I looked at a 6 cyc diesel engine turning a split case cent. pump today. Direct coupled @1785 rpm, common base, big flywheel coupling.
Pump readings were as follows. OA amplitudes between 1-3ips. Most vibration at 1.5x's rpm on both pump bearings, about 1.2 ips. Split seals keep failing, go figure. Why the 1.5x's? Is this common with 6 cyc diesels? Vertical and axial readings were the highest. I am told it was laser aligned! Any help is much appreciated. Thanks.

Hi Mike,

Is it just 1.5x or do you also see 0.5X,2.5x, 3.5x,etc? This is a sign of mechanical looseness/rub and at that amplitude, seals falling off is not a surprise. I've seen shafts fracture especially, when there are either no dampeners or the dampeners have lost their service life. Inspection may reveal broken/loose bolts at the early stages.

Cheers...Rajan Muthukrishnan

mostly at 1.5x's. This is a new unit.

diesel_driven_pump.doc (71 Kb, 21 downloads) pump vert and axial

Mike,

It is common for strong 1.5xSS excitation for a 6-cylinder engine. Is the engine a Detroit Diesel? You need to do a variable speed test and impact test to identify possible resonant structure. I also suggest torsional vibration measurements, since a torsional resonance is possible depending on shaft coupling design. I do this kind of work if you need assistance.

Walt
w_f_strong [at] msn [dot] com

Walt, it is a Cat Diesel. When I tested it it was just sitting on six (three on each side) 4x4's on a sandy beach!! Until it is actually installed I think bump and tosional test would not be of much help. I guess I should have mentioned that sooner, sorry. The frame it is mounted to appears to be very rigid.

It is typical of 4-stroke diesels to often exhibit the 1/2 orders (or multiples) as well as integer orders while 2-stroke diesels will typically exhibit the integer orders only. Which orders are exhibited in either type of engine is a function of crank arrangement, firing order and direction of rotation.

John from PA