The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 13, 1988
Filed:
Mar. 16, 1987
Applicant:
Inventors:
Riichi Uchida, Ibaraki, JP;
Seiji Tsuru, Ibaraki, JP;
Kazuaki Shiinoki, Ebina, JP;
Kotaro Naya, Ebina, JP;
Assignee:
Hitachi, Ltd., Tokyo, JP;
Attorney:
Primary Examiner:
Int. Cl.
CPC ...
F04B / ; F04B / ; F04B / ;
U.S. Cl.
CPC ...
417-2 ; 417247 ; 418-3 ; 418-9 ; 418 13 ;
Abstract
A two-stage vacuum pump apparatus has a first stage of vacuum pump constituted by a screw-type vacuum pump and a second stage vacuum pump constituted by an oil-sealed rotary vacuum pump operative to maintain the back pressure of the first stage vacuum pump at a level ranging from 1 to 100 Torr., whereby a high level of vacuum can be attained in a system to be evacuated without any risk of contamination of the evacuated system by oil. Also disclosed is a method of operating the two-stage vacuum pump apparatus.