BEHKEN& PUMP. 421
with the cylinder c 2 . m soon arrives at n, after which the point of the tooth of a works closed against ns, while at the same time the portion of the fluid enclosed between the two wheels is delivered back to IK. Meanwhile the fluid has been passing upwards through IK and round c v in the left wing of the chamber, while the fluid already above 5 in the right wing of the chamber has been simultaneously discharged through the delivery opening EF.
We notice that here a new idea is brought into the chamber- wheel gear, that of the closure of the central passage by lower pairs (here cylinder pairs), all the other forms of the Pappenheim machine having used a higher pairing for this purpose. The transition from this to the closure before us may be noticed in the lower pair-closure at the teeth points in the machines of Eepsold, Evrard and Koot, already examined. So far as closure goes the profiles mp and o t might be omitted ; it is, however, well to retain them in order to reduce the quantity of fluid returned, and there- fore the un-uniformity of the delivery, as far as possible. The volume delivered for each revolution is again very approximately equal to the tooth-ring volume of one wheel.
On account of the use of lower pairs the prevention of leakage is here more easy than in any of the former cases ; the Behrens' machine is therefore well suited for use as a pump. Its manu- facturer, Dart (in whose house in New York the inventor Behrens is a partner) , has constructed many for that purpose, and also as hydraulic motors, indeed he has also applied it as a steam-engine. One of these (of 12 H. P. nominal) was at work at the Paris Exhibition, and drove a Behrens' pump.* It may, however, be doubted whether permanently good results can be obtained in this application of the machine, for it will certainly be very difficult to make its working joints tight against high-pressure steam. At best it is far from reaching the completeness, in this respect, of machines of the ordinary form.
At the Vienna Exhibition there was a steam fire-engine in which engine, fire-pumps and feed-pump were all constructed on Dart's plan.
- Motoren u. Maschinen auf der Weltausstellung 1867, Vienna, 1868, p. 124.
