The logo for Valero Energy Corporation is shown at a Valero gas station in Encinitas, California, U.S., May 2, 2016. REUTERS/Mike Blake

HOUSTON (Reuters) - Valero Energy Corp shut a hydrocracking unit (HCU) and sulfur recovery unit (SRU) at its 335,000-barrel-per-day (bpd) Port Arthur, Texas, refinery on Monday, said sources familiar with plant operations.

The 45,000-bpd 942 HCU is scheduled to be shut until mid-September while the 545 SRU will be out of production for about 25 days, the sources said.