Pressure responsive fluid flow control valves

In one set of embodiments a selected section of tubular stock has its ends welded together to form a pillow-like pressure sensing device with an entry tube and an exit tube each configured to facilitate insertion of the pressure sensing device into the flow path of IV infusate in an IV administration set or system. Fluid pressure in excess of a predetermined amount reconfigures the pressure sensing device from a generally oval configuration to a generally circular configuration to restrict and/or cut off fluid flow into the device while permitting fluid flow from the device to reduce the fluid pressure again reconfiguring the device back to its generally oval configuration and permitting fluid flow into and through the device. In other embodiments a fluid pressure sensing device is formed with a fluid entry chamber and a fluid exit chamber interconnected by a passageway and provided with a piston that reacts to an increase in fluid pressure above a predetermined amount to close off the interconnection between the chambers and fluid flow into the exit chamber. Continued fluid flow from the eit chamber results in a reduction of fluid therein and reopening of the fluid passageway between the chambers.