The problem of large horizontal vibration of single-stage single-suction cantilever centrifugal pump
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There are several single-stage single-suction cantilever centrifugal pumps on site. The bearings on both sides of the bearing box use deep groove ball bearings, and no thrust bearings are installed. After disassembly and maintenance, large vibration problems often occur, and all of them are large horizontal vibrations. The basic items that should be checked have been checked, dynamic balance has been done, the shaft and impeller runout meet the requirements, and the footings and foundations have been checked and there are no problems. Since deep groove ball bearings do not bear axial force, it is now suspected to be an axial deflection problem. For a pump with deep groove ball bearings on both sides of the bearing box, how should the gap between the gland be left?
Most likely it's your installation clearance issue. It is recommended that you send the on-site installation film to facilitate discussion. Usually the positioning of this type of bearing cannot be adjusted. The bearing gland should have the function of containing oil and cannot produce pressure on the bearing. But some structures need to adjust the axial structure through the gasket of the bearing gland. They are mostly used in butterfly valves, for reference.
Normal centrifugal pump bearing box design should have two discs of angular contact ball bearings installed back-to-back on one side of the coupling, which can withstand axial force. For a pump like this with deep groove ball bearings on both sides, I don’t know how much clearance should be left for the bearing gland. Once, the gap left was small and the vibration value was high. A 0.2MM thick cushion was added to the end face of the bearing gland, which is equivalent to an extra 0.2mm gap between the gland and the bearing outer ring. The vibration value dropped significantly. Now I just don’t understand how to leave a gap in the gland for a pump with deep groove ball bearings at both ends. Is there a standard? I have searched a lot of information but there is no explanation in this regard.
It depends on the pump structure. Some pump impellers have a double-suction structure and do not require direct thrust bearings. The gap should not be connected with the shaft or bearing, it is just an end cover. It is best to send a pump tablet to facilitate discussion. If you describe it for granted, you will tend to induce problems and it will not be easy to discuss and solve the problem. For reference.
If the bearing gland clearance is too small, the bearing temperature will be high; if it is too large, it will cause shaft movement. Generally, leave 0.01~0.12mm for positioning on the drive side and 0.30~0.50mm for positioning on both sides. This gap will not cause large vibrations in the horizontal direction. If there is no problem with the center, you need to measure the impeller vibration. The impeller may be statically unbalanced.
It is an ordinary single-stage single-suction cantilever centrifugal pump, and the medium is clean water.
I don’t know what drive side positioning and side positioning you are referring to? Angular contact ball bearings are installed back-to-back on the drive end of the bearing box, and the NU series support bearing is used on the other side. Is this considered drive end positioning? When installing deep groove ball bearings on both sides of the bearing box, are they positioned on both sides? I don't know if I understand it correctly.
Because of the problem of large vibration, the impeller, shaft, and coupling have been dynamically balanced together, so the problem of unbalanced impeller can be eliminated.
The gap requirement for this gland is not very strict, as long as it is not subject to large temperature changes, it is generally fine. It's just that if the relative clearance is large, the efficiency will be low, and if the clearance is small, the impeller suction port will be ground. This gap measurement should be at the suction inlet of the pump, or by using the lead wire method. There should be a clearance requirement manual, or contact the manufacturer. Usually 1~2mm should be fine. Just a suggestion, give it a try. Regarding the vibration problem, it is better to check the bearings or try replacing them with a new set. In addition, whether the bearing positioning is in place during installation. For reference.