Earthstar Forums

The guys I know who had failures of their vacuum pumps were not using electric pumps. Some were on
airplanes and some on snow machines. They also never serviced them regularly.
The check valve in the vacuum pump is just inside the fuel inlet. If the diaphragm fails the electric pump will pressurize the vacuum pump from the output side and fuel will go through the hole in the diaphram into the pulse line.
This is why I just keep mine in series and replace the vacuum pump parts on a regular basis.


Mike S

Have you ever herd of that happing?
What about the check valve in the vacuum pump?
Happy Flying
Mark
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If you are running a paralell set up and have a failure of the diaphram in the vacuum pump the electric pump will send fuel through the pulse line as well.
Mike S

Disregard my previous post.
I guess I'm getting old and not remembering correctly because on further inspection I found that there are actually 2 check valves in the Mikuni pump that most of us are using so a diaphram failure on a parallel system probably would not send fuel into the pulse line.

Mike S

Cool
Happy Flying
Mark

Sent from my iPhone

Thank you all for clarifications. Now I know that both my electric fuel pump and my vacuum fuel pump should have built in check valves for preventing reverse flow. To that end I am attaching a rough schematic of what I now see as the preferred system set up. Of course, kindly give me your views and opinions but don't charge me a lot of money for your help. Gary (aka Tommy)

Gary writes,
"Of course, kindly give me your views and opinions but don't charge me a lot of money for your help." Gary (aka Tommy)

Reply from Mark,
???
Have you been charged for any of my advice?
No!

Your aileron push pull tube is on upside down and there should be a bolt not rivets so that the wing can be removed with out having To go up in to the wing to unbolt your push rod.
The fuel pumps can be parilil or in series. Both work well.
Dip tube needs to go to bottom of tank. Plastic tanks inside fuselage does not condense water like aluminum tanks do, so no sump drain is necessary.
Happy Flying
Mark


Sent from my iPhone

Hi Mark,
Thank you so much. Of course, I was only joking about the fees. I do deeply appreciate all the help on this site and particularly that of you Mark. I was just trying to inject a little humor to check the pulse (that is only on the pulse pump). Thanks again.
Tommy (aka Gary)

Some comments on your schematic. Probably already have these, but I want to
be sure.
Inside the fuel tank, there should be screens on the intake of the dip
tube, and the intake for the EP to keep large debris from clogging the
intake.
A simple 4 tube connector would work for the connection from the fuel pumps
to the carbs.
Your fuel tank needs to be vented, so air can enter as fuel is pumped out.
Instead of the sintered bronze filters, I like using automotive fuel
filters with paper filters. (NOT the replaceable filter cartridge). I look
around til I find ones that are made of clear plastic so I can see what's
caught in the filter. They last a long time, and seem to stop water.