Switching between the operating pump and the standby pump for the lubricating oil pump in large catalytic units

Without an interlock system, switching is done regularly; with an interlock system, switching must be carried out according to a set procedure

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Whether interlocking is present or not, regular switching is generally required, mainly to ensure the integrity of the backup pump (interlocking is essential in the lubrication systems of large-scale units). Switching steps: 1. Ensure that the inlet and outlet valves of the standby pump are both open. 2. Start the standby pump, check its operation status, and check the pressure. 3. If the pressure is fine, the main pump can generally be stopped after 30 seconds of operation. Additionally, some more advanced controls have incorporated the switching mechanism into their control logic; by simply turning the switching knob, the pump will switch automatically. However, the basic switching steps are still carried out as described above; it’s just that steps 2 and 3 become automatic.

Typically, self-acting control valves are installed in the circuits of gas stations to stabilize oil pressure. The opening degree of the self-acting valve differs between single-pump and dual-pump operation. During the short period of switching between dual-pump and single-pump mode, changes in the opening degree of the self-acting valve will inevitably cause fluctuations in oil pressure; therefore, such fluctuations are unavoidable. Based on this, the hydraulic interlock must be disabled during switching. Theoretical analysis is indicated, and practical operations are also based on this theory.

Pump reversal is performed regularly every two months； Switch the pump operation interlock to automatic mode, start the backup pump; as soon as the oil pressure reaches the required level, stop the original pump to prevent fluctuations in oil pressure caused by an excessive opening of the regulating valve. The switching process must be carried out quickly and efficiently. The overall interlock of the compressor has been in automatic mode.

Large-scale units do not necessarily require regular switching; our facility follows a regular maintenance schedule. This is because large-scale units generally do not have backup units, and frequent start-up and shutdowns are also not suitable for them； Furthermore, its lubrication system is online, with a dedicated lubrication pump; as long as the quality of the oil and the lubrication effect are maintained, there are no issues with the equipment operating over the long term. I’m not quite sure about your situation, but I suggest analyzing and checking it from the perspectives of maintenance and operation in order to identify the problem.

Large-unit lubrication oil pumps are never switched

Lubrication oil pumps in large-scale units generally come equipped with strict interlocks; as long as the electrical interlocks between the main and auxiliary pumps are functioning properly, if one pump stops, the other will start automatically. It should be noted that when making the switch, it is essential to ensure that all the electrical components and equipment of the standby pump are in good working condition. Additionally, lubrication pumps are usually screw pumps, so it is necessary to make sure that the inlet and outlet valves of the standby pump are fully open. To prevent fluctuations in lubricant pressure from causing unexpected shutdowns, we generally disable the process interlocks.

We don’t have any specific regulations regarding regular pumping, but the interlock is not disengaged during pumping. Once the backup pump starts operating, the oil pressure will definitely rise, and the outlet control valve will surely open wider to keep the oil pressure within the specified range. If you stop the main pump like that, the oil pressure will drop, posing a risk of shutdown; therefore, it’s necessary to close the outlet valve to maintain a higher oil pressure before stopping the main pump.

In large-scale units, the oil pumps are usually screw pumps. As long as the installation is proper, the standby pump should be rotated periodically to keep the electrical systems and valves in working condition; thus, the standby pump will not fail to deliver oil, no matter how long it has been standing by. Therefore, there is no need to keep switching pumps as long as the main pump is functioning properly. Unlike ordinary pumps, large-scale units have a direct impact on production, and any issue that arises with the pump can lead to shutdowns that cannot be resolved as quickly as with ordinary pumps. As long as the backup pump is in good condition and ready at any time, it will serve as a precaution. If it’s truly necessary to shut down the pump due to a failure, then the pumps should not be operated simultaneously for long periods of time; instead, one pump should be taken out of service. In that case, the pressure control valve has to make significant adjustments. When the operating pump is shut down, the pressure drops suddenly, and before the pressure control valve can adjust itself, the system pressure has already dropped significantly. Large-scale systems have pressure protection mechanisms, and if those mechanisms fail, it becomes necessary to shut down the system. One should check the pressure once the pump starts working; as soon as the pressure rises, the pump should be stopped immediately. Our pumps are all screw pumps, and they deliver a relatively uniform flow rate with no other issues. Once the pressure is established, it won’t drop again, remaining stable. This is one of the reasons why they are used

Some time ago I investigated a place where thorough renovations had been carried out to completely eliminate such problems; all that’s needed is to add a return system.

The lubrication oil pumps of large units don’t need to be switched regularly, as frequent switching can easily lead to shutdowns; it’s sufficient to check the interlock and automatic start-up functions before starting the unit, and after that there’s generally no need for any further switching.