A practical thermopneumatic valve

Previously, we reported a thermopneumatic silicone rubber membrane valve [1997]. This valve combined thermopneumatic actuation with a low modulus silicone rubber membrane. However, the leakage of the working fluid through the membrane rendered the valve unusable in a day or two. Here, we present extensive optimization and characterization of a redesigned valve structure. This new design has a suspended membrane heater optimized for low power consumption, a composite silicone rubber on Parylene membrane that exhibits low permeability and modulus, and a novel valve seat designed to improve sealing in the presence of particles. The valve has been extensively characterized with respect to power consumption vs. flow rate and transient response. Very low power consumption has been demonstrated. For example, less than 40 mW is required to switch a one slpm nitrogen flow at 33 psi. Water requires close to 100 mW due to the cooling effect of the liquid. The previously reported valve required more than 280 mW to switch a similar air flow.