Thanks for the replies. First, a little more about my setup. The boat
is a Swanson yacht, with a Kubota based main engine, consuming about 3.2 litres per hour under optimum conditions, possibly 6-10 litres under wide open throttle. I haven't been able to get any specs on fuel return, but think it would be about 3 litres per hour. The engine is new, recently installed it myself.
from the fuel return on the engine to the o/head tank (built into a cockpit
seat) is about 1.7 metres. The pressure coming out of the fuel return is near enough zilch. I have a mate Kev who is a injector/pump specialist of some 35 years experience, and he advises strongly against simply routing the fuel return to the o/head tank. He says the pressure build up in the return line would be enough to cause hydraulic lockup at the injectors (his words), resulting in the engine stopping.
The option of feeding off the o/head tank, running the return to the main tank, and periodically transferring fuel to the o/head tank is what I have at the moment, and I regard it as unsatisfactory, and bad practice. Everything I know and have read about fuel systems emphasises the importance of maintaining the integrity and separation of tanks, to avoid cross contamination and overfilling.
In my case I am particularily concerned about contamination. I have experienced contamination of the main tank, and on switching to the o/head tank, having the return go back to the contaminated main is not good.
The fuel return on my auxiliary, a single
ts60 feeding off the o/head tank, goes into the inlet of its primary fuel filter
. That works ok, but the Yanmar
only consumes 0.5 litres per hour, and the return would be miniscule. Stuff I have read on the web indicates such an arrangement leads to problems with larger engines. My mate Kev doesn't know, but instinctively doesn't like it.
Kev thinks putting an electric pump
in the fuel return line, carrying a few spare pumps in case of pump failure, is the way to go. At the moment, thats what I am going to do. My purpose in posting
was to find out any experiences here.
Thanks to "ex-calif" for the link to the dual valve, I didn't know such a thing existed. The one you have linked, while ideal in principle to my setup, is too large, but I am now googling for something similar and smaller.