CONTINUOUS DELIVERY FORCE PUMP. As used in Connection with the Armstrong Accumulator. N pressure per square inch, you would require a very large and very strong air vessel before it could be of any service. If a pressure of only 750 lbs. per square inch were used, then, since the normal pressure of the atmosphere is 15 lbs, per square inch, the air in the air vessel would be compressed to, or th of its original volume, in accordance with Boyle's law. Consequently, with an air vessel of 50 cubic feet internal capacity, there would be only I cubic foot of air in it, when the pump was in full action. Combined Plunger and Bucket Pump.-We have already seen that a suction pump discharges water during the outward stroke, and that a plunger pump discharges water during the inward stroke; consequently, by combining these two kinds, we get a double-acting pump. By making the cross area of the plunger half that of the barrel, half the water raised by the bucket during the up-stroke goes into the delivery pipe, whilst the other half fills the space left by the receding plunger. During the down-stroke the plunger forces the latter half up the delivery pipe. We do not happen to have a figure with which to illustrate these remarks, but if the student will first of all sketch a complete vertical section of a suction pump like that shown by the first figure in this lecture, and then draw a solid plunger, with stuffing-box and gland, like that in the second figure, in place of the pump rod and open cover in the suction pump, it will form a useful exercise in the designing of such a pump. Double-acting Force Pump.-The pumps which we have hitherto considered are all single-acting in this sense, that they do not both suck and discharge water during every stroke. This can, however, be accomplished by having two sets of suction and delivery valves placed at each end of the pump barrel, as shown by the accompanying figure. Then, during the outward stroke of the piston the pump draws water from the source of supply through the inlet pipe and suction valve SV,. At the same time the piston forces the water in front of it through the delivery valve DV, and outlet pipe. During the inward stroke, suction takes place through SV, and discharge through DV1, all as clearly shown by arrows in the drawing. The valves are provided with india-rubber cushions, IR, to ease the shock and minimise the jarring noise due to their reaction and natural reverberation when they are suddenly opened and closed. EXAMPLE III.-In a double-acting force pump the vertical height from the surface of the well to the point of delivery is 100 feet. If the area of the piston equal 1 square foot, what is the stress on the piston-rod during each stroke? ANSWER. Here we need not distinguish between the force required during suction and delivery, for both actions take place during each stroke. We have only to deal with the net force required to elevate a column of water to a height of 100 feet. Neglecting friction, the stress on the piston rod will therefore be the weight of a column of water of height 100' and cross area I sq. ft. ... P= HAW = 100' x 1' x 62'5 = 6250 lbs. pull and push. If 30 per cent. of the force applied be spent in overcoming friction, what will then be the stress on the pump-rod. Here 6250 is only 70 per cent. of the whole stress, for 30 per cent. of the whole is lost force. .. 70: 100 :: 6250:2 x = 6250 X 100 = 8928.5 lbs. pull and push. * We are indebted for the above figure to Professor H. Robinson's book on "Hydraulic Machinery," published by Messrs. Charles Griffin & Co. Students should refer to Lecture XXIV. of the Author's Elementary Manual on "Steam and the Steam Engine" for detailed illustrations and description of the air and circulating pumps of the SS. "St. Rognvald." LECTURE XIX.-QUESTIONS. 1. Explain the manner in which the pressure of the atmosphere is made serviceable in the case of the common suction pump. Sketch and explain by an index the details of this pump. 2. Describe, with a sketch, an ordinary suction or lifting pump, and explain its action. If the diameter of the bucket is 4", and the spout is 20' above the free surface of the well, what is the tension on the pump-rod in the up-stroke? Ans. 109 lbs. 3. Sketch and describe a force pump, drawing a section so as to show the packing of the plunger and the construction of the valves. How is an air-vessel applied to such a pump? Why is the air-vessel dispensed with when pumping water into an accumulator? (S. and A. Exam. 1890.) 