BOILER No. 10. 95 



regulator employed was that in which the pressure acts through 

 a diaphragm and a system of levers upon the damper. The 

 extreme variation of pressure was limited to 2 pounds. A 

 comparison of the results of these tests shows that the automa- 

 tic regulation secured an improvement over hand regulation 

 amounting to 2.5 per cent, based on coal, and 3.7 per cent, 

 based on combustible. It is a difficult matter to show by 

 means of a test the working economy produced by automatic 

 regulation, because so much depends upon the personal element 

 when the draught is controlled by hand. On such a test, the 

 fireman may have an incentive to do his best, which he might 

 not have in ordinary work. For this reason the tests reveal 

 the tendency which automatic regulation has to secure economy, 

 rather than the actual gain which may be secured under work- 

 ing conditions. In this connection it may be added that tests 

 were made on two large plants of boilers, to determine the 

 economy of automatic regulation over hand regulation, and 

 in one case the result was favorable to automatic regulation, 

 while in the other case it was favorable to hand regulation. 



The object of Tests No. 21 and No. 22 was to determine the 

 effect which the type of grates may have upon the economy. 

 The principal difference in the two grates lay in the proportion 

 of air space. Both tests were made with automatic regulation 

 of the draught. The grates with 50 per cent, air space gave 

 3.2 per cent, better result based on coal, and 1.7 per cent, 

 better result based on combustible, than the grates with 60 per 

 cent, air space. Subsequent tests were made under similar 

 conditions, with a slower rate of combustion. In this case the 

 gain due to the smaller air space was more marked, being 

 about 8 per cent. From this showing it may be concluded 

 that the slower the rate of combustion, the smaller should be 

 the opening for draught through the grates. The gain prob- 

 ably comes about by preventing the introduction of too great 

 an excess of air over that required for combustion. 



Comparing Test No. 21 with Test No. 20, both of which were 

 made with the same grates, it appears that the more rapid com- 

 bustion on Test No. 21 secured a noticeable advantage. It 



