What are the precautions in the trial operation of Roots blower?

The trial operation of Roots blower is the key link between installation and official commissioning. It is necessary to strictly avoid operational risks and timely investigate hidden dangers to ensure the safe and smooth transition of equipment to normal working conditions. In combination with equipment characteristics and industry norms, four core modules, namely, preliminary preparation, start-stop operation, parameter monitoring and exception handling, should be focused on during trial operation. The specific precautions are as follows:

First, before the trial operation: do a good job of "static investigation" to eliminate the hidden trouble of start-up.

Full-dimension inspection shall be completed before commissioning to avoid startup failure caused by "congenital defects". The core inspection items are as follows:

Review of foundation and connecting parts

Re-confirm the tightening state of the anchor bolt (re-tighten the torque according to the instruction to avoid loosening after installation), the pad iron is not displaced or loosened, and the equipment base is closely attached to the foundation (recheck with a 0.05mm feeler gauge, and the insertion depth is less than 1/3);

Coupling/pulley connection: the coupling bolt is free from missing and looseness, and the elastic pad is free from damage; The tension of the pulley is moderate (press the middle of the belt, and the sinking amount should be about 10-15mm), so as to avoid bearing load being too tight or slipping and heating caused by looseness.

Lubrication system confirmation (key! )

Gear box and bearing box should be filled with specified lubricating oil (such as 46# mechanical oil and 150# extreme pressure gear oil) according to the instructions, and the oil level should be at 1/2-2/3 of the oil level gauge (too low oil level will easily lead to insufficient lubrication, while too high oil level will easily lead to oil temperature rise and power loss);

Before the first operation, it is necessary to manually rotate the coupling/pulley for 2-3 turns to feel whether the rotor rotates smoothly, and there is no jam or abnormal sound (if there is jam, it may be due to improper adjustment of rotor clearance or foreign matter entering the casing, which needs to be disassembled for inspection);

Check whether the valve of lubricating oil circuit is fully opened, and the oil gauge and oil temperature sensor are firmly installed without leakage (soapy water can be applied to the joint to observe whether there are bubbles).

Calibration of pipeline and safety accessories

Valve status of air inlet/exhaust pipeline: During no-load trial operation, the air inlet and exhaust valves should be fully opened (to avoid sudden pressure rise in the casing caused by valve closure and damage to the rotor or seal); Before the load test run, it is necessary to confirm that the pipeline is free of blockage and impurities (the air inlet filter can be disassembled for inspection to prevent dust from entering the fan and wearing the rotor);

Safety accessories: the pressure gauge has been calibrated (accuracy ≥1.6, measuring range is 1.5-2 times of the design pressure), the take-off pressure of the safety valve has been set (1.05-1.1 times of the design pressure, and it has been confirmed to be flexible by manual jump test), and the installation direction of the check valve is correct (to avoid air flow backward impacting the rotor when stopping).

Electrical and control inspection

Wiring of the motor: make sure that the motor direction is consistent with the fan logo (you can jog the motor for 1-2 seconds to observe whether the rotation direction of the coupling matches the "arrow logo" on the casing, and the reverse direction will lead to insufficient air volume and abnormal vibration);

Control cabinet: the emergency stop button, overload protection (the current is set to 1.1 times the rated current of the motor), overtemperature protection (the upper limit of bearing/oil temperature is set according to the manual, such as the bearing temperature is ≥80℃ for alarm and ≥90℃ for shutdown) have normal functions, and the grounding resistance is ≤4Ω (rechecked with a grounding tester).

Second, in trial operation: standardize "dynamic operation" and strictly control operation parameters.

The trial operation is divided into two stages: no-load (1-2 hours) and load (4-8 hours). It is necessary to operate according to the process and monitor key indicators in real time to avoid equipment damage caused by illegal operation:

(1) No-load test run: focus on verifying "no-load stability"

Start operation specification

Before starting, it is necessary to inform the surrounding personnel to stay away from the equipment (especially the coupling and pulley cover area) to avoid accidents;

Adopt the process of "inching-delay-official start": inching the motor (1-2 seconds), after confirming that there is no jam or abnormal sound, wait for 5-10 minutes (let the lubricating oil fully lubricate the bearing), and then officially start the fan.

Real-time monitoring of core parameters

Vibration: the vibration speed should be ≤4.5mm/s(ISO 10816-3 standard) when measured in the "horizontal, vertical and axial" directions of the bearing seat with a vibrometer. If the vibration suddenly rises, it should be stopped immediately for inspection (possibly due to misalignment of the coupling and unbalance of the rotor);

Temperature: record the temperature every 15 minutes-bearing temperature ≤70℃ (rolling bearing) /≤65℃ (sliding bearing), temperature rise ≤ 40℃; Motor stator temperature ≤120℃(Class B insulation) /≤155℃(Class F insulation); Lubricating oil temperature ≤60℃ (without cooling system), if the temperature exceeds the standard, it is necessary to stop the machine for investigation (such as insufficient lubrication and poor heat dissipation);

Current and noise: the motor current should be stable and ≤ 50% of the rated current (no-load load is small, and excessive current may be caused by motor wiring error or bearing jam); The noise is measured at 1m ≤85dB (A), and there are no miscellaneous frequencies such as "metal rubbing sound, high-frequency scream" (the miscellaneous frequencies may be rotor shell rubbing and bearing damage).

