An improved shunt valve for the control of hydrocephalus provides for physiological atmospherically-referenced siphon control that is not adversely affected by overlying tissue. The valve includes one or more porous outer anti-fouling membranes to protect the flow control membranes from external mechanical tissue pressure, while permitting free movement of the flow control moveable membranes and permitting positive inlet pressure to regulate flow through the improved fluid shunt valve of the invention. The porous membranes are configured to prevent tissue ingrowth into the membranes pores while allowing adequate fluid flow across so as not to inhibit movement of the movable membrane.