Pump Primer

Water PipeConstruction jobsite pumps haven’t changed much in the last few decades. Their designs subtly evolve, of course, but the fundamental pump mechanism in all its variety is pretty well established. This stability is reassuring to pump purchasers, who know they are not investing in a beta product.

“Pumps in general are relatively simple machines,” says Thomas Aldridge Jr., Vice President of Griffin Pumps. “There is not a lot to be done to reduce the parts, just improve them.”

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The basic pump lineup for jobsites includes centrifugal, diaphragm and submersible units. A centrifugal pump takes in water, swirls it around (as in a centrifuge) and hurls it out an opening with enough pressure to keep it moving through a line. A diaphragm pump continuously displaces water. The diaphragm first expands to create a void in a chamber, sucking in water, then the diaphragm shrinks the space, pushing the water out the other end of the chamber. A submersible is a centrifugal pump that efficiently pushes up water from the bottom rather than sucking it up from the top.

Pump manufacturers and distributors say centrifugal pumps are the most frequently rented and purchased. If a customer wants a one-size-fits-all pump, a 6-in. centrifugal dry-prime trash pump comes closest to filling the bill. Why? In the first place, centrifugal pumps are user friendly.

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“A centrifugal pump operates dependably, without breaking or failing. Diaphragm pumps are easier to break,” says Dale Conway, Vice President of Engineering at Thompson Pump. “And it is harder to operate a centrifugal pump incorrectly. It is very forgiving.”

Add to that a centrifugal pump’s more efficient utilization of fuel and the case for renting or buying the pump is a good one. A trash pump model — as opposed to a dewatering pump —is preferred because its components are strengthened to let it handle water-borne solid elements up to a few inches in size. Thus, it can be used for emptying wastewater or for transferring cleaner water from one point to another (dewatering). The 6-in. size is popular because it has the capacity to handle most jobs. When a job is too large for a 6-in. unit, a second 6-in. pump can be set up to complement the work of the first one. Therefore, a contractor with a couple of 6-in. trash pumps in his equipment yard can accommodate most situations. A 4-in. trash pump is the second most popular model for these same reasons.

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Gorman-Rupp Co.Contractors don’t have to guess about which pump best suits a situation: Manufacturers and dealers work to eliminate the guesswork. Thompson Pump, for example, guides customers through a pump application checklist. Over at Gorman-Rupp Co., Rental Sales Manager Jamie Schoenian quotes a company saying: “We don’t sell pumps. We apply them.” To that end, customers are questioned about usage.

“The first thing we want to know is if there are going to be solids to account for,” explains Schoenian. “Rental, construction and wastewater customers need a pump that will pass at least a 3-in. solid piece. Then we want to see what vertical level a customer needs to reach. Finally, we need to know the makeup of the fluid.”

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The latter is important because different chemicals in the water or different chemical fluids require different seal and rubber components in a pump to avoid damage and leakage. As for distance and height to be pumped, there are variables to consider in choosing a pump.

“Distance is not as much of a factor and can be overcome by changing the size of piping,” Aldridge says, noting that enlarging pipe size cuts down on friction in the water’s movement. “Vertical distance is the more challenging part of it. Length you can overcome by upsizing piping; vertical you can’t change. That is a pure system constraint.”

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A partial solution is to not set up a pump more than 25 ft above the water inlet, the experts say, so that pump and engine don’t have to work needlessly hard to suck the water up through the system. While jobsite pumps are sturdy and reliable, they are not impervious to all materials and to misuse by operators. A common error is to mismatch a pump to a task and otherwise to fundamentally misunderstand hydraulics. Oversizing a pump can be as bad as undersizing it.

“If you oversize a pump, you can generate more heat because there is not a sufficient volume of water moving, and a lot of pumps have minimum flow they should have,” says Aldridge. “And people sometimes operate a pump at too high a speed, thinking it will help them pump more, when a slower speed will allow better suction. A customer needs to understand the application.”

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Schoenian speaks in terms of a “sweet spot” in pumping. He says that running a pump too far to the left or the right of an ideal hydraulic pressure point can create cavitation, or the formation and collapse of vacuums, which leads to damage in the area of a pump’s impeller. After choosing a pump, should a customer buy or rent? Aldridge says that any customer planning to use a pump 8 months or longer should consider purchasing it.

“The useful life of a pump is 4 to 5 years before a major overhaul,” he says, “so consider buying if the pump will be used 8 months over 4 to 5 years.” The decision is made easier when a pump distributor offers rent-to-own contracts, which some do.

As mentioned, pumps haven’t changed too much over the years. Improvements tend to come in the design of impellers, in the curved funneling area leading to the discharge point and similar refinements. Stronger bearings, more resistant seals, heavier shafts, new diaphragm materials — these are the incremental improvements introduced in subsequent generations of pumps.

“The biggest new development that we are seeing is preparation for the EPA Tier emissions requirements,” Aldridge says. “All manufacturers are making arrangements now on how to meet the requirements.”
Engine producers from Caterpillar and Perkins to Cummins and John Deere are reworking off-highway diesel engines to meet EPA certification requirements; Tier 4 Interim and Tier 4 Final are adding new after-treatment emissions systems to engines so they emit nearly zero emissions. Of course, downstream users of the engines — such as pump builders — must re-engineer their application of the engines. This has interesting implications.

“Say we had a 6-in. pump with a 50-hp motor on it,” explains Conway, “but after they put their new emissions devices on it, the engine only produces 42 hp. In that case, we either have to build new pumps or go up in size with the engine.”

Another example: Tier 4-certified engines often have after-treatment devices like particulate filters to capture soot and exhaust. When the filters begin to fill up with particulate matter, the engine diverts power to the task of consuming the unfired fuel (soot) and producing a cleaner emission. The problem for pumpers is that redirecting power from the pumping of water so the engine can do its housecleaning reduces the effectiveness of the pump.

“We’re working hand-in-hand with engine manufacturers to keep that power going to the pump while it is regenerating,” Conway says.

This new technology is going to require greater expertise for pump maintenance people, notes Aldridge. “In the past, a pump mechanic needed to know how to turn a wrench. Now he has to be able to troubleshoot electronics.”

Giles Lambertson is a freelance writer for Utility Contractor, based in Winchester, Kan.