Double expanding - Single expanding

The double expanding gate valve uses a two-piece gate-and-segment assembly: at full closure (and full opening) the two halves are mechanically wedged apart, pressing both seats against the body with a positive mechanical force that does not depend on line pressure. The result is a bubble-tight seal on both upstream and downstream seats, effective even at low differential pressure — a condition where conventional slab gates and ball valves rely entirely on line pressure to seal.

This makes the double expanding design (model B21; the B21/B41 family covers the expanding executions) the reference solution for positive isolation duties: launcher/receiver stations, metering skids, tank farms and any location where personnel work downstream of the valve. The valve provides a true double block and bleed in a single body and can be engineered to achieve DIB-1. The single expanding version applies the same wedging principle to one seat, in a shorter and lighter body.

Like all Valland through conduit gate valves, the bore is full and piggable, the back seat allows stem seal replacement in line, and SIL certification up to SIL 3 is available.