Replacement Fuel Line Size on Bukh DV20 Diesel

[squarehead]

I'm currently replacing my rubber fuel lines on my 31 year old Bukh DV20. I don't have any information on hose size so I have been copying what I replace. In doing so I found some inconsistencys, the previous owner may have replaced a hose or two I don't know.
This is what I have
A 1/4 inch hose from my secondary filter back to a 1/4 fitting on the fuel tank ( my return line )
A 5/16 hose running from the other 1/4 inch fitting on the fuel tank, to a 5/16 fitting on the primary filter, from there another 5/16 hose to my fuel lift pump.
I am curious as to why a 5/16 fitting wasn't used on the fuel line at the fuel tank.
To mount the fuel line to the lift pump the fitting appears to be 3/8 not 5/16, the hose was very difficult to remove.
The hose was either stretched or shrunk to fit
So my question is does anyone know the correct replacement fuel hose size for a Bukh DV20? or is it set up correctly already?

[squarehead]

Oh, the fittings are the hose barb attachments. My thought was why would you restrict the fuel flow with a 1/4 hose barb from the fuel tank when you could with 5/16 or 3/8?

[Stu Jackson]

Most likely the PO used what he had on hand. No reason you can't replace the barbs and use consistently sized hose. Our 21 hp and later 30 to 35 hp engines on our boats used 3/8 from the tank to the primary filters, then to the pump and then the engine. The return line is 5/16.

My engineering "best guess" is that they remain oversized for the flow rates, but I have not checked technically.

[squarehead]

Just finished the fuel lines this weekend
I went with a 1/4 return line, and for the rest I replaced the barb connectors to keep everything feeding the engine 5/16
I had a heck of a time with my connection to the lift pump, but still managed to get it on after I removed the fitting and installed the fuel line to it pryor to mounting it back on the lift pump
It just made it easier to remove it
I'm hoping to bleed, and start it up this week

[Aloha_float]

Going through the same issue. 1/4" return line with 5/16 supply .... Barbs on my Racor are meant for 3/8"
I am replacing my fuel tank with a moeller and am making some interesting discoveries and correcting them.

[squarehead]

The nice part about my Bukh engine is it only burns two litres an hour of fuel, so hopefully there are no other issues. I replaced my old Racor with a new one with a sight glass while I replaced my lines. It's a 1/4 inch pipe thread with a 5/16 barbed fitting

[Wotname]

FWIW, I used 5/16" everywhere when doing the fuel lines for a 2GM20 which uses about a litre / hour at say 2,200 rpm and somewhat more (maybe 1.5 or 2 l/h) at max continuos of 3,400 rpm. There have been no issues for the initial 200+ hours.

I chose 5/16" 'cause it felt right and I used it everywhere 'cause it was the easiest way to buy all the fitting / spares etc.

[Acushla]

My 1986 DV 20ME was originally fitted with 5/16" copper supply lines to the primary filter and lift pump. The return line is 1/4" copper. The supply line was renewed in 2007 with 5/16" rubber replacement fuel line due to a pin hole leak appearing in the copper at one of the bulkhead transition points where the fuel line could touch the sides of the through hole.
No problems since the refit.

Cheers

[Nicholson58]

Your fuel consumption rate is so low you can use about any reasonable size. I'd say 1/4" is minimum. If the lines are long or if you had to level multiple tanks you can justify/need larger lines. We have 5 tanks @ 75 gallons each. Lines are all 1". My feeder line to the pump is 1/4 inch and the return line is 1/8". Engine is 115 HP westerbeke 6-cyl. You get a lot of fuel through a 1/4 inch line.