wawrzynskivp
Well Known Member
Moroso 1.5 qt Heavy Duty oil accumulator burst inflight. 100 Hrs in service.
Accumulator installed per installation instructions on engine mount Not on engine.
Upper cap sheared its threads and separated from body inflight. Immediate loss of all accumulator oil. Engine oil pressure was preserved by failsafe spring holding accumulator valve shut. Messy but not flight critical.
Returned to manufacturer for engineering investigation. Engineers ignored the helical remnants of sheared threads and pictures of safety wire keeping the cap from turning. Their conclusion was that the cap unscrewed and there is nothing deficient in design or manufacture.
I have put the accumulator back in service using steel plates on top and bottom of accumulator connected by four (4) 1/4-28 grade 8 threaded rods. I estimate this gives me a safe service pressure of over 500 psi.
My accumulator has temperature witness strips and so far has not exceeded 150 degrees surface temperature. Highest witnessed pressure while hot was 120 psi.
I am a retired aircraft accident investigator and without lab testing am fairly certain the threads suffered fatigue cycle failure and were improperly cut for full thread major diameter. This is just my opinion.
I am confident that my accumulator was not safe to operate the way it was received. Highly recommend not using this accumulator without reinforcing its end cap retention.
Accumulator installed per installation instructions on engine mount Not on engine.
Upper cap sheared its threads and separated from body inflight. Immediate loss of all accumulator oil. Engine oil pressure was preserved by failsafe spring holding accumulator valve shut. Messy but not flight critical.
Returned to manufacturer for engineering investigation. Engineers ignored the helical remnants of sheared threads and pictures of safety wire keeping the cap from turning. Their conclusion was that the cap unscrewed and there is nothing deficient in design or manufacture.
I have put the accumulator back in service using steel plates on top and bottom of accumulator connected by four (4) 1/4-28 grade 8 threaded rods. I estimate this gives me a safe service pressure of over 500 psi.
My accumulator has temperature witness strips and so far has not exceeded 150 degrees surface temperature. Highest witnessed pressure while hot was 120 psi.
I am a retired aircraft accident investigator and without lab testing am fairly certain the threads suffered fatigue cycle failure and were improperly cut for full thread major diameter. This is just my opinion.
I am confident that my accumulator was not safe to operate the way it was received. Highly recommend not using this accumulator without reinforcing its end cap retention.