[FluidKo]

Hello everyone.
I'm studyng SIMPLE algorithm and PISO algorithm.
What I can't understand is what is the difference between SIMPLE and PISO.
In uploaded picture, SIMPLE is generated to 27~30 and that is repeated.
I can understand.
And in the case of PISO, 27 is carried out only one time but 28~30 are repeated.
But what I'm wondering is what is the difference between whether there is 27 in algorithm or not.

Equation 28 is derived from equation 27(momentum equation).
And equation 28 is reflected in equation 29(continuity).
So what I've thought is equation 27 is included in equation 29.

Then what is difference between cases that carries out equation 27 and not?
Equation 27(momentum equation) is reflected to equation 29(continuity) already.

Why SIMPLE carries out equation 27 obstinately?
What is the advantage of carring out equation 27 in comparison with not carring out that equation like PISO?
https://www.youtube.com/watch?v=ahdW5TKacok&t=2134s

Thank you