There is a slightly different way of flushing the toilet, and this is called the air valve or to give it its full name, an air admittance valve. One really great advantage of an air admittance valve is that they remove the requirement for holes through a roof or an external wall. These valves also reduce the pipework that is needed to fit an external, open soil or vent stack. The air admittance valve is very similar a really big non-return valve. Coulsden Plumbers only use qualified tradesmen. This valve lets air to enter into a system via its body, but blocks any foul odours from returning back into the immediate area of the WC and (or bathroom). This means that because in the drain there is a negative pressure, the valve will open up instead of a suction to move the water and waste. A Coulsden Plumber is trained to fit air valves. The admittance valve can be found in many sizes and sometimes this valve can be used to terminate the main waste drainage stack. The usual employment of this valve is where there are two soil stacks in the same building or lots of buildings are closely situated, so this type of valve really stops the need to run the high point of a soil discharge stack out of the roof. This will also remove the need for tiling etc. This also forms some protection for the building against rainwater ingress. The air admittance valve really is best installed higher than the critical level (also called the spill level) of any appliance. If this is not carried out and a block occurs it will back up with water and remove the valves watertight capacity. The condensate in the pipework can freeze, but as long as the valve has the correct insulation it can be fitted in the more exposed areas.