Plate L is noticeable for illustrating a method of drawing details not used elsewhere in this set of plates. On the other plates each piece is separately detailed. On Plate L the details of the valve, cover, seat, stem, and spring are shown assembled, and dimensioned without separation. This is an allowable method when clearness is not sacrificed, but it is usually found desirable only with simple construction. It concentrates parts on the drawing, and probably saves some time, besides showing the workman just how the parts go together. The only test which the student need to apply in this, as in any method of detailing, is the test for absolute clearness.
It is believed in the case of the valve as shown that the details are completely illustrated without sacrificing clearness. Special care in putting in dimensions is of necessity required.
The valve stem can be unscrewed either with a socket wrench on the inside or an ordinary fork wrench on the outside.
The seat, after being screwed to position in the deck, is often faced off, to true up any distortion caused by screwing in.
The valve itself, of rubber, can be bought of any desired grade of hardness. The specification for any given set of valves depends upon the quality of the water, the pressure, and the general service of the pump.
By reason of the simple nature of the parts on this plate, the molding and machining is left entirely to the original consideration of the student.