Hi there - this is my first post here so apologies if it is not in the correct sub-forum. I am working on a passive solar powered pump that uses pressure built up by heat in a closed cylinder (expansion chamber) to displace water from a sealed reservoir to an elevated target tank. I am trying to calculate the theoretical performance of this system but am struggling on the connection between the thermodynamics and hydraulics. The pressure exchange tube (between the cylinder and the reservoir) is connected to the top of the reservoir, and forces water out of a 15mm tube connected to the bottom of the reservoir to the target tank. I need to calculate the pressure threshold at which water will begin to be displaced by the expanding air to the elevated tank. Any ideas would be greatly appreciated.