Why must there be a straight section of pipe between the inlet elbow of the centrifugal compressor and the compressor flange?

Indeed, a straight pipe section must be provided between the inlet elbow of the centrifugal compressor and the compressor flange, and there are requirements regarding the length of this straight pipe section; it cannot be too short. The purpose is to ensure uniform and stable intake of air into the compressor, thereby preventing compressor surge.

==== It can’t be that serious, right? The inlet of the compressor is equipped with a filter, located in the straight pipe section.

Replacing the inlet filter screen is done from the straight pipe section.

Firstly, installing a filter screen is convenient; moreover, it can act as a buffer to prevent direct impact on the impeller

It is supposed to reduce inhalation resistance and prevent surge.

To reduce the vibrations caused by airflow pulsations, straight pipe sections need to be installed.

The piping structure at the inlet of the centrifugal compressor is designed in such a way as to facilitate even distribution of the fluid at the inlet. Between the suction pipe elbow and the compressor flange, a straight pipe section (without any branch pipes) must be provided; the length of this straight pipe should be at least 3 to 5 times the diameter of the pipe. The requirements for this straight pipe section are usually specified by the compressor manufacturer. The bend at the inlet should have a radius of curvature equal to or greater than 3 times the pipe diameter. The elbow at the outlet should be a elbow with R≥1.5DN. When the diameter of the suction pipe does not match the suction pipe interface on the compressor, a transition reducer should be used for connection; the use of flanges with different diameters is strictly prohibited. The angle of a standard reducer is typically 8–12°, while some compressor manufacturers require that the angle of the transition reducer be no more than 6°

It is used for purging pipes during maintenance, and its performance has nothing to do with that of the compressor. If purging is not necessary, then that straight pipe section you mentioned can be omitted.

What was said earlier about adding a filter is also correct – there’s a conical filter element that is easy to install and remove. As for things like stability, smooth operation, and anti-surge protection, that’s nonsense

To reduce the vibrations caused by airflow fluctuations, straight pipe sections need to be installed