Reed switch on pneumatic cylinder

[SteveD]

We would like to use an old bimba reed switch from a few years ago, however we are having problems with it. from what i understand, its just a magnetic switch that either swiches on, or off. We tested one with a voltmeter and a magnet and measured continuity between the two output wires. However, when we mount it on a cylinder with a 2'' bore, we cant get it to ever switch no matter where it is or where the piston inside is. Can anyone figure out what the problem might be? Does it not work on certain types of cylinders?