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Bypass valve action and design principles

2018-07-06 10:14:14

Bypass valves are critical in oxygen valves.

The bypass valve is typically connected upstream and downstream of the shut-off valve, the valve body of the ball valve, or the conduit. The bypass valve is intended to balance the pressure through the shut-off valve. Once the pressure is balanced, the balancing valve will be closed and the shut-off valve will be safely opened or closed.

The bypass valve is used to feed the downstream system of the valve body or piping, slowly pressurizing to mitigate hazards due to high velocity flow and rapid pressurization of the fluid. Since the bypass valve is subjected to impinging flow and high-speed turbulence throughout the valve body, the bypass valve should preferably be a shut-off valve. The material selection of the bypass valve should be based on the flow conditions at the inlet of the valve.

The design criteria for the bypass valve pressure balance system, the design of the bypass system on the shut-off valve should meet the following principles:

1, usually nominal size DN ≥ 80 high pressure oxygen valve, should consider the design of the bypass valve.

2. The “internal bypass valve” is not allowed for the shut-off valve, but the “external bypass valve” should be used.

3. The size of the bypass valve should meet the requirements for balancing the pressure within the range of 0.2MPa/min. Consider the overall strength of the bypass valve. The size of the bypass valve should be between DN25 and DN50. If the downstream piping volume is too large and the bypass valve cannot meet the equilibrium pressure requirement within its maximum allowable size DN50, the diameter of the bypass valve may be appropriately increased.

4. To minimize the amount of foreign particles passing through the bypass valve, the bypass valve should bypass the main pipe or above its centerline.

5. The downstream piping of the bypass valve shall be designed with at least one 90° elbow before being connected to the main piping. And the length of the downstream pipeline of the bypass valve should be not less than 8 times the diameter of the straight pipe section.

6. In order to protect the main circulation pipe from partial impact generated by the bypass valve, it should be noted that the bypass valve is not designed to remove dirt. There must be a 90° elbow made of “adaptive material” downstream of the bypass valve. All impurity particles will gradually decrease in speed after they can safely collide. ("Adapted material" means that it is not limited by the oxygen flow rate under defined pressure limits, material thickness and oxygen purity.)

 

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