Where Does the Td5 Air Bleed Valve Go?
Replacing a Td5 fuel filter housing often raises the same question: where do the air bleed valve and non-return valve actually fit? Get them the wrong way round and you can create hard starting, fuel starvation, or trapped air in the fuel system. This guide shows the correct positions, explains what each valve does, and helps avoid a common installation mistake.
Several Td5 fuel filter housing part numbers appear across different VIN ranges, but the basic housing layout is the same. The main difference is whether the housing is supplied without a water sensor, with the Defender Td5 water sensor, or with the Discovery 2 Td5 water sensor.
What the Td5 Air Bleed Valve Does
- Allows trapped air to escape from the fuel system
- Helps maintain stable fuel pressure
- Important for smooth running and easier starting
What the Non-Return Valve Does
- Helps stop fuel draining back when the engine is switched off
- Aids fuel system priming and cold starting
- If missing or faulty, extended cranking can sometimes result
Correct Placement on the Td5 Fuel Filter Housing
- The air bleed valve fits in port 2, as shown in the diagram below
- The non-return valve fits in port 3, shown in the image with the red cap
- The air bleed valve is the critical one and must be fitted correctly
Common Mistakes and Symptoms if Installed Incorrectly
- Air bleed valve and non-return valve fitted in the wrong positions can lead to hard starting and fuel system issues
- Damaged seals or incorrect tightening can cause fuel leaks or air ingress
- Missing or faulty valves can contribute to poor starting, uneven running and other fuel-related symptoms
Is the non-return valve needed?
Originally, the Td5 non-return valve was effectively just a restrictor rather than the later duck-bill style valve. The duck-bill version appeared later as Land Rover looked to improve starting behaviour on vehicles that had been left standing.
In practice, a Td5 with a healthy fuel pump and a correctly fitted air bleed valve should generally start and run properly without relying heavily on the non-return valve, especially if you allow the fuel system to prime before cranking. Turning the ignition to position 2 and giving the pump time to run is good practice.
The non-return valve can be fitted to ports 1 or 3, and the flow direction arrows on the housing should always be checked carefully before fitting. Port 4 should not be used.
On a new Td5 fuel filter housing, the non-return valve is normally fitted to port 3, with the individual fittings supplied loose for installation.
For a long time, the duck-bill type valve was not especially easy to obtain separately, but Britpart now produce repair kit DA3950 for this purpose.
Image Right: original "non-return valve" VUB503950
As you can see, more of a restrictor than a non-return valve.
Image Left: new non-return valve DA3950
Now widely available thanks to Britpart.
The key point is simple: fit the air bleed valve in the correct position and check the housing ports carefully before installation.
