Question regarding RO cartridges

[kilofey]

My lfs could not order a mechanical filter cartridge for some reason, he said I could get one at the hardware store but I didnt see anything saying mechanical filter. Is there other names? Is a pre filter and a sediment filter the same thing as mechanical filter?
Since I couldnt find what I was looking for, I will be buying it online. Does anyone know where I can get a 10" mechanical filter cartridge?
Also, when should I replace:
Mechanical filter
Carbon filter
Ro membrane
Di filter
I have a kent ro/di 75gpd unit, if that makes a difference. Thanks!

 

[aquaknight]

Pre-filter is generally the term applied to all the stages before the RO membrane. Generally there are 2 or 3, which would include your sediment filter and carbon stage(s).
I've not heard the term "mechanical filter" used to describe a filter/stage on an RO/DI unit. It does seem like it is just a term for a sediment filter however. As the sediment filter is always the first stage
Changing times for each filter really depends on the individual user and the amount of water they make, and their tap water. I seem to change my sediment filter and carbon block stages every year. My RO membrane is reverse flushed every 3 months, and replaced about every 15-18 months. DI is replaced strictly based on TDS readings and the color change of the resin.