a correctly sized tank remains a common solution.
Why does my booster set start so often?
Most often the tank is too small or poorly pre-charged, or there is a small leak downstream. Check the pre-charge pressure when empty, at about 0.2 bar below the start pressure.
Can a booster set be installed on a well or borehole?
Yes, but depending on the depth of the water level, a submersible pump may be preferable. See the guide choosing a submersible borehole pump.
How much does a water booster set cost?
The price depends on flow and pressure, fixed or variable speed, the number of pumps and the brand. The product pages in the Booster sets category show the price of each model; for a made-to-measure quote, call +33 3 44 25 91 01.
How can I increase the water pressure in a house?
If the mains, the tank or the well does not give enough pressure, a booster set provides and regulates it. First work out the pressure you need at the least favourable tap (see determining water pressure). For a supply from the public mains, check your water supplier’s connection rules.
How do I pre-charge the tank of a booster set?
Pre-charge it when empty, with no water and no pressure in the circuit, to about 0.2 bar below the pump start pressure. See choosing a bladder pressure tank.