Mechanical fuel lift pump suction head

[syvictoria]

Okay... dumb question alert!!! These are definitely becoming my speciality!!!

Beta state that the mechanical fuel lift pump can only supply a suction head of 0.25m. Where exactly is this measured to in relation to the pump? I've looked at lots of diagrams via Google, but nothing quite matches our set up which is the bottom of the diesel tank being (just) higher than the pump with the supply feed exiting from the top of the tank. Is the suction head to the maximum fuel level in the tank or the maximum level in the fuel line (i.e.: above the tank)?

Many thanks.

 

[vyv_cox]

Suction head is the difference between the fuel level and the pump level. For design purposes it would be the minimum level in the tank. The fact that the offtake is from the top does not matter as it cancels itself out, up and down side, although this might be a small problem from an empty tank with the line full of air.

 

[syvictoria]

Suction head is the difference between the fuel level and the pump level. For design purposes it would be the minimum level in the tank. The fact that the offtake is from the top does not matter as it cancels itself out, up and down side, although this might be a small problem from an empty tank with the line full of air.

Thanks so much - you're a star! We therefore meet the requirements by a mile (well, a good 15cm anyway!). Thanks again.

 

[macd]

We therefore meet the requirements by a mile (well, a good 15cm anyway!).

I suspect the specified 0.25m is quite conservative, anyway. In fact I have a nagging suspicion the figure used to be 0.5m.

 

[Steve_N]

They do seem to be tiny lift pumps on the Kubotas though, presumably not designed with drawing fuel up from a keel tank in mind. In fact you'd think that a mainstream engine mariniser might source and fit pumps more suited to the job in hand rather than just telling people to fit an electric pump inline.

 

[<152587>]

They do seem to be tiny lift pumps on the Kubotas though, presumably not designed with drawing fuel up from a keel tank in mind. In fact you'd think that a mainstream engine mariniser might source and fit pumps more suited to the job in hand rather than just telling people to fit an electric pump inline.

Yeah, but they are restrained by the footprint of the pump specified by the original engine supplier, the cam lift. the length and height of the cam follower etc. Not an easy fix by any means.

 

[Tranona]

They do seem to be tiny lift pumps on the Kubotas though, presumably not designed with drawing fuel up from a keel tank in mind. In fact you'd think that a mainstream engine mariniser might source and fit pumps more suited to the job in hand rather than just telling people to fit an electric pump inline.

Keel tanks are almost unheard of these days, although appreciate that more common in older boats that need new engines. Difficult to cope with every configuration using a standard engine that was originally designed for a completely different application.