The deal sees its 30-strong fleet of trucks taken-on by suction excavator firm SNC Holdings (NW) Limited.
Hercules started looking for a buyer last month after the suction excavator division caused a loss at the £100m turnover business in its latest results.
Hercules said the sale “will materially reduce the company’s debt and lease liabilities by approximately £9m immediately.”
The Suction Excavator business accounted for 88% of Hercules’ borrowings but less than 5% of its revenue in the company’s last financial year.
During the year it generated revenue of £6m and a pre-tax loss of £400,000 with gross assets valued at £11.8m.
Cash freed-up following the sale will allow Hercules to invest more in its core labour supply business.
Brusk Korkmaz, CEO of Hercules, said: “This is a hugely positive development for Hercules. As the UK carries out substantial construction and infrastructure upgrades within the nuclear, power and energy distribution, aviation, water, and rail sectors, our core Labour Supply business will now have greater resources to execute our strategy in these high-growth areas.
“This disposal gives the Company a clearer identity and we are laser-focused on growth in our core sectors and strengthening our balance sheet. We expect our earnings per share and profit before tax to be enhanced for the benefit of shareholders.”