THE DEAN BROS. PUMP.
The Dean Bros. pump is shown inFigs. 295,296and297.
Fig. 295.
Fig. 295.
The auxiliary valve, A,Fig. 297, has in its face two diagonal exhaust cavities, B B1. The ports, C C1, and the exhaust port, D, are placed in a triangular position with one another, the diagonal cavities diverging so that the cavity B, when the valve is in place, connects the ports, C1and D. Cavity B1connects the ports C and D, when the valve, A, is at the end of the stroke. The three small cuts show relation of auxiliary valve to ports.
Fig. 296.
Fig. 296.
The piston starts from left to right when the valve, A, moves in an opposite direction, opens the port, C, admitting steam to the auxiliary cylinder at the moment the main piston has reached the end of its stroke. The auxiliary piston, E, is forced to the left, opening the main port and admitting steam to the main cylinder, reversing the movement of the main piston the return stroke of the main piston reverses the movement of the auxiliary valve, whereby the port, C, is closed, at the moment the main piston reaches the end of its outer stroke. The port, C1, is opened by the valve, A, and reverses the valve piston, E, opens the main port and reverses the motion of the main piston.
Fig. 297.
Fig. 297.
This port arrangement admits of a short valve with a long travel. The stroke of the pump can be regulated by moving the stud up or down in the segmental slot,Fig. 296, which varies the travel of the auxiliary valve and reverses the stroke of the main piston as desired. By raising the stud the pump will make shorter strokes, and by lowering it will make longer strokes.
The motion of the auxiliary steam slide valve is like that derived from an eccentric. The ports leading to the valve piston, E,Fig. 297, remain closed, except at the moment the main piston is reversed; hence, there can be no waste of steam from leaks when the valve piston becomes worn.
Having a long stroke and a rapid motion, the auxiliary valve insures a certain reversal of the piston at the proper time.
To set the valve, turn the steam chest upside down. Put valve stem through the stuffing-box and secure in place the clamp for small slide valve. The diameter of valve stem is smaller where the clamp is attached.
Now screw up the stuffing-box nut (having previously removed the packing), then move the valve and stem so that the small port at right of valve will be open1⁄16inch and make a scratch upon the stem close to stuffing-box nut. The valve should then be moved in the opposite direction to open the other small port1⁄16inch and make a second scratch upon the valve stem next to stuffing-box nut. Prepare joint and replace steam chest on cylinder. To square the valve, slacken the screw in crosshead and move the latter to the end of stroke with edge of crosshead flush with the end of guide, then set the valve stem so that the first scratch is flush with the face of nut, same as when the scratch was made. Tighten screw in set screw under valve rod dog and move the crosshead to the opposite end of stroke, and note the position of second scratch. If it does not come to the position in which it was made,split the difference by slackening the set screw under valve rod dog and move the valve rod to equalize the travel of valve.
In replacing steam chest on cylinder, cover the opening with a thin board, or piece of sheet iron, before turning it over to prevent the valve from dropping out of place.
This slide valve has a fixed travel andthe process of setting is precisely the same as for that upon a steam engine with a plain slide valve.