A piping system for food and beverage process plants connecting a tank and process assembly to a pipe system via double seat valves mix-proof in the seat including valve distributor trees and the double seat has two serially disposed closing members with open and closed positions, the closing members delimiting a leakage cavity with a connection path to the surroundings of the double seat valve. A first closing member comes in sealing contact at a second closing member and transfers the second closing member into a sealed position. The second closing member having a hollow rod and a seat seal.