Carbon can plumbing

[dnb]

I noticed the other night that there is a restrictor in one of the hoses that feeds the evaporative emissions carbon can thingy in the Griff. The problem is that I don't remember whether it was supposed to be in the tank side or the engine side hose! (I suspect engine side)

Does anyone know for sure?

I'm also a little concerned about if the solenoid on the top acting up:

When it's off, there is an air path from the tank vent through the can to atmosphere. (The tank is therefore vented to atmosphere.) There are no non-return valves in the system and nothing passes throuh the hose that goes to the inlet.

When it's on, all three ports on the can seem to be connected together. IE the tank is connected to the intake and both are able to vent to atmosphere through the carbon can.
Should the tank connection be blocked off at this stage or not?

Thanks.

[spend]

The tank breathes THROUGH the carbon can - this is normal, any fumes should just be held in the carbon. I have always assumed this is a 2 way thing.

Solenoid only opens to suck excess fuel vapour trapped in carbon into the plenum at certain times .

Is your setup 2 units ie solenoid & can totally separate, or the later integral unit.
(They are readily available from LR or lowly Rover 200/400s in plentiful supply BTW)

I'm not clear what you mean by a 'restrictor' valve/reducer/cap?? The TVR 'breather hose' is not the same as the LR/Rover preformed plastic & clip, I would guess it is just some kind of jointing.

Dave

[dnb]

I know more-or-less how the can should work, but I don't think it does at the moment. (although I did misconfigure the VEMS once with some amusing results... )

The setup is the combined can and solenoid type. It all seems to function correctly to me when the solenoid is turned off. I'm just concerned that the tank input should be blocked when the engine is sucking on the can, so that the can is actually emptied rather than trying to create a depression in the tank to suck the vapours back into the tank.

The restrictor is just a little smooth plastic thingy in one of the pipe ends (I had to cut the hoses to get things apart) It's definitely not a joiner - not even TVR could use such a thing to join hoses together.

[spend]

dnb said:

I'm just concerned that the tank input should be blocked when the engine is sucking on the can, so that the can is actually emptied rather than trying to create a depression in the tank to suck the vapours back into the tank.

The tank should be sealed, vacuum will draw from the open air due to pressure differentials (between the 3 areas), AFIK its just getting a flow through the CC which pulls the trapped fuel into the plenum, its kind of vapour not liquid..

dnb said:

The restrictor is just a little smooth plastic thingy in one of the pipe ends (I had to cut the hoses to get things apart) It's definitely not a joiner - not even TVR could use such a thing to join hoses together.

Still cant visualize this... Where did it go, CC-Tank or CC-plenum - the only other connection is the overflow cum breather (which you can pipe out down thru the undertray if you like )

Dave

[dnb]

That's the problem with the restrictor. I can't remember if it was CC-Tank or CC-plenum. It definitely wasn't the breather as this hose wasn't disturbed.

So by your thinking (as well as mine), my solenoid isn't working properly.

[spend]

Nah, see what you read - I meant the tank itself (filler cap) will be sealed.. Pretty sure it is never blocked off from CC. Solenoid simply opens up CC to plenum. Manifold will suck then mainly from open air (since tank is a 'dead end' as long as your petrol cap has not been foobarred).

Dave

[GreenV8S]

As far as I understand it, the carbon cannister should be permanently connected to the tank on one side and fresh air on the other. Petrol fumes emitted from the tank are absorbed by the carbon cannister. In the line between the tank and the cannister there is a T that goes to the engine via the purge valve. When the purge valve is open this sucks air back in through the carbon cannister to the engine. It would make sense for this line to the engine to be restricted to control the rate of air flow when the purge valve is open since this flow is unmetered. I suppose in principle it would be possible to put the restriction on the 'fresh air' side of the carbon cannister instead, but that would limit the ability of the tank to vent and doesn't sound like a good idea to me.

[dnb]

Good. So this means everything here is (for once) working as it should. I agree with the restrictor placement Pete suggests, but since I'm calculating load by a blend of alpha-n and MAP then it's not as important as it was.

[spend]

The later version is a much simpler plumbing arrangement Pete. Solenoid is clipped on to the CC & has pipe to plenum, CC has single pipe to tank. Its not the spaghetti of the earlier versions with separate solenoid & cannister

Dave