Bellows actuator for pressure and flow control

Abstract

An actuator for controlling the pressure of fluid, such as water or steam, from a fluid source to a flow controlling orifice. The actuator can be used to apply such fluids to the web of a papermaking machine. The actuator comprises a housing having a first inlet connectable to the fluid source and a second inlet connectable to a pressure source. A resilient bellows structure extends between the first and second inlets within the housing to define an internal region of the bellows structure in sealed communication with one of the first and second inlets and an external region of the bellows structure in sealed communication with the other inlet. The bellows structure expands or contracts within the housing depending on the difference in pressures between the internal and external regions of the bellows. A valve member adapted to move with the bellows structure is provided to open and close the first inlet to vary the flow of fluid from the fluid source and maintain a pressure related to a balance of forces of the bellows structures. An outlet from the housing in communication with the first inlet permits the exit of the flow of fluid to a flow controlling orifice. A pneumatic control signal provided to the second inlet controls expansion or contraction of the bellows structure to control the pressure and flow of water or steam from the outlet. In a variation, the actuator is equipped with an additional inlet that is connectable to a source of atomizing air for the fluid flow. The actuator is a compact and rugged unit with a minimum of moving parts to ensure reliable and efficient operation in the harsh working environment of a papermaking machine.