. American engineer and railroad journal . ansbave been re-sorted to. In some cases fairly good results have been obtainedby making the valves very liglit, giving them but little liftand arranging them so that they shall .seat by gravity. Insome cases valves of this kind are so constructed that tlie air,in entering the cylinder, is compelled to pass througb a largenumber of very small openings. This is a very objectionablearrangement, not only on account of the increased amount offriction, but because ihe air, in passing over the metal gridsin thill streams, will .absorb quite a considerable a
. American engineer and railroad journal . ansbave been re-sorted to. In some cases fairly good results have been obtainedby making the valves very liglit, giving them but little liftand arranging them so that they shall .seat by gravity. Insome cases valves of this kind are so constructed that tlie air,in entering the cylinder, is compelled to pass througb a largenumber of very small openings. This is a very objectionablearrangement, not only on account of the increased amount offriction, but because ihe air, in passing over the metal gridsin thill streams, will .absorb quite a considerable amount of Vol. LXVII, Ko. lo.] AND RAILROAD JOURNAL. 471 heat from the heads, which, in the case of engines workingagainst liigli blast pressures, are made very hot by the heat ofcompression. This heating of the incoming air expands it and proportion-ally reduces the weight of air entering the cylinder at eachstroke. I have observed this in the case of an engine whichwas so constructed as to cause the air to travel about a in. over —Xi-f. the hot metal in thin films about -,^,; in. thick. Alongside of itwas another engine of the same size and make, except thatvalves were used which allowed the air to pass over about 1in. of metal, the openings being of such size that each streamof air was 3 in. in thickness. Careful and repeated tests ofthese engines, when both were in good order, showed thatwhile the indicator diagrams were practically the same, the one with the large valves would burn about 10 per cent, morecoke in the furnace—a result which could only be explainedon the supposition that, in the case of the engine with smallair openings, the incoming air, in passing through the smalland tortuous passages in the heads, was heated about 25° than in the case of the other engine. It is plain, there-fore, that a blowing engine should have air valves which will not only give ample area of inlet passage, but give, this in —[---X6-II ^>|~ a small number of good-sized
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