Changing alarm delays, tightening inventory tolerances, or adding a pressure switch before checking the interstice rarely solves this application. The two 10,000-liter petroleum tanks supply a continuously running generator, so normal level movement can mask a leak and turn inventory-only monitoring into a process-balance problem. Start by selecting the failure you need to detect, then verify that the sensor, wiring, controller input, and alarm path detect it independently of fuel consumption.
Why do the usual fixes fail?
Inventory reconciliation is often the first idea because the primary-tank level is already useful for operations. During continuous generator consumption, however, the observed level change combines fuel use, deliveries or transfers, water accumulation, measurement error, temperature effects, and any leakage. Tightening the allowed volume deviation does not separate those terms; it can produce nuisance alarms without locating the failure.
Interstitial pressure monitoring can detect loss of an intentionally maintained pressure or vacuum, but a pressure switch alone is not a universal substitute for a liquid sensor. The method depends on a closed interstice designed for pressure or vacuum service, stable tubing and seals, and an alarm threshold appropriate to the tank construction. Leakage in the monitoring circuit can look like a tank failure, while a liquid leak may not create the expected pressure change if the interstice is vented or not designed for that method.
A hydrocarbon-only sensor removes generator consumption from the measurement, but it can miss water entering the interstice. A water-only float has the opposite limitation. Moving alarm thresholds or replacing the controller does not correct an omitted leak mode, unsuitable sensor location, damaged cable, or incompatible input.
What is the real measurement problem?
The interstice is the direct observation point for a double-wall tank. A breach of the primary wall can place product there; a breach of the outer wall can admit water. A dual hydrocarbon/water sensor therefore addresses both liquid conditions at the location where either wall failure becomes observable. It also avoids estimating leakage from a primary-tank inventory that is changing because the generator runs continuously.
The complete signal chain matters. The sensor must encounter the liquid, change state as designed, pass that state through the field wiring and input interface, and cause the monitoring system to issue a distinguishable alarm. Tuning does not fix wiring.
| Signal | Source | Wrong-value symptom |
|---|---|---|
| Hydrocarbon presence | Interstitial hydrocarbon element | A dry indication during a product exposure points to placement, sensor, cable, or input-channel trouble. |
| Water presence | Interstitial water element or float | A permanently wet indication can result from standing water, a stuck mechanism, wiring state, or incorrect input interpretation. |
| Interstitial pressure or vacuum | Pressure transducer or switch on a sealed monitoring circuit | Drift or repeated pressure loss can come from monitoring-line leakage as well as a wall failure. |
| Primary-tank liquid level | Tank gauge | Unexpected volume loss can represent consumption, transfer, measurement effects, or leakage; it does not identify the leak path by itself. |
| Primary-tank water level | Water-detecting tank probe | Rising water identifies water inside the primary tank, not necessarily liquid in the interstice. |
Which monitoring method fits these tanks?
For the lowest routine maintenance, use passive interstitial liquid detection when the tank geometry lets leaked liquid reach an accessible low point. A dual hydrocarbon/water sensor is the strongest default because it detects product escaping outward and water entering inward without maintaining a pressure source or calculating a consumption-adjusted inventory balance.
Use pressure or vacuum monitoring only when the tank manufacturer identifies the interstice as suitable for that service and provides the required operating limits and test method. This approach can supervise interstitial integrity continuously, but it adds seals, tubing, pressure-producing or vacuum-producing equipment where applicable, and diagnostics to distinguish a tank-wall event from a monitoring-circuit fault.
Retain primary-tank hydrocarbon and water measurements for inventory, delivery control, generator operating visibility, and secondary leak evidence. Do not make them the sole double-wall integrity measurement while the load continuously consumes fuel.
A Veeder-Root TLS 350 or OPW iSite can be considered as the annunciation platform, but select the field method first. Before procurement, obtain written confirmation that the exact sensor type, input module, cable arrangement, alarm behavior, and required supervision are supported by the installed controller configuration.
