4N3411 Valve Fits Caterpillar 5230 5230B 776 776C 776D 784B 784C 777 777C 777DOne New Aftermarket Replacement Relay Valve Fits Caterpillar (Fits CAT) Construction Equipment This 1 1 2 inch air relay valve is a key component in the air starting system on Fits Caterpillar (Fits CAT) large construction and mining equipment. The relay valve controls the flow of compressed air to the air starting motor holding air back until the starter control valve is activated, then opening the supply line to crank the engine. A failed or leaking