Railway car cushioning device

A hydraulic-pneumatic cushioning unit comprising:

• a cylinder having front and rear end portions, a piston mounted within the cylinder for reciprocal movement, a piston rod secured centrally to a rear face of the piston and extending through an opening in the rear end portion of the cylinder, said cylinder forming a high pressure chamber adjacent a front face of the piston and a low pressure chamber in which the piston rod is mounted adjacent the rear face of the piston, said high pressure and low pressure chambers having a mixture of gaseous and liquid fluids therein under a preload fluid pressure with the gaseous fluid in the high pressure chamber containing at least 5 percent of the total volume of the high pressure chamber, said piston having an opening therethrough at a position radially spaced from the longitudinal axis of the piston rod;
• and
• normally closed valve means mounted within said piston opening to control fluid flow between the low pressure and high pressure chamber, said valve means including a relatively large buff flow passage and a restricted draft flow passage, said valve means when moving with the piston in buff travel from extended position being adapted to remain closed for an initial buff travel of a predetermined distance to permit the mixture of gaseous and liquid fluids in the high pressure chamber to reach a predetermined high value and effect further mixing of the gaseous and liquid fluids before opening of the buff flow passage for the metering of the mixed gaseous and liquid fluids from the high pressure chamber to the low pressure chamber, said valve means upon return draft travel after buff travel closing the buff flow passage and permitting opening of a restricted draft flow passage to permit the metering of the mixed gaseous and liquid fluids from the low pressure chamber to the high pressure chamber and return of the cushioning unit to neutral position.