10. Steam (Siphon Type) Pumps.-An economical steam-actuated pump much used in construction work operates on the familiar ejector plan. Its lift is limited but the amount of water handled ranges from 5 to 200 gal. a minute according to size and boiler pressure available for its operation. Its main advantages are portability and freedom from breakdown, as there are no moving parts.

The pump proper consists of a discharge pipe open at both ends. Through one side near the bottom, a small pipe is inserted and bent up, preferably at and concentric with a constriction in the internal diameter of the main pipe. The other end of this small pipe is connected to a steam boiler. The discharge pipe dips into the water at its lower end. Steam issuing from the small tube forms a vacuum in the pipe sufficient to lift water to the constriction, then carries it up and out through the discharge.

The pulsometer (Fig. 33) is a type of pump used to great advantage where steam is available, the quantity of water large, and the lift fairly high. This pump is said to operate where sand with gravel and stones as large as 6-in. in diameter are to be removed with collected water. Having no moving pistons, the pump will not clog; and, by having large valves, stones and refuse of considerable size will pass. The pulsometer may be mounted on a truck with boiler, but in most installations it is suspended by chains or ropes over the water to be removed. Steam and water connections are made with rubber hose so that the outfit is easily moved from place to place. Pulsometers may be connected in series where the total lift is greater than the lifting ability of one alone.

11. Pressure Pumps. For removing water from deep foundations, pumps of high lift are required. Diaphragm and pulsometer pumps are sometimes used in unwatering foundations, the latter to quite an extent, but centrifugal or steam cylinder pumps are better employed.

FIG. 33.-Pulsometer steam pump in operation. Pulsometer Steam Pump Co., N. Y.

11a. Centrifugal Pumps.-Centrifugal pumps comprise a circular or spiral casing having suction at the center with discharge at the outer circumference. They are made vertical or horizontal, but the latter is more common as the means of driving is simpler. Inside the casing is a circular disk or impeller, provided with curved vanes which revolve at high speed throwing the water outwardly, so that it escapes under pressure through the discharge.

Pumps of this type are made either single or multiple stage, the latter being several units placed in one casing to increase the lift. No valves except a foot valve on the suction line are required with this type of pump and for this reason a certain amount of sand can be handled with the water. This will, however, cause wear of the blades and soon will reduce the efficiency of the pump.

Centrifugal pumps may be driven by steam or gasoline engines, but owing to the high rotative speed required, electric motors direct connected are preferably used. Means of priming the pump must be provided, such as a pet cock at the top of the casing through which water is admitted until the suction line and casing are full after which suction is established and maintained through rotation of the impeller in the full casing. In some installations a small pump is fitted to the casing for priming.

Centrifugal pumps are an intermediate step between simple suction pumps and high-lift pumps. They are best suited to handle large amounts of water under medium heads.

NUMBERS, SIZES, CAPACITIES, DIMENSIONS, AND WEIGHTS OF THE IMPROVED PULSOMETER

116. Steam Cylinder Pumps. Steam pumps for medium or high lifts are built in great variety, from small donkey pumps, in which a steam actuated piston carries on its outer end a water piston working in an opposed cylinder, up to large duplex pumps, both simple and compound, for higher pressures and equivalent lifts. For very high lifts, triplex or quadruplex pumps may be used, but these are of the rotating shaft, crank-driven type.

In all cylinder and plunger pumps, the maximum suction head is about 20 ft., which necessitates the pumping machinery being placed at that height above intake, lifting beyond this being produced by positive pump pressure on the discharge side. In construction work, they have as a disadvantage their inability to handle sand or grit, which cuts the cylinders and valves. Care must therefore be taken with their use to provide proper sumps and adequate settlement and straining-out of refuse.

11c. Triplex Pumps.-Triplex pumps consist of three cylinders, each connected to the suction and discharge lines by manifolds. A crank shaft with cranks set 120 deg. apart operates the pistons. Each cylinder has its own inlet and outlet valves so that each works independently of the others. Triplex pumps may be driven by belts, steam, or gasoline engines, or by electric motors. They are rated as slow speed, or about 100 to 150 r.p.m.

This type of pump is used for high heads ranging from 100 to 500 ft., and will handle from 70 to 100 gal. per min. They are mounted on a solid frame, space being left for the driving power.

CONCRETE EQUIPMENT

BY NATHAN C. JOHNSON

12. Handling Forms for Concrete.Forms should be so designed that column forms may be removed first without disturbing supports of beams and girders in order to give early strength to columns through drying and hardening. Beam and girder slabs are next taken down, with temporary struts having wedged bearing against planks on the underside as temporary supports. Wall forms may be removed when the concrete is sufficiently hard to bear its own weight.

Dependent upon the size of the form panels, their weight, and the headroom available, one or another method of handling forms may be adopted. Derricks, gin-poles, and winches, or blocks and falls enable even large sections to be readily handled. Smaller sections may be better handled manually. Initial loosening of forms may be brought about by pinch bars or other levers by pulling with blocks and falls, or by jacks, care being taken not to pry against green concrete.

1 For forms for concrete, see Sect. 5, Art. 39.

13. Equipment for Bending Reinforcement.

13a. Hand Benders.-Fig. 34 shows the Universal bar bender which may be fastened to any bench or plank. It is a light portable device weighing about 60 lb. and capable of bending all ordinary sizes of reinforcing bars to any angle desired without any adjustment being necessary. The top half of the bender can be removed and used to bend bars after they are in place. The bar rolls around the pin in bending, thus distributing the strain along the bar and reducing the chances of fracture at the bend. The bender is equipped with a 5-ft. crowbar for a handle which may be removed and used for other purposes. To bend large bars easily, the handle should be lengthened by using an iron pipe over the crowbar.

