37. Valve Seats.
a. All water valve seats must be of bronze composition. They may be either screwed into the deck on a taper or forced in on a smooth taper fit. With either arrangement, the seat must be either flanged out on the under side all the way round or be provided with a substantial lug opposite each rib, these lugs being expanded out after the valve is inserted.
If the valve seats are not expanded after being put in place, there is a possibility that now and then a valve seat will work loose and come out, thus crippling the pump.
b. The under side of the valve deck must be rounded over to give good bearing for the expanded part of the seat.
c. Three-inch valves must have four or five ribs, three and a half inch valves five or six ribs, and four inch-valves six ribs.
Enough ribs must be provided to give proper support to the rubber valve, but too many are objectionable, as small ports would be liable to obstruction by refuse.
d. The edges of the valve-seat ports must be moderately rounded over, to remove such sharp edges and points, as would be liable to cut, or damage the rubber valve when under pressure.
38. Valve Stems.
a. All valve stems must be of 3⁄4-inch Tobin bronze and of the fixed type, and must have the guard fastened on by one of the methods shown in [Figs. 9] and [10].
