Regarding the issue of the interlock switch location for the lubricating oil pumps in large units
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Friends, I have a question and would appreciate it if those who are familiar with instrument interlocks could help answer it. It is about the position of the interlock switch for the lubricating oil pump of large units – where it should be placed. Simply put, the standby pump is definitely set in interlock or automatic mode; there’s no need to say more. So, what should be the setting of the interlock switch for operating the pump? Personally, I think it should be set to the “manual” position. But there is another theory that it should be set to automatic mode. Please share your opinions.
The operating pump, which is the main pump, should be set to the manual position, while the standby pump should be set to the automatic position.
Question: 1. If the main pump is also set to automatic mode, will the following problem occur? If automatic mode is activated before starting the pump, will it start operating on its own? If the pump outlet valve isn’t open, won’t that cause the pump to overpressurize? 2. If the main pump is also set to automatic mode, will the on-site power control panel prevent the pump from stopping? 3. If the main pump operates in automatic mode, it is to serve as a backup for the standby pump once it starts up – can this achieve the intended goal? Who has witnessed any of the above, and will it actually happen?
I will answer your questions one by one: 1. If you are using automatic mode, I would like to ask whether the conditions for the pump to start automatically have been met? If lubricant pressure is the criterion, it will start only if the value is below this level; otherwise, it will not start. If it is conditional on the pump being in operation, self-starting will only take effect when the main operating pump stops. 2. As for your concern that the pump outlet valve might not be open, a situation where the pump gets stuck almost never occurs. Because the standby pump is required to have its outlet valve open; otherwise, there would be no point in it being able to start automatically. 3. If you need to stop the pump, change the control on the operation column to local manual mode and then stop the pump. 4. As for your third concern... I personally think it’s also an overreaction. After all, this plan has been in use for such a long time. I wouldn’t say it’s 100% successful, but at least the probability is over 99%. Getting back to the topic: The common approach is to set the main operating pump to \"manual\" mode, mainly because failures in the pump itself can cause abnormalities that lead to a low-pressure interlock. At this time, the backup pump is in standby mode and can be started promptly due to the low lubricating oil pressure setting, ensuring that the oil pressure returns to normal as soon as possible.
Our lubricating oil pumps come with two modes of operation: automatic start-up when pressure is low, and automatic stop-start based on electrical signals. Both the main pump and the backup pump are set in automatic mode; when there is a power outage, the pump that meets the conditions for automatic start-up will begin operating, which helps to prevent accidents caused by low lubricating oil levels due to the inability of the pumps to start quickly
All are automatic positions, with sequential activation
Only after normal startup should automatic operation be enabled along with interlocking