A bar bender designed for heavy work and manufactured by the Wallace Supplies Mfg. Co., Chicago, Ill., is shown in Fig. 35. This machine has an auxiliary ratchet lever which operates a pinion against a series of teeth in the frame at a large ratio, thus developing great power. The ratchet panel may be thrown out of engagement and machine operated with the regular lever for light work.

136. Power Operated Benders.-Fig. 36 shows a power operated truck mounted bar bender designed to bend any size of reinforcing rod that is likely to be used in building operations. Any size of bar from 4 to 14 in., round, square, or deformed, can be bent to any

angle desired; or spirals formed from 6-in. diameter to any required size. Weight, complete, ready for shipment, 2700 lb. The machine is manufactured by Kardong Bros., Minneapolis, Minn.

14. Machine vs. Hand-mixing.-Except in relatively small quantities, hand-mixing of concrete is not to be economically considered. Furthermore, hand-mixing is inferior to machine-mixing, with no comparison in quantity output. The province of a mixing machine is essentially the thorough incorporation of materials-one of the fundamentals in the production of sound, enduring concrete. Mixing, therefore, should be accorded the respect due its importance, and the best possible means chosen for its accomplishment.

15. Types of Mixers.-The general types of mixers which have endured and are on the market at the present time may be classified as drum mixers, trough mixers, gravity mixers, and pneumatic mixers. 15a. Drum Mixers.-Drum mixers (Fig. 37) are essentially of a type, differing mainly in excellence of mechanical construction and arrangement. The action of all of them is about the same so far as mixing is concerned, the operation being accomplished by agitation, lifting, and pouring of the several materials by blades and scoops attached to the inside of the mixer drum. With the exception of tilting mixers, discharge of the materials from the drum is accomplished by inserting a trough into one side of the drum, in such position as to catch the concrete as it is poured from the mixing buckets. Minor differences in charging mechanisms and arrangements are to be noted in different makes, but the action of all is essentially the action of a churn, in which capacity they would function if filled with cream, instead of with stone, sand,

cement, and water.

FIG. 37.-Drum mixer.

Of the low-charging mixers, the mixer shown in Fig. 38 is typical. Small pot mixers such as shown in Fig. 39 are excellent for small work.

156. Trough Mixers.-Trough mixers are paddle mixers of one type or another. They may be batch mixers of the shoveling type (Fig. 40) or continuous mixers (Fig. 41) in which a sectional screw rotates in an open trough. Continuous mixers have not met as general favor as have batch mixers since many engineers object to these mixers on the ground of uncertainty of charging operations.

15c. Gravity Mixers.

Gravity mixers are essentially a series of large funnels or pans suspended one above another with bottom gates which can be opened successively, permitting materials to flow from one into the other with incidental mixing to a greater or less extent. Gravity mixers are often urged in preference to power-driven mixers on grounds of cheapness in operation and low first cost, permitting their being scrapped when worn; but many engineers do not advocate their use because of the inherent uncertainty of their mixing operation and oftentimes the requirement of detrimental quantities of water to prevent the mass sticking in the pans. 15d. Pneumatic Mixers.-Pneumatic mixers have been developed by various inventors. At the present time there are two main types on the market. In some of these machines premixing is had before delivery, either mechanically or by the agitation of air pressure, while in others the charge is introduced into a chamber, dependence of mixing being placed on what may happen in transit through pipes under the delivering air pressure. Pneumatic mixers have their own particular field-that of placing concrete in forms where access is particularly difficult but because of the large compressor plant which must be installed for each mixer,

and for other reasons which are valid and of importance in many classes of work, their use is relatively restricted. 16. Machine Mixing.

16a. Time of Mixer Operations.-Considering the concreting plant proper as an installation for mixing together raw materials to form concrete, the plant cycle can be considered as complete in three operations, viz., charging, mixing, and discharging.

In charging and discharging the mixer, a time limit is imposed both by the physical laws

governing the flow of materials from one container to another, and also (in the case of power-loading, or side-loading hoppers in par

FIG. 39.-Small pot mixer.

ticular) by the physical limitations of operatives and of the mechanism itself. As plant refinements are given consideration (particularly with regard to the gravity loading of measuring or charging hoppers from overhead bins) this loading time is diminished; but when a side-loading hopper, or a measuring hopper is charged by wheelbarrows, the time is lengthened more or less according to the perfection of the runway arrangements and the speed at which the men work.

166. Time of Mixing.-Insufficient time is given to the mixing operation itself

in most commercial work. Too long a period may possibly be indulged, but it usually is not; and no fear need be entertained of injuring the concrete by a mixing interval up to and including 30 min. The mixing operation proper comprehends not only admixture of materials, but also reaction between cement and water with distribution of the products of this reaction over the surfaces of sand and stone. The time required for such thorough incorporation, and, to a certain extent, for the hastening of the reaction between cement and water, depends upon the adequacy of the blading and cleanness of the mixer. Oftentimes mixers are put on work with the drum half-choked with concrete or full of holes, or the blading so worn that they cannot handle the materials. Necessarily such mixers will not produce the same result as a clean mixer, properly bladed and having a tight drum. Also, mixers are not all equally efficient.