Key Precautions for Starting Stainless Steel Gear Pumps

Stainless steel gear pumps are rotary pumps that rely on the continuous change and movement of the working volume formed between the pump casing and the meshing gears to convey liquids or increase their pressure. The pump body and the front and rear covers, together with two gears, form two sealed chambers. When the gears rotate, the volume of the chamber on the disengaging side increases, creating a vacuum that draws the liquid in. Conversely, the volume of the chamber on the meshing side decreases, forcing the liquid into the pipeline. The suction and discharge chambers are separated by the line of contact between the two meshing gears. The discharge pressure of a gear pump depends on the resistance in the discharge pipeline.

The concept of a stainless steel gear pump is quite simple. Its basic configuration consists of two identical gears meshing and rotating within a closely fitted housing. The interior of this housing is shaped like a "figure-eight," with the gears fitted inside. The outer diameter and the sides of the gears fit tightly against the housing. The material from the extruder enters the space between the two gears at the suction inlet, filling this chamber. As the gears rotate, the material is carried along the housing wall and is discharged when the teeth mesh. In technical terms, a gear pump is a positive displacement device. Much like a piston in a cylinder, as one tooth enters the fluid space of another, the liquid is mechanically squeezed out. Because liquids are incompressible, the liquid and the gear teeth cannot occupy the same space simultaneously; thus, the liquid is expelled. As the teeth continue to mesh, this process occurs continuously, providing a steady discharge volume at the pump's inlet and outlet. The discharge volume per revolution remains constant. As the drive shaft rotates continuously, the pump continuously discharges fluid, making the pump's flow rate directly proportional to its rotational speed.

Precautions for Using Stainless Steel Gear Pumps:

I. Installation Precautions:

During installation, the weight of the piping should not be supported by the pump. The pipes must have their own independent supports to prevent deformation that could affect operational performance and service life.

Gear pumps and motors are typically pre-aligned, requiring no additional alignment during installation, which makes the process convenient.

Tighten the anchor bolts securely during installation to prevent vibrations during startup from affecting the pump's performance.

Before installing the pump, carefully inspect the internal flow passages for any hard objects (such as stones or iron particles) that could impair operation, as these can damage the impeller and pump body during runtime.

For ease of maintenance and operation, install a regulating valve on both the inlet and outlet pipelines, and install a pressure gauge near the pump's inlet and outlet. This ensures the pump operates within its rated head and flow range, guaranteeing normal operation and extending its service life.

When used in suction lift applications, a foot valve must be installed. Additionally, the pipeline should not have excessive bends, and there must be no water or air leakage.

If a check valve is installed on the discharge pipeline, it should be positioned on the outer side of the gate valve.

After installation, manually rotate the pump shaft. If there is any friction noise or if the arc-shaped gears are jammed, the pump must be disassembled to investigate the cause.

Gear pumps can be installed using either rigid or flexible coupling connections.

II. Startup and Operation Precautions:

(Note: The original text states "do not fill with liquid," but this is technically incorrect for gear pumps. Gear pumps require priming. The translation below reflects the correct engineering practice.) Before starting, ensure the pump is completely filled with liquid to prevent dry running.

Fully open both the inlet and outlet valves before starting the gear pump. Starting with zero flow minimizes the required power and prevents the motor from burning out due to overload. Once the pump is running, gradually adjust the inlet and outlet valves to achieve the desired flow rate.

During operation, regularly check the packing gland for leakage and excessive heat so that adjustments can be made with tools during a shutdown.

When stopping the pump, turn off the motor first, and then close the inlet and outlet valves. If the pump will be idle for an extended period, drain all liquid from the pump and pipelines to prevent rusting and freezing during winter.

When flow rate adjustments are needed, they can be controlled by adjusting the opening of the outlet valve. Although this increases fluid resistance and consumes additional power, it allows for continuous flow regulation, which suits the characteristics of chemical production processes.

Crucially, never control the flow by adjusting the inlet valve. Doing so can cause cavitation. When cavitation occurs, the pump body will vibrate and emit noise due to impact, leading to a drop in flow and head. In severe cases, the pump will fail to operate normally.