FARCOT'S IMPROVED WOOLF COMPOUND ENGINE.
In a preceding article, we have described a ventilator which is in use at the Decazeville coal mines, and which is capable of furnishing, per second, 20 cubic meters of air whose pressure must be able to vary between 30 and 80 millimeters.
In order to actuate such an apparatus, it was necessary to have a motor that was possessed of great elasticity, and that nevertheless presented no complications incompatible with the application that was to be made of it.
In the ventilation of mines it has been demonstrated that the theoretic power in kilogrammes necessary to displace a certain number of cubic meters of air, at a pressure expressed in millimeters of water, is obtained by multiplying one number by the other. Applying this rule to the case of 20 cubic meters under a hydrostatic pressure of 30 millimeters, we find:
20 × 30 = 600 kilogrammeters.
In the case of a pressure of 80 millimeters, we have:
20 × 80 = 1,600 kilogrammeters.
If we admit a product of 50 per cent., we shall have in the two cases, for the power actually necessary:
600 / 0.05 = 1,200 kilogrammeters, or 16 H.P.
1,600 / 0.05 = 3,200 kilogrammeters, or 43 H.P.