174 The Trials of Suction Gas Plants at Derby, 1906. 
therefore to be decided as a matter of judgment based on the 
design of the various plants. There was no difficulty as regards 
the engines themselves, for the reliability of the usual design 
is undoubtedly as great as that of any ordinary piece of 
mechanism ; and with due care, especially as regards the 
cleaning of the valves, it is certainly on a par with that of 
the steam engine of the same size. Attention was paid to the 
arrangement of the exhaust valve springs and to the air and 
gas valve springs. As already pointed out the springs used 
in the magneto gear are of necessity somewhat delicate, and 
the provisions made in this respect in the case of some of 
the engines were far better than in others. The producers 
are more likely to give trouble than the engines, and the 
arrangements for regulating the air and the water supply 
were specially considered, as well as those for minimising 
clinkering and its bad effects. 
Lubrication . — The lubrication of the crankshaft bearings 
was in most cases effected by ordinary drip sight-feed lubri- 
cators. In a few cases, however, ring lubrication had been 
applied, a very obvious improvement, as this method gives 
a better and more copious lubrication and is not affected by 
forgetfulness on the part of the attendant. The cylinder and 
piston were lubricated in general by means of a drip sight-feed 
lubricator, the oil being suitably conducted on to the piston 
body. Sometimes, instead ©f a sight-feed, a rotating pin, dipping 
into an oil reservoir and carrying up a drop of oil with it each 
time, was used. There is an objection to this latter arrange- 
ment for, as the level of oil in the reservoir falls, so the size of 
the drop carried by the pin becomes smaller, and the amount 
of lubrication diminishes. To obviate this difficulty a duplex 
pin lubricator was fitted to the Davey-Paxman engine ; the 
pin dips into a small reservoir which is overfed by another 
revolving pin from the main reservoir so that a certain portion 
of the oil flows back, and the small reservoir is always kept 
full. A drip feed lubricator has however the objection that 
should there be a leak past the piston rings the oil will be held 
back in the supply pipe and the lubrication may fail. In the 
National engine this difficulty is got over in an ingenious 
manner ; the pressure in the cylinder at the end of the stroke 
is utilised to force the oil into a groove around the cylinder. 
In the Campbell and in the Dudbridge engines the difficulty 
is got over by using a force pump, but in both cases additional 
mechanism is required. 
From these trials it can be deduced that the following 
fuel and water consumptions may be expected with a good 
suction producer plant, when working continuously at the 
loads specified and under the best conditions : — 
