What is a Break Tank

A break tank is an intermediate water storage tank installed between two parts of a water supply system so that they are not directly connected hydraulically. Water enters the tank through an inlet and is then drawn from the stored volume by a separate downstream system, often using a booster pump. Because the downstream side does not simply continue the upstream pressure, the tank creates a hydraulic break between the two sections.

Break tanks are used where pressure needs to be controlled, where a building requires a stored volume of water, or where separation between the incoming supply and downstream distribution is required. They are common in larger buildings, boosted water systems and installations where a direct connection between different pressure zones would be unsuitable.

The term describes the function of the tank rather than one particular tank design. Capacity, inlet arrangement, overflow provision, pumps, controls and backflow protection all depend on the system in which the break tank is installed.

How a Break Tank Separates Pressure Zones

In a directly connected pressurised system, pressure from the incoming main is transmitted into downstream pipework, subject to losses through pipes, valves and fittings. A break tank interrupts this relationship.

Incoming water discharges into the tank and becomes part of a stored body of water. The downstream supply then starts from the tank rather than remaining directly pressurised by the upstream source.

A simplified arrangement is:

Incoming supply → inlet control → break tank → pump → downstream distribution

The water level in the tank is maintained between operating limits. When water is drawn from the downstream system, the tank level can fall and the inlet replenishes the stored volume. Where a booster set is installed, the pump takes water from the tank and generates the pressure required by the downstream network.

This arrangement allows the pressure after the tank to be determined independently from the incoming mains pressure. For example, the incoming water supply may have sufficient pressure to fill the tank but not enough to serve upper floors of a tall building. A booster set downstream can then provide the required distribution pressure.

The reverse situation can also occur. An incoming supply or higher-level pipeline may provide more pressure than a downstream zone requires. Breaking the hydraulic connection allows the downstream system to operate under separately controlled conditions.

The main hydraulic differences can be summarised as follows:

The tank does not itself increase pressure. Where downstream pressure must be higher than the available static head from the tank, pumping equipment is required. This distinction is important because a break tank and a booster pump perform separate functions even when installed as part of the same system.

Pressure Control in Multi-Zone Water Systems

Pressure increases with vertical depth in a static body of water. As a useful approximation, a 10 metre difference in water elevation corresponds to about 1 bar of static water pressure. Actual operating pressure in a pipe system also depends on friction losses, flow rates, pump performance and other factors.

This relationship becomes important in tall buildings and systems covering substantial differences in elevation. If the entire installation were operated as one pressure zone, equipment at lower elevations could experience substantially higher static pressure than equipment near the top.

Dividing a system into pressure zones can make pressure easier to control. A break tank can form the boundary between these zones.

For example, one pumping arrangement may serve a lower section of a building while another system draws from a break tank and supplies higher floors. The exact arrangement depends on building height, required flow, allowable component pressures and the selected pumping strategy.

Pressure zoning can help:

• keep operating pressures within the limits of pipes, valves and fittings;
• provide appropriate pressure at higher elevations;
• avoid unnecessarily high pressure at lower outlets;
• separate sections served by different booster arrangements;
• provide a defined hydraulic boundary between parts of a system.

Pressure-reducing valves can also reduce downstream pressure and may be appropriate in many systems. They do not, however, create the same hydraulic separation or storage function as a break tank. The two solutions should therefore not be treated as interchangeable solely because both can form part of pressure-management strategies.

The required approach is determined by the complete hydraulic design. Building height alone does not establish whether a break tank is necessary.

Tank Capacity and Water Turnover

A break tank must contain enough water for the duty it is expected to perform, but simply installing the largest tank that will fit is not good design. Excessive storage can increase water residence time, while insufficient capacity can allow the level to fall too quickly during periods of high demand.

Tank sizing depends on factors such as:

• expected peak water demand;
• available incoming flow rate;
• required operating reserve;
• pump capacity;
• pattern of demand through the day;
• required response to temporary interruptions;
• space and structural constraints.

The relationship between incoming supply and peak demand is particularly important. If downstream demand temporarily exceeds the rate at which the incoming main can replenish the system, the stored volume provides a buffer. The tank level falls during the peak and recovers when demand reduces.

A tank is not an unlimited source of water. If downstream consumption remains greater than the incoming replenishment rate for long enough, the stored volume will eventually be depleted.

Pump controls therefore need to respond to water level. Low-level protection can prevent pumps from continuing to operate when insufficient water remains at the suction. Depending on the installation, additional level alarms may provide warning of abnormal conditions.

Turnover also matters. Water that remains stored for unnecessarily long periods can deteriorate in quality. Tank capacity should therefore be based on realistic system requirements rather than an assumption that additional storage is always beneficial.

The usable capacity is also different from the tank’s total geometric volume. Space above the normal maximum water level, operating level differences and low-level pump protection can mean that part of the physical tank volume is not available for normal supply.

Inlets, Overflows and Other Essential Connections

A functional break tank requires more than an inlet and an outlet. Water level must be controlled, excess incoming water must have a safe route away, and the tank needs provisions that allow inspection and maintenance.

