Equipment Care had 2016 sales of $180m. Completion of the transaction is expected to close in Q4.
Audax has invested $4bn in 107 platform and 607 add-on companies.
Douglas M. Baker Jr, Ecolab chairman and CEO, said: “This sale enables us to sharpen our strategic focus on our core businesses, while assuring Equipment Care customers will receive excellent ongoing service.
“In addition, our Equipment Care colleagues will benefit from Audax’s focus on the business and will have access to resources that will support future growth.”
Ecolab also signed an agreement to acquire the paper chemicals business from Georgia-Pacific last month.
The business had 2016 revenues of $43m and the deal is expected to close by the end of the year.
Ecolab said it would enhance its position in the Tissue and Towel and Packaging and Board segments of the paper industry.
Christophe Beck, EVP and president of Nalco Water, Ecolab’s water management business, said: “The chemistries gained through this transaction will complement our existing solutions and provide greater opportunity to customize end-to-end programs that meet the needs of our customers.”