4 mm Air Line Non Return Valves, these simply fit in line and prevent water from the system back siphoning back into the Air Pumps if the power fails or when maintaining the system and the power is switched off.
These simple 4 mm Air Line Non Return Valves (check valves) are very important if you cannot mount your air pump above the water level in your system. Remember accidents can and do happen, don't let it happen to you for the sake of a few pence, always have a few on hand as you never know when you may need them.
Fits all the 4 mm Silicon and clear Airline above.
