The sealing effect of the rotary valve mainly relies on the airtight gap between the rotor and the housing.
Author :
Yiyun
The sealing effect of the rotary valve mainly relies on the airtight gap between the rotor and the housing. When the rotor rotates, each cavity between the blades acts like a small "cargo hold," filling with material and discharging it downward. If the gap is too large, it is like a crack in the hold, allowing gas to escape upward through the gap. If the gap is too small, the rotor's rotational resistance increases, not only adding to the motor load but also potentially causing material blockage. Generally, a gap of 0.1-0.3 millimeters is most appropriate, although this may vary depending on the material properties. For example, when conveying fine powders like cement, a smaller gap is required, while for larger granular materials, the gap can be slightly larger.
I. Preparations Before Adjustment
1. Power Off and Ensure Safety
This is the first step in any equipment adjustment and must be strictly followed. First, press the stop button on the control cabinet and wait for the rotor to come to a complete stop. Then, disconnect the main power supply and hang a "Do Not Close" warning sign on the switch. Put on insulating gloves and use a multimeter to check for any electrical leakage on the motor housing to ensure a safe working environment.
2. Disassemble and Inspect for Issues
Loosen the connecting bolts between the rotary valve and the upper and lower flanges, and carefully remove the main body of the rotary valve. At this point, you can inspect the internal conditions of the rotor and housing, carefully checking for any wear or deformation of the blades and any buildup or clumping of material inside the housing. Measure the existing gap with a feeler gauge and record the gap values between each blade and the housing. Typically, the gap near the inlet may be larger due to wear.
3. Clean and Maintain for a Solid Foundation
Use compressed air to blow away any residual material from the housing and rotor. For stubborn clumps, gently scrub with a soft brush dipped in a small amount of kerosene. Avoid using metal scrapers to prevent damaging the inner wall of the housing. Check the lubrication of the bearings; if the lubricant has dried or hardened, clean it out and apply new high-temperature grease. Lithium-based grease is generally recommended, with the amount filled to 1/2-2/3 of the bearing cavity.
II. Three-Step Adjustment Method
1. First Step: Rotor Coaxiality Alignment
Place the main body of the rotary valve on a clean workbench. Fix a dial indicator on a stand with the tip touching the edge of the rotor. Manually rotate the rotor and observe the dial indicator's movement. Under normal conditions, the runout should not exceed 0.2 millimeters. If the runout is excessive, it may be due to a loose bearing housing or a deformed rotor shaft. For a loose bearing housing, loosen the fixing bolts, gently tap the bearing housing with a copper bar to adjust until the dial indicator shows an acceptable runout, and then tighten the bolts in multiple steps symmetrically with a torque of 20-25 N・m. If the rotor shaft is deformed, a new shaft must be replaced, ensuring precise assembly between the shaft and rotor, with a tight keyway fit.
2. Second Step: Gap Adjustment Techniques
1. Shim Adjustment Method (for Fixed Housing)
Adjust the axial gap between the rotor and housing by adding or removing shims between the bearing housing and the rotary valve housing. First, measure the existing axial gap. For example, if the measured value is 0.5 millimeters and the desired gap is 0.2 millimeters, add 0.15 millimeters of shims on both sides of the bearing housing (since the axial gap is symmetrically distributed). Use stainless steel shims with a thickness accuracy of ±0.02 millimeters. Ensure the shims are flat without any creases, reinstall the bearing housing, and retighten the bolts. Measure the axial gap again to ensure it meets the requirements.
2. Bolt Adjustment Method (for Adjustable Housing)
Some rotary valve housings are designed with adjustable bolts. By rotating these bolts, the housing can be moved to adjust the radial gap. First, loosen the housing fixing bolts. Then, turn the adjusting bolts clockwise to slowly move the housing towards the rotor. Measure the radial gap between the blade tip and the housing with a feeler gauge while rotating the rotor. The angle of rotation for the adjusting bolts should not be too large, generally controlled at 15°-30°. Adjust while rotating the rotor until the gap is between 0.1-0.3 millimeters and the rotational resistance feels moderate. After adjustment, tighten the locking nut of the adjusting bolts first, then symmetrically tighten the housing fixing bolts, checking the gap regularly during the process to ensure it remains stable.
3. Third Step: No-Load Test Run for Verification
After completing the gap adjustment, reinstall the rotary valve into the system, connect the upper and lower flanges, ensure the gasket is intact, and evenly tighten the bolts. Connect the power supply and perform a no-load test run to observe whether the motor current is normal. The normal no-load current should be between 30%-50% of the rated current. Listen closely to the rotary valve for any abnormal noises; normal operation should only produce a slight rotor rotation sound without any friction or impact sounds. After running for 5-10 minutes, stop the machine and measure the gap again to check for any changes. If the gap remains stable, the rotary valve is ready for load testing.
III. Load Testing and Common Problem Handling
Load Testing for Effectiveness
Open the feed valve and allow material to slowly enter the rotary valve. Observe whether the discharge is smooth and whether there is any noticeable air leakage at the discharge port. Place a thin sheet of paper near the discharge port; under normal conditions, the paper should remain still. If the paper is drawn towards the discharge port, it indicates air leakage, and further gap adjustment is needed. Meanwhile, use a pressure gauge to measure the pressure difference between the inlet and outlet of the rotary valve. Ideally, the pressure difference should be stable between 500-1000 Pascals.
IV. Routine Maintenance for Long-Term Effectiveness
Regular Inspection and Record-Keeping
During daily inspections, observe the operation sound of the rotary valve, motor temperature, and current value. Use an infrared thermometer to check the bearing temperature, which should not exceed 70°C. Record the gap measurement once a week and plot a gap change curve to detect abnormal wear in a timely manner.
Proper Lubrication
Depending on the operating frequency of the equipment, lubricate the bearings every 1-2 months. Inject the lubricant slowly until the old grease is squeezed out from the gaps in the bearing end cover, ensuring full lubrication inside the bearings.
Attention to Material Properties
When the particle size, moisture content, or temperature of the conveyed material changes, the sealing gap should be readjusted in a timely manner. For example, when the moisture content of the material increases, it is prone to sticking to the blades and housing. In such cases, the gap can be slightly increased and the cleaning frequency raised.
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