US Patent 7357151 Fluid control devices

Improved fluid control devices are provided for metering pressure effectively in environments that may contain solid particles and in which the ambient pressure is subject to change. Such a valve comprises a valve body containing a plunger assembly contacting a first spring, said plunger assembly having a cavity and including a second spring and a poppet assembly engaged to said second spring within said cavity; and valve seat means located in position to contact said poppet assembly and essentially prohibit flow through the valve when fluid pressure at the valve inlet is less than a predetermined differential pressure plus a fluid pressure at the valve outlet.