Odd pipe sizes; which end goes where?; should I move my stove?; prop rope-cut­ters

Canal Boat - - This Month -

QI am re­plac­ing the fuel sys­tem on my BMC 1500 diesel and have no­ticed that the ex­ist­ing fuel sup­ply from tank to lift pump is 8mm, but the re­turn pipe is 6mm and 1/4in. The spill rail at the in­jec­tors is 3.5mm and the re­turn fit­ting into the tank has a very small in­ter­nal di­am­e­ter, much less than the pipe. Can I ig­nore this and just use con­ve­nient pipe sizes and fit­tings? I will also at­tempt to solder in re­place­ment parts of the bro­ken spill rail: again, would a big­ger di­am­e­ter be okay?

PETERI, via the CB web­site

ATONY REPLIES… On no ac­count soft solder the spill rail. The Boat Safety Scheme re­quires such fuel sys­tem joints to be sil­ver sol­dered or com­pres­sion joints. It would be eas­ier to buy a new rail.

The way the BMC fuel sys­tem is de­signed, the lift pump will sim­ply stop pump­ing if there is too much fuel/pres­sure in the sys­tem. There should be al­most no flow through the small in­jec­tor leak off pipes so its size does not mat­ter.

The main re­turn should be fed from the banjo bolt in the top of the fuel fil­ter via a 0.5mm hole in the bolt so 0.5mm di­am­e­ter or larger should be fine for that pipe. It is this hole that cre­ates any ‘back pres­sure’, so there is no rea­son not to use a larger bore pipe on the re­turn.

Back pres­sure is only re­quired to en­sure suf­fi­cient fuel gets to the in­jec­tor pump rather than flow back into the tank.

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