Hydraulic Motors vs Electric Motors for Operating Slurry Pumps

Learn about the differences between using electric motors and hydraulic motors for slurry pump applications.
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Finding the right slurry pump for particular applications is only the beginning. Once a particular pump model and size is selected, it’s up to the system engineer to match the suitable motor to power it correctly. Slurry pumps typically operate under challenging and heavy-duty loads; the motor powering them must be up to the task. The hydraulic and electric motor can power this electric hydraulic pump well. With multiple benefits and requirements for each pump motor type, an engineer must account for varying factors before matching the motor type to the pump applications. The following considerations all play a role in deciding between electric and hydraulic units for slurry pumps.

Slurry Pump Motor Costs

Electric motor and diesel-powered hydraulic power units (HPUs) vary in upfront and ongoing operation costs. An electric motor is widely available at a reduced cost for standard use, such as slurry pumping. However, the actual electrical power system tends to require additional equipment. The entire pump power system may cost more when built around an electric motor.

Electric motors and HPUs also require greater maintenance and, thus, higher costs. If appropriately sized and operated under an approved load level, an electric motor can run for years without interruption or maintenance. On the other hand, hydraulic generators are powered by liquid fuel. However, they need routine cleaning, filter replacements, tune-ups, and fluid changes.

Yet electric motors can still cost more if there’s an emergency, such as an overload that causes a stall, as this type of event will destroy an electric model and necessitate a total replacement. The increased durability and better response to load changes offered by the hydraulic motor lower the expected replacement cost for the pump system over the long run.

Slurry Pump Motor Size

Electric motors are best used for relatively low-torque situations. Since slurry pumping requires high peak torque when solids pass through the pump, the system needs a large electric motor to handle the highest possible power demands. Since sludge and slurry operations take up much space, finding room for a massive motor is sometimes impossible.

In contrast, hydraulic motors are efficiently designed to produce high torque levels in a much smaller package. When space or financial budgets are limited, HPUs are the better choice.

Electric Slurry Pump Motor
Hydraulic Power Unit

Environmental Conditions

The difference in how hydraulic and electric motors generate power will determine how well each type of motor handles challenging conditions. Electric motors use magnets and copper wire windings to create electricity. These windings change resistance when covered in fine dust or moisture, and salt spray results in corrosion.

Hydraulic motors are powered by separate diesel engines which generate power by burning liquid fuel (gas or diesel) to compress hydraulic oil inside of a cylinder that powers the pump. Hydraulic oil is a fluid designed to resist compression from moving pistons that can power practically anything. HPUs work well in the dirtiest and most challenging environments with no electricity being generated and no delicate windings involved. HPUs are also enclosed and operated at a distance from the actual pump, keeping them clean. They’re also the best for submerged installation since hydraulic units are more easily sealed than electric motors.

Challenges that develop during the slurry pumping process also pose a risk to the motor. When the load on the motor increases dramatically, both hydraulic and electric models will eventually stall. The hydraulic system will usually start back up again with no damage, while full stalling usually leads to severe damage in an electric motor. With slurry pumps capable of causing sudden load changes, it’s hard to prevent damage to an electric motor without oversizing it.

Secondary Equipment

Operating a slurry pump is never as simple as hooking any motor directly to the pump and getting good results. Slurry pumping causes dramatic changes in power demand during regular operation, so electric and hydraulic motors require secondary equipment for proper pump operation.

HPUs are relatively easy to connect to slurry pumps with few other accessories. These units tend to include governors and other built-in features that help the diesel engine scale to the pump’s demand with few extra parts. If more control is needed for precise slurry movement, programmable logic controllers (PLCs) are easily integrated.

Most electric motors require some kind of step-down controller placed between the motor and the pump. This is because an A/C motor, the most common electric model, only generates a fixed amount of power. Since moving a slurry with mixed solids leads to rapid changes in power demand, variable frequency drives (VFDs) are often necessary, especially for a sizeable 3-phase motor used for pump operations.

How to Size the Motor

Regardless of which type of motor the engineer chooses, picking a specific model capable of handling a slurry pump’s requirements requires the same calculations. Start by determining the various input factors, such as the flow rate in gallons per minute and the desired amount of pressure. This allows the engineer to choose the right pump to check for required RPM and torque numbers. Avoid trying to size a motor’s maximum operating output directly to these requirements; instead, pay attention to the optimal operating range. This range is often only 50% of peak possible power output. Keeping the motor in that range as much as possible during ideal pump operation reduces wear, a longer lifespan, and fewer equipment failures that lower productivity.


If you’re unsure of what motor would suit your pump application the best, our engineering team can help you select the best option based on the variables presented.

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