Booster pumps

The rule that shapes every solution

So the options all involve either storing water and pumping from the store, or storing pressure rather than volume.

The three approaches

Which is right depends entirely on a measurement, and the distinction that matters is between pressure and flow.

Accumulators, which deserve more attention

An accumulator is a vessel containing a bladder, pre-charged with air, connected to the incoming main. During quiet periods the mains slowly fills it. When demand exceeds what the main can supply – two showers at once, a bath filling while somebody showers – the stored water is pushed out by the compressed air, supplementing the mains flow.

Why it is frequently the right answer:

• No pump, so nothing to fail, nothing to run dry, no noise and no electricity.
• No break tank, so no stored water hygiene consideration in the way an open tank creates.
• It solves the actual problem in many houses, which is not that the main is inadequate on average but that it cannot meet a short peak.
• It works well with an unvented cylinder on a marginal supply, which is one of the commonest situations we meet.
• Maintenance is minimal – checking the charge pressure periodically.

The trade-off is space. Accumulators are physically large for the volume they store, and a useful one takes up room in a garage, a loft or a cupboard. That is usually the deciding factor.

Break tanks and booster sets

Where the main genuinely cannot deliver enough water even on average, storage plus pumping is the answer.

1. A break tank fills from the main at whatever rate is available, with an air gap so there is no backflow risk.
2. A booster set – usually a variable-speed pump, sometimes two for resilience – draws from the tank and pressurises the distribution.
3. Controls maintain a set outlet pressure and protect the pump from running dry.
4. Tank sizing has to cover peak demand plus refill time, which is the design calculation.

Considerations that come with it:

• Stored water needs managing – a lidded, insulated tank, and attention to turnover, because stored water at ambient temperature is a legionella consideration. That is a real obligation in commercial premises and good practice domestically – see water hygiene and legionella.
• Power dependency. No electricity, no water.
• Noise, from the pump.
• Space, for both tank and pump.
• Maintenance, because a pump is a moving part.

Where this comes up in Norfolk

• Rural properties at the end of long supply runs, where the main is small and the distance is considerable.
• Properties on private supplies – boreholes and wells – where a pump and pressure vessel are the system rather than a boost to it, and where the design is different again. See agriculture.
• Larger houses with several bathrooms on a supply sized for a smaller property.
• Conversions, where a barn or an outbuilding has been turned into a dwelling on a supply that was never intended for it.
• Top floors of tall properties, where static head alone reduces pressure noticeably.
• Properties wanting an unvented cylinder on a supply that will not feed one – and here the choice between upgrading the supply pipe, an accumulator, or staying with a gravity system and pumping is the whole conversation.

Getting the specification right

1. Measure properlyStatic pressure and dynamic flow at the stopcock, and ideally at the time of day the problem occurs. An afternoon reading may not represent a seven o’clock peak.
2. Establish whether it is pressure or flowPressure adequate but flow insufficient at peak points at an accumulator. Both inadequate points at storage and boosting – or at a supply pipe upgrade first.
3. Check the supply pipe itselfBecause upgrading an old narrow main is frequently cheaper and better than boosting around it – see water main replacement.
4. Calculate the actual demandSimultaneous outlets and their flow rates, not a rule of thumb.
5. Size storage or accumulator capacityFor the peak plus refill.
6. Consider resilienceDuty and standby pumps where a failure would matter.
7. Plan for maintenanceAccess, isolation, and somewhere the noise is acceptable.

The honest first question is always whether the supply pipe is the constraint. Replacing an old narrow main frequently removes the need for any boosting at all, and it is a simpler system to live with.