Pumps and Hydraulics, Part 1 (of 2)

by N. Hawkins

THE FOSTER.

Fig. 257.

The Foster single cylinder pump valve motion is a compound valve piston and slide valve in one piece and performs the office of both a main and auxiliary valve. It seats over the main steam cylinder on the web or casting connecting together the valve pistons, and is provided at the bottom with vents or openings, A and B, [Fig. 257], for opening and closing the main steam ports to the main steam cylinder. The sides of this valve are cut to form the recesses, C and D, which are for the purpose of opening and closing the small steam ports, which admit steam to the valve pistons; it is also provided with L shape slots for the purpose of alternately exhausting steam from the valve pistons through the steam ports.

Fig. 258.

Fig. 259.

Fig. 260.

In operation the main piston rod commences its forward stroke, motion is communicated to the vertical arm, which moves forward on the rod until it engages with one of the cams, E, [Fig. 259], adjusted on the valve stem. The arm coming in contact with the inclined faces of the cam imparts a rolling or oscillating movement to the stem and valve, opens one of the recesses, C or D, cut in the side of the valve and admits steam through a port to one of the valve pistons. At the same time this oscillating movement of the valve opens the slot, F, [Fig. 260], opposite the first, and exhausts steam through the alternate port from the other piston. Steam thus admitted to one of the pistons (while exhausts from the other piston), carries the valve over its seat, and by means of the vents, A and B, steam is admitted through one of the main ports and exhausts through the other. When the main piston has completed one stroke, it moves backward on its return; the arm strikes against the other cam on the valve stem and communicates a reverse motion to the valve which closes and opens the alternate ports to admit and exhaust steam to and from the pistons. It also cushions the piston at the end of each stroke which prevents the piston from striking the heads.

To set the valves. This can best be done by starting the pump slowly and adjusting the cams, E, so as to open the valve at the proper time to compel the piston to make a full stroke. A little experimenting combined with good judgment is all that is necessary, unless the piston valve be badly worn, in which case a new valve must be substituted and fitted to the valve chest.