The Armstrong OB-30 and OB-31 are direct-acting temperature regulators that require no external source for operation. Simple and compact, the units are suitable for a wide variety of heating/cooling applications. Installing, adjusting or maintaining the OB-30 and OB-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 and OB-31 come in .5″, .75″ or 1″ (15–25 mm) sizes and is available with a choice of five temperature ranges and three capillary lengths.