The different locks in caravanning

If you own a motorhome, a caravan, or even if you are planning to buy one, you will inevitably at some point need to unravel the mystery of the locks on your vehicle. I've spent a lot of time trying to figure out the differences between the two, so I'm going to give you a brief article on these locks so you won't be lost in the mess.

This article does not talk about the carrier locks (for motorhomes), because you have to go to the carrier's dealer to get them (and/or reprogram the electronics). On the contrary, I will focus on the locks of the cell and its various hatches & ports.

There are many manufacturers of locks for caravanning, but, by skimming the forums, I realized that there are really only 3 main manufacturers (the caravan and other motorhome manufacturers get their locks from them, like Valéo and Bosch for cars).

How they work

For the majority of these manufacturers, the locks work in the same way. The lock is composed of a metal part (or plastic for some) of a very particular shape (with an almost cylindrical hole) which is fixed on the element to close. We call this element the cylinder.

Inside this cylinder is the barrel which will either turn in the cylinder or make the cylinder turn. The barrel is cylindrical in shape with small perpendicular metal tabs that drop down when the key is inserted into the cylinder, which changes the radius of the barrel's head (and therefore allows it to turn in the cylinder).

The variation between manufacturers consists mainly in the dimensions and shape of the cylinder (and therefore of the barrel, although it is possible to make a cylinder compatible with all barrels).

ZADI

Zadi keys and locks are quite easy to recognize: the key is round, with a number often engraved at the bottom of the round part. There are only 10 possible combinations for these keys (very low security, in my opinion), but there are 2 sizes of locks, for a total of 20 possible combinations (from 0 to 9). The key numbers are 9001 to 9010 and 8001 to 8010.

The cylinder of a ZADI key respects these dimensions:

The barrel is completely cylindrical (easier to manufacture) and longer than other barrels.

On this diagram, you can see the last tab of the cylinder (top right). This tongue normally never comes down, and it is the tongue that prevents the barrel from coming out of the cylinder.

However, since it is necessary to be able to change keys (in case of loss/breakage or theft), there is a master key that lowers this tab, so here is the draft:

You can also order it online for around 15€:

(Personally I use a fine tool to click the last spring and then pull the barrel).

The procedure for replacing a barrel is like this:

1. Insert the official key into the barrel
2. This drops all the tabs and allows the barrel to turn
3. Turn the key about 20° (this will depend on your cylinder, and since you won't know, you should try a little in every direction)
4. Pull the key out and insert the master key (or a thin, strong wire) to press the last spring
5. Use a hook to pull the cylinder out.

In general, Thetford safe doors use Zadi barrels (put differently, if you have a round plastic key marked Thetford, it's a Zadi key)

FAP

FAP is an Italian manufacturer of parts for caravans and motorhomes. It also produces various locks and cylinders.

Unlike Zadi, there is a large number of FAP keys and sizes. They are arranged in series (2000, 4000, 8000, etc...). However, it is only the barrel that changes, the cylinder in the vehicle is compatible with all series.

Most FAP keys have a small window with a number, like this one:

I couldn't find a diagram of the barrel on the web, so I modeled the barrel:

For a 3D view, click here

The FAP barrel is not perfectly cylindrical, there is a "key" at the bottom of the barrel which allows to orientate it correctly in the barrel and to limit its rotation.

There are FAP cylinder for Thetford safe doors, but they are now unavailable. Moreover, the Narbonne gadget sellers charge close to 60€ for this plastic part. So I have modeled the FAP cylinder for Thetford gates to avoid having to change your keys, which will cost you a few cents to print instead.

Oberholz

I don't have much information on Oberholz locks. They look like FAP keys and the barrel is probably FAP compatible:

I've never had these keys and barrels in my hands, so if you have any, please confirm or correct the dimensions in the comments.