As per API 6D "Detail for Pipeline Valves" norms, a twofold block-and-drain (DBB) valve is a "solitary valve with two seating surfaces that, in the shut position, gives a seal against strain from the two finishes of the valve, with a method for venting/draining the depression between the seating surfaces.
As the definition, a twofold block and drain ball valve has two seats, and every one of the seats gives a seal against pressure separately. In other words, one seat is fixing the liquid from upstream and the other seat is fixing the liquid from the stream. For a trunnion ball valve with two old blocks and drain, when the valve is in shut position and the liquid comes from the upstream, it pushes the seat against the ball to understand the fixing. The other seat is fixed similarly.
Trunnion ball valve twofold block and drain
How does the capability of venting/draining work? At the point when the pipeline is under pressure, the trunnion ball valve is shut with the liquid caught in the ball and afterward, there is tension in the ball. At the point when the temperature in the ball becomes higher, the strain in the ball will rise as well. It is important to vent/drain the tension in the event of a hazard when the strain in the ball turns out to be sufficiently high. For a trunnion ball valve with drain capability, the tension in the ball pushes the seat back as the spring behind the seat packs. Then, at that point, there is a vent/draining between the fixing surfaces. As a rule, venting/draining is expected at the tension of under 1.33 seasons of the plan pressure rating for the ball valves as API 6D details. Some basic task solicitation to vent/drain at the strain of under 1.1 seasons of the plan pressure rating. (eg. For a PN20 trunnion ball valve, the tension caught in the ball will vent/drain at the strain of under 2.2 Mpa).
Trunnion Ball Valve Bleeding
How to Test?
To test the twofold block capability of a trunnion ball valve.
Make the ball in a half-open position, and afterward infusion the water into the ball. Close the ball valve when the valve ball is loaded with water. Then, at that point, infuse the valve with strain at 1.1 seasons of configuration tension from the upstream to check on the off chance that, is any spillage from the help valve (open the alleviation valve before the test). On the off chance that the rankle is found at the relief valve, there is spillage; on the off chance that no rankle, there is no spillage from upstream. For the downstream, it is the same way.
To test the venting/draining capability of a trunnion ball valve
Make the ball in a half-open position, and afterward infusion the water into the ball. Close the ball valve when the valve ball is loaded with water. Infusion of the strain to the valve ball through the alleviation valve simultaneously at the tension of 1.33 times to check whether there is any spillage, if the spillage is found, the venting/draining is Ok.