CREATE TABLE table_28018 ("Class" CLOB, "Firebox" CLOB, "Cylinder size" CLOB, "Valves" CLOB, "Valve gear" CLOB, "Number built" CLOB, "Years built" CLOB)

How many types of valves were used on this engine that was built on 1902-05?
SELECT COUNT("Valves") FROM table_28018 WHERE "Years built" = '1902-05'
SELECT COUNT("Valves") FROM "table_28018" WHERE "Years built" = '1902-05'