Description The Veeder-Root 794390-409 Non-Discriminating Interstitial Sensor for double-wall fiberglass tanks detects the presence of liquid in the interstitial space of the tank. The Interstitial Sensor detects the presence of liquid between the double wall of fiberglass tanks. Liquid triggers an alarm signal to your automatic tank gauge. You’ll know immediately where the problem is so you can take action to prevent serious and costly safety and environmental problems. Key Features Used in the annulus of a fiberglass tank with a riser pipe of 4IN Detects leaks in interstital space of fiberglass tanks Cable length of 25' UL and NWGLDE approval Compatible with gasoline, diesel, kerosene, jet fuel, aviation gas, waste oil, motor oil, gasoline with up to 15% ethanol, diesel with up to 20% biodiesel Includes: Installation Kit P/N 312020-949 No additional mounting hardware required.