The block-and-bleed valve combines an isolation function and a bleed/drain function into a single compact valve body — providing the same fundamental capability as a 2-valve manifold but in a more compact and lower-cost form factor. The valve has two distinct stems: a main stem that opens and closes the primary process flow path (the block function), and a smaller bleed stem that opens and closes a small bleed port that connects to atmosphere or to a low-pressure drain (the bleed function).
In typical service, the main stem is opened (connecting the upstream process to the downstream instrument or sampling point) and the bleed stem is closed (containing any pressure on the downstream side). When the downstream instrument needs to be isolated for service, the main stem is closed first (isolating the upstream process from the downstream side), then the bleed stem is opened (relieving any pressure trapped on the downstream side). This is the same procedural logic as a 2-valve manifold but executed in a single compact valve body.
Block-and-bleed valves are commonly used at instrument primary isolation points, sampling tap-offs, drain points on process equipment, vent connections on pressure vessels, and any other single-point isolation requirement where a separate dedicated bleed valve would add unnecessary cost and complexity.
A related fitting style is the double-block-and-bleed valve, which adds a second isolation valve in series with the first, with the bleed port between them. The double-block-and-bleed configuration provides positive verification that no process fluid is leaking past the first block valve — if the bleed port shows no leakage when the first block valve is closed, then the isolation is confirmed before opening downstream equipment. This is particularly important for high-pressure or hazardous-fluid service where leak-by past a single isolation valve could create a safety risk.
Materials and end connections follow the same patterns as other oilfield and process instrumentation valves: C37700 forging brass or 316 stainless steel, with NPT, BSP, or instrument tube fitting connections.