Backflow (basics)

Posted by in br2 plumbers boiler repairs, on April 13, 2014

Backflow, as it is called, is when water which could be contaminated is drawn back into the plumbing system. There are basically two causes of backflow: Back pressure and Back Siphonage. BR2 Plumbers are experienced in backflow.Back pressure is where the water may be caused to flow in the opposite direction. This could occur, for example, in an unvented heating system where pressure increases due to the expansion of the water as it heats up.Back Siphonage is defined as when pressure in a supply is lower than the pressure in the plumbing system, imagine a childrens play pool filled by a hose from an outside tap. Once it is full you turn off the hose and the water stops flowing. Imagine this pool being higher than the tap. When you switch off the hose you may leave it in the pool in case it needs topping up later. Unless there is a device to stop it happening, the water could start to flow backwards because the pool is higher than the supply point and gravity will be pushing it downwards. Air Gaps.A way of stopping backflow is an air gap between the water supply outlet and the top water level in an appliance. The gap means that water containing any dirt or bacteria etc. cannot be sucked back into the supply.Check Valves.If this air gap cannot be done, it could be possible to fit either single/double check valves in its place. One of the most common DIY tasks where you would have to consider this is when fitting an outside tap. This would be deemed to be a level 3 risk and meeting the regulations to prevent backflow from an outside tap can be achieved by fitting a double check valve. However, check valves cannot be used for all situations. If the fluid risk is greater than level 3, check valves are not acceptable. So using a check valve on a kitchen sink is not suitable as the fluid risk here is level 5 because potential contamination. Sinks may be used for washing blood from meat or soil from vegetables and these represent a significant health hazard so an air gap device must be used. This is also used in toilet cisterns. BR2 Boiler Repairs are qualified plumbers who can fit all plumbing equipment.

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