Abstract: High vacuum pumping system employs a poppet valve having dual seats for respectively seating a pair of vertically disposed spaced valve discs thereon to define a closed position. A refrigerated cold trap is located within a dome portion of the valve, i.e., above the upper of the valve discs while seated, and a diffusion pump is mounted below the valve to evacuate the vacuum process chamber when the discs are elevated or unseated to define an open position. The cold trap and diffusion pump are mounted in parallel and form a common axis with the poppet valve thereinbetween. Means are provided to equalize the pressures within the dome and vacuum process chamber when the discs are seated.