"Air Supplier Tube" Question

[DC871F]

11 hours ago, texasz said:

GREAT CATCH!!  I would believe the FSM and the picture you show here is exactly what I was asking (which direction is the flow of each hose).  Thank you for the update on this topic.

How does the flow FROM the air cleaner go against the vacuum?

I'm confused.

[Racer X]

So the large line from the crankcase goes to the balance tube, where the PCV valve is. During engine operation the crankcase vapors are drawn into the engine through that connection with engine vacuum.

The fuel tank vapor, and any residual aromatic hydrocarbons lingering in the airbox from any fuel slosh from the carburetor throats, vapors from the cam cover hose, all get sucked along and ingested with the incoming air fuel mixture.

 

 

[DC871F]

14 hours ago, Racer X said:

So the large line from the crankcase goes to the balance tube, where the PCV valve is. During engine operation the crankcase vapors are drawn into the engine through that connection with engine vacuum.

The fuel tank vapor, and any residual aromatic hydrocarbons lingering in the airbox from any fuel slosh from the carburetor throats, vapors from the cam cover hose, all get sucked along and ingested with the incoming air fuel mixture.

 

 

The tube from the cleaner to the flow guide valve moves in what direction? Isn't under vacuum being inside the cleaner?

FSM says it goes out of the cleaner to flow guide valve.

[Racer X]

2 hours ago, DC871F said:

The tube from the cleaner to the flow guide valve moves in what direction? Isn't under vacuum being inside the cleaner?

FSM says it goes out of the cleaner to flow guide valve.

Correct.

And at the flow guide valve, it joins the fuel vapors from the tank, and is drawn to the large pipe at the crankcase vent, then drawn to the PCV valve and ingested by the engine.

Notice in the picture you posted the arrow at the flow guide valve, showing the flow towards that pipe (I can't see that as your picture cuts it off, but pretty sure that is where the flow goes).

[Racer X]

Also keep in mind that the flow is not constant during engine operation, as the vacuum changes as engine operating conditions change. At idle there is sufficient vacuum to pull the vapors into the engine. During acceleration vacuum drops, at wide open throttle it is at zero, and during deceleration it will be at the maximum.

 

 

[foosman]

I believe the flow guide flows both directions - when the fuel vapor pressure in the tank builds, it flows toward the engine, and opens the spring-loaded valve in the (2) circuit, sending the fuel vapors toward the crankcase vent tube to be burned.  When the fuel tank creates a vacuum (as the fuel level drops) it opens the spring-loaded valve in the (1) circuit, and draws air from the air cleaner back to the fuel tank.

[Racer X]

38 minutes ago, foosman said:

I believe the flow guide flows both directions - when the fuel vapor pressure in the tank builds, it flows toward the engine, and opens the spring-loaded valve in the (2) circuit, sending the fuel vapors toward the crankcase vent tube to be burned.  When the fuel tank creates a vacuum (as the fuel level drops) it opens the spring-loaded valve in the (1) circuit, and draws air from the air cleaner back to the fuel tank.

How can the fuel tank create a vacuum?

[Captain Obvious]

On 3/15/2023 at 3:29 PM, DC871F said:

The cleaner is vacuum. So FROM can't mean routing in the FSM surely, or does it? But do arrows lie?

The cleaner is not vacuum. The cleaner is atmospheric.

OK... Physics dictates it must be a tiny, tiny bit of vacuum or the air wouldn't flow in that direction, but for the purpose of this discussion, the air cleaner interior can be assumed to be atmospheric, not a vacuum. The connection to the air cleaner box is simply a supply source of clean filtered air for the crankcase ventilation system.

If the engine is not running, nothing flows in that tube.

If the engine IS running, that tube supplies clean air to one side of the crankcase to replace the air that the PCV sucks out.

The PCV side of the loop (connected to manifold vacuum at the balance tube) is at a much higher vacuum than the tiny tiny amount of vacuum inside the air cleaner box. And that's why for the sake of this argument the inside of the air cleaner box can be assumed to be atmospheric.

[Captain Obvious]

1 hour ago, Racer X said:

How can the fuel tank create a vacuum?

