Ball-valve concrete pumps Long used for lowvolume pumping, now some are taking on more demanding jobs BY FRANCIS C. WILSON CONSULTANT WAUKESHA, WISCONSIN ore ball-valve pumps are in use than any other kind of concrete pump. Most are lowvolume units with output capacities less than 30 cubic yards per hour. Although the small models are often called grout pumps, many can be used for structural concrete and shotcreting where low-volume output is suitable. They’re used for repairing underwater concrete, filling fabric forms, placing concrete in heavily reinforced sections, and building bond beams for masonry walls. Some hydraulically dri ve n models have pumped stru c t u ra l concrete at outputs exceeding 150 cubic yards per hour. M A ball valve is actuated entirely by flow of the concrete. On the intake cycle (above), ball movement at the feed hopper is limited by bars or an off-center cam. On the discharge cycle (below), concrete flow seats the ball. The ball at the discharge cylinder seats during intake and opens during discharge. How the ball valve works Operation of the ball valve is simple (see figure). The valve is actuated entirely by flow of the concrete, reversing swiftly with the flow. No springs or actuators are needed. If on one cycle the ball doesn’t seat fully, the flow tends to take out any obstruction that isn’t oversize and the valve returns to full function. Some models permit controlling the ball movement with off-center cams or bent bars. Adjustments can be made while the unit is running. The balls themselves last for long periods and are changed easily. Balls with differing weights are used for pumping concretes with differing unit weights—lightweight, cellular, heavyweight, and normalweight concrete. The same ball seat is used for all ball weights and can be replaced easily. There isn’t enough force from concrete flow pressure against the ball to push larger rock mixes out of the path from the ball to the seat. Because of this, most ball-valve pumps can’t pump concrete with aggregate larger than pea gravel size (100% passing the 1⁄2-inch sieve, also called l⁄2-inch minus material). Don’t confuse this with aggregates having a nominal maximum size of l⁄2-inch (ASTM Size No. 7) which can have as much as 10% passing the 3⁄4-inch and retained on the l⁄2-inch sieve. These oversize particles may prevent the valve from seating. Drive mechanisms for ball-valve pumps Many ball-valve rigs are mechanically driven. These have one concrete pumping piston driven off a series of belts, chains, and a crank. The resulting uneven output rate is leveled out to more uniform flow by a second compensating piston driven with a cam or heavy spring. The unit works well with sand grout mixes and with mixes having up to about 30% aggregate under l⁄2 inch. Hydraulic-drive ball-valve pumps use a two-cylinder hydraulic drive much like those on larg e - ro c k pumps. These pump models require a junction pipe or siamese just as h a rd rock pumps do. The shear face at the junction creates considerable flow resistance, but not much greater than that developed around the flow compensator in mechanical pumps. With large-diameter (4 to 6 inches) hydraulic cylinders and long strokes (24 to 42 inches), flow in a h yd raulic ball-valve pump doesn’t pulse as often as flow in a mechanical pump. The resulting smoother flow is especially useful in wet shotcreting. Another benefit of longer strokes is fewer valve actuations, and thus less valve wear. Hyd ra u l i c - d ri ve pumps can pump concrete at a faster rate and at higher pressures than mechanical pumps, permitting concrete to be pumped higher and further. When a jam from oversize or foreign materials begins to form, ball-valve pumps with self-regulating oil pumps swiftly sense the obstruction buildup, reduce oil flow, and increase oil pressure to usually cause the jam to pass through. Pumplines Because the maximum aggregate size doesn’t exceed l⁄2 inch and highvolume output isn’t needed, smalldiameter delivery line and hose are commonly used for ball-valve pumps. With an inside diameter of 2 or 21⁄2 inches and a low pressure rating, the hose cuts contractor labor costs because it’s lighter and easier to handle. Depending on the drive mechanism, maximum concrete line pressures may range from 300 to 900 psi. On most jobs 100 to 150 psi is all that’s needed. For higher pressure work such as forced grouting or high-lift pumping, higher rated (stronger) line and hose are needed. For high-pressure work, lines, hoses, and