Hydraulic disconnector

A hydraulic backflow preventer is a pollution control device that protects the drinking water network against backflow (against pressure or siphoning) from technical installations such as boiler rooms, air conditioners, domestic hot water systems, irrigation systems, and process water systems. Unlike a simple check valve, it creates a hydraulic separation with discharge to the sewer system, preventing any potentially contaminated water from flowing back into the main water supply. It is the essential component for filling heating circuits, supplying water heaters, or any interface between the public and private water networks that are at risk.

Disconnector: definition, types and principle

A backflow preventer consists of isolation devices, controllable valves, and an intermediate zone with reduced pressure and an open discharge point (visible air gap/drain). In the event of suction from the network or overpressure on the installation side, the zone depressurizes and discharges the water to the sewer instead of allowing it to return to the potable water supply.

Main families (from most protective to simplest):

- Type BA (RPZ – controllable reduced pressure zone): reference for high-risk applications (boiler room, process). Testable and sealable.

- Type CA : similar principle, less protection depending on the context.

- Type EA (controllable anti-pollution valve): for limited risk; does not replace a BA when the risk is significant.

Good installation practices : upstream/downstream isolation valves, pressure taps and test valves, upstream filter, visible and non-submersible sewer discharge, accessibility for testing and maintenance.

Where, why and how to exploit it (advantages, limitations, key points)

Main interests

• Sanitary safety: blocks siphoning and back pressure (treatment products, sludge, DHW, additives).
• Compliance: meets the anti-pollution requirements of public distribution systems.
• Clear operation: periodic tests possible (on BA), defects visible by rejection.

Limitations to be aware of

• Significant pressure losses (to be taken into account in the sizing).
• Mandatory maintenance: regular (and traceable) checks; seals/springs to be replaced.
• Sensitivity to impurities: without upstream filtration, there is a risk of leaks or untimely discharges.

Points of attention in planning/operation

• Choose the type according to the level of risk (process, chemistry, heating, watering).
• Location: accessible, frost-free area, visible gravity discharge, clear labeling.
• Upstream: screen filter + valve; sufficient pressure available after losses.
• Downstream: avoid overpressure (water hammer); provide an expansion vessel on closed systems.
• Testing: plan periodic functional tests (BA) with pressure measurement and log entry.
• Heating/DHW filling: provide a dedicated filling station with disconnector, removable hose and sealable tap.

Anecdote — “A backflow of water avoided in Boulogne-Billancourt”

In Boulogne-Billancourt, a boiler room supplied a network whose expansion vessel was improperly adjusted. During a sudden shutdown, the backpressure attempted to force the treated water back into the main supply. The BA backflow preventer opened its discharge zone and released the water into the sewer: no contamination of the drinking water network. After inspection, the team added an upstream filter, recalibrated the expansion vessel, and scheduled an annual test of the backflow preventer. The manager commented: "A little water down the drain is better than an entire building being declared unsafe to drink."