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Fuel Demand Valve
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| skram |
Posted on 11/09/12 - 3:23 PM
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Due to the new expansion fuel tanks (3, 6, 9 Gal) from Moeller and others, the new Montauk 170's come with a Fuel Damand Valve between the tank and the bulb.
Does anyone have any experience with these??
Whaler is installing Attwood # 9300FDV7 (Mercury # 8M0044687) Demand Valves. They say that anyone with new fuel tanks should have one installed to avoid the pressure in the tank from "pushing the fuel" into the engine and flooding the engine. This has now become a common problem
"Provides fuel to a marine engine "on-demand" vs. due to pressure build-up in the tank. Eliminates possibility of fuel spillage from downstream fittings and/or marine engines. Eliminates engine functionality issues created by pressurized fuel lines."
http://www.attwoodmarine.com/prevent-engine-flooding-with-fuel-demand-valve
Anyone have any experience with these with the new fuel tanks and the demand valves?
Really appreciate a discussion around this.
Thanks
skram
2003 170 MT - 2003 Merc 90 ELPT |
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| Swamp |
Posted on 11/09/12 - 3:36 PM
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Just disconnect the fuel line from the tank. Problem solved. No experience with these new valves though.
Edited by Swamp on 11/09/12 - 3:37 PM |
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| Phil T |
Posted on 11/09/12 - 4:00 PM
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While I agree with Swamp, here iare two thoughts.
If you have a carbureted motor it may make sense.
For those with non-EFI engines, I don't see why this is required. Even with 4.9 psi of pressure in the fuel line, how would the fuel be forced through the low and high pressure fuel pumps and the injectors?
Edited by Phil T on 11/09/12 - 4:01 PM |
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| skram |
Posted on 11/09/12 - 5:41 PM
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I agree with you for carbureted engines that it make sense (which is what I have and maybe why I have had flooding issues with the new EPA tanks). However Whaler says they are installing them in new boats for fuel injected engines.
2003 170 MT - 2003 Merc 90 ELPT |
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| Turpin |
Posted on 11/10/12 - 7:28 AM
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This is great, I've had my tanks look like a tick about to pop because i forgot to leave the vent slightly open and now I have to apparently leave a gas cap loose (if i get a new tank).
1963 13' Sport 50hp Evinrude
Maintaining a level of sanity that is socially acceptable |
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| Finnegan |
Posted on 11/10/12 - 9:10 AM
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Turpin - I love the photo of your pooch with the goggles.
It's the best one on the site.
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| Turpin |
Posted on 11/10/12 - 9:19 AM
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yeah he's a little camera shy, can't you tell?
1963 13' Sport 50hp Evinrude
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| skram |
Posted on 11/11/12 - 12:31 PM
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Love the dog but...
Does anyone have any experience with these Fuel Damand Valves?
2003 170 MT - 2003 Merc 90 ELPT |
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| Mtierney |
Posted on 11/11/12 - 8:16 PM
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I don't get it. Someone please correct me if my high school physics fails me. As I recall, fuel is a liquid, and as long as the tank is vented, the pressure should be due to the height of the liquid column, compared to the engine, not the tank size. This is why we need bulbs to get fuel to the engines in the first place. If you disconnect the engine side of the line, and left it on the deck, I could see a fuel leak, due to the deck being lower than the liquid in the tank.
I also thought that the engine itself then generates the vacuum to suck fuel from the tank, once it gets going. So why now, after decades of use do we need one more gadget?
1985 Newport 17 w/ 70 yamaha |
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| wezie |
Posted on 11/12/12 - 6:47 AM
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VALVES AND GADGETS
The Good People, want you to do things their way, and will not stop with these gadgets.
I am very sure more ges is spilled with the new spouts than before.
They are terribly slow to begin with.
Any valve in th flow system will cause problems. If for no other reason than they fail. Now we have a demand valve and a pressure relief valve! Two is always better than one, don't ya think?
That you are 20 miles out at that time is no problem for The Good People. They go home very smug in their successes, while you and yours drift about.
Good Luck!
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| gary0319 |
Posted on 11/12/12 - 10:02 AM
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Mtierney wrote:
I don't get it. Someone please correct me if my high school physics fails me. As I recall, fuel is a liquid, and as long as the tank is vented, the pressure should be due to the height of the liquid column, compared to the engine, not the tank size. This is why we need bulbs to get fuel to the engines in the first place. If you disconnect the engine side of the line, and left it on the deck, I could see a fuel leak, due to the deck being lower than the liquid in the tank.
I also thought that the engine itself then generates the vacuum to suck fuel from the tank, once it gets going. So why now, after decades of use do we need one more gadget?
I'm not sure if I have all the details correct, but the idea is that there is no proper "vent" to open on the new EPA tanks. A pressure relief valve will open when the pressure inside the tank (presumably from heat) exceeds the valve limit, 4 or 5 psi. The problem is that if the line is left attached to the engine, fuel may be forced down the line and into the engine at a psi lower than the psi required to release the valve. Result is flooded engine.
I suspect the "on demand valve" is like a one way valve that keeps the fuel from going down the line into the engine until the engine calls for it.
I'm looking at Moeller 12 gal Topside tank for my Dauntless and so this issue is on my mind as well. For sure, just one more thing to go wrong in the fuel supply chain.
