Overview
The Veeder-Root 0794390-420 interstitial leak sensor is a proven, non-discriminating float switch designed for continuous monitoring of the interstitial space in double-wall steel storage tanks. This sensor detects the presence of liquid between the double walls of the tank, triggering immediate visual and audible alarms on compatible Veeder-Root TLS monitoring consoles. Used widely in fuel storage, this sensor helps operators comply with EPA and state environmental regulations while minimizing cleanup costs and downtime.
Key Features
- Non-discriminating detection of liquid between double walls of the tank
- Can be used in the annulus of steel tanks with a sensor riser pipe 1.5″ I.D. or greater; only two wires required to connect to a TLS or ILS system
- Triggers alarm in automatic tank gauge console with visual and audible notification for immediate action to prevent safety and environmental issues
- Reed switch / float activation mechanism
- Available with 16-foot (4.88m) cable; alternative 30-foot (9.14m) cable configuration also available
Technical Specifications
- Operating Temperature: -4 to +140°F (-20 to +60°C)
- Product Activation Height: 1.4″ (3.56cm)
- Dimensions: 2.5″ (6.4cm) high, 1.5″ (3.8cm) diameter
- Detection Mechanism: Reed Switch / Float
- Cable Length: 16 feet (4.88 meters)
- Warranty: 1 Year Parts & Labor (when purchased with system); 1 Year Parts Only (when purchased separately)
Typical Applications
The Veeder-Root 0794390-420 is used in petroleum and fuel distribution environments where regulatory compliance and early leak detection are critical:
- Underground storage tank (UST) systems for gasoline, diesel, and heating oil
- Double-wall steel tank annulus monitoring in fuel service stations
- Environmental compliance and spill prevention programs
- Fuel facility asset protection and liability management
Compatibility & Replacements
Compatible With
- TLS-450, TLS-350R, TLS-350, TLS-350J, ILS-350, TLS-300i, and TLS-300C monitoring consoles
- TLS-250i and ILS-250 consoles with on-site alarm capability
- Veeder-Root TLS-3XX/TLS-450 Series Consoles
- Veeder-Root TLS4 (8601 Series) Consoles
- Double-wall steel fuel storage tanks with 1.5″ I.D. or greater riser pipes
Replaces / Drop-In Replacement For
- 794380-420 (legacy 16ft cable version)
- Other non-discriminating interstitial sensors of equivalent specifications for steel tank applications
Works With
- Veeder-Root automatic tank gauge (ATG) monitoring systems
- Two-wire sensor connection standard (compatible with all TLS/ILS console wiring harnesses)
- Fuel compatibility: gasoline, diesel, kerosene, heating oil, and blended fuels


















