If you are an owner or leasing a property where your business is subject to a high or medium risk hazard rating, then your properties drinking water should by law be protected with testable back flow prevention devices. These devices are mechanical backflow valves that rely on spring tensions, seatings and ‘o` rings to retain efficient protection.
At some point these mechanical parts will fail and require replacing. Yearly testing on these backflow valves provides us with information on leaking seats, seals and spring tensions that may have lost pressure. If this occurs we will replace the seals or faulty mechanisms and retest, returning the valve to working order.
Here is a common and typical looking testable backflow valve called an RPZD. Rpzd valves are the highest hazard rated valves on the market.
RPZD dumping water from the relief port
The reduced pressure zone device (RPZD) relies on differing water supply pressures to maintain an efficient working device. The red zone in the picture above is the mains pressure water coming into the valve forcing the first check spring open and forcing the diaphragm in the relief port closed. The water in the blue zone is of a lesser pressure than the red, due to the force it has to exert to open the first spring. This allows the diaphragm in the relief port to stay closed when the blue zone is full of water. As the water passes through the second spring into the white zone the water pressure is further reduced by between 7-10kpa. If water is forced in the opposite direction through the valve by back pressure or back siphonage, the increased pressure in the blue zone (back pressure) or decreased pressure in the red zone (back siphonage) forces the diaphragm open and first check spring closed and dumps all the contents of the blue zone through the relief port, protecting the upstream water supply.
- Some signs that suggest you get RPZD valves checked before their 12 month checkup is due are:
- If the valve is discharging water continuously from the bottom relief port, this suggests that there maybe a blockage in the valve but it is unknown till a test can be carried out on the valve.
Dripping relief ports:
-Act as a tell-tale for a faulty No 1 check valve assembly.
-Provide a safety barrier in the event of a pressure loss in the water supply system upstream.
-Act as a tell-tale in the event of a faulty No 2 check valve assembly through backpressure.
Also, check that the downstream isolation valve directly after the backflow device is open. If it’s closed this could cause pressure build up in the device and cause it to dump water or drip continuously. If dripping continues after opening the valve this is worth getting it checked to determine the cause.
- If the valve randomly spits or discharges water but then stops the valve is more than likely just doing its job.
RPZD valves are one of the most common backflow valves on the market and are used for high risk areas. However, there is another valve called a double check valve which is rated for medium risk areas and is usually seen on fire services of all sizes.
Backflow valves are there for your safety, protecting your drinking water from possible contaminants, do the right thing and get them checked as faulty valves have the potential to cause serious harm or even death.