Gary
Edited by gary0319 on 11/12/12 - 10:07 AM
1998 Dauntless 15 - 1998 Mercury 60 |
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| skram |
Posted on 11/12/12 - 3:30 PM
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Gary, You described the issue better than I could.
While Whaler is now including them with new tanks, I understand that other high end boats are too wherever the new EPA tanks are installed.
Since the new tanks are NOT vented, the Fuel Demand Valve block the built up pressure in the tanks (best for carburated engines) from pushing fuel to the engine.
I just cant find any definitive info about them.
How they work?
Are they water tite and can be exposed to the sun (like if they are installed by the bulb next to the engine inlet)?
Downsides?
When the engine "calls for fuel" how do they work?
Etc.
2003 170 MT - 2003 Merc 90 ELPT |
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| BillDemers |
Posted on 11/12/12 - 4:24 PM
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I think Gary is on the right track, I think the fuel demand valves are probably " pressure reducing valves " New epa tanks are not venting into the atmosphere unless heat causes fuel to vaporize and increase pressure beyond the relief setting which is probably enough pressure to over come the fuel in bowl forcing the float to close the needle unless there was a pressure reducing valve to keep the pres in the line at a pres that the needle and float can deal with.
Mtierney, yes preasure of a liquid is related to its level. not volume.
i.e. the preasure of a column of water 1 foot high is roughly 0.45 psi ,gas would be different. the diameter of the column doesn't matter either.
Edited by BillDemers on 11/12/12 - 4:39 PM
BillD
1999 Dauntless 18' - 135 Mercury Optimax |
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| Mtierney |
Posted on 11/12/12 - 8:21 PM
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Ok, now I think I get it, the new tanks are not effectively vented, therefore as the tank heats up, the gas above the fuel expands and pressure can build up and force fuel down the line. Sounds like we need a better cap, not another valve, or keep it simple and install a simple fuel shutoff valve between the tank and engine.
1985 Newport 17 w/ 70 yamaha |
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| gary0319 |
Posted on 11/13/12 - 12:46 PM
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Or, as I'm want to do....have my dealer find me a pre-EPA tank. He says it shouldn't be too hard to do.
Gary
1998 Dauntless 15 - 1998 Mercury 60 |
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| SaintGeorge |
Posted on 11/13/12 - 9:01 PM
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The purpose of these design changes is an attempt to reduce fuel spills (squirts) at hose connection/disconnection, as well as evaporation from open vents on fuel tanks. Essentially the effort is to eliminate the open vent like the thumbscrew vent cap as common on many tanks. Instead the fuel tank is "sealed" for so fumes are not ejected with pressure changes inside the tank. There are even the "click" effects when the cap is tightened. Instead of an open vent, there is a check-valve sort of vent that only admits air to the tank under vacuum. If the tank gets pressurized it holds the pressure (unless you open the cap--- which defeats the whole effort of containing the gasoline fumes from evaporation).
If there is pressure in the tank the fuel is also pressurized into the hose with conventional connectors, so there are other changes. A "non-squirting" connector is put in use at the tank end at least. Then there is a "demand valve" that is mean to stop fuel from being pushed under pressure through the hose. It only allows fuel to be pulled under vacuum from the primer bulb or motor fuel pump.
All of these changes are efforts to reduce evaporation of gasoline to the air, which is a photochemical smog contributor. It is not about protecting the engine itself, that is not the purpose or priority.
Hopefully the valve will work smoothly when the tank is pressurized by heat or barometric pressure change. This situation can be overcome by opening the tank cap, and then re-sealing it, but as stated that defeats the whole effort to reduce fuel evaporation. Users of these new tanks will have to find out what works for them as they adapt to new fuel tanks.
The statements that these tank designs have anything to do with attempts at better running motors does not convince me. It is a system that has been mandated first by CARB and then 49 state EPA to attempt to engineer a reduction in gasoline evaporation from the conventional vented fuel tanks.
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| Finnegan |
Posted on 11/14/12 - 2:24 PM
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Who wants bulged-out, pressurized tanks on a your boat on a sunny day? It sounds to me like the solution is to put a conventional vent-screw cap on a new tank. The whole situation sounds like trying to kill an elephant with a BB gun.
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| skram |
Posted on 11/18/12 - 2:18 PM
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Mercury Marine now seems to have answered the question on Fuel Demand Valves, saying they must be used on all of the new EPA required new tanks:
http://www.mercurymarine.com/parts-an...uel-system
"Whenever a pressurized fuel tank is used, a fuel demand valve is required to be installed in the fuel hose between the fuel tank and primer bulb. The fuel demand valve prevents pressurized fuel from entering the engine and causing a fuel system overflow or possible fuel spillage."
Yech... something else to worry about.
Edited by Phil T on 11/18/12 - 3:03 PM
2003 170 MT - 2003 Merc 90 ELPT |
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| SeaLevel |
Posted on 11/19/12 - 4:35 AM
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I've said it before in another thread and I'll say it again here, any system that causes pressure or vacuum to build up in a fuel tank on a boat is a really bad idea
"It's just a forty eight year old Whaler but it's all mine"
Joseph R Palmieri |
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| Cape Fear |
Posted on 08/11/15 - 4:48 PM
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Has anybody experienced problems with these?
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