A process of elimination

Renting the next pump you need instead of investing in and storing a pump that sits idle between jobs is just common sense, says Carlo Cavecchi, chief executive officer of HSS RentX. “You’re likely to find that the pump you bought isn’t the right one for your next job,” he says. “It’s not an item I think a contractor should buy.”

Brain probe
But just walking into a rental store and saying, “I need a 3-inch pump” won’t cut it. “The biggest mistake contractors make is assuming all pumps are created equal,” says Dennis Mitchell, general manager of Service Pump and Compressor, a Hertz Rental company in Baton Rouge, Louisiana, “because they are quite different.”

“Don’t assume the type of pump you’ve used in the past will suit your next job,” says Mark Conrardy, sales engineering manager with Wacker.

With all the pump options out there, you’ll need to exchange a significant amount of information with your rental dealer in order to get the right pump for your job. (For a more thorough discussion on pump types, refer to the June 2003 issue of Equipment World, page 70.)

“The rental center person has to play 20 questions,” says Steve Spence, pump product manager for Multiquip. “When I started out in the pump rental business in the 1970s we were told to paint a picture, to literally write down and illustrate what they were talking about. With pumps, it’s crucial.”

In fact, says Jim Widrick, manager of construction equipment sales for Gorman Rupp, you could save “money and many headaches if you allow the rental salesman to look at the jobsite in order to quote the correct equipment.”

Get impatient with the probing and you may find yourself with a rental pump that’s giving you less-than-stellar performance. In fact, the Q and A session inherent in any pump rental is so key that just getting a quickie answer and being shown the door with a pump off the shelf may be a good indication this is not a store you want to rent pumps from. “It’s a good way to find out if the rental people know what they’re talking about,” says Gary Roesler, project manager for Griffin Dewatering, which both manufactures and rents pumps. “If they don’t ask, it’s difficult for them to give you the right pump.”

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Based on your answers, your rental dealer will run the numbers through some set formulas. It should be something they’re comfortable with and used to doing. Or if they’re not, they should have immediate access to someone who can help them out and get you quickly out the door.

Here are a few of the questions you should expect to answer:

What are you pumping?
Is it clean water or does it contain solids? “The water may be clean-looking on the surface,” Cavecchi warns, “but can be very different on the bottom.”

“You should tell rental dealers what you’re pumping instead of asking for a specific size pump,” Roesler says. “For instance, if you have a pump that will pass 2-inch solids that means spheres and not a 2-inch-thick slurry. You’ll need a mud pump for that.”

Is it muddy? If so, how thick is the mud?
“What you think of as muddy water may be entirely different from what I think of as muddy,” Spence says. “It needs to be defined. There’s also a misconception out there that a trash pump can pump anything short of shopping carts. We’ve even had some come in with concrete in them. There are definite limitations to what they can do.”

And your rental dealer will need to know if you’re pumping acidic material, Conrardy says. “Certain caustic or abrasive fluids can damage the pump and the hose/piping system,” he comments. “In that case, parts of the pump will need to be made or surfaced with the appropriate materials, such as stainless steel.” And let them know if the temperature of the liquid is a factor, he adds.

How high of a suction lift do you need?
The laws of physics are especially at work when you pump. On a surface-mounted centrifugal pump, the total suction lift (or head) is the measurement from the surface of the liquid being pumped to the centerline of the pump’s impeller. “The rental counter person needs to know how much suction lift is required to get the water up to the pump,” Conrardy says. “The maximum lift is usually about 20 to 25 feet, depending on local elevation. Contractors typically underestimate this height, which results in the pump not producing the amount of water flow desired. The higher this lift height is, the less flow that will be produced, as high lifts put a lot of load on the pump’s engine. It’s always best when the pump is located as close to the water as possible.”

“For example,” Mitchell says, “if you take a 6-inch pump that pumps 2,000 gallons per minute at 5 feet, and you move the position of the pump up to 25 feet above the liquid surface, the same pump will only produce 1,000 gpm.” This number might even prompt the switch to a submersible pump, which excels when the suction lift is more than 25 feet.

You should also be aware that the water level of the area you’re pumping from may drop during pumping, so your rental dealer should ask you what the lowest level will probably be to make sure the pump he gives you stays within the maximum suction lift of the pump, says Spence.

When you get your rental pump on the jobsite, make sure you use the proper size suction hose, says Widrick. While you can increase hose size on the discharge end, you must, for example, put a 3-inch hose on the suction end of a 3-inch pump.

Will there be any vertical rise from the pump to where the liquid is discharged?
Defined as total discharge head, this has a direct impact on how much horsepower your rental pump will need. “Sometimes you need pressure pumps,” Mitchell says. “You and your rental dealer will have to figure out the head conditions and run some friction loss calculations to determine if the pump being considered is suitable for running up a 200-foot hill.” By taking the total suction head and adding it to the total discharge head, you and your rental dealer will come up with the total head required for the project.

How far away will the liquid be discharged?
Your rental dealer will need to know this in order to estimate the amount of hose or pipe you’ll need to rent. Typically, a pump will come with 25 feet of discharge hose, but don’t assume it’s included in the price. Rubber compound hose is usually used for shorter distances, with plastic and light-weight steel pipe used for longer distances. “Which to use varies depending on the application,” says Mitchell. “If you need zero leak tolerance, for instance, I’d use fused plastic piping.”

