The Crucial Role of an Impeller in a Trash Pump

What is a trash pump?

A trash pump is a pump used to transfer fluids that contain soft and hard solids like mud, silt, leaves, pebbles, and twigs. A trash pump is also known as a sludge, sewage, or wastewater pump. Centrifugal pump manufacturers design this type of pump in various sizes to suit different heads and flow rates. The sizes range from small to large trailer-mounted pumps. An electric motor or diesel engine powers the pump. Different trash pumps have different impeller designs, enabling them to handle different sizes and materials.

Figure: Trash pump in use.

What is an impeller?

A pump impeller is a disc component designed with vanes around it. The use of an impeller in a trash pump is to transfer mechanical power from the pump motor to the fluid being pumped. The impeller is connected to the prime mover (diesel engine or electric motor) via a metallic shaft to enhance power transfer.

Figure: Trash pump impeller.

How does an impeller work to transfer fluid in a trash pump?

A trash pump operates when the prime mover is turned on. Once turned on, the prime mover provides mechanical power to the pump shaft. As such, the shaft rotates and thus causes the pump impeller attached to it to spin at the same rpm. The rotation of the impeller and its vanes creates a low-pressure level inside the pump. This low-pressure level causes water and solid particles to enter the pump via the suction line. While the liquid enters the pump, the impeller imparts kinetic energy through its rotational energy. These increase the flow speed, and the media proceeds to the casing. Trash pump manufacturers design the casing to reduce flow speed while pressure rises. The increased pressure helps to transfer the liquid and contained solids.

Figure: How impellers transfer liquid and solids inside a trash pump.

Features of impellers used in trash pumps

  • Large and spaced open impellers.
  • Corrosion resistance.

Features of trash pumps

  • Large suction and discharge ports. These pumps are designed with larger suction and discharge ports to allow the entry and exit of liquid and solids without getting clogged.
  • Large-spaced impellers. The impellers are open to prevent solids from getting stuck and causing pump failure.
  • Powerful prime mover. The engine or motor is relatively more robust to ensure the pump can transfer solid and abrasive material.
  • Some trash pumps are designed with a lock mechanism to enhance security. They also have steel enclosure helping to reduce noise levels.
  • Corrosion resistance. Trash pump manufacturers use corrosion-resistant materials such as steel to enhance service life by overcoming corrosive media such as sewage and acidic fluids.

Types of trash pumps

Self-priming sewage pump

As the name suggests, this trash pump is designed to prime itself. It has the advantage over other pumps in which the user must prime them before pumping. One characteristic of a self-priming sewage pump is its large housing/casing. When the pump starts, liquid moves and mixes with air inside the pump. The air is less dense than the water. Thus, air rises on the water and finally exits via the discharge port. The water goes back to the casing, mixes with any remaining air, and moves up to discharge the air. The process repeats until all the air is removed and normal water pumping starts.

Figure: Self-priming trash pump.

Submersible Sewage pump

This pump is designed to operate while submerged in the fluid being pumped. This pump is mainly used to pump sewage and wastewater in municipal areas. The pump is special because it is fully covered to ensure no water enters it to damage electrical and electronic components like the motor. It also has a long power cable from the pump to the outside of the well or sewage. Other pumps must notify the user when the pump develops mechanical or electrical problems.

Figure: Submersible trash pump.