Iron farm not working

[Gamen_met_Joost]

I have created three different iron farm designs in an attempt to have one work on my server. The problem must be related to the server somehow because the farms did work when tested on singleplayer.
If anyone has any experience with farms like these and/or knows how I can fix it, all help is greatly appreciated.

The farms I tried are these:

 

[RabidOtter]

Which plugins do you have installed on your server? I just built the third example you listed on my server, so it should work.

 

[Arceus]

I have created three different iron farm designs in an attempt to have one work on my server. The problem must be related to the server somehow because the farms did work when tested on singleplayer.
If anyone has any experience with farms like these and/or knows how I can fix it, all help is greatly appreciated.

The farms I tried are these:

How exactly does it not work? Is it just slower than its supposed to be, or it doesnt work at all?

(Also do note that almost all farms will work much better on pure Vanilla than on Bukkit servers.)