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BigMike

Member Since: 13 Jul 2010
Location: Lancashire
Posts: 2253

Fuel tank breather valve

Is it one way or two way? Ie is it there just to suck air in when the fuel level drops to prevent a vacuum or does it work both ways?

5th Apr 2011 8:42am

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 8172

2011 Defender 110 Puma 2.4 USW Stornoway Grey

std one in the cap on an early vehicle is meant to be one way with a plastic ball actuating a lever, when the fuel hits the ball (side slope) its meant to lift the ball, and tilt the lever to close the seal.

in practice they dont always work that well after a while. Cheers

James
110 2010 XS Utility
130 2011 M57 bespoke Camper
90 2010 Hardtop
90 M57 1988 Hardtop

5th Apr 2011 8:49am

BigMike

Member Since: 13 Jul 2010
Location: Lancashire
Posts: 2253

Cheers James, should have said puma

5th Apr 2011 8:50am

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17612

2007 Defender 110 Puma 2.4 DCPU Stornoway Grey

I think it is there primarily to let air in as fuel is used, but also to let air out and avoid pressurizing the tank as the temperature increases. So, two way. I believe that there is a second, much larger, breather just inside the filler cap to allow air to escape when the tank is being filled. So, two way.

The tank breather is so small that it could not possibly let air out at the rate a forecourt pump can pump it in.

5th Apr 2011 8:50am

BigMike

Member Since: 13 Jul 2010
Location: Lancashire
Posts: 2253

I've extended the vent pipe upto the engine bay as the valve has failed. I'm wondering whether it would be worth putting on a two way valve on the pipe rne in the engine bay and I'm passing demon tweeks thus morning so could pick one up

5th Apr 2011 8:54am

willy eckerslike

Member Since: 15 Jun 2009
Location: North yorks
Posts: 1789

2007 Defender 110 Puma 2.4 HCPU Keswick Green

FUEL TANK BREATHER SYSTEM
The filler tube incorporates a tank vent which allows air and fuel vapor displaced from the tank when filling to vent to
atmosphere via the filler neck.
A breather spout within the tank controls the tank 'full' height. When fuel covers the spout it prevents fuel vapor and air
from escaping from the tank. This causes the fuel to 'back-up' in the filler tube and shuts off the filler gun. The position
of the spout ensures that when the filler gun shuts off, a vapor space of approximately 10% of the tanks total capacity
remains. The vapor space ensures that the Roll over Valve (ROV) is always above the fuel level and vapor can escape
and allow the tank to breathe.
The ROV is welded on the top surface of the tank. The ROV is connected to the atmospheric vent pipe. The ROV allows
fuel vapor to pass through it during normal vehicle operation. In the event of the vehicle being overturned the valve
shuts off, sealing the tank and preventing fuel from spilling from the atmospheric vent pipe.
The atmospheric vent pipe includes a two-way valve which allows for over-pressure relief one way and allows for air to
enter the tank as the system operates in depression.

Original Member Pie n Pea Club.
110 HCPU Tipper

5th Apr 2011 11:15am

BigMike

Member Since: 13 Jul 2010
Location: Lancashire
Posts: 2253

Cheers Pete. Awesome

5th Apr 2011 7:03pm

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