PRESSURE RELIEF

It’s stipulated in API 6D:”AII valves with double seal must has a pressure difference relief function when used in a liquid medium”. The relief pressure difference is generated from the changes in the ambient temperature. In the normally-closed state, the cavity pressure of the valve with double seal can increase rapidly due to the temperature rise, and if such a pressure difference is not bled promptly, it can have a serious impact on the valve’s operation.

Generally, the double seal rail valve with manual operation has the following two pressure relief systems

(1]Manual pressure relief system: The manual pressure relief system is generally a needle valve mounted on the end capfsee Fig.l). When the medium is a liquid which can be slightly bled into the atmosphere, it can be equipped with such a pressure relief system.

(2]Differential thermal pressure relief system: The differential thermal pressure relief system is a pipeline system with a one-way valvefsee Fig.4). In Fig.3, the needle valve 1, the tee 1, the one-way valve 1, the tee 2 and the needle valve 3 make up the diferential thermal pressure relief system In the system, the needle valve 1 is normally-closed and the needle valve 3 is normally-open. When the medium is a liquid which cannot be bled into the atmosphere, it shall be equipped with such a pressure relief system (generally pressure relief to the upstream pipeline).