_d._ The hand-wheel of each of these valves must be marked as per Fig. 15, so that the pump operator I may clearly understand their use. The lettering must be very open, clear and distinct, not liable to be obscured by grease and dirt, and of a permanent character. [Illustration: FIG. 15.] [Illustration: FIG. 16.] _e._ There must be provided and fitted to each combined valve a check and umbrella-top air vent, as shown in Fig. 16. This fitting must have a clear passageway through it, the full equivalent of a 1/2-inch bore. The check-valve is to permit the outflow of air, but to prevent the influx when the plunger is sucking. This method is preferred to the one using rubber priming checks, as now and then a rubber valve will stick on its seat and thus prevent priming of one of the chambers. In this arrangement the pump operator has absolute control over the priming water into each chamber. Another advantage is that the connection of the air-vent with the priming valve ensures that the air-vents will be opened; and further, by the vigorous spurting out of water as soon as the pump is primed, the pump operator is reminded that the priming valve should be closed. Should the pump operator, however, through a mistaken idea of the proper method of operation, think that the priming should be continued until all air was exhausted from the suction pipe and the pump running in normal condition, there would be some by-passing between chambers, but as there is a free vent for the air, the main result would be simply to limit the amount of air exhausted per stroke, from the main suction, by the amount of water which entered a chamber in this way. The amount of water thus entering, however, would not be appreciably greater than that which would enter from the priming-tank with the check-valve arrangement. If, even in spite of the warning given by the spurting air-vents, the pump operator should neglect to close the priming-valves when the pump was running normally, the priming-tank would eventually be overflowed; but this would not be as serious as the drawing in of air from an exhausted priming-tank, which would result with the check-valve method, were the main 2-inch valve similarly neglected. RUBBER CHECK VALVES. _f._ Four rubber check valves, one for each pulsation chamber, and similar to ordinary pump valves, must be provided. The chambers for these should preferably be made as a part of the pump cylinder, thus securing a compact arrangement. Figure 12 shows this arrangement in outline. _g._ The valve seat should have three ribs to the central hub, supporting the rubber valve. The net port area through the valve should be not less than 1-1/2 square inches.