filter on vacuum or pressure side?

[Rickbaro]

I have a Volvo Penta 200 (chevy) with a water separator and a glass inline filter before the pump (the filters are operating in a vacuum). Has anyone had better luck putting these filters before or after the pump? Mine is a cam driven diaphram type. The reason I ask is that it would appear that the sealing rubber on the water outlet at the bottom of the separator bowl would work better while the filter is pressurized rather than under a vacuum. I'm having a starvation problem that I may have solved when I found a small piece of Form-a-gasket that had swollen to the size of an asprin. I think this was gettin caught in the shut-off valve at the tank outlet. But while I'm working on the boat, I wondered if it would be a good time to re-do the plumbing.<br /><br />Anybody have this before?<br /><br />Thanks

 

[scottyb]

Re: filter on vacuum or pressure side?

Hi Rick,Id sugest making sure your run from carb to tank is clear.Nice to have water sep & filter prior to motor.Pretty much irrelavant where filter is in line-to a performance standard.Its only gonna flow what it can.Your not feeding 800 hp there.Id go for pressure check at carb-make sure pump is pumping.UnderWay-by the way-idle doesnt cut it.3/8 all the way-make sure you dont have a small fitting in the midst.Are all lines & valves good or new from tank to motor?Stock should work fine,if ya can-keep it that way.Let us know how it makes out.<br />see ya

 

[Walter]

Re: filter on vacuum or pressure side?

Most I/O water separators-filters that I've ever come across are on the suction side. I can't say for certain why, but the folks who engineered it thought best to do it that way.<br /><br />Personally...I'd leave it the way it came from the factory.<br /><br />MHO<br /><br />Walt

 

[Rickbaro]

Re: filter on vacuum or pressure side?

Thanks guys. The line is clear and 3/8" except for the shut-off valve. It's the same one sold at Boaters World/West Marine and it looks like it's about 1/4".<br /><br />All this was added after the boat left the factory( the previous owner installed the separator, and I installed the filter) so I thought I'd check it out. I'll keep everything on the suction side.<br /><br />The thing that's strange is that when the engine is starving at or near wot, the bowl on the separator is still full even though the inline filter has emptied out and the motor is bogging down. I'm taking it out this weekend so we'll see if I cleared it up by removing the rubber thing from the tank.<br /><br />Thanks again

 

[ODDD1]

Re: filter on vacuum or pressure side?

Rick, all aftermarket filters are used on the suction side....for safety sake nothing but hard line on the pressure side of fuel system....on deisel engines, a bowl type separator can be used, because of the relatively low volatility of the fuel...for gasoline use, I dont think you can find an approved one [Coast Guard spec/SAE J***] the most common one I see in boats is a spin on metal canister filter/water separator, similar to an oil filter...when having a fuel starvation problem, adding more filters just makes it worse...every one adds a pressure drop...best to have one GOOD one, and one only...

 

[Rickbaro]

Re: filter on vacuum or pressure side?

Thanks ODDD1, now that you mention it, that makes sense, additional filters mean additional drops in pressure the same way additional components drops voltage in an electrical series circuit. <br /><br />Also I didn't know that it should all be hard tube beyond the pump (mine is). Good stuff to know!<br /><br />Actually I looked at the West Marine catalog tonight and right in the text for the Racor separator it says it is designed to be used on the suction side. D'oh! <br /><br />Regarding the piece of debris I found in my tank, after it dried out, it shrank to the size of 1/16" ball. But while saturated with fuel, it was the size of an asprin. Note to self: be careful when using that gasket material in a tube so as not to get any extra in the tank. It probably was a small piece that came off the end of the screw holding the sender down. The previous owner must have covered the screw hole and when the screw was driven through, it punched out this little piece.<br /><br />Armed with my new knowledge, I'm going to button everything back up and see how she does this weekend.<br /><br />Thanks for everyone's advice.

 

[Scottj25]

Re: filter on vacuum or pressure side?

Your problem maybe that you have too many filters, and from what I've read your glass inline filer is for O/B only due to them not passing the fire test. At this point you may be using four filters, there are filters at the carb, fuel pump, your inline and the fuel/water.<br /><br />Part two of your external filters should be on the suction side.

 

[Spidybot]

Re: filter on vacuum or pressure side?

ODDD1 got it right.<br /><br />It is a safety matter and it is absolutely not a thing to alter.<br /><br />Any gasket or hose leaking is a 'no harm and maybe performance drop' if it is under vacuum. It turns your boat into a floating bomb if it is on the pressure side.<br /><br />For the same reasons you must use marine fuel lines and fittings. Car rubber hoses (no matter certified for gas) are NOT to be used in marine setups.<br /><br />Trust me - I was onboard one that blew up