Installation of mechanical seal
There are several checkpoints that should be followed before and during the installation of a mechanical seal. These checkpoints are mentioned here. Take permits according to the company before equipment disassembles. And follow the safety as mentioned in JSA, RA. Use all PPE which is mentioned in the permits’ system. Follow the LOTO system of the company for equipment electrical and process isolation and verify your self physical at the site before working on any equipment. Start disassembly of equipment part step by step as mentioned in SMP or equipment manufacturer’s instructions documents. Check all necessary clearance during disassembly of equipment and note the same for record purposes. Extract existing seal arrangement or mechanical seal. Clean seal chamber and shaft, inspect surfaces under gaskets to ensure free from corrosion, foreign particles, or scratches. Ensure during assembly should be used always new gasket. Clean corners on shaft steps, threads, reliefs, shoulders, keyways, etc. over which gasket(s) must pass and/or seal against.
Check shaft and shaft sleeve OD, seal chamber bore like concentricity and seal chamber squareness, seal chamber depth, gland plate cleanness, stud bolts diameter, stud bolt pattern and distance to first obstruction to ensure they are dimensionally the same as shown in the seal assembly drawing. You should have checked manufacturers seal assembly drawings for any modifications (reworks) to be made to the equipment for mechanical seal installation and act according. The equipment must be properly earthed to prevent sparks due to static electricity discharge.
Check point during installation
Most important check point needs to be confirmed before installation of mechanical seal in equipment. They are following.
- Shaft Runout
- Shaft Endplay and bearing paly
- Seal chamber squareness
Shaft runout should be checked properly with the equipment manufacturer’s specifications (Recomended) and match this tolerance with the seal manufacturer. If need to rectify do accordingly. Generally, as per most manufacturer recommendation, should not exceed 0.05 mm (0.002 inches) TIR (Total Indicator Reading). At any point along the shaft for ball or roller type bearings. For sleeve type bearings, refer to manufacturer instructions. If the equipment can not completely dismantle, then verify runout near seal location. The mentioned tolerance values apply to shaft speeds in the range from1000 to 3600 RPM. Below mentioned figure explain clearly how to check runout of shaft.
As per most manufacturer recommendation Shaft endplay must be within 0.25 mm (0.010 inch) TIR limits, Regardless of thrust bearing type. For case of Radial bearing play should be checked at seal chamber face area Against the equipment manufacturer’s specifications. Generally 0.05 – 0.10 mm (0.002 – 0.004 inches) will be applicable for ball or roller type bearings. For sleeve or journal type bearing tolerance will generally be 0.10 – 0.15 mm (0.004 – 0.006 inches). If equipment is found outside of the given tolerance in this article, it needs to be consulted with the equipment manufacturer representative to verify the equipment’s suitability for the seal.
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Seal chamber squareness
Seal chamber squareness to be checked to the shaft centerline and should be within 0.0005 mm/mm or in inches (0.0005 inches / inches) of seal chamber bore TIR. Note: Check carefully and make sure that shaft endplay should not affect the reading chamber’s squareness reading. Verify the smoothness of the seal chamber face for a tight fitted gasket joint.
The definition of Concentricity, it is a 3-dimensional cylindrical tolerance zone that is defined by a datum axis. But for seal chamber area Concentricity of the shaft should be checked to the seal chamber bore or gland pilot register. It should be within the limit recommended by the manufacturer, 0.025 mm per 25 mm shaft diameter (0.001 inch per 1 inch shaft diameter) to a maximum of 0.125 mm (0.005 inch) TIR.
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