A double check valve prevents back siphoning and contamination of fresh water supplies. It consists of two non-return check valves mounted in one housing for redundancy and efficient seating. Backflow contamination is a major source of freshwater contamination, and check valves rely on a spring- or gravity-loaded plunger or diaphragm to allow fluids to flow in only one direction. Dual shutoff valves and test taps are usually found on larger industrial variants, while domestic double check valves are smaller and simpler.
A double check valve is a plumbing fitting that prevents back siphoning to protect fresh water supplies from contamination. This fitting is typically installed on fresh water supplies for garden irrigation, combination boilers and fire supplies where there is a risk of back flow contamination. The unit consists of two standard non-return check valves mounted in series in one housing. The basic concepts behind these valves include redundancy and more reliable seating of each valve. Larger industrial-style double check valves often include an isolation valve at both ends and test cocks at various points, while residential examples are typically sleek and inline.
Backwater or backflow is a major source of freshwater contamination and has been positively linked to many waterborne disease outbreaks. Risks of backflow contamination exist wherever fresh potable water supplies are used to feed sprinkler systems, garden or farm irrigation, chemical dosing systems or combination boilers. If no backflow protection is installed in these configurations, any significant drop in fresh side pressure will see the contaminated water flow back into the potable mains. The best way to protect fresh water supplies from this backflow is to install a backflow prevention device such as a double check valve.
A check valve is a fairly simple, robust, and reliable one-way valve that relies on a spring- or gravity-loaded plunger or diaphragm to allow fluids to flow in only one direction. This is typically achieved by constructing the valve such that the valve disc opens when exposed to pressure from one side and is forced positively to close upon a pressure drop or reversal. The double check valve features two such units mounted in series with the water flow path. The concept behind this design is a dual combination of redundancy and efficiency.
The redundancy benefits of the dual check valve are pretty self-explanatory; one valve is always able to support the other in the event of a blockage or failure of the mechanism. From an efficiency standpoint, the pressure difference between the two valves during operation means that both are able to sit more effectively, thus increasing the overall effectiveness of the system. The flexibility of the dual check valve is further enhanced by the inclusion of dual shutoff valves at both ends of the fitting allowing both sides of the circuit to be isolated if the need arises. These and smaller test taps used to test the operation of the system are usually found on larger industrial variants. Domestic double check valves are generally smaller and simpler and are typically in-line designs or are built into standard faucets or bibs.
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