The inlet normally incorporates a mechanism that regulates filling according to water level. Depending on the system, this may use a float-operated valve or another controlled inlet arrangement.

An overflow provides protection if the inlet control fails or water continues entering after the normal maximum level has been reached. The overflow needs sufficient capacity and should discharge to an appropriate visible or otherwise suitable location so that abnormal operation does not simply result in concealed flooding.

A warning arrangement may also be required depending on the installation. Its function is to provide an indication that the normal level-control system is not operating correctly.

Typical break tank components can include:

• controlled water inlet;
• appropriate air gap or other required backflow protection;
• overflow and warning arrangement;
• outlet or pump suction connection;
• drain or washout connection;
• access for inspection and cleaning;
• screened ventilation where required;
• water-level sensors or switches;
• low-water pump protection.

Connection positions influence how the tank operates. An outlet located too close to the bottom may be more exposed to settled material, while poor inlet and outlet positioning can create areas with limited water movement.

The tank also needs to withstand the load imposed by stored water. One cubic metre of water has a mass of approximately 1,000 kg, excluding the mass of the tank itself and associated equipment. A tank holding several cubic metres therefore represents a substantial structural load that must be considered when selecting its location.

Break Tanks and Backflow Protection

One important use of a break tank is to create physical separation between the incoming supply and a downstream system. Where an appropriate air gap is incorporated, the arrangement can prevent water from the downstream side being forced or siphoned back into the upstream supply.

An air gap is a physical vertical separation between the point where water enters and the maximum water level or spillover level of the receiving vessel, depending on the specific arrangement. Because there is no continuous pipe filled with water across this separation, reverse flow cannot travel directly through the gap.

This is fundamentally different from relying only on a mechanical check valve. A check valve contains moving components and remains part of a continuous pipe system. An appropriate air-gap arrangement provides physical separation.

The required backflow protection depends on the nature of the installation and the risk presented by the downstream system. Not every tank configuration provides the same level of protection, so the presence of a storage tank should not automatically be assumed to create a compliant air gap.

This distinction is especially important when terminology is used loosely. A cistern, header tank and break tank can look similar physically, but their functions and connection arrangements can differ. A tank becomes part of a backflow prevention strategy only when its inlet and spillover arrangements provide the required form of separation.

Pumping from a Break Tank

Where a break tank supplies a boosted system, pump selection and tank design have to be considered together. The pump must receive water reliably over its operating range without drawing air or operating dry.

The suction connection should be arranged to minimise hydraulic problems at the pump inlet. Available suction conditions, pipe losses and the relationship between water level and pump position all affect performance.

Booster sets may use multiple pumps rather than one large unit. This can allow capacity to respond to changing demand and can provide operational resilience where the system is designed accordingly. Variable-speed drives are also commonly used in modern booster systems to adjust pump output in response to pressure demand.

The tank level and pump controls must interact correctly. If the incoming supply cannot replenish the tank as quickly as the pumps remove water, the level falls. Continuing to pump after the available water has been exhausted can damage equipment and interrupt supply.

A well-designed control system may therefore monitor:

• tank water level;
• downstream pressure;
• pump operating status;
• low-water condition;
• abnormal high-water condition;
• faults within the booster set.

The break tank provides hydraulic separation and stored volume, while the booster set creates downstream pressure. Treating these as separate functions makes fault diagnosis easier. Low downstream pressure, for example, may be caused by pump performance even when the tank is filling correctly, while repeated low-level alarms may point towards inadequate incoming flow or excessive demand.

Water Quality and Tank Condition

Because a break tank stores water rather than passing it continuously through a closed pipe, its physical condition can affect water quality. The tank should be protected from contamination and remain accessible for appropriate inspection.

Covers, access points and vents need to prevent unnecessary entry of dirt, insects and other contaminants while still allowing the system to function correctly. Internal materials should be suitable for the water being stored.

Sediment can accumulate over time, particularly if material enters with the incoming supply or internal surfaces deteriorate. Stagnant zones can also develop where tank geometry and connection positions produce poor circulation.

Inspection can identify issues such as:

• sediment or debris inside the tank;
• damaged covers or access seals;
• corrosion or deterioration of components;
• malfunctioning inlet controls;
• blocked or damaged overflow arrangements;
• abnormal water levels;
• evidence of leakage around connections.

The appropriate inspection and cleaning regime depends on the application and applicable water-system requirements rather than one universal interval.

Changes in demand should also be considered over the life of the installation. A tank sized for a building with high water consumption may become oversized if occupancy or use later changes substantially. Conversely, an increase in demand can make an existing storage volume or inlet rate inadequate.

A break tank is consequently both a hydraulic component and a water storage vessel. Its effectiveness depends on maintaining the intended separation between pressure zones while providing sufficient usable storage, reliable level control and suitable conditions for the water it contains. In systems using downstream boosting, the tank and pumps must be designed together so that changes in incoming supply, stored volume and demand do not compromise the operation of the pressure zone.