Common Problems

Common Problems

One-stop Solution for Valve Products

How the bypass valve is matched with the main valve

Release time:

Sep 26,2025

    The functionality of bypass valves relies on proper design and selection, with particular attention required to the following four core parameters to ensure compatibility with the main valve and piping system.

 

(1) Nominal diameter selection: Typically 1/4 to 1/8 of the main valve's diameter

The primary function of a bypass valve is ‘pressure balancing’ rather than ‘flow conveyance’, hence an excessively large diameter is unnecessary. It is generally 1/4 to 1/8 of the main valve's nominal diameter. For example:

- For a DN1000 main valve, the bypass valve diameter may be selected as DN150 (1/6.7) or DN200 (1/5);

- For a DN600 main valve, the bypass valve diameter may be selected as DN100 (1/6) or DN80 (1/7.5);

- For a DN300 main valve, the bypass valve diameter may be selected as DN50 (1/6) or DN40 (1/7.5).

An excessively large diameter may cause pressure equalisation to occur too rapidly, potentially inducing locally excessive flow velocities; conversely, an excessively small diameter prolongs pressure equalisation time, adversely affecting operational efficiency.

 

(2) Pressure Rating: Consistent with the Main Valve's Nominal Pressure (PN)

The bypass valve must withstand the same system pressure as the main valve; therefore, its nominal pressure must correspond to that of the main valve.

For example, if the main valve is PN1.6MPa, the bypass valve must also be selected as PN1.6MPa; if the main valve is PN4.0MPa (high-pressure pipeline), the bypass valve must be selected as PN4.0MPa to prevent valve body rupture due to pressure mismatch.

 

(3) Valve Types: Preferably use globe valves or ball valves

Bypass valves must feature ‘flexible operation’ and ‘high regulation accuracy’. Common types include:

Globe valves: Suitable for scenarios requiring fine flow adjustment (e.g., system commissioning, temperature regulation). Their ‘low-in, high-out’ flow design ensures stable regulation, though flow resistance is slightly higher;

Ball valves: Suitable for rapid opening/closing scenarios (e.g., emergency bypass during main valve maintenance). Achieving full opening/closing with a 90° rotation ensures convenient operation and low flow resistance.

Both must be constructed from materials compatible with the main valve's medium (e.g., stainless steel valve bodies for acidic/alkaline media; cast steel valve bodies for high-temperature steam).

 

(4) Installation Position: Adjacent to the main valve for ease of operation and interlocking

Bypass valves are typically installed on either side of the main valve, connected to the upstream and downstream pipelines via short pipes. The following requirements must be met:

- The centreline of the bypass valve shall be parallel to that of the main valve to minimise pipeline resistance;

- Sufficient operating space shall be reserved near the bypass valve to facilitate manual or electric operation;

- Where the main valve incorporates an electric actuator, the bypass valve may be interlocked with the main valve actuator (via a PLC control system) to achieve automated operation sequences such as ‘open bypass first, then main valve’ and ‘close main valve first, then bypass valve’, thereby enhancing intelligent functionality.

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