Auto Shut Off RO 1 With Quick Connections - Automatic shutoff valve for reverse osmosis systems. ASO ASV Easy to use 1/4" OD Tube with quick connections. The "in & out" markings are on the top of the valve. The top side of the valve is the high pressure side and the bottom side is the low pressure side. The high pressure from the filter housings goes to the "in" on the top of the valve. Then the high pressure "out" goes to the membrane housing "in". The membrane housing low pressure "out" connects to the "in" on the bottom side of the valve. The "out" on the bottom goes to the tank. The valve automatically shuts off production when the tank pressure reaches approximately 65% of the incoming line pressure.