Is it okay if I add a non return fuel valve before the pre filter? Any harm?

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Boater On Thames

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As I found my fuel tank has no cock. So I am thinking to add one. And in the mean time, I am also thinking to add a non return fuel valve at the pre filter inlet as the tank at the lowest point of the whole system. So that the hose between tank to pre filter won't be empty even I forgot to shut the tank cock the next time when I change filter.

Is this a good or bad idea? Thanks.
 
Seriously BAD idea to add a non return before the filter. Personal experience. Went to help a friend collect a boat from Ireland he'd just bought a few years ago. It was a piece of s*1t and had he had not already paid for it, I'd have suggested we got the next plane home. Long story short - on the last leg the engine quit - we had to be towed in by Invergordon life boat - weather foul and impossible to open the heavy engine cover with the boat rolling so hard - Following morning we pulled the filters - they were clean - eventually traced to an in-line non return valve in the fuel line that was clogged solid.

Don't do it. Just don't!
 
fwiw, I've done it (due to suspected liftpump valves and general main filter leaking and emptying when tank was half full)
works fine...
 
NRV valves require a pressure to open on the flow side. This pressure is provided by atmospheric pressure plus head pressure of fuel due to the fuel being sucked by the fuel pump. ie a negative pressure on the outlet. This sucking may not be enough to open the NRV
 
Rocksteadee said:
NRV valves require a pressure to open on the flow side. This pressure is provided by atmospheric pressure plus head pressure of fuel due to the fuel being sucked by the fuel pump. ie a negative pressure on the outlet. This sucking may not be enough to open the NRV
Click to expand...
correct, there's a bolt iirc inside the nrv using it you can regulate the opening pressure. Try and get a setting where it works and wont leak back, not that difficult.
 
Good. Thanks for the input.
When I learning about the fuel system. I see a diagram as below. It looks interesting. With a inline electric pump and a ball valve in an extra return line after the pre filter. So that not only can polish the fuel, but also can easily prime the system if it empty in some occasions. What do you think?

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So if the diagram is correct you have 3 units though which the fuel flows Before the Primary filter.

The primary filter is just that - Primary - If there is crud in the fuel it should block the filter - that's why it's there.

All IMHO of course
 
The diagram downloads online. I think the Fuel Purifier and the Conditioner is no needed. My point is just the Electric Pump and the Ball Valve in the extra return line might worth to think about to add. So that way might solve the prime problem easier in the future, and it can circulate the fuel through the primary filter to remove some dirt then return to the tank to keep less dirt in tank. It might be better for some cases like me as the tank is not accessible.
Just a thought. See if any idea from you guys.
 
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Is your prefilter below the tank ? (gravity fed).

Add the Stop valve between tank and prefilter as you stated.
You then know to close the valve when changing filter otherwise fuel will pour out the Top of the filter. You can use the stop valve to control the refill to the brim of the filter Prior to refitting top cover. You may get a tiny amount of air after the filter but unlikely as this would flow back through filter as you top up. This small amount of air will just get sucked through the engine once restarted.
 
My tank below the prefilter. So it's very hard to prime after the filter changed. I still not be able to finish the priming by using the little hand prime pump at the engine now after filter changed two weeks ago! It just can't be done! Especially the hose between the tank to prefilter is around 6 meters. Because the tank under the after cabinet, the hose run more than 3 meters to the middle of the engine room vales to select which tank for which engine, then run another 3 meters to the prefilter. Total around 6 meters hose between the tank to prefilter.
 
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Don’t understand the need for the complexity. When I change/drain off the prefilter I prime the filter using a bottle of diesel which I pour into the top of the Racor before fitting the top. My Racor is difficult to get at so I have the diesel in an old oil bottle with a flexible spout. If fuel drains back to the tank when the engine is off there must be an air leak somewhere which needs fixing as otherwise the engine will suck air whist running. Surely the less ‘stuff’ between the tank and engine the less likely a leak somewhere?
 
On my fuel system From the tank I have a ball valve right at the point where fuel is drawn out of the tank ( safety requirement) then an outboard priming bulb (this has 2 NRV in the prime bulbs. I then have a sediment filter/strainer followed by my primary filter .

I did have an electric fuel pump but found it useless as the valves in the electric pump kept blocking so the electric pump would not pump . With the hand prime bulb the valves don't seem to get blocked
 
Great. A lot of great input. Thanks.
I have tracked all the pipes and fittings from tank to engine and found no any leaking. So I think the only reason I can not finish the priming is the suction from the tank to the little hand prime pump is too long. There is around 6 meter from tank to prefilter with highest lift point to 1.4 meters. Then plus around 1 meter from prefilter to engine. Total around 7 meters. So everytime after I topped up the prefilter, I pushed the hand prime pump, then fule go to engage in a few seconds no problems as the venting screw has fule come out. But then if I continue pushing the prime pump, it will continue pump the fule from prefilter to engine, it will suck air only after the prefilter fule run low to its inlet level. So I reckon the little amount of fuel I topped up to the prefilter is not enough to clear the 6 meters long empty piep air from tank to prefilter.

Maybe I need to try to top up the prefilter again and again before the fuel reaching its inlet level, and do it over and over again should clear the 6 meters pipe air. I will try. But still this is too hard. So maybe easier if an electric pump inline. Just a thought.
 
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End up I added an electric fuel pump with non-return valve after the prefilter. Then I found it still can't prime the system. Eventually, I found the real reason for prime failed is because the two engines actually fed by the empty tank! I think one of the previous owner or engineer swapped the fuel pipe position between the port and starboard tank. So, when I follow the original label selected all engines feed by the port tank, it will actually be connected to the empty starboard tank! OMG!

Now, it prime easily without the need of the electric pump after switched back to the full tank. The electric pump becomes useless! OMG! Anyway, I will just keep the electric pump in the system then.
 
Lucas Gan said:
End up I added an electric fuel pump with non-return valve after the prefilter. Then I found it still can't prime the system. Eventually, I found the real reason for prime failed is because the two engines actually fed by the empty tank! I think one of the previous owner or engineer swapped the fuel pipe position between the port and starboard tank. So, when I follow the original label selected all engines feed by the port tank, it will actually be connected to the empty starboard tank! OMG!

Now, it prime easily without the need of the electric pump after switched back to the full tank. The electric pump becomes useless! OMG! Anyway, I will just keep the electric pump in the system then.
Click to expand...
See, I told you there was air in the pipes :)
 
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