Family-owned Busch already holds 27.2 percent of Pfeiffer's stock and has secured additional shares taking its holding to 29.98 percent stake, the cusp of the threshold at which it will be forced to make a public offer for all outstanding stock, the group said.

Shares in Pfeiffer, which have gained around 20 percent over the past year, were up 7.2 percent at 99.50 euros by 1105 GMT.

Busch manager Sami Busch told Reuters that the idea was not necessarily to secure full ownership of Pfeiffer.

"We want both companies to operate independently and Pfeiffer to remain stock exchange listed," Busch said.

Pfeiffer makes pumps used by manufacturers including semiconductor firms and makers of analytical devices such as electron microscopes. Busch describes itself as one of the world's largest makers of vacuum pumps, blowers and compressors supplying all industry sectors.

Busch has already received firm commitments from lender LBBW to finance the deal, which is not conditional upon any minimum acceptance threshold.

A spokesman for Pfeiffer said Busch's move came as a surprise. Management and Pfeiffer's supervisory board will have to examine the offer and make a recommendation to shareholders.

($1 = 0.9313 euros)

(Reporting by Maria Sheahan and Anneli Palmen; editing by Jason Neely and Keith Weir)