Dewatering and Trash Rental Pumps


Written by:
Mike Grant, Tsurumi Pumps

Big opportunities for small pumps

Often lost in the discussion of rental pumps is that the majority of pumps that are rented are small pumps.  “Small” actually means portable pumps. For instance, single-phase electric submersible pumps up to 3-horsepower and engine-driven centrifugal dewatering and trash pumps up to 11-horsepower are portable, “small” pumps.

More than 12,000 equipment rental operations conduct business in the U.S. and Canada. According to Manta, there are 2,281,023 building and construction companies in the U.S. Not included in these figures are the potential homeowners and municipal and industrial users. The possibilities seem endless with needs not only dictated by economic growth but by weather events, sump pump replacement, infrastructure work, utility work, plant maintenance and municipal upgrades.

With many choices in the market the age-old mantra, “You get what you pay for” applies here. A top quality pump will maximize the return on investment and help minimize headaches caused by poor quality.   

Electric Submersible Pumps

In looking at electric submersible pumps for the rental market, the two most popular types are clean water dewatering pumps and dirty water, or trash, pumps. A standard dewatering pump will have a top discharge with a flow-through design that provides maximum motor cooling efficiency, which allows for continuous-duty operation at low water levels and extended dry-run capability. A quality electric submersible trash pump will be designed to pump sand, solids and debris with minimal wear and clogging. Some components to consider are described in this section.

Continuous-Duty Motor

A continuous-duty motor with 100 percent copper windings is a feature of a quality pump. Pumps with intermittent-duty motors are often found in retail stores and may be less expensive, but the life expectancy is lower when compared to a pump housing a continuous-duty motor. While running a pump dry is never recommended, in a rental application, it will likely happen. While the top discharge allows for air to be pulled through to cool the motor jacket when running dry, a rental pump must also have motor protection. Look for a pump that has a miniature or circle thermal motor protector that will shut down the motor if it overheats.

Pump Protection Add-Ons

What if a pump’s cable jacket is cut, and this is not noticed prior to its next rental? This is not an unusual occurrence because rental pumps encounter a myriad of abuse rolling around truck beds or being pulled up from a hole by the cable itself. A quality manufacturer will offer protection, such as an anti-wicking block, which stops the water from wicking all the way to the heat source (the motor). A feature such as this will result in having to replace only a cable and not the whole pump when these instances occur. 

 

Mechanical Seals

Also, look for features such as a dual, an inside mechanical seal with silicon carbide seal faces. A quality mechanical seal translates to longer pump life. As these portable pumps do not depend on close impeller tolerances to maintain performance, manufacturers offer unique impeller material and designs—such as urethane rubber coated semi-vortex impellers. 

A urethane rubber coated impeller will be more resistant to wear from abrasive particles, such as sand, than a cast iron impeller. Some pump manufacturers incorporate an agitator attached to the shaft through the impeller which mixes and suspends sand and debris. This design is favorable to a non-clog type trash pump for a construction or dirty water application.  

 
An engine-driven trash pump

 


Trash pump

Lubrication

Clean and adequate lubrication is also important. Many end users, particularly of rental pumps, may not check/change the oil in their pumps, even though most manufacturers recommend that the oil is checked every six months and changed on a yearly basis. With some electric submersible pumps, the wet end of the pump must be taken apart to gain access to the seal/oil chamber. This requires time and money. 

Some manufacturers allow access to their oil chamber from a plug on the outside of the pump. This results in less maintenance time. Even though this makes checking the oil easier, many end users will still not check the oil. Some manufacturers offer an oil lifter as a standard on all electric pumps. The oil lifter provides lubrication of the seal faces down to one third of the normal oil level by actually lifting the oil to lubricate even as the oil level drops. This new technology makes the job easier and provides a safety net for the pump’s components. 

Engine-Driven Pumps

Electric submersible pumps are often rented, but so are engine-driven pumps, up to 11-horsepower. As with electric submersible pumps, the quality of materials of construction is important. 

The Engine

A name-brand engine driving the pump is important relative to dependability, parts availability and warranty. Also, when the time comes to upgrade a fleet, the resale value of the used equipment increases significantly with a name-brand engine. 

The Frame

Consider the frame of either a dewatering or trash pump. The cage frame as a standard will be composed of tubular steel. Is it a complete frame, or are costs cut by running just one tube across the top middle portion? A full, four-side cage frame with a heavy gauge of tubular steel is recommended. 

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See also:

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