The principle and setting of whether the valve needs to install by-pass valve

Occasionally, we can see some relatively large valves in some pipes and always install bypass valves. Why is that? What is its main function? Under what circumstances do you need to install? And what is the caliber size of the by-pass valve of the corresponding equipment?
In fact, set up bypass valve in the pipeline, its role, in general, can be divided into two major points: first, play a protective role (balance the pressure at the end), and two is an emergency standby!
A protective effect, can also be said to be a protective measure of the main valve, prevent the valve before and after the pressure is too large, caused by open resistance, the valve does not open, especially in some large caliber or high pressure pipeline. Before the high pressure pipeline is opened, the pressure is released by the bypass valve to avoid the sudden inflow of high pressure and form an impact on the pipeline below the valve. Or the pressure difference between the ends of the valve is too large, the opening torque is too large, in order to avoid torque damage to the valve, bypass pressure relief, and then open the valve.

Two, emergency role, as a standby pipeline to use, the biggest advantage is that when the main valve failure, or need maintenance, repair, you can open the bypass valve flow, and does not affect the normal production.

Whether the valve needs to install bypass valve specific requirements and settings: (for reference only)

2.5MPa level, DN400 above; 4.0MPa class, DN250 above; 6.4MPa class, DN200 above; 10MPa class, DN150 or more;

DN100~DN200 valves whose bypass and bypass valves are DN20; DN250~DN600 valves whose bypass and bypass valves are DN25; valves over DN600; their bypass and bypass valves are DN40.