Fuel Pump - Which End is Up?

[Windborne]

I purchased a replacement fuel pump for what appears to be the original on my 1988 Universal M25. If it is not the original (I don't know their life expectancy) it's certainly many years old.

The original is the barrel/cylinder type and the replacement by Facet is identical in size and shape. However, the installation instructions for the Facet suggest my current fuel pump is installed upside down.

The pump is mounted vertically. The instructions with the Facet say the inflow should be at the bottom and the outflow at the top. This also means the removable cap to replace the internal filter is on the bottom making changing the filter messy at best.

My old pump is mounted vertically but with the inflow and cap at the top and the outflow at the bottom. This has apparently served the boat well for very many years.

I imagine gravity and potential airlocks come into play. Does it really matter which end is up? I would like to install the new pump with the cap on top. Thank you,

Len Keller
Madeira Beach, FL
(on Florida's left coast)

 

[Stu Jackson]

Len, you can do it either way, although I've always seen them with the filter on the bottom, but the best way to avoid having to deal with the filter in the pump at all is to correct the plumbing. The primary filter should be first, then the pump, then the engine. Most builders did it wrong and put the pump, with its tiny filter, first. If you make the fix, then you'll never ever have to deal with the filter in the pump.

 

[Windborne]

Thanks for the reply Stu. I guess there is a reason you always see them mounted with the cap on the bottom. I just found this on the Facet-Purolator website http://www.facet-purolator.com/faq.php

"The fuel pump should be mounted with the outlet above the inlet. This will help with eliminate vapor lock issues. Never located the pump so the outlet is below the inlet. Horizontal mounting will not effect fuel delievery performance."

I don't know what causes vapor locks or how often they occur but apparently my pump is mounted upside-down. The crusty thing has probably been like that for 25 years. -- Len