Allison ATT-52549 AVB Spring CompressorAllison ATT 52549 AVB Spring Compressor The ATT 52549 AVB Spring Compressor has been developed to minimize the risk of damaging the internal surfaces of the aluminum valve body when removing and installing valve retention hardware. The sleeve of the two piece tool is used to guide the tool into the second section of the Converter Regulator Valve. Only ATT 52549 AVB Spring Compressor is to be used on the aluminum valve body. The tool for iron valve