Changing the primary and secondary fuel filters using a priming pump.

I know that this topic has been widely discussed but I am going to ask anyway. Please forgive the redundancy!

I have 6-71 N's JT modified with duel racor primaries and canister mounted element filters for the secondaries. My boat came with a fuel priming pump mounted between the racors and the secondaries. Both engines fire right up and run great.

My first question; I know that I can put new filters in both the primary and secondary filters DRY and then prime the system with fuel using the priming pump. What happens to all that air? Does it have to be bled and if so from where?

My second question; The owners manual for my engine (last revision 2004) specifies a P550540 filter element for the secondary filter. I looked up the specs on this filter and it is rated as a 22 micron filter at 99% efficiency. My understanding is that Detroit Diesels specify 30 microns primary and 10 microns on the secondary. Thoughts please. Thank you!


Jon

Not sure about the second question. The air is pushed through the entire system back into the fuel tanks.

I prefer the pump before the racors so you push fuel in after the element is in place with the top off. Then when the racor is full put the cover and you almost have no air in the system.

The priming pump will push fuel into the secondary

RACOR specifically states it need to be on the suction side. Do not install on a pressure side of a fuel system it's not only not designed for that but it could cause a bad spill.

I know some people will tell you different but consider the fact that their not engineers with the manufacturer and their expertise is self defined.

https://www.sbmar.com/articles/squee...powered-boats/

Scott - I think I understand your point and agree that the primer pump should be placed (downstream) between the Racors and the engines. Beside the obvious safety issue, Parker says that if the electric pump is in front of the Racor, it will emulsify any water and thus defeat the purpose of the separator function. I have attached a sketch - too much spare time with crappy TV reception in the islands
Attachment 33154

Apologies if the image takes up way too much real estate.

Just because I like simple.

If I put a t between the last filter and the engines fuel pump and a hose barb and valve on the t I can use a bulb into a jug so I can pull fuel to all the filters and have no electrical problems.

I use primer bulbs for priming engines all the time. I just attach the hose. Pull some fuel. Fill a bottle or jug and check for water or other debris.

I don’t think it matters much when it comes to priming pumps as they are low pressure.

For Insitanve this is factory setup Lazzara used (this one is an 84 with C32s) but I ve seennthr same layiut in others.

Feed lines from the 2000 gal keel tank run up to the Reverso priming pumps for the C32s and the smaller inline pumps for the gensets (on the edge of the pic). From there it goes to the dual racors. It works.

As mentioned you can use the priming pumps to fill out the open racors with new elements with fresh fuel. I have seen the same set up on other boats from other builders.

Rather urgent question. I’m changing my secondary fuel filter on 12v71 and did not pay attention to if the side of filter with rubber gasket faces up or to bottom of filter case. Please help!