These recommendations will ensure consistent, high lifts.
by Lindsey Thorp, Thompson Pump

Submersible pumps provide a powerful solution when high heads or high lifts are required at some job sites. The submersible pump end also eliminates suction lift limitations, allowing pumping in deep excavations, manholes, open pits, quarries or mines.

Hydraulic Submersible Pump Basics

A hydraulic submersible pump set is a two-piece system comprised of a hydraulic power unit and a submersible trash pump. The hydraulic power unit is equipped with a hydraulic pump that is powered by a diesel engine or an electric motor, a hydraulic oil reservoir, and three connections for hydraulic hoses. These hoses supply oil to and from the hydraulic motor that powers the submersible trash pump. The submersible pump is a trash pump because it can handle solids suspended in the pumpage.

The hydraulic power unit is a positive displacement, external gear-type, single hydraulic pump. The pump head, which is submersed into the pumpage, is a centrifugal pump end. The oil from the power unit is pumped to the hydraulic motor, which turns the submersible pump end. The engine turns the hydraulic pump, and the hydraulic motor turns the impeller of the submersible pump end. The hydraulic oil is returned to the tank through the return line hose.

Why Choose a Hydraulic Submersible Pump Set?

Unlike a suction lift pump, hydraulic submersible pumps are capable of high lifts because they pump up from the bottom rather than lift. Contractors, public works operators and mining operations commonly use these pump sets if suction is a concern, such as dewatering gravel pits, mines, quarries, trenches and pipelines. Wet prime and dry prime trash pumps are only able to lift water approximately 28 feet because of physical restrictions such as friction and atmospheric pressure.

In addition to overcoming high suction lifts, hydraulic submersible pumps can handle viscous liquids—such as sewage, sludge, slurries or muddy water—without suction-line clogging problems that occur in suction pumps. A variable engine speed allows for different flow rates and heads in deep applications.

The hydraulic power unit is accessible for servicing and fueling while the submersible pump end remains in the source. The maximum recommended hydraulic hose length for connecting the power unit and the pump end is 100 feet. Consult the pump manufacturer’s applied products department if additional hose length is required.

A hydraulic submersible pump set empties a lift station.

Recommended Accessories

Barrel floats prolong the life of the submersible pump by preventing it from burrowing into the bottom. The floats work like pontoons, keeping the pump end submerged but not allowing it to touch the bottom. This prevents dredging, which can damage the impeller and other rotating components. A barrel float also protects the pump from large solids and locks the pump in place, preventing excessive movement, which will cause damage to the pump and associated piping.

A slurry gate works best for applications that require special agitation of the pumped liquid, such as pumping out sludge lagoons and removing debris from storage tanks. The gate consists of a revolving door and hydraulic cylinder mounted on the submersible pump. The power unit controls the door opening and closing remotely to agitate and pump slurry.

Adding an automatic start-stop system to a hydraulic pump set simplifies operation and takes less time, which minimizes labor costs. The system energizes and de-energizes the hydraulic circuit while automatically adjusting the speed of the hydraulic power unit. Typical hydraulic power units require manual start and stop, needle valve and speed adjustment. An automatic start-stop system allows for considerable fuel savings and reduced engine wear because of the automatic throttle control, which allows the engine to warm up and cool down with ultimate precision.

A barrel float prevents the submersible pump from touching the bottom.

Setup & Operation

When installing the hydraulic pump set, place the power unit on a firm, level surface as close as possible to the intended location of the submersible pump. This reduces the required length of hydraulic hoses. Leave room for proper operation, maintenance and refueling of the power unit.

Lay out hydraulic hoses in a direct path from the power unit to the submersible pump, out of the way of traffic and without any loops or kinks in the lines.

Attach the hydraulic hoses to the power unit first, then to the submersible pump. This sequence ensures that any hydraulic pressure buildup in the hoses can be vented back to the hydraulic reservoir. Connecting the hydraulic hoses to the submersible pump without first connecting to the power unit can damage the submersible pump’s mechanical seal. Be sure to tighten all the hydraulic connections fully to the proper mark on the couplings to engage the valves in the quick disconnect fittings.

A hydraulic submersible pump set dewaters a rim ditch application.

Before installing the submersible pump, attach cables or chains to the submersible pump to restrain it and avoid any possible tension in the hydraulic hoses. Then, install the submersible pump on a suitable flotation device and place the device and pump in the fluid to keep it out of the mud. Make sure the strainer is submerged sufficiently to prevent pulling in air during pumping.

Before starting the pump, perform these prestart checks: