Oil pressure spikes, pump or relief valve?

[Clive J]

[Clive J]

Not sure how many of you monitor Yahoo or Matronics so thought I'd post the links to some videos of some testing of pressure readings taken using a mechanical gauge in the pump discharge tapping.

 

I did some investigation some time ago when my almost new Jab 3300 was giving very poor oil pressure numbers when warm (it still does). What I found was really bad pulsing showing on the gauge, needle goes into a blur.

 

Later a friend had an engine failure after his cooler burst, though that cooler was brand new and the first flight, it reminded me of how many cooler failures I was aware of.

 

There was much discussion about pump performance and the SB of course. Some called it cavitation which I suppose you could but it was down to restrictive porting of the pump plate as you all probably know. That's been fixed or course but there were some who suggested the pump caused the pulsing and that in turn (with cold oil) was stretching coolers. I don't believe that is the case. With cold oil the relief valve will be quick to open and dump our precious oil to the sump and our coolers are rated way above the relief valves setting.

 

A gerotor pump, as the Jabiru uses, doesn't pulse in fact it's good point is constant flow (with good plate porting,,,,), so why was I seeing crazy pulsing on my mechanical gauge? Relief valve bounce......

 

At this point take a look at the selection of video clips:

 

 

Late 2200 with hydraulic tappets:

 

 

Given this is the same engine I hope that those that suggest the pump puts out the pulses will now see it isn’t the case.

 

 

I plan a slightly more tapered plug as the final design. The blunt end will still ensure ‘relief’ properties while the taper will ensure the smooth pressure control that will stop cooler damage and wear on pressure senders.

 

 

Unfortunately it can’t stop leakage through engine casings so my engine still needs to be split. The healthy pressure in the video drops back when the engine is really warm and at tick over I only see 10 psi. The joys of Jabiru ownership…..

 

Will let you know the final outcome of the plug design and profile. I have sent the info and vids to Jabiru, I had some early discussion based on the SB but the latest video has promoted no response .

 

Regards, Clive

 

3300 # 1460 39hrs

 

2200 #596 1300hrs