This is a question for those who feel the same cartridge with a seringe.
This might sounds a little silly but I am asking because I never did it or tried it:

How many times can you fill the same cartridge untill it will not be good any more ?

I think the most I've tried is 3 times, and that worked well (I sold the pen at that point, thus preventing fill #4). You just need to make sure the cartridge doesn't get wobbly.

I'm up to three or four myself on one cartridge. I do pay close attention when I insert it, especially to make sure it fits snugly on the feed.

I've got a cartridge in one of my Waterman Graduates that I'm sure I have filled at least six times. I'm careful removing it and replacing it each time. So far, it has continued to seal well in the pen. I've had no leaks at all.

So far, the longest lived carts I have have been filled at least 15 times, and still going strong. As long as you don't squeeze the cart, don't use a metal needle to refill, and don't play around with it too much, then most carts hold up fine.

EDIT - Let me be fair, since it does look like my cartridge experience is quite different than posters thus far. The long lived carts I have are Sailor and Pilot carts which are open mouthed. I don't refill internationals, Parkers, Lamys, Watermans, or Cross, because I'm quite satisfied with the converters. I would suspect that the nipples on these Western carts might run into trouble. Most Shaeffer carts I've used have failed after a few fills.

I have also found that three or four times is about the max. The end of the cartridge that connects with the nipple in the section just wears out and starts to get sloppy. I have had a couple of brave cartiridges that went to as much as seven fillings, but they were exceptions.

I have a Pelican future pen at the office whoser cartridge I have filled DAILY for over one year. Do i get a prize for stupidity?

Well, if it works, what's to stop you, right? I think this post will motivate me to swap out some of my Western pens to carts and see how long I can get a cart to go.

Just depends on the cartridge itself. Not all are created equally.

It's not like the cart will fail instantaneously between refill #5 and refill #6. Try to remember how a new cartridge feels when you plug it in. It should fit snugly and tightly. Over time, removing the cartridge to refill it and reinserting it will just eventually cause the lip to wear out, but, there's no reason a cartridge can not be refilled dozens of times.

Here is my "test". Once I refill and reinsert the cart, I give the cart a simple 1/4 to 1/2 turn rotation. If I feel a little resistance there, I know the seal is pretty good. It it rotates too easily, then I start to get a little suspicious. If it feels too loose, then I toss it. Unfortunately, there's no way that I can really explain qualitatively what "too loose" is for me.

And hey... don't worry. A disaster is unlikely. The worst that can happen is you'll start to notice a little leakage around the lip the next time you refill, and you'll know it's time to change carts.

Practically indefinitely, if you don't squeeze the cartridge. I imagine at some point the opening may widen and then the cartridge won't attach firmly to the feed bayonet. At that point, I suspect it would be very old and thus time to switch to another cartridge. They are cheap, afterall.

How about a prize for being smart and environmently friendly.You are ok in my book.

I almost posted this exact question! How about for LAMY cartridges - can any share the # of times they refilled a Lamy cartridge before it crapped out?

Three. It takes exactly three licks to get to the center of a Tootsie Roll Tootsie Pop.