Standard Hydraulic Cylinder Replacement for Univent, Thermovent, Optivent, Ventomax, & Sesam Liberty Window Opener Replaces worn out Piston Rod from your J. Orbesen Teknik Brand Univent Window Openers The core technology is the hydraulic cylinder that contains a plant-based wax This special designed cylinder containing this wax, works as the greenhouse window openers thermostat, thus there is no need for electrical power supply You don't need any electricity in your greenhouse; the window opener will be very environmental and CO2-friendly throughout its whole lifetime Our renowned hydraulic cylinders replace our small range of window openers: Optivent, Univent, Thermovent, Sesam Liberty Vent, and Ventomax