Brake change - pads and pistons

Hi All,
I wondered if any of you could answer the following:
I've got to change the front discs on my L322 ( 02 ), having read the RAVE page I was surprised to see that to get the pistons back it suggests you crack the bleed nipple as you press the pistons back into the calipers. Would this just entrain air into the system?
Normally I'd just take the lid of the reservoir.
Any advice on this would be helpful. Thanks in advance.

I never do that, I just push them back.

but i have been told that doing this just forces crud up into the brake system

Done the pads in july in mine - I used a G Clamp to push the pistons back.

No need to bleed if you do that, and crud shouldn't enter if the rubber boot is still in good shape along with the piston seal.

Speak to mr "1992lse"

He's the man on brakes
He done mine for me and had no need to bleed the system as far as I know

Just took the lid off the reservoir

The reason it suggest cracking the nipple is one it will ease the pressure when returning pistons and two if you don't remove the cap on the Reservoir you could destroy the master cylinder or servo rubbers

A few points. You will not shove anything back into the system other than brake fluid. If car is maintained properly fluid will be at correct level in header tank. It is important not to overfill. So opening bleeder is recommended, so fluid is not pushed back into header tank meaning it would have to be drained of excess. It will not introduce air into the system by doing that. Use an old pad across the pistons apply slight pressure with a G clamp crack bleeder open and tighten G clamp until pistons are returned nip up bleeder. Simple job no sweat.

Thanks Everyone - roll on Saturday.