The mystery of the “3-second delay” in the turbine’s lubricating oil pump

Ours is the same! I’m not exactly sure how many seconds it is either!

Most units have this kind of instrument interlock, and no issues such as shutdown due to insufficient oil pressure as mentioned by the poster have been observed. Some delay in the instruments is expected, but it shouldn’t be as long as 3 seconds.

I recall hearing that there is a 3-second delay, but it seems it’s not for automatic startup when oil pressure is low, rather it’s for automatic startup in the event of a power loss. (Maybe I’m mistaken; I hope everyone can provide corrections and feedback!) ）

I agree with what was said above; there is a 3-second delay, which applies both to the instruments and to the operation of the electrical relays. To enhance reliability and prevent the oil pump from starting accidentally due to various abnormal conditions, centrifuge units are equipped with a 3-second delay added intentionally. What the teacher upstairs said seems to be that there is a mechanism in which, in the event of a sudden power outage, the electrical relay remains connected for 3 seconds to ensure the proper operation of the unit while waiting for power to be restored. If power is not restored after those 3 seconds, an interlock shutdown is triggered, thereby reducing unplanned interlock shutdowns caused by brief power fluctuations within 3 seconds.

I disagree with what was said above. Ensuring the safe operation of the unit is of top priority. If, due to some other abnormal condition, the oil pump starts automatically, and a 3-second delay is introduced manually, yet the unit still shuts down because of low pressure in the main pipeline and the auxiliary pump does not start in time (as a result of that 3-second delay), then this not only fails to improve the reliability of the unit’s operation but also creates safety hazards. Secondly, the proper operation of the lubrication system is a prerequisite and guarantee for the safe operation of the unit. Therefore, as long as the lubricating oil system meets the conditions for the auxiliary pump to start automatically, the auxiliary pump must start operating immediately. If it is later found that this was a false alarm, the auxiliary pump can be stopped manually, preventing at least a shutdown due to low oil pressure. If unplanned shutdowns of the unit are caused by the need to prevent sudden voltage fluctuations, I believe this interlock needs further improvement. For example, electrical interlocks can be added: if the main pump loses power, the auxiliary pump should start automatically. In the event of voltage fluctuations in the power grid, the electrical relay shall remain connected for 3 seconds. The unit is equipped with a lubricating oil system interlock and electrical interlocks to jointly ensure safe operation of the unit.

I believe there should be no 3-second delay required for the backup pump to start automatically when the pressure at the lubricating oil pump outlet is low. Typically, systems are equipped with circuits A and B, and it’s highly unlikely that both circuits will fail simultaneously and cause a power outage. By supplying power to the main and backup pumps from circuits A and B respectively, it is prevented from happening that a failure in one circuit leads to a situation where neither the main nor the backup pump can operate. A 3-second delay is usually applied to the vibration interlock shutdown mechanism, in order to prevent the unit from shutting down due to an instantaneous increase in vibration levels caused by measurement distortions, which might reach the set interlock value.

My understanding is that the auxiliary oil pump starts automatically within three seconds after the main oil pump stops, thereby preventing a shutdown.

The 3-second delay does not mean that the lubricating oil pressure has dropped to the level at which the standby pump starts automatically; rather, the standby pump starts 3 seconds later； Rather, it means that the engine shuts down after a 3-second delay; the engine only shuts down if the lubricant pressure reaches the required level within those 3 seconds.

A 3-second delay before startup is definitely not correct, but there will certainly be a delay in the startup of the backup pump as well； The solution to this problem is to add more accumulators. The reason for shutdown due to low lubricating oil pressure is insufficient pressure in the accumulators of the lubrication system, which results in a temporary drop in lubricating oil pressure and thus causes the machine to stop.

Ours is the same, but we have now changed it to one second, and the pressure value for sequential activation has also been increased

My understanding is that the main oil pump failed and the unit stopped; the auxiliary oil pump did not start within 3 seconds, and at that point the unit stopped due to low lubricating oil pressure. Is there something wrong with the original design? I don’t think a 3-second delay should be set for starting the auxiliary oil pump. At the same time, the poster did not specify whether the main oil pump is driven by a turbine or by an electric motor. This post was last edited by daqing01 on 2009-2-13 22:39.]

I fully agree with the views expressed by Ah Dai Ah Mu on the 5th floor. In fact, our lubrication system is also equipped with a 3-second delay before startup, which is very helpful in maintaining stable system oil pressure and preventing frequent automatic startups due to artificial fluctuations in system pressure (such as those that occur when switching oil pumps, changing lubricating oil, or operating oil filters). When the lubrication pressure in the main system lines is indeed low, the backup pump starts after a 3-second delay, without compromising the safety of the unit.

Personally, I think the 3-second delay should occur at startup, when the oil pump starts operating for 3 seconds before the unit begins to run； Or when the machine stops, the oil pump shuts down 3 seconds after the machine does (this is to ensure that the frictional components of the machine have sufficient lubrication) ； During operation, oil pressure protection should be divided into two levels: one is an alarm when the oil pressure is low, and the other is an automatic shutdown when the oil pressure drops to a certain level (that is, a sequential alarm is triggered at that point, with an indicator light turning on and a buzzer sounding to alert the operator) ； When the oil pressure drops to its limit due to lack of timely treatment, the unit shuts down again for self-protection

The 3-second delay is intended for electrical interlock signals; it is generally used to prevent the relay from tripping immediately after the main oil pump loses power due to fluctuations in the power supply, by providing a 3-second delay that gives an opportunity to restart the pump. Moreover, there is no time delay in the instrument interlock signal for the automatic start-up of the auxiliary oil pump when the oil pressure is low. The two signals do not affect each other. In other words, if the oil pressure drops to the level at which the auxiliary oil pump will start automatically, the auxiliary oil pump will start immediately. Actually, what friends 4 and 5 said is completely correct. As for what the meter technician from the original poster’s unit said, it is completely wrong; there should be a problem with the meter interlock system, or the position of the handle for the backup oil pump, or the indoor interlock isn’t set to the automatic mode. This post was last edited by Lu Junrang on 2009-2-14 09:51]

Agree with points 4, 5, and those above; the 3 seconds is for automatic activation during power fluctuations, not as a delay for the interlock between the main and auxiliary pumps.

I fully agree with the views expressed on floors 5 and 15; our plant’s main catalytic fan has experienced accidents where fluctuations in oil pressure led to low oil pressure, resulting in the fan shutting down as a result of the oil pressure interlock mechanism. Improvement measure: Increase the oil pressure interlock value; when the oil pressure reaches the interlock level, the main fan will shut down after a 3-second delay ； Instead of the auxiliary pump starting after a 3-second interlock delay, it should be such that as soon as the oil pressure of the main pump falls below the set interlock value, the auxiliary pump starts immediately, while the main fan shuts down after a 3-second delay. This prevents the situation where the oil pressure of the main pump drops below the set value or causes the system to shut down; in such cases, the auxiliary pump starts up, but if the oil pressure in the auxiliary pump does not reach the required level, the main fan shuts down as well.

I suspect you have a misunderstanding. Whenever the oil pressure falls below the set value, the auxiliary oil pump must start automatically. The correct understanding is that the machine stops only when, within 3 seconds, the pressure of the lubricating oil does not reach the required level, triggering the interlock mechanism.