How do rat valves work?

The theory behind them…

Rat valves or ‘rat flaps’ are simple devices that stop rats travelling past a certain point within a drainage system.

Drainage systems flow from A to B – inherent to all drainage networks is a gradient to achieve this.

This flow of water therefore carries momentum and it’s this momentum that lifts a valve flap – gravity then closes it.

The valves are designed so the flap will only lift in one direction – in the direction of flow.

As rats live in sewers and drains flow to sewers, then rat valves stop rat traffic traveling up from the sewers (i.e. against the direction of flow).

If you have a drainage defect under your house that you don’t want rats to emerge from then a correctly positioned rat valve will stop them reaching it yet allow waste to flow to the sewers in the normal fashion.

This as hugely more economic solution compared to digging up your floor and fixing the defect directly (as typically the defect involved doesn’t affect the drainage but just allows rats to infest your building).

Flow and gravity are constants within a drain so the valve needs no maintenance.

Simples eh?

The reality…

Not all drains have good flow – most these days have areas of poor flow due to pipe sag or joint misalignment.

Poor flow means low momentum which in turn means solids may not pass cleanly through the valve which in turn reduces flow further and problems arise (blockages).

The ability of gravity to close the valve depends on the valve having a free-acting hinge mechanism.

Some hinge designs clog with gunk over time and eventually introduce a friction level that wins over gravity so the valve sticks open.

Here is the real shocker… most rat valves on the market can be lifted by rats. Yes really. We are not going to give all our competitors the edge and explain how but they can and do.

And once you see how they do it, it is a truly humbling experience in terms of this creatures ability to problem solve and adapt to challenges within its environment.

You will never under-estimate them again!

Bad valves…

Bad valves are anything plastic – rats will shred these and chew the flaps off within minutes.

Bad valves are anything with a poor hinge mechanism – drains are harsh environments so a lot of thought needs to be given to the hinge mechanism to ensure it can last many years without sticking.

Bad valves are anything that reduces the internal dimensions of the pipe – sudden restrictions reduce flow and give solids an anchor point to snag on.

Bad valves are anything with non-serrated flaps – rats will try and lift these flaps so the serrations play an important part.

Bad valves are anything that has less than 2 flaps – double flaps are an important part of the rat defence strategy.

Good valves…

Good valves have all components 316 stainless steel – that way nothing rusts and gums up for many, many years.

Good valves have a body design that doesn’t reduce the internal dimensions of the pipe nor introduce any snag points.

Good valves have a flap design that requires minimal momentum from the water to lift and which glide over the top of any passing solids.

Good valves have double, serrated flaps to ensure there is no chance of rats getting past them.

Danish valves…

We only use Danish valves here at Pestology.

Why? Because its law in Denmark to fit rat valves to all public buildings so they are 20 years ahead of the game compared to the UK.

Danish valves are fully evolved and fully rat proof – they don’t clog and they have long, maintenance free service lives.

We wouldn’t fit anything else – it’s a false economy.