2-stage filter losing prime

[Horsepoor]

What would happen if you mounted the filters at an angle and installed your own air bleed valve up stream where the air would collect?

[Ronmar]

IS that primer bulb between engine and filters?  IF so, that is probably where your leak is comming from.  They are only designed to pull enough vacume to lift fuel a little ways up from a gas tank.  They are way better at pushing fuel thru a fuel line to prime an outboard motor than pulling fuel... 

How high is the injector pump in relation to the fuel level? I would at the very least raise the tank so the bottom of the tank is at the same height as the IP.

I would also loose the primer bulb.  I would put a "T" with a valve and small hose barb pointing up at the last filter outlet(highest point in the system). and a shutoff valve at the injector pump inlet.  To prime the system, close the valve at the IP, connect a handheld vacume pump to the small hose barb and pump a vacume there, then open the valve.  The vac pump will allow you to pull enough vacume to lift fuel up into the filters, and air in the system will be expelled thru the pump out that high point untill it is all exhausted and the system is full of fuel  You should be able to get all the air out of hte filters that way.  IF you never let the barrel go empty, the only time you should have to reprime is if you service the filters...

I would say those filters are designed to have fuel pumped thru them, or if on hte suction side are well down in the system so are exposed to little vacume.  IF they are sealed with "O: rings, that may be the issue as they typically work better with pressure...  I would loose the primer bulb first, that gets my first vote for the vacume leak...   

[quinnf]

What Ron said.  I had** the primer bulb on my system between the fool tank and the filter, reasoning that I can squeeze more pressure into the filters than the primer bulb could suck.  That's really not worded right, but the idea is that the primer bulb, when you release it, can't produce much suction, but when you squeeze it, you can generate quite a lot of pressure, depending on the masculinity of your handshake.  

Kubota used to provide small electric fuel lift pumps with their small marine engines.  The pumps can run continuously and maintain positive pressure in the fuel lines all the way through the fuel filters and to the injection pump, thereby minimizing the chance of sucking a bubble of air at a critical time.  I now have one on the fuel pick line to my engine.  Got tired of priming the injection system after I had the system open.  My right elbow complains too much.  So now I switch on the fuel lift pump and evict all the air bubbles and then crank the engine and it starts right up.

I'm with everyone, saying there's an air leak between the two filters, and I've also been warned never to use Teflon tape on fuel systems.  To allow you to fill the water separator/evict the air from the headspace, consider installing a 3-way valve like this http://www.amazon.com/Seasense-8-Inch-Female-Three-Valve/dp/B004XAFKB2/ref=sr_1_5?ie=UTF8&qid=1344439727&sr=8-5&keywords=three+way+valve between the filters.  Reduce the free port to a hose-barb connector and attach a short length of clear Tygon tubing to allow the air to escape.

**( It replaced the outboard priming bulb with the 'lectric lift pump). 


Quinn

[Jay L]

Thanks for your tips and insight, all good info...

Finally got it all solved with both filters staying completely full.

I was going to put bleeders on top of both filters but it wasn't needed in the end.  What I did was get a small 1-3 psi diesel pump and used it to push fuel through both filters until all the air was out.  I put a tee in the supply line on the other side of the second filter and another tee in the return line near the fuel drum to direct the pumped fuel back to the drum.  Also added a shutoff valve after the supply tee so I could shut off the return line once all the air was removed.  I used the same quick disconnects on the pump as the supply side of the filters so I can plug in the pump when needed, and remove it when done.  Because the quick disconnects are dual shutoff, no (or only a tiny bit) of air gets in the supply line which keeps everything full.  I added a few pictures to make it more clear.  Anyway, I will only have to use the pump when I change the filters once a year, so I think it's a pretty good solution.  The 1-3 psi pump is a bit slow, took like 20 minutes to clear all the air, so maybe I'll get a more powerful pump someday, but it's fine for now.

Thanks again for all your help!
Jay.