Dresser-Rand Company recently announced that it has signed an agreement with Gas & Air Specialty Products, Inc. to sell and service a unique capacity control system for reciprocating compressors. According to D-R officials, the new patented system not only extends the range of compression capacity, but also saves energy and reduces operating costs.

Known as a "gas-controlled stepless pocket," or "GSP," it enables equipment operators to vary the capacity of their reciprocating compressors. But unlike conventional pockets that limit capacity to a specific percentage, the new device is adjustable and can maintain capacity continuously over a wide range at approximate constant efficiency. Because the pocket is adjustable, it is also energy efficient when compared to fixed devices that waste excess capacity.

"The GSP is notable for its simplicity," said Dave Williams, manager, reciprocating product upgrades at Dresser-Rand. "The GSP takes advantage of the pressure of discharge gases to control capacity, and does not rely on any hydraulic mechanisms. This increases reliability and makes it easier to install and to service. In fact, the only maintenance items are a modified compressor valve and standard pressure-control valves."

A significant feature of the GSP – often thought impossible – is that it can turn existing fixed clearance pockets into variable pockets.