Pump Primer

There are many reasons to rent for your pump needs. Perhaps these tough economic times demand a less expensive investment, or maybe job duration doesn’t warrant the cost of new equipment. Regardless of the growing factors, more and more contractors and do-it-yourselfers are turning to rental companies to provide quality equipment and information to do the job — especially when it comes to pumps.

Experience and expertise on product information is a must for any rental company as the trend for rental equipment continues to rise and there are more questions being asked. In the past, the inquiries were for general information; today’s questions are about technical applications and dealers and rental lots need to understand their pumps. The rental salesperson needs to be well versed on pumps and applications, but also on the customer’s specific installation. Knowing pumps is not enough as there may be some contributing factors in the specific site that would lead to incorrect selections if not known. As an example, a typical customer may ask for a diesel driven pump capable of pumping 500 gallons per minute (gpm). Well, there are multitudes of pumps that will meet this requirement.

Before discussing pump sizes and types, defining the applications involved in portable pumping is critical. For contractors, applications pretty much fall into two categories: 1) light-duty, short-term pumping and 2) heavy-duty, higher-volume and potentially continuous pumping. The pump sizes and categories vary, based on which application category you address. Let’s look at each one briefly. Light-duty portable pumping is usually defined as short-term (several hours or less) and lower volumes (up to 200 gal per minute). The pumps typically have 2- or 3-in. suction and discharge hoses and are powered by a gasoline engine. The vast majority of these pumps are wet self-priming pumps, meaning that water must be poured into the body of the pump to get it to prime. Common applications include landscaping, jobsite dewatering and utility junction box dewatering.

Heavy-duty portable pumping is defined as larger volume and potentially continuous pumping that requires either a diesel engine or an electric motor as a drive unit.

The most popular sizes in the heavy-duty pumping range are 4- and 6-in. solids handling, or trash, pumps that can produce flows in excess of 1,500 gpm. The priming system on these pumps differs by manufacturer. Applications include stream diversions, larger jobsite dewatering projects and sewer bypasses, just to name a few. In both light-duty and heavy-duty pumping, the pumps described are designed primarily for horizontal pumping or transfer of product. Pumping vertically against gravity resistance or into a pipeline under pressure requires a much stronger and more expensive type of pump.

Other items that must also be considered are the size of the suction and discharge lines — pressure ratings, valves required and a host of other factors that are generally not thought of unless there is past experience. Renters most talk to their dealer about specs such as total dynamic head (TDH), suction lift and net positive suction head (NPSH), both “available” (NPSHa) and “required” (NPSHr) — all play a big roll in deciding your exact pumping needs.

When identifying the proper pump, the rental salesperson must be well versed in not only the application, but also in the proper sizing of pumps. There are various formulas that must be used to properly size pumps. As an example, one of the most basic is to determine Break Horsepower (Bhp) required to drive a pump which is Bhp = (gpm x head, in ft of water x specific gravity of the liquid) / (3,960 x Pump Efficiency). The best trained salesperson is one that not only has classroom experience but also has practical field experience. While there are numerous books written about all phases of pumps and applications, it is the field or hands-on experience that will make the difference not only on pump selection, but also when problems occur as there is no better tool than experience, and experience can not be taught.

As more and more contractors are venturing out of their area of expertise, it may lead to lesser experienced companies or people becoming involved in projects where they may not have sufficient experience. That may put some projects in jeopardy as the lure of doing something new without the proper experience causes problems. Big money is being advertised on infrastructure work such as sewer repairs requiring big bypasses and while the work may look straight forward, there are going to be problems if the contractor does not call upon the experience of a good rental company.   

When buying or renting a pump, size matters. Light-duty, gasoline-powered pumps can be purchased for a few hundred dollars for a 3-in. trash pump. Meanwhile, a 6-in., diesel-powered, trailer-mounted pump may list for $20,000 to $40,000, which is why rental is an attractive option for heavy-duty pumping applications.

Another thing to remember when talking about pump rentals or sales is that the end-user is not acquiring just a pump. He or she is acquiring a pumping system, complete with accessories such as suction hoses and screens, and discharge hose, pipe and fittings. The amount of accessories on an application will determine the final pricing. The pump rental is only a portion of the total cost. As for rental costs, pump rentals follow the same pricing structure that general rental equipment uses for daily, weekly and monthly rentals.

Jerry Soto is based in Houston, which is headquarters of Griffin Dewatering Corp. and  Griffin Pump and Equipment Inc.

Liquid Excavation

Five Popular Choices of Dewatering Pumps

The Wellpoint Pump

A wellpoint pump is designed to pump clean water and effluent for a wellpoint dewatering system and lowers the groundwater table to drain construction excavations. It has the highest air handling capacities on the market and can pump water, while removing large quantities of air without shutting the pump down. A typical 6-in. wellpoint pump is capable of pumping 1,500 gpm with head pressures of 100 ft or more. The water being pumped by a wellpoint pump must be relatively clean. Well suited for: Wellpoint dewatering and sock dewatering.

The Trash Pump

A trash pump is designed to pump clean or dirty and trash-laden effluent, and most models will pass 3-in. diameter solids without becoming clogged. These pumps can handle clean, muddy, mucky or trash-laden water, and incorporate an open impeller and wear plate. A 6-in. trash pump is capable of pumping 1,500 gpm with 125 ft of head. Trash pumps are widely used because of their reliability and versatility. Well suited for: Flood drainage, sewage bypass, pumping polluted wastewater and pumping settled sludge.

The High-Pressure Jet Pump

A high-pressure jet pump is designed to be used as a fire pump to jet casings or wellpoints without drilling or digging to pressure agricultural irrigation systems, as well as in mining and quarry applications where high head capacity is required. Jet pumps are powerful pumps capable of satisfying requirements for high-head capabilities. A typical 6-in. jet pump is capable of pumping thousands of gallons per minute of clean water with several hundred feet of head or more. Non-jet pumps aren’t designed to handle much more than a 100-ft head. As anyone in the mining industry knows, sometimes you can pump water up near 100 ft and still be a long way from the discharge point. A high-pressure jet pump may be capable of achieving discharge heads over 500 ft. You won’t find another pump type that’s better at pushing water that far uphill. Well suited for: Quarries and mining, jetting wellpoints, jetting casings, pipe cleaning, pipe testing, water blasting and marine construction.

The Hydraulic Submersible Pump

The hydraulic submersible pump is designed for dewatering applications in construction, mining and sewer rehab projects. The benefit of using a submersible pump is that it can be used in areas that would flood and disable a conventional pump. Power units can be installed and operated remotely for safety from flooding and ease of maintenance. The pump head requires less space requirements at the point of pumping. For example, a well designed 6-in. hydraulic submersible will fit into most manhole openings. Hydraulic driven pumps are an effective solution to those applications where the suction limitations of aboveground pumps make them ineffective or non-useable. Well suited for: Open pit, lake unwatering, manholes, flood control, mining and sewer bypass pumping.

The Non-Clog Pump

The non-clog pump offers the best of the pump world by being able to fill multiple roles such as wellpoint excavation dewatering, sewage bypass pumping, sumping, flood control or other applications that require the pumping of trash-laden effluent. Its non-clog impeller is capable of handling stringy materials and solids up to 3 in. in diameter and large clean out ports offer hassle-free removal of large debris without removing the suction pipe or hose. Well suited for: Wellpoints, flood control, sewer bypass and sumping.