I’ve consulted various experts – the VCM Dalian Empire shielded pump frequently experiences bearing burnout; where exactly is the problem?
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I pay my respects to all the experts and moderators here. With an open mind that can embrace everything, I’m posting this as my first message as a newcomer – please bear with me. I’m new to equipment management and encounter difficulties; I hope the experts will kindly offer their guidance. Our company’s chlor-alkali plant produces PVC using the calcium carbide process, and two shielded pumps from Dalian Empire are used for VCM transportation. These two shielded pumps have their bearings burning out frequently; it has happened 4 times already this year. The repair costs have exceeded those of a new pump. The problem has been identified: 1. The selected net positive suction head is too high. The margin provided by the design institute for the device was 1.3m, and for the pump it was 1.9m. So should we pressurize the monomer tank, or keep burning continuously? No pressure is applied now; the liquid level is kept at 3 meters, but it still burns. 2. The material returning from the polymerization tank to the monomer tank contains some impurities. The first repair was to seal a leak in the tail pipe of the shielded pump; a filter was installed (it was already there during installation but not in use), and there has been no further leakage for 4 years. The inside of the shielded pump is still very dirty. It still burns frequently. Personally, I think the filter increases the pipe resistance, making it easy for the liquid at the pump’s inlet to vaporize. I have an idea – I wonder if it’s feasible: to use a pump from Hydramatic without a filter. Since Hydramatic pumps don’t have tail pipes, there’s no need to worry about blockages in those pipes. The bearings made of silicon carbide are very hard, and the impurities involved are mostly polymers, so there’s little risk of problems with them. I wonder if this idea is feasible? Since the pumps produced by Empire are of grade 8 and require dynamic balancing, our company does not have the capability to carry out this task; we rely on the after-sales service provided by Dalian Empire for such work. The repair costs are too high. Are there any other places where repairs can be done? Looking forward to the great god’s reply~~~ Thank you! ! ! !
:Lol, Haimi and Empire are both manufacturers that entered the field of canned motor pumps later on. Don’t ask me why I know; I used to be a salesperson.
3 brands that I know. Think about it yourself. 1: Dalian Empire. 2: Haimi 3: Shanghai Nikkiso Shielded Pump (Japanese brand). Back then we were in sales (sorry, it was only 3 months due to time constraints), and we knew that both Empire and Haimi had entered this field later; in terms of expertise, they couldn’t compare to Nikkiso. For Nikkiso’s shielded pump models, numerous confirmations were required throughout the selection and procurement process before the pumps could be delivered – it wasn’t something that could be done simply and quickly. In your case, an expert is needed to help analyze what exactly is going wrong. I can only tell you that the best in terms of quality are still the Nikkiso shielded pumps.
Are the thrust disc and bearings worn? Has it been considered that it could be caused by axial thrust?
Has the outlet pressure of the pump, as well as its vibration, remained normal? Are there any crackling sounds inside the pump chamber? If cavitation occurs in the pump, the bearings can easily be damaged due to dry friction.
Excessive wear of the bearings in shielded pumps is usually caused by poor lubrication, vaporization of the medium, insufficient lubricant supply, or inadequate temperature control – all of these factors can lead to rapid damage. You can consider improving the situation by controlling the temperature of the lubricant and increasing its flow rate. In China, Nippon Seiki offers good products; Imperial’s high-temperature and ultra-high-temperature pumps are also very durable. Huanyou Pumps are another option, and SeaRay Pumps are also satisfactory – you get what you pay for
For shielded pumps with grade 8 impellers, the structure should be fixed, arranged symmetrically back to back, with axial forces self-balancing； The inlet pressure at the guide bearings should be the inlet pressure plus the head generated by the 4th stage impeller; this prevents flashing and dry grinding at the guide bearings (unless the cooling circuit is blocked). The remaining possibility is a problem with rotor deflection. Generally, manufacturers are unable to achieve dynamic balancing for such large rotors; a dial gauge can be installed on the first-stage impeller to check for deflection. Furthermore, it is necessary to consider whether there are system operation issues; for example, operating under conditions of low flow rate for extended periods of time or running in parallel can all affect the lifespan of the guide bearings. You might also want to take a look at the shielded pumps produced by Jiamusi Motor Factory; it is said to be an established state-owned enterprise that has been in operation since 1960.
I’m not the manufacturer; I’m just sharing my experience with pumps. If the medium is relatively clean, then the Dalian Empire pumps and other similar pumps will work fine. However, if the filters get clogged or there’s an imbalance in the axial forces, the pumps can easily get damaged. In this regard, Haimi pumps are superior to Empire pumps (the tailpipe design of Empire pumps is likely a flaw); you could try using a pump from another manufacturer. For reference only.
1. This year, the bearings have burned out 4 times; it’s necessary to compare this with the situation over the previous 4 years to identify any other changes in the system. 2. The main reason for bearing burnout is a lack of lubricant. If systems equipped with exhaust pipes – which can quickly remove gases generated through evaporation or heating – still cannot prevent the accumulation of large amounts of gas, it is not recommended to use silicon carbide bearings. Using such bearings in a gas-phase environment will result in the motor being damaged. 3. It seems that the issue of cavitation has not been properly addressed; more solutions need to be considered. 4. In media containing self-polymerizing substances, the use of shielded pumps will inevitably lead to the accumulation of these substances in the circulating fluid. This is not only a problem related to the friction pairs but also poses risks to the circulation within the motor. It is necessary to control the operating time and maintenance intervals based on experience. For reference only!