Automatic control valve

Manual valves need to be installed at both ends of the control valve to facilitate maintenance; basically, all automatic control valves require a bypass. The basic purpose of installing a bypass valve on a control valve is to allow production to continue in the event that there are problems with the control valve. Therefore, devices that can be stopped at any time for maintenance do not need to be equipped with bypasses, whereas those that must be maintained continuously do require them. Additionally, when the flow capacity of the control valve is insufficient, a bypass can be installed as a supplement; although no control theory endorses this approach (as it severely reduces the quality of control), it remains a temporary solution. In summary, whether a bypass is needed has nothing to do with the control scheme; the focus should be on the requirements for maintenance. The standard installation for control valves involves installing stop valves at both ends, with a bypass valve connected to the outside of these stop valves.

However, bypasses are generally not provided for control valves in pipelines carrying slurries, materials containing solid particles, or those with many impurities

In fact, there are quite a few considerations in terms of design, such as whether it is easy to maintain, whether maintenance can be carried out online, and whether a handwheel is available for online maintenance, etc. Factors like pipeline size also come into play; bypasses are not considered for pipelines of extremely large sizes. However, specific requirements will likely need to be checked with the designers!