Membrane tank is a pressure water tank that is equipped with a membrane in it. The tank is mounted on the piping strip on the press pump. Membrane Tank Function When a faucet is opened, the water pressure in the pipe will drop. The water pressure in the pipe will drop slowly, this is because there is a reserve of pressure in the tank, which also presses the water into the pipe. Once the pressure in the pipes and tanks reaches 2 bar then the pump will turn on, raising the pressure into the pipes and tanks, and so on.