I have two diesel engines on a ship. They are supplied fuel by a single line from a fuel circulation pump and a fuel booster pump. This system has a few valves etc. There is excessive vibrations on the fuel lines and the valve. On the inlet pipe we have read vibrations above 100mm/sec. There is beating and my beat calculations show that beat period is close to what we observe but the amplitudes on the circ pump is about 10 times higher than the booster pump. Would such a huge difference still lead to beating? Or is this flow related and how? Apparently valve opens only above certain pressures; would its chatter be related to pressure pulses?

As if all this was not enough I have done bong tests to find out that fuel line natural frequency falls smack on top of engine rpm which explains occasional ruptures. To make matters worse this is a fuel tanker. What bad luck!

Anyone have any experience with the screw pumps and their vibration characteristics?

Regards
Ibrahim

How long has this happened? Is this a new line or has operated for sometimes? Do you have enough pipe supports?

You'll have to provide more info, in particular the main offending frequency or frequencies, how the vibration depends on operating conditions etc.
100 mm/sec could get this system into trouble pretty quickly, particularly if there are details of layout / valve mass / support / welds etc leading to high dynamic stresses. In the short term, try to get an idea of where the large dynamic stresses would be, and find a way to reduce them.
To get to 100 mm/sec you undoubtedly have a mechanical or fluid dynamic resonance, or perhaps both. If it's fluid dynamic, there are a number of possibilities. Diagnosis will require good data. As stated above, knowing the offending frequencies and how they vary with conditions will be important.