Step-by-Step Guide to Starting a Stainless Steel Gear Pump

Stainless steel gear pumps consist of a pair of meshing gears. The driving gear is fixed to the driving shaft, while the other end of the shaft extends outside the casing to be driven by a prime mover. The driven gear is mounted on a separate shaft. As the gears rotate, liquid enters the suction space through the suction pipe and is squeezed along the upper and lower casing walls by the two gears into the discharge space, where the streams merge (before the teeth mesh), and is then discharged through the pressure pipe.

During the operation of gear oil pumps, issues such as unexpected shutdowns and seal failures may occur after the pump stops. Gear oil pumps are considered high-quality among oil pumps and have specific application ranges. However, unexpected faults like shutdowns can still happen during operation. Analyzing the main causes of these shutdowns helps prevent unnecessary mechanical damage. Shutdowns are primarily caused by mechanical seal failure, which usually manifests as leakage. The main causes of leakage include the following:

Shutdown procedures for gear oil pumps must strictly follow the equipment's technical documentation. After shutdown, the pump should be turned manually by half a turn every 20 to 30 minutes until the pump body temperature drops to 50°C.

After a centrifugal oil pump stops, the inlet valve should be closed. Once the pump cools down, the valves of the auxiliary systems should be closed sequentially. Drain any accumulated liquid from the pump to prevent rust and freezing.

For pumps conveying media prone to crystallization, solidification, or precipitation, the pump and pipelines should be promptly flushed with clean water or another suitable medium after shutdown to prevent blockages.

For high-viscosity oil pumps conveying media prone to sedimentation, crystallization, or solidification, the pump and pipelines should be promptly flushed with clean water or another suitable medium after shutdown to prevent blockages.

Unless otherwise specified, the pump should always be kept full of liquid, and the suction and discharge valves should remain open. For low-temperature pumps with double mechanical seals, the level controller and the seal liquid in the pump seal chamber should maintain the pump's priming pressure. After a centrifugal oil pump stops, close the inlet valve; once the pump cools, close the auxiliary system valves sequentially. Drain accumulated liquid to prevent rust and freezing.

When shutting down a low-temperature gear oil pump, unless otherwise specified, the pump should always be kept full of liquid, and the suction and discharge valves should remain open. For low-temperature pumps with double mechanical seals, the level controller and the seal liquid in the pump seal chamber should maintain the pump's priming pressure.

Wear of internal components in stainless steel gear pumps can cause internal leakage. The large leakage area between the floating bushing and the gear end face is the primary source of internal leakage, accounting for approximately 50% to 70% of total internal leakage. In gear pumps with wear-induced internal leakage, volumetric efficiency decreases, and the pump's output power falls below its input power. The energy loss is entirely converted into heat, leading to pump overheating. If the mating surfaces are tightened, the slight movement of the floating bushing during operation will cause further wear. This can result in slow or failed lifting of agricultural implements. Such floating bushings need to be replaced or repaired.

Advantages of Stainless Steel Gear Pumps:

Simple structure, good manufacturability, and reasonable cost.

Compact structure and small size compared to other pumps of similar capacity.

Excellent self-priming performance, reliably achieving self-priming at high or low speeds and even in manual conditions.

Wide speed range. The transmission parts and gears are basically balanced, so high speeds do not generate significant inertial forces.

Relatively unaffected by dirt in the oil, making them resistant to seizing.

Disadvantages of Stainless Steel Gear Pumps:

Significant flow and pressure pulsations cause vibration in pipelines and valves, resulting in high noise levels.

Low working pressure. The unbalanced pressure on the gears, shafts, and bearings creates a high radial load, limiting pressure increases. Gear pumps are mainly used in low-to-medium pressure systems.

Low volumetric efficiency due to significant end-face leakage.

Specific Startup Steps for Gear Pumps:

Manually rotate the pump coupling; it should feel smooth and offer uniform resistance.

Adjust the relief valve pressure to the protective operating range of the hydraulic system.

Check whether the valves in the system are within the set permissible pressure range.

Fill the discharge port with the medium to prevent internal component damage from dry friction during startup.

Verify that the pump's rotation direction matches the indicator on the pump nameplate. If not specified, the standard direction for most gear pumps (when viewed from the motor end) is inlet on the left and outlet on the right.

Check if the hydraulic system has an unloading circuit to prevent full-load startup or shutdown.

Run the pump under no-load conditions for at least 2 seconds to check if the operating sound and flow direction are normal.

Jog the motor to observe whether the pump's rotation and sound are normal.

Adjust the relief valve pressure to below 1.0 MPa and run for about 10 seconds to check if the system's actions, external leakage, noise, and temperature rise are normal.