One of the many challenges encountered in urban drainage design is the cost-effective connection of development drains to the existing public sewer system. Generally, both surface water and waste water systems drain by gravity flow, and pumped solutions are avoided where possible due to increased capital and maintenance costs. Sometimes, even though the site levels and the existing sewer gradients allow for the new drains to discharge by gravity, there is a concern regarding the impact of surcharge in the existing system on the site drainage.
Thus, measures need to be taken to reduce the risk of sewer flooding on site. The Checkmate inline check valve from Tideflex is an ideal device for backflow prevention in a surcharged system draining public areas such as these. Its unique design means that it is more than up to the challenge of difficult environs and provides many advantages over other types of check valves. It also offers odour abatement and protection from rodents, which is always a concern with waste water drainage systems.
Rubber construction - flexible, durable & strong
Unibody construction with smooth surfaces and no sharp edges
Low cracking pressure
Located inside the pipe / ends flush with the headwall
Does not warp, freeze or corrode so maintains long-term function
Easy to fit
No maintenance - saving operational time and money
25+ years service life - long-term capital cost savings
Reliable, proven track record - no unpleasant surprises
Drains and self-clears in relatively flat designs - ideal for low-flows
No areas or parts that trap or snag debris - no blockages or loss of function
What is Sewer Surcharge?
Sewer surcharge is when a sewer is overloaded beyond its design capacity and results in full pipes flowing under pressure and flooded manholes. Unfortunately, in many older urban areas new development has meant that existing drainage networks are inadequate to the task and new sites need to take precautions when connecting to them. Surface water drainage design is most prone to this and is addressed with attenuation and flow regulators to control peak discharge. Foul or waste water drainage does not usually pose as much of a problem, except where existing sewers are combined, and thus also carry surface water.
Whether the connection is made using gravity or pumps, there needs to be a backflow prevention device, otherwise known as a non-return valve or check valve. This type of valve allows flows through, but closes to prevent waste water from flowing back up into the system when the water level rises at the connection. During the period when the check valve is closed, the design includes for either storage of the water in the internal drainage system until it can safely drain away by gravity, or pumping at a high level into the external system (called overpumping).
Once the water level in the external system has fallen, the water level in the site drainage system will push open the valve and drain the system down.
One of the many factors that can affect the proper function of a check valve in a drainage system is "ragging" due to a large volume of toilet waste and other solids being flushed into the system or litter entering through road gullies. This is particularly an issue in systems draining public bathrooms and carparks, for example, in shopping centres and on college campuses. Oftentimes an issue only comes to light after a flooding incident and we have been approached on a number of occasions to provide retrofit solutions. Obviously this can be a messy, and hazardous, business!
MeasurIT now supply the upgraded CheckMate® UltraFlex™ inline valve which is suitable for raw sewage in 225mm & above, which opens to allow flows through even in drains with shallow gradients and slow-moving solids in low-flows.
CheckMate valves have been retrofitted on a college campus with a flat site which experienced backflow issues from a surcharging public sewer. These valves have been functioning as expected for a number of years.
You can view the flow through this valve in the video below.