clamps also should be inspected frequently for damage. On the parts of a job where it’s feasible, steel slickline has seve ra l advantages: • Lower first cost • Reduced pumping pressures • Greater durability For pumping concrete ve rt i c a l l y more than 100 feet, use of slickline is much preferred. The vertical lines must be firmly supported by brackets or lashing, and bolt line couplings should be used, especially where access is difficult. Latch clamps are suitable for low-pressure pumping but shouldn’t be used where several sections of hose or pipe are supported only by the clamps. A falling pump line can cause severe injuries. Using the pump efficiently Mixes with aggregates heavy in the sand sizes require relatively high water contents to make them workable. To get the needed strength, cement contents may range from 550 to 900 pounds per cubic yard. The higher cement contents increase cost, drying shrinkage, and heat generation and also may make the concrete sticky and hard to pump. One commonly available solution is to replace some of the cement with fly ash. This reduces cement cost and improves pumpability. Concretes made with crushed stone and stone sand are hard if not impossible to pump. Blending in a small amount of natural sand greatly improves pumpability. So does mixing pea gravel (rounded particles) with crushed stone. Most sands are suitable for pumped concrete but dredge sands typically lack fines. Pumpability is improved by adding as little as 30 pounds of crusher dust, wash tailings, blow sand, or fly ash to a cubic yard of the concrete. Almost any gain in pumpability as a result of aggregate blending also improves concrete finishability, surface appearance, and strength. Uniformity is the key word for ball-valve pump mixes, just as it is for mixes pumped by all rigs. Consistent concrete makes the pump and the job run smoothly. For trouble-free operation, avoid oversize aggregate particles, frost balls, clay lumps, and random inclusions such as tramp iron. Keep the hopper grate in place. Also inspect and repair damaged hoses and lines that might cause rock jams. Pump safety Ball-valve pumps have few safety problems when concrete discharges freely and the line isn’t exc e s s i ve l y long. If there’s a line blockage, howe ve r, the line and couplings could be subjected to excessive pressure that can cause bursting. Ball va l ve s operate as solid check valves and special care is necessary to relieve p re s s u re. Even during routine disconnections,such as after filling a cavity, care must be taken. The pressure can be relieved safely by controlled, gradual opening of a coupling. Also, some machines have either a surge chamber valve or a long lever on the first coupling for pressure dissipation. Before buying a pump A ball-valve pump has several advantages. First cost is low and there are few wear parts. Because of its simple design, the pump is easy to clean and maintain. The units are small and maneuverable, the hoses easy to handle. This pump is primarily limited by pumping rate and aggregate size re- strictions. Although hydraulic models have pumped at rates up to 150 cubic yards per hour, typical uses are for jobs requiring no more than 30 yards per hour. The units can’t pump 3⁄4-inch-aggregate concrete or l a rg e r. Before buying a pump, consider what concrete you’ll usually be pumping and what output volume and pressures you’ll need. Also check the availability of l⁄2inch minus aggregate in your area before buying a pump. In some areas 1l⁄2-inch and 3⁄4-inch aggregates are available for concrete to meet state highway department specifications, but l⁄2-inch material may be wasted or ground into sand. In such a re a s, ball-valve pumps are limited to pumping sand grout mixes. For information about reliability, ease of operation, and technical backup from manufacturers, talk with users of ball-valve pumps. Learn what sort of jobs users do and how their pumps have perf o rm e d . Ask about the pump’s tolerance for an occasional unfriendly mix. How easy is it to clear blockages and to clean the machine at day’s end? What are the maintenance costs and how much time is spent keeping the unit in operating condition? Finally, how responsive is the manufacturer to requests for help in diagnosing problems? Studying manuf a c t u re r s’ literature and service manuals can help you make a buying decision. But talk with users before choosing your pump. PUBLICATION#C880145 Copyright © 1988, The Aberdeen Group All rights reserved