STATIONÄRY ENGINES.

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of the pump and the discharge pipe, and in this way the water atthe down stroke of the piston, being forced through the dischargevalve, one-half flows above the piston and the other half is dis-charged up the stand pipe; until the up stroke takes place, whenthe other half is also discharged. Thus in the up stroke the pistonis drawing the water up the suction pipe, filhng the pump barreland discharging one-half of its cubical contents at one and the sametime; while during the down stroke the water is forced out of thebarrel, one-half of it fills the vacuity above the piston and the otherhalf is discharged. It will thus be seen that a smaller stand pipewill suffice for this dass of pump; and where the flow of water fromthe pump requires to be uniform, this arrangement has a decidedadvantage over the foregoing examples. At the bottom of the airpipe a suction piece iS fitted, having a number of holes of abouti inch in diameter, to prevent extraneous matter lodging in thepump and destroying the proper action of the valves. All classesof pumps are so fitted, and lifting sets have in some cases a footvalve placed at the bottom of the air or suction pipe.

In connection with the stand pipe and suction pipe in liftingarrangements with solid bücket a small pipe is fitted, having abranch to the space between the suction and the top valve. Theobject of this pipe is to allow water from the stand pipe to flowinto the pump and suction pipe, as at times, when the pumpsare not working, the water would flow past the valves, and werenot the air in the pipes ejected by the water flowing in from thestand pipe, the shock to the machinery would be very great. Thereare three plug valves, one on each end of the small pipe andbranch, to shut the water off when the pipe and pump are full,which is known by the small pet plug tap placed below the dis-charge valve passing water—a sure sign that all the air is expelled.At the bottom of the suction pipe a loaded valve is placed a littleabove the water in the well, or sttmp, the technical term for thespace below the roadway at the pit bottom where the water is col-lected. This valve is loaded to a pressure of 15 lbs. per squareinch, and is used to test the action of the valves. Should the suctionvalve be passing water when the solid bücket is lifting, the valvewill discharge water, simply because the water sucked up the airpipe is forced down again, and as it cannot pass the foot valve whenm good working Order, it naturally escapes at the loaded valve,where the pressure on the valve is not so great as on the discharge