The T-4000 Series Pneumatic Room Thermostats provide individual space temperature control in all types of heating and cooling applications. By producing a proportional output signal, these thermostats modulate controlled devices in response to load changes in the space. This imposes the least demand on mechanical heating and cooling apparatus. A variety of high volume output and low volume output controllers are available to meet the functional requirements of any control system. Auxiliary devices are available to perform functions such as two-position action, high-low pressure selection, sequencing, etc.