WillScot Mobile Mini Holdings Corp. said Monday it has struck a deal to sell its tank-and-pump segment to private-equity firm Kinderhook Industries for an enterprise value of roughly $323 million, part of WillScot's efforts to focus on its modular and storage operations.

The flexible-workspace and portable-storage-solutions company said proceeds from the sale would be used to support the ongoing reinvestment in its core operating segments. The transaction, which remains subject to customary closing conditions and regulatory approval, is expected to close in the third quarter, it said.

Eric John, senior vice president of the tank-and-pump segment, would serve as the chief executive officer of the newly independent business, WillScot said.

In premarket trading, the company's shares were 0.7% lower after ending last week at $41.44, up more than 50% over the last 12 months.

In mid-July, the company said it bought the rental fleet and related assets of Modulease Corp., adding more than 400 mobile offices and about 100 portable storage containers to its existing operations in New England.

Write to Robb M. Stewart at robb.stewart@wsj.com

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