Abstract: A pressure responsive apparatus may include a valve body having an input to be exposed to pressure in a fluid line and an output to drain fluid from the valve body, and a plunger positioned in the valve body. A pressure chamber may be defined in the valve body between the plunger and the input such that the plunger is exposed to the pressure in the fluid line. The plunger may be movable between a seated position characterized by the plunger blocking fluid movement out of the pressure chamber through the output, and a release position characterized by the plunger permitting fluid movement out of the pressure chamber through the output. A biasing assembly may be configured to bias the plunger toward the seated position and being adjustable to apply an adjustable amount of biasing force to the plunger against the pressure of the fluid in the pressure chamber.