Fuel Pressure Pulsation

[bobcharl]

Hi All.

 

On the last flight in my Sav (912 uls) I noticed a pulsation in the fuel pressure.

 

Occurs when the motor is running, irrespective of whether the electric pump is on or off.

 

Does not occur when motor is not running but electric pump is on.

 

Which to me indicates the problem is somehow related to the mechanical pump.

 

Have discussed the issue with Floods who could not come up with a reason other than that the vent tube may be blocked , so I disconnected tube at the pump and blew air through it. No blockage!

 

Floods also mentioned that the location of the discharge end of the vent tube can also cause weird pressure readings, (I seem to remember the manual mentioning this) but were at a loss to explain how this could be relevant after 100 hrs of satisfactory operation.

 

Any thoughts out there?

 

Bob

 

 

[planesmaker]

Pump problem? I have had a couple of the new pumps fail.

 

 

[Kyle Communications]

Make sure you have taken the rubber grommet out of the back of the fuel pressure gauge. It causes wierd stuff...its a small rubber plug

 

 

[Downunder]

If you have an air box, the vent lines should go inside it.

 

 

[JerzyGeorge]

I had similar event and installed new mechanical fuel pump which fixed problem.

 

Second event fuel pressure was dropping while on mechanical pump only, flew home on electric pump All the way and installed new mechanical pump (again) and problem went away, put a post on this forum some time ago. Perhaps fuel pumps are not as used to be??? Have not changed anything else.

 

Another possibility blocked vents ( unlikely).

 

George

 

 

[IBob]

Are you able to give any more detail:

 

Is this a rapid pulsation, or a slow one? And how big is the pressure swing?

 

 

[JerzyGeorge]

first time swigs were about 25 deg on the dial gauuge do not recall exact numbers it was 2.5 years ago

 

The second time pressure was dropping gradually and I switched electric pump on before it reached zero.

 

After few minutes I switched electric off and problem came back, left electric on for duration of flight and modified my route home to have many outlanding options open.new pump is 350$ but perhaps you can swap with spare one borrowed from friends.

 

George

 

 

[IBob]

first time swigs were about 25 deg on the dial gauuge do not recall exact numbers it was 2.5 years agoThe second time pressure was dropping gradually and I switched electric pump on before it reached zero.

After few minutes I switched electric off and problem came back, left electric on for duration of flight and modified my route home to have many outlanding options open.new pump is 350$ but perhaps you can swap with spare one borrowed from friends.

 

George

Okay. I was meaning can BobCharl give more info, but this is useful too. Thanks.

 

 

[bobcharl]

Thanks all for the replies.

 

Mark: Remember putting a hole in the rubber grommet during assembly.

 

Downunder: Floods tell me that on each shutdown there is a minute discharge of oil through the vent . Don't know about this going into the airbox. Is that the way yours is?

 

JerzyGeorge:Think this might be where I am heading!

 

IBob: The pressure swing is in the order of 0.5 to 0.75 psi. I could only describe the pulsation as rapid, without putting a frequency on it.

 

Thanks again, keep the suggestions coming.

 

Bob

 

 

[Kyle Communications]

Not sure about the discharge...I havent seen anything

 

 

[JerzyGeorge]

I do not like the idea of oil Beiing discharged to air box air box should be by definition clean without risk of air filter clogging up.

 

 

[JerzyGeorge]

Any suggestions recommendation of different manufacturer of fl uel

 

pump or perhaps supplier of the old style??

 

Perhaps old design was better than a new one???