How to successfully select the right pump

Pierce

Will Pierce periodically receives requests from customers who want to purchase a pump off the shelf.

Pierce will go the off-the-shelf route if a customer ultimately demands it. But the reality, he says, is that the most successful pump purchases involve a decent amount of dialogue between vendors and end users.

“What happens a lot of the time is someone will say ‘I need a 6-in. pump,’” says Pierce, vice president of engineering at Schurco Slurry. “There’s typically more to it than that. That 6-in. pump may work, but we want more information. What do you want that 6-in. pump to do so we can help define it better and give you a customized solution.”

The best starting point to determine the right pump solution, he says, is to define the application and system.

“Are you using a cyclone,” Pierce says. “Are you taking effluent from sand screw overflow and sending it to a pond? Or, are you taking that effluent, doing fines recovery and going to a thickener?”

The tonnages producers intend to move matter, as well.

“Depending on the tonnage and the type of application, it’s going to be mixed with a certain amount of water,” Pierce says. “We take that tonnage and the volume of water with it, and define a slurry.”

With a volumetric flow rate such as gallons per minute (gpm) in hand, Pierce says a pump size can more easily be selected.

“If you need 1,000 gpm going somewhere, that’s probably going to fit well in a 6-in. x 4-in. or maybe an 8-in. x 6-in. pump,” he says. “If you need 5,000 gpm, that’s probably a 12-in. x 10-in. or maybe a 14-in. x 12-in. pump. The volume being moved is generally going to dictate the pump size you need.”

Other determining factors

Still, a manufacturer’s job is not done there. Pierce, for one, will analyze what he calls “system resistance,” which encompasses a variety of things.

“What is the slurry or fluid we’re pumping moving through,” he says. “Are there elevation changes? How far are you pumping? A lot of end users tell me I want to use HDPE (high-density polyethylene) pipe. We say we can help with that, but there are a lot of things we have to consider such as how fast slurry is moving through the pipe.”

According to Pierce, a manufacturer’s goal is to minimize the energy required to move a slurry or fluid while maintaining an optimum flow rate and velocity through the pipeline.

“If you can picture water with sand in it moving through a pipe at a foot a second, the sand will drop out and sit at the bottom of the pipe, creating a plug,” Pierce says. “So we try to maintain velocities anywhere from 9 to 10 ft. per second up to 13 to 15 ft. per second – especially if you’re dredging – to keep particles suspended.”

Many operators understand they must keep a slurry moving, he adds, but some can be further educated on the tradeoffs made between line velocity, power consumption and settling slurries.

The end-of-pipe discharge condition is another variable manufacturers must know for system analysis.

“Are you pumping out to a pond or another tank, essentially open discharge,” Pierce says. “Are you going into a cyclone or another unit operation that has another pressure requirement. All these questions are factors when selecting a pump.” 

The number of variables impacting pump selection are seemingly endless.

“One question we get all the time is: ‘How long is it going to last,’” Pierce says. “That’s a question that generates 1,000 other questions. It depends on the materials of construction, pump speed, the concentration of solids, the size and shape of those solids, are you giving us enough info to size the bearing assembly or the rotating assembly – the shaft that takes the load.

“If we give you a rotating assembly rated to only 75-hp and you put a 150-hp motor on there, you may snap a shaft and we would never anticipate that unless you have those conversations upfront,” he adds.

Featured photo: PamElla Lee Photography