5. FUEL SYSTEM MXU 500 IRS Float Float Tang Check the float and float tang for deformation or damage. Check the float valve and valve seat for foreign substance, clogging or damage. Check the tip of the float valve, where it contacts the valve seat, for stepped wear or contamination. Check the operation of the float valve. Piston Valve Check the piston valve for scratches, wear and damage. Check the rubber diaphragm for tears. Rubber Diaphragm 5-14