Abstract: A push-pull valve for gas sampling is formed by assembling a body including a receptacle having a bore and a plug having a nose which seats in the bore. The plug has a through bore with a shoulder at its lower end serving as a lower stop and defining a hole at the bottom of the through bore. A hollow stem slides in the through bore, between an extended, closed position, and a retracted, open position. The stem has ports set above the foot of the stem a distance such that, in an upper position of the stem, the port is blocked by an O-ring, and in a lower position of the stem, gas can flow through the stem, the ports, an annular space around the stem, and out through the hole at the bottom of the through bore.