This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
It is of greatest importance that the stopcocks at the fixtures should be perfectly tight. It is rare to find a house piped for gas where the pressure test could be successfully applied without first removing the fixtures, as the joints of folding brackets, extension pendants, stopcocks, etc., are usually found to leak more than the piping. The old-fashioned, "all-around" cock should never be allowed under any conditions whatever; only those provided with stop pins should be used. Various forms of cocks with stop pins are shown in Fig.. 43, 44 and 45. All joints should be examined and tightened up occasionally to prevent their becoming loose and leaky.