_Hydraulic Machine Tools._ Probably in no department of engineering has the use of hydraulic power met with more success than in its application to certain machine tools. This success is owing to the peculiar suitability of pressure—water as the motive agent for the performance of a certain class of operations requiring the exertion of a great force with comparative slow motion, as in punching, riveting, forging and the like. The wide spread and successful use of hydraulic machines—of which a few only have been described and illustrated upon the pages of this book—is due to the necessity for such tools and the inventive ability of our tool designers. _A large fixed hydraulic riveter_ is shown in Fig. below; it is capable of exerting on the rivet a pressure of 40 tons or more; the machine has a _working pressure_ of 1,500 pounds per square inch. Working pressures of 5,000 to 10,000 pounds per square inch are used in _hydraulic forging presses_, but in the riveter much less pressure is required. [Illustration: Large fixed hydraulic riveter.] NOTE.—_The proportions_ of this machine are immense. The platform weighs 22,500 lbs. and is operated by a single lever shown in the side view. The “_gap_” is 8 feet across. The machine has a large steel “_stake_” carrying the stationary die; this is held in tension strain by the two steel bolts shown, one upon each side of the machine. The other part of the jaw is cast iron. CLASSIFICATION OF PUMPS [Illustration: FIG. 155.—THE BELLOWS PUMP.] CLASSIFICATION OF PUMPS AND PUMPING ENGINES. The simplest division of the subject matter relating to this branch of practical mechanics is that which goes back to the very earliest of times; it is thus: 1. Hand Pumps. 2. Power Pumps. The names indicate the dividing line between the two. The following are more modern divisions, indicating the method of action distinguishing each: 1. Suction or Lift Pumps. 2. Force Pumps. 3. Suction and Force Pumps. These again may be reciprocating or rotary. The powers actuating pumps are, in the main, as follows: 1. Manual. 2. Animal. 3. Belts. 4. Water. 5. Wind. 6. Steam. 7. Gas. 8. Electricity. These various motors give distinct names to general classes, thus, electric pumps, belt pumps, elevator pumps, etc. A sub-division of titles indicating differences in construction are these: 1. Vertical Pumps. 2. Horizontal Pumps, or again 1. Single Acting Pumps. 2. Double Acting Pumps. The list is still further extended, as pumps vary in design to suit their several uses, and are defined as rope, chain, diaphragm, jet, centrifugal, rotary, oscillating, cylinder. It is with the last named with which this volume has principally to deal; cylinder pumps cause the last given classification, as they are either single or double acting. A single acting pump does its work through one end of the cylinder or barrel of the pump.