Membrane sealed sanitary valves for use in processing and controlling fluid flow. The valve bodies are substantially straight through with no internal obstructions to flow and do not present stagnant flow regions. During use of the membrane sealed sanitary valves, the membrane does not stretch or abrade. The new valve body cavity and seat are formed by an infinite number of radii sealed laterally and decreasing in size from the top of the body cavity to the valve seat. The membrane of the present invention acquires, upon assembly, a 180 convolution which telescopes up and rolls in downward motion.