What are the precautions for gear oil pumps

Gear oil pumps, as a common type of positive displacement hydraulic pump, are widely used in fields such as mechanical manufacturing, petrochemicals, and ship engineering for transporting viscous media like lubricating oil and hydraulic oil. Due to its compact structure and strong self-priming ability, but at the same time, it has high requirements for medium cleanliness, speed matching, etc. Improper use can easily lead to wear, leakage or performance degradation. The following are the key precautions for the use of gear oil pumps, covering aspects such as installation, operation, maintenance and safety:

I. Precautions Before Installation

1. Medium compatibility check

Oil selection: Choose compatible hydraulic oil or lubricating oil based on the material of the pump (such as cast iron or stainless steel). For example:

The common gear oil pump is suitable for mineral oil (such as ISO VG32-68), with a temperature range of -10℃ to +80℃.

Stainless steel pumps can convey water-based hydraulic fluid or food-grade oil (such as H1 grade lubricating oil), but corrosive media containing chlorine and sulfur should be avoided.

Viscosity matching: If the viscosity of the medium is too high, it will cause difficulties in starting (for example, preheating is required in winter when the temperature is low), while if it is too low, the leakage will increase. The recommended viscosity range is 10-500 CST (at 40℃).

2. Foundation and Pipeline design

Foundation stability: The pump body should be installed on a concrete foundation or rigid support to prevent the loosening of bolts due to vibration transmission. The basic flatness error should be ≤0.1mm/m.

Pipeline layout

The inlet pipe diameter should be no less than 1.5 times the pump's inlet diameter, and the length should be as short as possible (≤3m), reducing the number of elbows (avoiding right-angle bends).

A pressure gauge (with a range of 1.5 times the rated pressure of the pump) and a safety valve (with a set pressure of 1.1 times the rated pressure) need to be installed on the outlet pipeline.

The return oil pipeline should be inserted below the oil level in the oil tank to prevent the return oil from splashing and generating bubbles.

3. Alignment and coaxiality

Coupling installation: When the motor and the pump shaft are connected through an elastic coupling, the radial deviation should be ≤0.05mm and the axial deviation ≤0.1mm.

Belt drive adjustment: If belt drive is adopted, the tension of the belt should be moderate (measured with a spring scale, the deflection is 1/100 of the center distance between the two pulleys).

Ii. Precautions During Operation

1. Startup and shutdown specifications

Pre-startup check

Manually turn the wheel 2 to 3 times to ensure there is no jamming or abnormal noise.

Open the inlet valve and discharge the air inside the pump through the exhaust valve (until the liquid flows out continuously).

Check whether the motor rotation direction is consistent with the arrow direction of the pump body (reverse rotation will cause no oil output or damage to the shaft seal).

Start-up sequence: First, jog the motor briefly to confirm the rotation direction, and then start at full voltage. It is strictly prohibited to run for a long time without load (more than 1 minute).

Shutdown steps: First, close the outlet valve, then stop the motor. If maintenance is required, the pressure should be released only after the pump body temperature drops below 50℃.

2. Monitoring of operating parameters

Pressure and Flow

The outlet pressure must not exceed the rated pressure of the pump (for example, the rated pressure of the CB-B type pump is 6.3MPa); otherwise, the pressure must be released through the safety valve.

When the flow fluctuation exceeds ±5%, it is necessary to check whether the inlet filter screen is clogged or whether the viscosity of the medium has changed.

Temperature control

The bearing temperature is ≤75℃, and the oil temperature is ≤80℃(which can be maintained through the oil tank cooler or forced air cooling).

Before starting in winter, the oil should be preheated to above 20℃ (avoid dry friction).

Noise and Vibration

The normal noise should be ≤85dB(A). If there is a sharp friction sound, it may be due to poor gear meshing or bearing damage.

The vibration value should be ≤4.5mm/s(measured in the horizontal direction of the pump body with a vibration meter). When it exceeds the standard, the alignment or the rigidity of the foundation needs to be checked.

