Flange gasket failure on 4 bolt flapper valves is a frequent transformer leak problem. (Figure 1) Once the gasket fails additional bolt tightening will rarely stop the leak. To repair the gasket normally the radiator bank must be drained and the bank removed. Many utility maintenance personnel drain the oil from the main tank also because often the flapper valves cannot be trusted to hold the oil in the main tank. Usually all gaskets are replaced while the radiator is removed. The transformer is lost from service during this costly repair method.
TDS Repair Technique
The TDS repair procedure is done without draining the oil and can be accomplished while the transformer is energized if the leaks are located on the bottom connections. If upper leaks are to be repaired, depending on the proximity of the leaking component to high-side, low-side, and neutral bushings, and other energized components, the transformer may have to be de-energized and grounded. To repair the failed gasket, TDS drills and taps 4 equidistant holes into the gasket groove. Injection valves are threaded into the holes as sealant is pumped into the failed gasket area using low-pressure hydraulic techniques. (Figure 2) The sealant flows into all the failed areas, thereby fixing the leak. Pipe plugs are placed in the tapped holes after the sealant has cured. Usually a 4-bolt flange can be repaired in two hours.