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Figure 8: The anti-siphon device: The black arrow represents the direction of CSF flow from the cranium. Black sheet represents the flexible membrane valve. Red marking represents another membrane dividing the reservoir into 2 halves. (a) In recumbent position of the patient with DP <OP, there is no flow across the valve; (b) In recumbent position of the patient with DP >OP, flow occurs across the two membranes; (c) In vertical position of the patient, the proximal part of the reservoir (above the red membrane) exerts a PUSHING pressure (PP; single black arrow) to open the black membrane valve, while distal part of the reservoir (below the red membrane) exerts a negative SUCKING pressure (SP; double black arrows) which prevents the black membrane from opening. When PP >SP, CSF flow occurs. When PP

Figure 8: The anti-siphon device: The black arrow represents the direction of CSF flow from the cranium. Black sheet represents the flexible membrane valve. Red marking represents another membrane dividing the reservoir into 2 halves. (a) In recumbent position of the patient with DP <OP, there is no flow across the valve; (b) In recumbent position of the patient with DP >OP, flow occurs across the two membranes; (c) In vertical position of the patient, the proximal part of the reservoir (above the red membrane) exerts a PUSHING pressure (PP; single black arrow) to open the black membrane valve, while distal part of the reservoir (below the red membrane) exerts a negative SUCKING pressure (SP; double black arrows) which prevents the black membrane from opening. When PP >SP, CSF flow occurs. When PP<SP, no CSF flow is seen