(II) Load trial operation: focus on verifying "adaptability to working conditions"

Load loading principle

It is not allowed to load to the design pressure/flow rate at one time, but it needs to be "gradually boosted and steadily loaded": first, start the load of 30% (adjust the opening of the exhaust valve), run for 30 minutes without abnormality, then increase it to 50% and 80%, and finally reach the design load of 100%, and stabilize it for 15-30 minutes after each step of loading, and observe the changes of parameters;

During the loading process, it is necessary to monitor the pipeline pressure synchronously (avoid overpressure, and check whether the downstream pipeline is blocked if the pressure rises suddenly).

Monitoring and upgrading of key parameters

Air volume and wind pressure: when measuring the actual air volume with flowmeter (such as orifice plate and vortex flowmeter), the deviation from the design value shall be ≤ 5%; Exhaust pressure deviation ≤ 3% (based on the reading of outlet pressure gauge, pipeline resistance loss shall be deducted);

Current and protection linkage: the motor current is less than or equal to 105% of the rated current at full load (if it exceeds the requirement, check whether the load is too large or the fan leaks); Manually simulate "overpressure (closing the exhaust valve) and overtemperature (heating the oil temperature sensor)", and confirm that the safety valve takes off and the alarm shutdown function of the control cabinet is normal (after shutdown, check whether the check valve can effectively prevent airflow from flowing backwards);

Seals and pipelines: there is no obvious leakage at the shaft seal (oil and gas leakage ≤5 drops/hour, mechanical seal has no visible leakage); The flange and valve joint shall be inspected with soapy water, and there is no bubble (to avoid pressure loss or potential safety hazard).

Iii. Exception handling: Follow the principle of "giving priority to shutdown" to avoid fault expansion.

In case of any of the following abnormalities during the trial operation, it is necessary to immediately press the emergency stop button to stop the machine, and then restart it after the causes are investigated and solved:

Main points of handling possible causes of abnormal phenomena

If the vibration speed is greater than 6.3 mm/s, check the coaxiality of the coupling, the rotor is unbalanced and the bearing is damaged, check whether there is foreign body in the rotor and replace the damaged bearing.

If the bearing temperature is above 80℃ (rolling), the lubrication is insufficient, the oil type is wrong, and the bearing is installed too tightly. Replenish the lubricating oil, confirm the oil type, disassemble and check the bearing clearance.

The motor current suddenly rises beyond the rated value, the load is too large, the motor wiring is wrong, and the rotor is stuck to unload the load. Check the motor wiring, and manually turn the car to check the rotor.

There is a metal rubbing sound in the casing. The rotor gap is too small (the casing is scraped), and foreign objects enter the casing. Stop and disassemble, adjust the rotor gap, and clean the impurities in the casing.

If the safety valve does not jump but the pressure exceeds the design, the safety valve calibration fails, and the valve is blocked, re-calibrate the safety valve and clean up the impurities in the valve.

IV. After the trial operation: Make a "closing record" and keep the acceptance basis.

Shutdown operation specification

After the load trial run, it is necessary to unload the load first (open the exhaust bypass valve and close the downstream pipeline valve), and then stop after the fan pressure drops to near atmospheric pressure and the current drops to no-load level (to avoid uneven stress on the rotor caused by shutdown with pressure);

Observe for 30 minutes after shutdown, record the process of bearing temperature dropping to ambient temperature, and check whether the lubricating oil has emulsification and impurities (if so, replace the lubricating oil).

Document record retention

Collate the Commissioning Record Form, including the measured data such as "time, voltage, current, bearing temperature, oil temperature, vibration value, air volume and wind pressure", which need to be signed and confirmed by the operator and the supervisor;

Keep records of abnormal handling (such as shutdown reasons, troubleshooting process and solutions) to provide reference for subsequent equipment maintenance;

If there is a slight deviation in the trial operation (such as the noise is slightly higher but meets the standard), it is necessary to clarify the rectification plan and time limit, and the acceptance can only be completed after the re-inspection.

Summary of core principles

The core of Roots blower's trial operation is "safety first, step by step, data speaking": avoid illegal start (such as closed valve start and reverse operation), strictly control the parameters within the standard range, and handle the abnormalities in time, and finally verify the installation quality of the equipment through complete data, laying the foundation for formal commissioning.