United Recovery Systems has closed a deal for Array Services Group.

Sartell, Minn.-based Array provides revenue cycle management, receivables management and call center services to hospitals, health care systems, retail business and financial services institutions. Terms of the deal were not disclosed.

United Recovery, headquartered in Houston, provides receivables management for the financial services, education and health care markets. The company is backed by private equity firm Audax Private Equity, which bought United Recovery in 2008. Since then, the firm has made four add-on acquisitions, including Array. The three previous acquisitions were Financial Health Strategies, purchased in January, Enterprise Recovery Systems Inc., purchased in March 2012, and Plaza Recovery Inc., purchased in October 2011.

Boston-based Audax focuses on investing in lower middle-market companies. The firm has about $5 billion in assets under management.

Marion Financial Corp. was Array's financial adviser for the deal. Edwards Wildman Palmer LLP acted as United Recovery's legal counsel.