The Mystic Rubber Tube Demystified

from Rookie’s keyboard

Hello, friends

I am about to demystify another bike topic today. 

Bike repair kits include tire patches, self-vulcanizing fluid, and a mysterious small rubber tube.

The function of the patches and the cement is obvious, but the role of the rubber tube is a mystery to many people.

No more. 

The rubber tube is designed to fix a leaking Dunlop valve.

Dunlop Valve

A Dunlop (a.k.a. Wood valve and English valve) valve has the following components:

1. Stem

The stem connects the valve to the inner tube and acts as an enclosure for the internal components.

2. Rim Nut

The rim nut prevents movement of the stem by fastening it to the rim.

3. Top Nut

The top nut stabilizes the plug and prevents air from leaving the tube.

4. Plug

The plug has two functions – it allows the user to inflate the tire and keeps the air in.

Classic/retro Dunlop valves rely on a latex rubber tube that acts as a valve itself.

When you’re inflating the tire, the air of the pump expands the rubber tube ever so slightly, passes through the openings on the plug, and gets into the inner tube.

When you stop, the rubber tube deflates and seals the plug.

Older Dunlop valves are slow and difficult to pump because it takes a lot of effort to expand the rubber tube wrapped around the plug.

If the rubber tube is leaking, the valve will fail to hold air and the tube will deflate.

Signs That You Have a Dunlop Valve

Dunlop cannot be mistaken for a Presta (those are too thin), but you can confuse them for an auto/Schrader valve.

A Dunlop valve has the thickness of a Schrader but is slightly longer.

It’s easy to distinguish a Dunlop valve from a Schrader one by looking at the stem. 

Dunlop stems have a long thread reaching all the way to the rim.

Another difference is the plug. Once you remove the dust cap, the plug of a Dunlop valve will be sticking out.

Don’t Use a Schrader Pump

Dunlop valves are compatible with standard Presta pumps (or a Presta add-on). Schrader pumps won’t work because Dunlop valves have a smaller diameter.

If you want to use a Schrader pump on a Dunlop valve, you will need an adapter.

To pump a Dunlop valve, follow these steps:

1. Clamp the Presta pump on the Dunlop valve.

2. Pump air in.

3. Once you’re done, remove the pump.


The Pros of Dunlop Valves

1. Rigidity

Dunlop valves are sturdier than both Presta and even Schrader valves.

2. Replaceable

The plug of a Dunlop valve is easy to replace. This makes Dunlop valves serviceable.

3. Simplicity

Dunlop valves have a simple mechanism and are straightforward to use once you’re familiar with the way they operate.

4. High Air Pressure

Dunlop valves are known to maintain high air pressure without losing air.

The Downside of Dunlop Valves

1. Low Availability

Dunlop valves are difficult to find in countries where mountain and road bikes dominate the scene. Chances are that the average biker hasn’t even heard of a Dunlop valve before.

2. Difficult Inflation

Dunlop valves relying on a latex rubber tube may require a lot of effort to inflate them.

3. Cannot Be Inflated With a Compressor

Just like Presta valves, Dunlop valves cannot be inflated at a gas station because the air compressor there is designed for Schrade/auto valves. To use it, you will need an adaptor.

4. Inaccurate Air Pressure Measuring

Air pressure gauges do not work on Dunlop valves because the mechanism is internal. Thus, the valve cannot be opened from the outside like a Schrader, for example.

In consequence, the air pressure can be measured only during inflation.

However, this method isn’t accurate either, because air must be going into the valve to open it. You cannot just stop to look at the gauge as with other valves.

This is a major shortcoming for competitive cycling. Hence why Dunlop valves are not present on professional bicycles.

A Word On Blitz Valves

Blitz valves are an improved version of the original Dunlop valves and don’t rely on an external rubber tube to seal the plug.

Instead, there’s a rubber ball mechanism which opens during tire inflation and closes afterward


Blitz valves do not use the rubber tube in the puncture kit. To repair them, the entire plug has to be replaced.

The image above illustrates how a Blitz valve operates.

When air from the pump enters the valve, the rubber ball goes down and opens a “gate” through which the air reaches the inner tube.

When the airflow from the pump ends, the rubber ball returns to its previous position and seals the valve.


Dunlop valves are commonly found on Dutch and Japanese utility/commuter bicycles. They are also used in Korea, China, India, Pakistan, and Sri Lanka.

Rubber Tube Installation Tip

If you have a hard time sliding the rubber tube on the valve, spray some water on the plug or the rubber tube.

Do not use metal tools such as tweezers or small pliers because they can easily tear the rubber tube as it’s made of soft latex.

Reducing Air Pressure

To reduce the air pressure of a Dunlop inner tube, you will have to partially unscrew the top nut a.k.a. flanged knurled nut.

Don’t unscrew the nut all the way unless you’re replacing the plug.

A Stuck Plug

A Blitz plug may get stuck if the tire is inflated to very high air pressure and kept at it for a long time.

This happens because the air in the tube is pushing hard against the plug and wedges the internal rubber ball against the plug’s openings. Consequently, the valve gets clogged.

The common solution is to press the pump with a burst motion to free the openings.

If this method doesn’t work, the plug will have to be replaced. Luckily, they aren’t expensive.

My Opinion On Dunlop Valves

This may come as shock, but I wouldn’t bother messing with a Dunlop valve. I prefer Schrader as it’s super popular and compatible with pretty much any bike pump on the market. It also doesn’t require messing with some rubber tube. 

Until next time

– Rookie





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