How should the system be selected and installed?
- Confirm the construction of each
10,000-litertank. Identify whether the interstice is dry, liquid-filled, vented, sealed, or specifically designed for pressure or vacuum monitoring. - Identify every liquid that can reach the interstice. At minimum, evaluate stored petroleum from the primary wall and water through the outer wall.
- Inspect the interstitial geometry and locate the true collection low point. Account for tank slope, internal obstructions, access risers, and any path that could trap liquid away from the sensor.
- Select a dual hydrocarbon/water sensor when both liquids can collect at the sensing point. Verify material compatibility with the stored product and confirm whether the sensor is reusable after exposure or requires replacement.
- Match the sensor output to the proposed
TLS 350,iSite, or other monitor. Check the controller documentation for the exact input interface, line supervision, permitted wiring, alarm labels, and fault behavior. - Route and terminate the cable so environmental moisture, junction-box leakage, shielding errors, or conductor damage cannot imitate a wet sensor or hide a real one.
- Configure separate, recognizable indications for hydrocarbon, water, sensor fault, and controller or communication failure wherever the selected equipment supports those states.
- Document the alarm response: verify the affected tank, protect generator fuel continuity, inspect the interstice, and investigate which wall may have failed before removing an alarm from service.
How do you prove the alarm works?
Look at the trend first. Record primary fuel level, primary water level, interstitial state, and any pressure or vacuum measurement before testing. A stable dry indication is only a baseline; it does not prove that the field element can detect liquid.
Perform the controller and sensor functional tests specified for the selected devices. Exercise each supported state at the sensing point or through the manufacturer-defined test feature, then trace it through the entire chain: local sensor response, input status, alarm text, remote notification, operator acknowledgment, and return to normal. Confirm that an open or otherwise failed field circuit produces a fault rather than a false dry condition when line supervision is available.
For pressure or vacuum monitoring, isolate tank integrity from monitoring-circuit leakage using the tank manufacturer's test procedure. For liquid sensing, verify that a test quantity placed at the approved test location can physically reach the sensor and can be removed after the test. Record the initial test result as the maintenance baseline.
What recurring pitfalls create false confidence?
A sensor mounted in an access opening is ineffective if leaked liquid collects elsewhere. One shared input for multiple tanks can also identify an alarm without identifying which tank caused it, extending response time. Map every field device to its tank and channel during commissioning.
Do not treat primary-tank water measurement as interstitial water detection; the two sensors observe different boundaries. Likewise, do not infer a pressure-monitoring design from the presence of an interstitial connection. Obtain the tank manufacturer's permitted monitoring method and limits before applying pressure or vacuum.
Bypassed alarms, untested remote notifications, and input states that fail dry are control-system failures even when the sensing technology is correct. Schedule proof tests around the sensor's exposure and reset requirements, and keep test records by tank, sensor, input channel, and alarm destination.
FAQ
Can I use tank-level variation as the only leak alarm?
No. With a generator running continuously, measured volume change includes normal fuel consumption and other inventory effects. Use tank level for inventory and corroboration, with direct interstitial monitoring for double-wall integrity.
Does a dual hydrocarbon/water sensor reduce maintenance?
It can, when both liquids drain naturally to one accessible sensing point. It avoids a maintained pressure or vacuum circuit, but still requires periodic functional testing and inspection after exposure.
Can a Veeder-Root TLS 350 monitor both tanks and piping?
Only when the installed TLS 350 configuration has compatible sensors, input interfaces, and alarm functions for each monitored point. Verify the exact hardware and wiring combination in the manufacturer documentation before purchasing field devices.
When should I stop troubleshooting and contact official support?
Stop if tank construction is unknown, the interstice cannot be inspected, a proof test does not reach the sensor, or the controller cannot distinguish alarm from circuit fault. Isolate the affected monitoring channel according to site procedure and contact the tank or monitoring-system manufacturer's official support channel with tank construction details, controller configuration, wiring records, and proof-test results.