Can excessive negative pressure in the engine’s fuel tank cause oil to flow back, resulting in significant shock vibrations in the tank?
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For the 64000 air separation MTU unit, there is a pressure transmitter in the main oil station tank; it shows that the negative pressure in the tank is -41 mbar, which is equivalent to 4.1 Kpa. The values given in the accompanying documentation for the negative pressure range from -200 to -400 Pa, which is 10 times higher than the actual operating value. The control oil for the turbine is supplied separately by a control oil pump located at the top of the oil tank, at a pressure of 18 bar. Currently, the control oil pipeline downstream of the control oil filter is experiencing significant vibration; the pressure gauge installed on site has been damaged as a result of this vibration. The vibration also affects the oil pipelines for the turbine’s quick-shut valve and governor valve, posing a serious risk. Guess: If the negative pressure in the fuel tank is too high, could it cause the oil to return too smoothly? This smooth return of oil could create vibrations due to the impact on the fuel tank, which in turn might be transmitted to the control oil pipelines, or it could lead to resonance or similar phenomena. Need an explanation for this. Control the oil pressure fluctuation within 0.1 bar.
It is obvious that there is a problem with the turbine filter elements installed in your equipment. Perhaps the filtration accuracy specified by the manufacturer for you at the beginning was incorrect, or maybe the filter element has become clogged over time. For specific parameters, you can consult Lüt Hall Filtering; they supply turbine filter elements directly to power plants, and the performance of these products is excellent
The negative pressure in the fuel tank is too high; it should generally be within -1.5 Kpa. This value can be adjusted, and this will also help to control the oil flow rate. Check whether this reduces pipeline vibration. Additionally, does the oil filter have a pressure difference gauge? Might it be necessary to replace it?~~
In one of our units, we also experienced fluctuations in oil pressure, with small bubbles continuously escaping from the top of the filter. At that time, we suspected a problem with the inlet pipeline, but the issue was later resolved. A shutdown provides an opportunity to empty the fuel tank. The tank is divided into four compartments, with filters between each compartment; these filters are covered with fibers. The oil level is high at the indicator position, but it drops in a stepped manner as one moves towards the fuel pump. The inlet of the fuel pump also draws in air due to the low oil level, resulting in pressure fluctuations. At that time, I didn’t pay attention to the negative pressure in the fuel tank, so I can’t remember it. During normal operation, the negative pressure in our fuel tank is between -1.5 and 2.5 kPa
“The fuel tank is divided into four compartments, with filters between them; these filters are covered with fibers. The oil level is high at the position where it is displayed, but it drops in a stepped manner as one moves towards the fuel pump. The inlet of the fuel pump draws in air due to the low oil level, which results in pressure fluctuations. ” Thank you! I’ve learned it!
First, determine whether it is a problem with the pump itself – does this phenomenon occur when both the primary and backup pumps are started? Check whether there are any leaks or valve stem vibration issues with the safety valve and the oil pressure self-regulating valve; it doesn’t seem to be related to the backpressure-induced return oil shock you mentioned.
Both the main and auxiliary oil pumps are the same; there is no leakage
The control oil pump is located at the top of the fuel tank, and the pump itself does not vibrate much
Generally, -1.5 kPa is sufficient; a manual valve in front of the oil mist fan can be used to draw in air.