What causes power steering fluid to foam?

Both of your posts seem to be related. Foaming fluid is caused by air getting into the system. If you can find no obvious places, the rack and pinion will leak at the seals and pull ait into the rack when turning the wheel. This will cuse the air to increase the pressures in the system. As air comes n, the fluid has to go somewhere.

Thank You, I bled the system and for know the problem has stopped. I will be on the look out for leaks.