Will you be required to maintain a specific flow during the rental?
If the length of time it will take to pump out an area is a concern, then your rental dealer will need to know the volume of the liquid being pumped in order to match a pump speed with your desired time frame. “Another consideration is a measurable flow of moving liquid, such as a stream or sewer line,” says Brad Fine, director of marketing for Thompson Pumps.

“If the pump cannot keep up, the site will not be dewatered.”

“If you’re going to pump 1,000 gpm through a 2-inch hose then it will take much greater horsepower than pumping 1,000 gpm through a 10-inch hose,” Roesler says. Keep in mind pumps will not usually run at their stated maximum gpm since you have to figure in the friction loss if you run any length of discharge hose.

Will you be required to maintain a specific pressure?
While pressure is usually not an issue when dewatering a hole, one example where this would matter is the installation of underground sprinkler systems.

What is the altitude of the jobsite?
Altitude makes a big difference with pumps. Atmospheric pressure is reduced at higher elevations, which in turn reduces suction lift. In addition, due to thinner air, both gas and diesel engines lose 3 percent of their power for every 1,000 feet of elevation.

What power is available?
This is especially significant for electric submersible pumps. “Make sure your electrical power supply is up to the job,” says Cavecchi, “because there’s quite a lot of surge on these pumps.”

“Sometimes you can convert a 460-voltage pump to match an available 230 voltage, but your rental dealer needs to know this ahead of time,” says Radu Murgescu, manager of construction and mining markets for ITT Flygt. “And the distance from the power supply might create a critical voltage drop.”

Does your job require any pumping redundancy?
If it creates an emergency situation if a pump goes down, then you’ll need to have the pump rental dealer figure in 100 percent redundancy. An example would be a sewer bypass where you have just 20 minutes to get a down pump going or you’re in a sewage overflow situation. “We’ll put in a separate suction line with separate pumps so you can just valve off the down equipment and start the other pumps up while you’re fixing it or swapping it out.”

What environment are you pumping in?
For example, you wouldn’t want to use an engine-driven pump in an explosive environment, Roesler says. And you may need a noise-dampened pump if you’re working in a residential area.

Also let your rental dealer know how many hours per day you expect the pump to operate, Widrick says. A 24-hour duty cycle will require a pump that won’t self-destruct if it starts to suck air.

What’s included in the rental price?
Know up front if you’ll be charged extra for hoses, filters or other pump accessories. Ask whether or not you’ll be charged for service calls, Widrick advises, and who’s responsible for maintaining the pump. You should also take into account the other costs you’ll have to foot, including fuel, especially if the pump is running 24/7.

When things get serious
If your job requires special attention be paid to pump operations, there are rental companies that specialize in offering installation and engineering consulting, all included in the price of the rental. “Ninety percent of the time we can come up with a solution that can move the liquid cheaper than what the client originally thought,” Mitchell says.

Keep in mind there are generally options on certain applications depending on what you want to accomplish, Roesler says. For instance, on a sewer bypass, you could use a bypass trash pump capable of passing the size of solids the job calls for or a hydraulic submersible that would fit in a manhole.

On the job
Spence claims that three-fourths of the distress calls a rental dealer will get about a surface-mounted centrifugal pump on the fritz will come down to one cause: it’s missing the seal that goes where the suction hose attaches to the pump body.

For loss of that simple rubber gasket, the pump sucks air instead of water. It’s the problem Cavecchi remembers most when he worked at the rental branch level. “That seal can get easily lost or taken off to be used on another pump and then the customer thinks the pump is useless,” he says. “The rental dealer should hand it to the contractor and say, ‘here it is, use it.'” When Spence was in the rental business, his company wired a couple of these seals on each pump so an extra was always at hand.

Also be aware of the limitations of any type of pump you rent. Spence tells the story about a complaint passed on by one of his company’s rental dealers about a non-performing pump. When they investigated, they found out the user was throwing the trash pump into the water, treating it like a submersible. “Of course it ruined the engine,” he says.

To maintain each pump in ready-rent condition, your rental dealer should check at least two key factors: engine rpm and vacuum. A 10 percent loss of rpm will mean losing 20 percent of the pump’s performance. Rental center technicians also need to run a vacuum test to check the pump’s pumping and priming capabilities.

You have to do your part, too. “The biggest problem is letting your pumps run out of fuel,” says Widrick. “This single oversight causes the most unnecessary service calls.”

On call
Your rental dealers have a ready resource in the pump manufacturers they carry. “I also cover compaction and concrete vibrators for Multiquip and by far I get the most questions on pumps,” says Spence, who’s worked both sides of the pump rental picture, first from behind the rental counter then with a pump manufacturer. This expertise, plus the number of questions he gets from rental centers all around the country, prompted him to create an Excel worksheet where his clients can plug in the numbers they get from contractors to help determine which pump they should offer to their customers.

Still, those interviewed would much rather answer all your questions than be accused of making or renting a shoddy product. They know, too, that when it comes to pumps, the answers are usually needed immediately.

“Years ago a guy told me, ‘You people are like doctors,” Roesler relates. “If I’m well I don’t want to see you, but if I’m in trouble, I want to see you right now.'”