I want to join some PVC pipes. I've got primer (from a store that only sells paint) and on the back it says it's suitable for PVC. I doesn't say anything about paint or joining. Can I use this kind of primer with PVC cement? The pipes should be airtight and should be able to withstand 3-4 bar.
I highly doubt a paint store sells what you are looking for. When you join two pieces of PVC, you aren't joining them together, but welding them together. PVC Cleaner (AKA Primer) cleans all dirt, and oils off the parts and soften them a bit, so they weld together properly and the glue can penetrate the PVC deeper. The glue then works on a molecular level I think to "melt" the pieces together to make one piece of PVC. You need to go to a hardware store to get the correct product. You can get PVC Cleaner/Primer and Glue separate, or you can get a Cleaner/Glue product in one can.
Paint primer that says it's suitable for PVC can be used for painting PVC siding, Vinyl window surfaces, fencing, etc. It is a paint primary coat for weatherproofing surfaces and enabling other paint coats to stick to the plastic so they don't peel, not a pipe assembly agent. See Gunner's comments for proper materials needed for pipe assembly. it's a whole different item altogether.