The Armstrong OB-30/31 is a direct-acting temperature regulator that requires no external source for operation. Simple and compact, the unit is suitable for a wide variety of heating/cooling applications. Installing, adjusting or maintaining the OB-30/31 is quick and easy, because interchangeable capillaries mount in any position and disconnect by simply loosening the union nut. No stem packing, so there’s no leakage. Single composition seat for tight shutoff. The OB-30/31 comes in 1/2", 3/4" or 1" (15–25 mm) sizes and is available with a choice of five temperature ranges and three capillary lengths.