3. Medium cleanliness management

Filtration accuracy requirements: The accuracy of the imported filter screen should be ≤25μm(NAS 1638 grade 7), and it should be cleaned regularly (every 200 hours or based on pressure difference alarm).

Moisture control: The water content in the oil should be ≤0.03%(detected by Karl Fischer titration). Excessive moisture will accelerate gear corrosion.

Bubble removal: If air is mixed into the oil (such as when the oil tank level is too low), it will cause pressure fluctuations at the pump outlet and needs to be dealt with through a defoamer in the return oil pipeline.

Iii. Key Points for Maintenance and Care

1. Regular maintenance cycle

Daily inspection: Check the oil level (at 1/2-2/3 of the oil window) and leakage (the leakage of the shaft seal should be ≤5 drops per minute) every shift.

Monthly maintenance

Clean the inlet filter screen and replace the filter element of the breathing valve (if a closed oil tank is used).

Check the wear condition of the elastic block of the coupling (replace it if the wear exceeds one-third of the original thickness).

Annual major overhaul

Disassemble the pump body and inspect the end face clearance of the gears (the standard value is 0.04-0.08mm. Gears need to be adjusted or replaced after wear).

Replace the shaft seal (mechanical seal or skeleton oil seal) and apply high-temperature resistant grease (such as Molykote X-5).

2. Standards for replacing key components

Gear wear: Replacement is required when the gap between the tooth tip and the housing exceeds 0.15mm, or when pitting or spalling occurs on the tooth surface.

Bearing damage: If the bearing clearance exceeds 0.1mm(measured with a feeler gauge), or if the temperature abnormally rises during operation, it must be replaced immediately.

Shaft seal leakage: When the flatness error between the end faces of the dynamic and static rings of the mechanical seal is greater than 0.01mm, grinding or replacement is required.

3. Lubrication and Sealing maintenance

Lubrication method

Oil immersion lubrication: The gear part is immersed in the oil pool (the oil level is above the gear centerline).

Forced lubrication: Oil is supplied to the bearings through an external oil pump (suitable for high-speed pumps with a speed >1500rpm).

Sealing improvement

For high-temperature media (>120℃), fluorine rubber O-rings should be used instead of nitrile rubber ones.

For highly corrosive media, double-end face mechanical seals (such as John Crane 58U type) are adopted and are equipped with flushing fluid.

Iv. Safety Operation Specifications

1. Personal protection

When operating, protective glasses (to prevent high-pressure oil from splashing), oil-resistant gloves (to avoid skin contact with hydraulic oil) and anti-slip shoes (to prevent slipping from oil stains) must be worn.

2. High-pressure risk prevention and control

It is strictly prohibited to disassemble the pipelines or instruments when the pump is running. The pressure must be released to atmospheric pressure before operation.

Blind plates should be installed at the inlet and outlet flanges of the pump during maintenance to prevent system pressure backflow.

3. Fire and explosion prevention measures

In flammable and explosive environments (such as gas stations and chemical plants), explosion-proof motors (Ex d IIB T4) and static grounding devices should be selected.

No open flames are allowed within 3 meters around the fuel tank, and dry powder fire extinguishers (MF/ABC4 type) should be provided.

V. Common Faults and Handling Methods

Possible causes and handling methods of the fault phenomenon

The pump does not discharge oil, the inlet is blocked, the rotation direction is incorrect, and the shaft seal is leaking. Clean the filter screen, correct the motor rotation direction, and replace the shaft seal

Insufficient flow, gear wear, excessive clearance, high medium viscosity. Adjust the gear clearance, replace the gears, preheat the oil or replace it with low-viscosity oil

When there is a large pressure fluctuation and air is mixed in, or when the safety valve malfunctions, check the oil tank level, exhaust, and repair the safety valve spring

Excessive noise causes bearing damage and poor gear meshing. Replace the bearing and adjust the axial clearance of the gear (by adding or removing gaskets).

Severe leakage of the shaft seal, wear of the sealing surface, improper installation, grinding of the sealing end face, reinstallation and adjustment of the spring compression amount (mechanical seal), or replacement of the O-ring (skeleton oil seal)