Priming bulb before or after filter?

Andy Young2 · 22 January 2009, 00:46

I am refurbishing a rib that has fuel lines which are all over the place. It has an internal fuel tank with twin fuel lines (disconnected) as well as two fuel cells (connected) and two seemingly redundant lines that have engine fuel line fittings. The previous owner reported the fuel lines from internal tank fed insufficient supply to two 75hp motors. (This may have been because they were very narrow bore and were teed off a single feed off main tank) I have cleaned the tank, added a wider bore outlet (2 x 10mm spigots) and I am ready to re-run fuel lines.

I shall strip out all existing lines but seek advice on the bore of the fuel lines that I should run from tank to filter inlets, is 10mm okay? Also where to put priming bulbs in-line. Should they be before the filter or between the filter and the engines?

Finally, I live in the Middle East and will be running the engines regularly however bearing in mind high ambient temps should I run the engines after use (and flushing etc) to drain fuel system or is it okay to leave fuel lines connected and system full

Many thanks for any advice.

jwalker · 22 January 2009, 01:02

I've always used: tank>bulb>filter but I don't imagine it is critical. I guess the filter has some resistance to fuel flow and fuel is drawn into the bulb only by its own expansion after it has been squeezed, so putting the filter before it will slightly restrict the flow to the bulb.

Andy Young2 · 22 January 2009, 01:45

Thanks JW
I even wondered about 2 priming bulbs one either side of the filter however I am always wary of using too much pressure to push fuel into engine fuel system.

jwalker · 22 January 2009, 02:01

Quote:

Originally Posted by Andy Young2

...I even wondered about 2 priming bulbs one either side of the filter...

Nah, more to go wrong.

biffer · 22 January 2009, 08:43

dont really think there's wrong or a right way, but just think, bulb pulling fuel from tank also pulling any particials thats in the fuel, i'd rather the filter have them first than my primer bulb, does that make sense?

mdt · 22 January 2009, 08:59

I rigged a rib with twins on it last year and I cocked up cutting the fuel lines, I think I may have been thinking more about getting out and playing sorry "running them in"

than the job in hand. I ended up with the bulbs after the filter and... it did not work. It was with empty brand new filters etc but the bulbs seams to have more push than suck and could not suck fuel into the filter.

Tank - Bulb - Filter - Engine

Dirk Diggler · 22 January 2009, 09:11

Tank-filter-bulb-engine is how I was taught!

biffer · 22 January 2009, 09:18

i was probaly taught that to, but i put it in the logical part of my brain and forgot someone actually told me

doggypaddle · 22 January 2009, 09:28

I agree with j walker and MDT
I would definetley put the primer bulb BEFORE the filter, ie Tank/bulb/filter/and this is my logic behind it.

The primer can only lift fuel a small amount so it should be as close to the tank as possible there will be a strainer in the tank which will filter out any crap that could block the bulb.(and if theres that much crap in the fuel tank then its going to cause problems anyway)
If you end up in the situation where the filter partially blocks with the bulb after the filter, the fuel pump in the engine will suck and collapse the primer bulb and the engine will stop. there is nothing you can do other than change the filter at sea.
with the filter after the bulb, if you get a partial blockage in the filter you still have a primer bulb that can suck fuel up from the tank, and you stand a chance of getting to safety by getting someone to continuously squeeze the bulb to pump the fuel through the filter so you can get to safety,

as someone pointed out, bugger all suck but a fair blow

Dirk Diggler · 22 January 2009, 09:28

Common sense really, under normal use, the primer bulb is the only thing you'd need to access, hence the reason for these!

Chris · 22 January 2009, 09:32

Quote:

Originally Posted by Dirk Diggler

Common sense really, under normal use, the primer bulb is the only thing you'd need to access, hence the reason for these!

Nice ! I like those plastic fittings. (Zipping Anorak up)

Chris · 22 January 2009, 09:34

10mm is good and more than enough for your application.

I would put the primer before the filter however I have had one after a filter and not had any problems.

The only thing I would make sure is the bulb is in a vertical position with the arrow up as they pump much better like that.

biffer · 22 January 2009, 09:53

i will bow to everybody else's experience if they have fitted more of them than i have

9D280 · 22 January 2009, 10:07

On my old boat I had 2 plastic tanks, one at the bow, one at the stern with a permanent hose form the bow tank to the engine, theoy beingwhen one ran dry, I just swapped the connection from the "standard" across from tank to hose (or vice versa) at the engine, one line with primer by the engine.

Those bulbs, as everyone says, push well, but don't suck a lot (sure I could have phrased that better

) but are also hopeless at shifting air. on the current setup, when I swap to / from the front tank, the primer goes at the tank end, and the fuel line from the front is long enough to reach the engine.- it means if I empty the long hose it's easier to refill it.

Or, in short, put it as close to the tank outlet as package / access space will allow so you can prime the priimer more easily!

biffer · 22 January 2009, 10:27

primer bulbs dont push anymore air or fuel than they suck, it just seems that way with the pressure of you squeezing, what goes in must come out, same in, same out, only difference is you squeezing if you have proper quick release fittings on any tank or outboard it will shutoff and keep the fuel in the tube

JSP · 22 January 2009, 11:13

I'm glad this has been brought up. The bulb is after the filter on mine and it seems to take for ever to get the bulb to go hard.
I'm re-doing the fuel lines soon so may try the bulb before.

doggypaddle · 22 January 2009, 11:29

Quote:

Originally Posted by biffer

primer bulbs dont push anymore air or fuel than they suck, it just seems that way with the pressure of you squeezing, what goes in must come out, same in, same out, only difference is you squeezing if you have proper quick release fittings on any tank or outboard it will shutoff and keep the fuel in the tube

yes but were talking pressure not volume.
primer bulbs dont suck well, they blow well. Like ANY pump.
even if they creates a high vacuum (which they certainly dont) they could only lift fuel a few 10s of feet.

biffer · 22 January 2009, 11:31

jsp, there is a knack if the fuel backs to your tank that makes it quicker, as follows:- squeeze bulb, crimp tube, release bulb, release tube, and repeat, this creates a vacuum upflow of the bulb thus pulling it through quicker

doggypaddle · 22 January 2009, 11:36

Quote:

Originally Posted by biffer

jsp, there is a knack if the fuel backs to your tank that makes it quicker, as follows:- squeeze bulb, crimp tube, release bulb, release tube, and repeat, this creates a vacuum upflow of the bulb thus pulling it through quicker

Far better to move the bulb to before the filter which IMO and quit a few others is the right place for it

The other advantage as well as all the others i previously listed is you can pressurise the whole fuel system including the filter making it easier to find leaks.

biffer · 22 January 2009, 11:47

i was one of the guys who rigged the boats for the camel trophy (60+) so give me your views doggypaddle, 3 built in tanks, cross over valves, filter, engine, primer bulb.
crossover by filter, would you put 3 bulbs before the filter or 1 near the engine