Charlotte-based SPX Corp. is close to announcing an agreement to buy Gardner Denver Inc., a producer of industrial air compressors, for more than $4 billion, said a person familiar with the matter.

SPX, which produces industrial equipment for a variety of industries, emerged as the leader in the sale process earlier this month, said two people who asked not to be named as the process is private. Gardner Denver canceled meetings with four private-equity firms also bidding, they said.

A deal would mark a victory for activist investor ValueAct Capital Management LLC, which owns 5.1 percent of Gardner Denver’s stock, according to data compiled by Bloomberg as of Sept. 30. The San Francisco-based firm started pushing for a sale in July after Gardner Denver Chief Executive Officer Barry Pennypacker quit.

Vikram Kini, a spokesman for Gardner Denver, didn’t immediately return a message seeking comment. SPX spokeswoman Jennifer Epstein declined to comment.

Gardner Denver, based in Wayne, Pa., had hired investment banking firm Goldman Sachs Group Inc. to advise on how to deal with ValueAct, people familiar with the matter said earlier this year.

Gardner Denver disclosed in October that it was working with the firm to explore a possible sale. Gardner Denver is valued at about $3.7 billion based on Wednesday’s closing share price of $76. Reuters earlier reported SPX was close to an acquisition of Gardner Denver.

SPX makes a wide range of equipment, from food and beverage systems to fare collection equipment to large-scale power transformers. During a conference call with analysts last month, CEO Chris Kearney said the company is working to narrow SPX’s focus and improve the company’s earnings.

SPX has been shuffling its business units around to achieve that goal. Last year, SPX acquired Scottish pump company ClydeUnion for $1.25 billion.

And earlier this month, SPX completed the sale of its Service Solutions business group, netting about $1 billion. The company said it would use $350 million of that to pay down debt and $275 million for share repurchases, which would leave it with about $1.8 billion worth of debt.

SPX employs some 250 people in Charlotte. Its headquarters is in Ballantyne, where SPX is preparing to move into a new, nine-story building.

Observer reporter Ely Portillo contributed