ADDING ,CLARKSON TUBES TO THE EARLY SENTINEL BOILER.
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Tr"OLD type of Sentinel boiler, now superseded by theSuper-Senti.ne.1,_has h.orizontal tubes, six to a jayer,. and with a wide gap between the third . and fourth tubes, 'and • each layer of tubes being at right angles to that above or. below it. .The squarecentral space acts as a stoking shout,' and conveys the burnt gases to the funnel. There are many of these old boilers still in use giving • good service, and we -recently _came across a fleet of them in Lancashire, the owner of which had conceited the idea of increasing their steaming capacity by adding two rows of Clark-son thimbfe tubes to the fireboxes.
The circular part of a firebox was drilled to take 16 thimble tubes in a single row, whilst just above this row, on each one of the four flat sides of the squared portion of the firebox,, feur tubes were fitted in a staggered 1*.V. Our plau and elevation, with the thimble tubes shaded, show clearly how the addition has been effected. One half of the plan view shows the thimble tubes fitted in _the circular part and the other half the tubes fitted, in the squared portion of the firebox, whilst the: dotted lines indicate the central space left, through the original' rows of tubes, and they also. show that this space is not encroached upon by the added thimble tubes.
The users state that this small improvement has so increased the steam-, ing powers that a saving in fuel of about ZtO per cent.' is possible as a result. We
referred ,this matter to Mr. Thomas .Clarkson, who said that this limited Use of thimble tubes was' certainly interesting, and could be regarded as an indiCation of the good results. that could be obtained from a.firebox which was fitted entirely with thimbles. 'He could not tell us of any old Sentinel boilers which had thus been entirely ,converted, but. old Leyland boilers, with their 'Q-shaped
tubes, are being converted to thimbles in large niunbers and are giving greater satisfaction, as the scaling which occurs i with the tubes is absent n the ease of the thimbles. _
Mr. Clarkson added that he .did not altogether recommend the fitting of thimbles to the . square . part -of the Sentinel firebox, because of possible inherent weakness of conStruction, but said that one row of thimbles can easily be fitted to the circular portion with a resulting improvement in the steaming pow.ers. Where, however, the firebox is
ufficiently worn to •call for replac.ement, the new firebox -should be completely equipped with thimble .tubes.