<p>A valve block assembly with internal delivery channels and a common outlet channel is provided. The assembly has two delivery valve surfaces with access to the common channel. The common channel comprises easily cleaned linear sections running alternately from one surface to the other, and connecting surface grooves at the valve sites. Diaphragm valves with relief grooves to accommodate deformation of the diaphragm are provided. The V-like cross-section of the connecting grooves of the common channel and the conical shape of the nearby outlet of a delivery channel assure that the valve may be opened by only a small actuating force. Reservoirs feeding the delivery channels have an inert atmosphere controlled by pressurizing and venting channels in the valve block. Exposure of plastic tubing to oxygen is kept to a minimum. The assembly is particularly adapted for use in a protein sequencer to supply reactants without cross-contamination or oxidative decomposition.</p>
