The Burlington, Mass., company called Crane's offer "low-value, highly conditional and opportunistic."
Circor said in a Thursday statement, "Execution of the company's strategic plan will deliver significantly greater value in the near and long term."
A merger would bring together two producers of valves and fluid-control components. Crane also produces vending machines, airplane brakes and other industrial products.
Crane on Monday increased its offer for Circor, boosting its bid by nearly 7% to $48 a share cash.
In a statement Crane said the sweetened offer is a 57% premium over the stock's May 20 close, and about 46% above the three-month and 61% above the six-month volume-weighted average share prices.
Stamford, Conn.-based Crane's shares were up less than 1% to $81.54.
Circor shares fell the most since May 7, though they are up more than 92% year to date.