4. Explain the use of an air-vessel in connection with a force pump. Sketch a section through a double-acting force pump, showing the valves and the connection of the pump with the air-vessel, and explain the action of the pump. (S. and A. Exam. 1887.) Water is forced up to 100 feet above the air-vessel; what proportion of the volume of the air-vessel is occupied with water, and what is the pressure of the air therein? Ans. 74.6 per cent.; 43.4 lbs. per sq. in. above the atmospheric pressure. ; 5. The leverage to the end of the handle of a common force pump is five times that to the plunger, and the area of the plunger is 5 square inches what pressure at the end of the lever handle will produce a pressure of 45 lbs. per square inch on the water within the barrel? Ans. 45 lbs. 6. A force pump is used to raise water from a well to a tank. The piston has a diameter of 1.6", and is 20' above the free surface of the water in the well, and 40' below the mouth of the delivery pipe leading into the tank. Find the force required to work the pump-(1) Neglecting friction; (2) when 30% is spent in overcoming friction; (a) when sucking, (b) when forcing, (c) what is the work put in and got out per double stroke of 6"? Ans. (a) (1) 17.45 lbs.; (2) 24·93 lbs. ; (b) (1) 34.9 lbs.; (2) 49.86 lbs. ; (c) 37 39 ft.-lbs. ; 26.17 ft.-lbs. 7. What is the difference between a double-acting and a single-acting pump? The area of the plunger of a force pump being 3 square inches, find the pressure upon it when water is forced up to a height of 20'. Ans. 26.04 lbs. 8. Describe, with a sketch, some form of pump which will deliver half the contents of the barrel at each respective up-stroke and down-stroke of the pump-rod. Name the valves. (S. and A. Exam. 1892.) 9. Sketch and describe a "double-acting force pump.' If the diameter of the piston be 12", the stroke 3', the distance from pump to well 20, from pump to position for delivering the water 40', and if the number of strokes per minute be 40, what is (1) the theoretical horse-power required to work the pump, (2) the actual, if 30 per cent. of the power be spent against friction. Ans. (1) 10.71; (2) 15.3. 10. What is the difference between a single and a double acting pressure pump? Sketch in section a double-acting force pump for working at high pressure, showing the arrangement of valves, and indicate of what material the several parts should be constructed. (S. and A. Exam. 1893.) LECTURE XX. CONTENTS.-Bramah's Hydraulic Press-Bramah's Leather Collar Packing-Examples I. II.-Large Hydraulic Press for Flanging Boiler Plates-The Hydraulic Jack-Weem's Compound Screw and Hydraulic Jack-Example_III.-The Hydraulic Bear or Portable Punching Machine-The Hydraulic Accumulator-Example IV.-Questions. Bramah's Hydraulic Press. This useful machine was invented by Pascal, but he could not make the moving parts watertight. Bramah, about the year 1796, discovered a means by which this difficulty was effectually overcome; and thus the instrument has been handed down to us under his name. As may be seen from the following figure, it consists of a single-acting force pump in connection with a strong cylinder containing a plunger or ram, which is forced outwards from the cylinder through a tight collar by the pressure of the water delivered into the cylinder from the force pump. From what was said in Lecture XIX. about force pumps, we need not particularise about this part of the machine, except to say that the suction and delivery valve boxes can be disconnected from the pump, and the valve cover-checks removed at any time for the purpose of examining the parts, or of regrinding the valves into their seats. The plunger extends through a stuffingbox and gland filled with hemp packing, and is guided by a centrally bored bracket bolted to the top flange of the pump. The lever fits through a slot in this guide-bar, whereby it has an easy free motion, when communicating the force applied through it to the pump plunger. The relief-valve RV has a loaded lever, adjusted like the lever safety valve in Lecture IV., so as to rise and let the water escape when the pressure exceeds a certain amount. It may also be used for taking the pressure of the object under compression, or for lowering the ram R by simply lifting the little lever and pressing down the table T, when the water flows easily from the cylinder, and out of DP by the relief valve. The delivery pipe DP is made of solid drawn brass, and the ram cylinder is carefully rounded at the bottom end, instead of being flat, in order that it may be naturally of the strongest shape.* * In the case of large cylinders for very great pressures, the lower or |