The trailer-mounted concrete pump is a common item found on job-sites. Although often overlooked, this piece of equipment can be critical in getting the job done right. But, not all trailer pumps are created equal.
A good place to start in evaluating this tool is a review of its main features—a hopper, cylinders, and a valve. Beyond these basic features, machines vary based on engine size, outlet and hose diameters, and other ancillary features.
Hoppers. The concrete feeds directly out of the ready-mix truck into the hopper. Hoppers may seem standard across a line of trailer pumps. However, they can vary in shape, capacity, and reinforcement to withstand heavy concrete.
“Too little hopper capacity can have serious consequences if the mixer driver isn't paying close attention,” says Mike Newcomb of Reed Concrete Pumps. “It takes only a few seconds to let the hopper get empty, and you've got a safety issue when you pump compressed air.”
Ian Tover of Olin Pumps says the shape of the hopper can be more important than capacity. “The hopper is not a silo holding concrete,” he says. “It is a funnel through which the concrete flows.” Olin's hoppers tend to be smaller but steeply sided with few dead spots where concrete can collect. Either way, there is a lot of engineering that goes into the pump's point of entry.
From the bottom of the hopper, the concrete is sucked into one of two cylinders located beneath the engine. The concrete is then forced out of the cylinder, by way of a valve, into the hose where it eventually finds its way to the far end for placement into forms, block walls, or slabs.
Cylinders. Tover at Olin Pumps says there are two basic questions when considering a trailer pump: “What are you pumping and how fast are you pumping it?” Aggregate size, and whether you are pumping grout or concrete, will largely determine what pump you need.
Cylinder diameter, cylinder length, and strokes per minute go into calculating the output of the machine. Cylinder diameter frequently is larger than the outlet and hose diameter, so there is a reduction in the diameter of the slug of concrete going through the pump, which results in increased pressure. And pumps that can overcome greater pressure are able to pump concrete farther. Some manufacturers opt for larger cylinders and shorter stroke lengths, making up for the increased pressure by supplying larger engines.
The interplay between cylinder diameter and stroke length is also a function of the concrete application. Small grout pumps typically have cylinder diameters of 4 or 5 inches, and cylinder lengths of not much more than 14 inches. Midrange trailer pumps typically feature 6-inch diameter cylinders with stroke lengths from 14 to 39 inches. Larger volume pumps gain greater capacity through larger cylinder diameter and length, with diameters up to 8 inches and lengths up to 79 inches.