The pot scourer has everything to do with it, inducing a 'thermal lag'. This is a closed system, there is no 'valve' anywhere. 1. Add heat, gasses expand, pushing piston out. Gasses in and around the 'heatsink' (pot scourer) flow outward, mixing with the hot air, cooling it quickly causing contraction. Momentum carries the flywheel around, helping press the piston back in; mixed with the contraction of the gasses pulls it in. The heatsink maintains relative 'coolness' from high contact area with a large surface area behind the flame. Heat applied quickly warms the area and pressure rises again; Repeat Again, there is no valve, no transfer of gasses in or out.