_a._ Only “Standard Duplex pumps” are acceptable.
So-called “Duplex” pumps consisting of a pair of pumps with
“steam-thrown valves” actuated by supplemental pistons are not
acceptable.
Experience shows that duplex pumps are more certain of starting after
long disuse. The whole power of the main cylinder is available for
moving a corroded valve or valve rod, whereas on a single pump with a
“_steam-thrown_” valve no such surplus of power is available.
Further, the direct acting duplex has the great advantage over a
fly-wheel pump of not suffering breakage if water gets into steam
cylinder.