Modular actuators tackle a tight squeeze

The Allegheny County Sanitary Authority (ALCOSAN) had problems with manually operated valves controlling the flow of raw sewage into primary treatment tanks at its facility next to the Ohio River, in Pittsburgh’s North Side district. ALCOSAN provides wastewater treatment services to 83 municipalities including the City of Pittsburgh with a total capacity of 250 million gallons (950,000 m3) a day.

The original 600mm inflow valves had non-rising stems that were permanently submerged in raw sewage. The exposed threads on the valve stem collected debris; making the valves hard to operate. The solution for this problem was to convert the non-rising stem gate valves over to rising stem types that would be less prone to fouling. To free up operators for other tasks, the new valves would also be fitted with electric actuators linked to the plant’s control system.

In January 2017, AUMA supplied 72 SA multi-turn actuators with GK gearboxes, floor stands, new stainless steel valve stems and thrust blocks. All the actuators are equipped with AC controls and Modbus RTU communications.

The ability to fit into tight spaces was an important reason why ALCOSAN chose AUMA actuators. The center of each valve stem is less than 100mm from a concrete block wall. Thanks to AUMA’s modular design, which offers flexible mounting positions, the company provided a compact GK multi-turn gearbox that fits into the narrow space without having to modify the wall.

Price and previous experience were also significant factors behind ALCOSAN’s decision. AUMA is the company’s preferred actuator supplier and there are now around 300 AUMA actuators on site.