A local aircraft manufacturer has a fuel farm of ten large tanks, each storing 30,000 gallons of Jet A fuel. A valve on each tank opens to allow fuel to flow in and out to tank trucks or other tanks. When one of these valves failed, the customer called in ACES.
The ACES Control Systems Investigator on the scene started by pulling the explosion-proof cover off of the valve, and immediately saw that parts of the valve were corroded — including the contacts in the circuit board — and consequently the valve motor wouldn’t run.
This led the CSI to ask himself the question, “Why is there corrosion inside of this explosion-proof sealed case?”
Upon further examination the CSI ascertained that a small, gel-cell, lead-acid battery which was part of the valve unit had frozen and busted open, releasing sulphuric acid inside the sealed enclosure to eat away at the circuit board, wires and components. The purpose of this small battery is to run the motor and close the valve if for any reason the electricity shuts off, due to fire or other emergency. This is a safety measure to lock down a tank full of highly volatile jet fuel.
The life span of these batteries is typically two years, but this particular one hadn’t been replaced for 14 years. In the event of an electrical failure the valve would have remained wide open.
The CSI deduced that the valves on the remaining tanks probably hadn’t been replaced either — and he was right. When he pulled the covers off, he discovered seven of the nine remaining batteries had also frozen and ruptured and were starting to corrode. All of these valves were still functioning, but none of them would have closed properly in an emergency.
The CSI installed a new valve unit, including valve head, gear train, rotor and circuit board on the failed valve. On all the others he cleaned out the corrosion and battery acid and installed new batteries. Now the customer’s valves not only work flawlessly on a day-to-day basis, but will also close themselves down properly if the electricity goes off.