Couple ways... First (as foosman mentioned) as fuel is removed from the tank, the volume of that fuel must be replaced. Another way is if you park the car with a hot tank of fuel, that fuel will contract as it cools and could cause a vacuum.

In any event, the solution to this is NOT the flow guide valve, but is in fact the gas cap. There is a one way check valve built into the gas cap that will allow air to pass through the cap into the tank to alleviate tank vacuum.

The direction of air through the flow guide valve is uni-directional. They are check valves. No guarantees if they still seal after all this time and gunk, but they are supposed to be check valves.  

 

[DC871F]

9 minutes ago, Captain Obvious said:

Couple ways... First (as foosman mentioned) as fuel is removed from the tank, the volume of that fuel must be replaced. Another way is if you park the car with a hot tank of fuel, that fuel will contract as it cools and could cause a vacuum.

In any event, the solution to this is NOT the flow guide valve, but is in fact the gas cap. There is a one way check valve built into the gas cap that will allow air to pass through the cap into the tank to alleviate tank vacuum.

The direction of air through the flow guide valve is uni-directional. They are check valves. No guarantees if they still seal after all this time and gunk, but they are supposed to be check valves.  

 

I read in the FSM that the 240 has a sealed system, no bypass in the gas cap. Somewhere it reads do not install a vented gas cap.

[Racer X]

40 minutes ago, Captain Obvious said:

Couple ways... First (as foosman mentioned) as fuel is removed from the tank, the volume of that fuel must be replaced. Another way is if you park the car with a hot tank of fuel, that fuel will contract as it cools and could cause a vacuum.

I agree on the second point that cooling fuel will contract, and a vacuum will result. When the engine is not running, the vapor line can pull air in from the air cleaner side of the flow guide valve. 

I also agree on the first point, that as fuel is removed to feed the engine,  and the PCV (and the vapor recovery) system is pulling fuel vapors from the tank, a provision to replace the volume must be in place, and as you point out the gas cap has a one way check valve to allow volume compensation.

40 minutes ago, Captain Obvious said:

In any event, the solution to this is NOT the flow guide valve, but is in fact the gas cap. There is a one way check valve built into the gas cap that will allow air to pass through the cap into the tank to alleviate tank vacuum.

^^^^ Yes. 

40 minutes ago, Captain Obvious said:

The direction of air through the flow guide valve is uni-directional. They are check valves. No guarantees if they still seal after all this time and gunk, but they are supposed to be check valves.  

 

I agree that after 45 to 50 years the seats for the check valves may not seal as they did new, but by design they are meant to be one way only. So the flow passes through the air cleaner inlet, past the first check ball, then joins with the fuel tank inlet, past the second check ball and is drawn into the pipe at the crankcase vent, which gets drawn into the engine as I described earlier.

When the car is parked, vapors in the fuel tank are contained in the tank headspace, and the surge tank (provided the check ball in the flow guide valve is still seating properly).

Edited March 18, 2023 by Racer X

[DC871F]

56 minutes ago, Racer X said:

I agree on the second point that cooling fuel will contract, and a vacuum will result. When the engine is not running, the vapor line can pull air in from the air cleaner side of the flow guide valve. 

I also agree on the first point, that as fuel is removed to feed the engine,  and the PCV (and the vapor recovery) system is pulling fuel vapors from the tank, a provision to replace the volume must be in place, and as you point out the gas cap has a one way check valve to allow volume compensation.

^^^^ Yes. 

I agree that after 45 to 50 years the seats for the check valves may not seal as they did new, but by design they are meant to be one way only. So the flow passes through the air cleaner inlet, past the first check ball, then joins with the fuel tank inlet, past the second check ball and is drawn into the pipe at the crankcase vent, which gets drawn into the engine as I described earlier.

When the car is parked, vapors in the fuel tank are contained in the tank headspace, and the surge tank (provided the check ball in the flow guide valve is still seating properly).

I've been chasing raw fuel vapor coming from my car, with dropping the tank, replacing hoses, pressure tested vapor tank, I them moved this flow guide valve lines. 

I wonder if a bad or clogged check valve in the flow guide valve can be the source of vapor I smell in the garage?