Abstract: A differential expansion control assembly is provided for a pump. The pump has a pump body with a base portion and cover portion of a first material with a first thermal expansion coefficient and a pumping mechanism of a second material with a second thermal expansion coefficient different from the first thermal expansion coefficient. The differential expansion control assembly includes at least one member disposed between the base portion and cover portion to negate a difference between the first thermal expansion coefficient and the second thermal expansion coefficient and maintain a relative controlled clearance between the cover portion and the pumping mechanism. The differential expansion control assembly also includes a seal disposed between the cover portion and base portion to allow for differential expansion of the pump body without leakage of fluid between the cover portion and base portion.