The vacuum releaser is like an airlock. I draw the hole system down to a moderate vacuum which pulls the sap in from the trees. Once the upper tank is full I have to get the sap out somehow. If I just open a valve the vacuum will suck air in but the sap won't run out. The vacuum releaser closes a valve to the vacuum pump and opens a valve to the air. That releases the vacuum. When the air rushes it it closes a check valve that keeps all the tubing in the woods under vacuum then the weight of the sap pushes another check valve open and the sap runs into the lower tank. When the sap has all run out the valves reverse, a vacuum is drawn in the top chamber, and the sap starts coming in from the trees again.

The idea is to get the sap out of the vacuum without letting all the vacuum all the way out to the trees go. It takes a while to get the whole system back down to vacuum so I preserve as much of it as I can.

It's like an airlock. The whole system is under vacuum. The vacuum sucks the sap in from the trees and it fills the top chamber. When the top chamber is full valves change that isolates the vacuum pump and releases vacuum in the upper chamber by letting air in. That forces a check valve in the tubing from the trees closed so the tubing stays under vacuum. Then, the weight of the sap pushes another check valve open and lets the sap run into the lower chamber. When the sap has all run out of the upper chamber the valves reset and it starts sucking sap in from the trees again while a pump pumps the sap from the lower chamber into a IBC.