Model 2230/4430 is a normally-closed, 2-way valve which is opened by increasing temperature of engine cooling water, lubricating oil, high pressure gas or other fluids. The 2230/4430 can also be used for sensing high bearing or packing temperatures. Opening of the valve vents control pressure from an AMOT Mater Safety Control such as Model 2800 or 4261, and protects the engine, compressor, pump, gear case, and industrial machinery from over-temperature