Cryogenic Double Block Valves

A Cryogenic Double Block and Bleed (DBB) Valve is a specialized isolation valve designed for extremely low-temperature service.
It incorporates two independent sealing barriers (typically two balls or dual seats) within a single compact body, plus an intermediate bleed or vent port.
This configuration provides positive double isolation from process pressure while allowing the cavity between the seats to be safely vented, drained, or monitored.
An extended bonnet and stem keep the packing and actuator away from the cryogenic fluid.
These valves deliver reliable bidirectional shut-off for fluids such as LNG, liquid nitrogen, oxygen, argon, and hydrogen at temperatures down to –196°C (–320°F) or lower, combining the safety of traditional dual-valve systems with reduced weight, space, and leak paths.

How a Cryogenic Double Block and Bleed Valve Works

In the closed position, two independent seating surfaces form seals against process pressure.
The intermediate cavity between these seats is connected to a bleed/vent port (often a needle or small ball valve).
Opening the bleed confirms seat integrity, vents trapped fluid, and creates a pressure-free zone for safe isolation verification or maintenance.
An extended bonnet raises the packing box well above the cold zone so the packing does not freeze.
Cavity-relief features (upstream-facing hole, self-relieving seats, or dedicated relief path) prevent dangerous pressure buildup when trapped cryogenic liquid warms and expands.
Operation is typically quarter-turn (ball-type) via handwheel, gear, or actuator, providing full-bore or reduced-bore flow with minimal pressure drop when open.