What Is The Rubber Tube In a Puncture Kit For?

A lot of bike repair kits sold at dollar shops and convenience stores include tire patches, self-vulcanizing fluid, and a mysterious small rubber tube.

The purpose of the patches and the cement is obvious, but the function of the rubber tube is an enigma to many people.

Condensed answer:

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

Over time, the rubber tube sealing the valve’s plug deteriorates and causes a leak.

If you have a spare rubber tube, you can replace the old one without special tools, pump the tire, and continue your commute.

How Does a Dunlop Valve Work?

To understand the mechanism of a Dunlop valve (a.k.a. Wood valve and English valve), it’s necessary to get acquainted with the valve’s anatomy.

A Dunlop 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

As with other valves, the plug has two functions – it allows the user to inflate the tire and keeps the air in.

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

When you’re pumping 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 pumping, the rubber tube deflates and seals the plug’s body once again.

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

If the rubber tube has a leak in it, then the valve will fail to hold air and the tube will deflate.

How Do I Know If I Have a Dunlop Valve?

A Dunlop valve has the thickness of a Schrader (auto) valve while being a touch 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.

It’s easy to differentiate a Dunlop valve from a Presta one too. Presta valves also have a threaded stem, but it’s notably longer and slimmer.

How To Pump a Dunlop Valve?

Note: Dunlop valves can be pumped with a standard Presta pump. 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.

It’s really that simple.

What Are The Advantages of a Dunlop Valve?

Dunlop valves have the following benefits:

1. Rigidness

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.

What Are The Downsides of Dunlop Valves?

The downsides of Dunlop valves are:

1. Difficult to Find

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 to Inflate

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

3. Cannot Be Inflated at a Gas Station

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.

What Are Blitz Valves?

Blitz Valve

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 benefit from 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.

In Which Countries Are Dunlop Valves Popular?

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

I Have Trouble Inserting The Rubber Tube On The Plug. Any tips?

Spray some water on the plug or the rubber tube and slide the tube into place.

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.

Can You Inflate a Dunlop Valve Without an Adapter?

If you have a Presta pump, you can use it on a Dunlop valve directly. But if you have a Schrader only pump, you will need a Schrader to Presta adaptor to inflate the tire.

I’m tired of Dunlop valves. Should I switch to Presta or Schrader?

If you want to abandon Dunlop valves, it’s common to switch to Schrader tubes because the diameter of both valve stems is similar.

Therefore, the valve hole of a rim originally designed for Dunlop valves would easily accept Schrader valves without stability issues.

Using a Presta tube, however, would be a bit problematic. Presta valves are slimmer and aren’t sturdy when installed on a Dunlop/Schrader rim.

To secure the valve of the new tube, you will need a Schrader – Presta grommet – a shim that fills the space around the Presta valve and stabilizes it. If you want to know more about this topic, consider reading this article.

How Can I Reduce The Air Pressure Of a Dunlop Inner Tube?

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.

My Dunlop Tire Isn’t Inflating. Why?

Sometimes Dunlop valves feel blocked and make it impossible to inflate the tube.

The possible reasons are:

A Leaking plug

It’s the plug’s responsibility to hold the air in the tube. If the rubber seal is leaking, you can replace it and try again.

If you have a Blitz valve, you will have to change the entire plug.

А Contaminated Plug

Dirt (e.g., dust, small particles, oil, grease…etc.) around the plug may be preventing it from getting fully sealed.

Hence why it’s recommended to keep the dust caps on the valve. If this is the culprit, gentle cleaning of the valve should alleviate the problem.

Note: This problem is more common with Blitz valves.

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.

Dunlop Valves vs. Presta and Schrader (What’s Best?)

Theoretically, an inner tube using a Dunlop valve should outlast one with a Presta or a Schrader valve because you can keep replacing the rubber tube seal or the entire plug forever.

In practice, however, Presta and Schrader valves are durable enough to match the life of the tube. In other words, you’re a lot more likely to bin a tube due to multiple flats than a failed Presta or Schrader valve.

Failure can, of course, occur, but it’s not that common. This greatly diminishes Dunlop’s advantages over other valves.

At the same time, Presta and Schrader valves allow users to accurately measure the pressure of the tire at any time. This makes both valve models more practical.

Another benefit of Schrader tubes is that they can be pumped at gas stations without an adapter.

For the reasons above, many people migrate from Dunlop valves to Presta or Schrader.

Personally, I found Schrader valves a better choice as they are very versatile and easier to use because you don’t have to worry about rim nuts.

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