Exhibit 32.2

CERTIFICATION PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

(18 U.S.C. SECTION 1350)

In connection with Amendment No. 1 to the Annual Report of Flow International Corporation, a Washington corporation (the “Company”), on Form 10-K/A for the year ending April 30, 2005 as filed with the Securities and Exchange Commission (the “Report”), I, Douglas P. Fletcher, Principal Financial Officer of the Company, certify, pursuant to § 906 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. § 1350), that to my knowledge:

(1) The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and result of operations of the Company.

/s/    DOUGLAS P. FLETCHER        

Douglas P. Fletcher

Principal Financial Officer

November 23, 2005