Flow General Inc., the troubled biomedical products and applied sciences firm, has announced that Robert E. Wengler will become the company's chief executive officer on July 1, the beginning of Flow's 1986 fiscal year.

Wengler, president and chief operating officer of the company since March 1984, will replace Grant C. Ehrlich, who will retain the position of chairman.

Ehrlich, 68, a founding member of Flow's board of directors, assumed the titles of chairman and CEO in March 1983. He has led efforts to turn around a company plagued with heavy losses, high debt and messy lawsuits under prior management.

For the last two years, Ehrlich and Wengler have worked closely together to reorganize the company around its traditionally successful applied-scientific businesses, while shedding some of its high-risk biomedical ventures, Wengler said. "You won't see anything different" until July, Wengler said, adding that he will unveil new plans for the company when he assumes the CEO job.

Although given high marks by analysts, the current management team has not yet stopped the flow of red ink, and has suffered its own legal problems. Flow lost $7.4 million (88 cents a share) on sales of $136.7 million for its fiscal year ended June 30, 1984, and reported a first-quarter loss of $1.9 million (22 cents) on sales of $33 million for the three months ended Sept. 30.

The McLean company was forced to close its biomedical products manufacturing facility for two weeks last summer after federal officials seized products made there, acting on complaints of impurities and other production problems. Flow reached an agreement with the government settling the matter, but the biomedical group remains "emotionally on probation," Wengler said.

"We still have problems, but it's getting better," Wengler said. "Everything except the biotechnology operations are doing well. On balance, there's more good news than bad."

Wengler joined Flow in 1968 after working as a director for advanced technology programs for Northrop Corp. At Flow, he has served as president of the General Research Corp. subsidiary and as director of the applied sciences group. He was a founder and president of Flow's Effects Technology Inc. subsidiary.

"This change in senior management represents the type of orderly process we sought when we initiated the company's transition program two years ago," Ehrlich said.