I am planning to buy a Parker 51 and I have two options:

1- Vacumatic fully restaured (Made in USA)
2- Aerometric New Old Stock (Made in Canada or USA)

As I am new on this topic of vintage pen, I would like some suggestions from more experienced users.
Which is the best option?
Which is the most reliable and rugged system?
What should I look for before choosing one of this pens?
Any other piece of information is welcomed.
Thanks in advance for your help.

Either pen will last 20 years or longer. The Vacumatic holds more ink. The Vacumatic supposedly lays down a bit more ink so...??

The Blue Diamond caps are nice - they are interchangeable. The nibs and and collectors are identical.

Personally, I think the Aeromatic may be a bit more durable/rugged than the Vacumatic. But this is also like looking at the top ten finishers in an International Beauty contest. One fellow may have a different selection order than the fellow next to him but, both will probably agree there are several absolutely stunning young females on stage.

This is not like getting married .... You CAN have both and not get in trouble, arrested or thrown in jail.

Ron

There have been lots of posts on this very thing recently. I would suggest you do a search in this forum for aero vs. vac, or just scroll through. I believe their have been at least two posts in the last two or three weeks about this very thing.

If you can swing it, I'd recommend getting both. Otherwise it mostly boils down to personal choice. I prefer the vacs because they hold more ink and feel a tad more substantial in my hands. I also prefer Double Jewel models and they only come in vacs.

For your questions:

1. Only you can decide what are the best options for you.
2. Both are pretty rugged, but the Aero system is probably known to be more "rugged" than the vacs. They rarely give you any problems, but I have purchased two that ended up having corroded breather tubes, so anyone who says they "never" need to be rebuilt is simply wrong. As I said earlier, I prefer the vacs for various reasons (don't get me wrong, they are both great filling systems and I have both types in my collection), and as far as having them rebuilt, some people will say the diaphragm will last 5 years, others say much longer (like 15 or more years). A service for a new diaphragm costs about $35 from a retorer. I'll gladly pay it to keep the pen(s) I use functioning well.
3. You look at the same things you'd consider on any pen. Condition, color, nib, etc. I like to use my 51s, although I must admit that I haven't been able to include them all in my rotation. One of the main considerations with a 51 is the cap. Barrels can be polished, but caps are a bit more tricky (and therefore are more expensive to repair, when repair is possible).

I'm sure some aero lovers will chime in here too. Either decision you make will likely result in making you happy. Congratulations and welcome to one of the most addictive pens there is!

Aerometric, no question.

Why?
Clear sac allows you to see how it is filling and kinda how much ink you have left.
Pli-glas sac lasts almost forever.
Filler is easy to use - idiot proof, IMO.
Easier to rinse than a vac.

Why not vac?
I think the filler is a pain.
A properly serviced resac AND using the proper filling technique is necessary for best results.
The sac in the vac does not last forever.
The only vac I really love is my clear demo model, where I can SEE how it's filling.

There's a reason Parker changed from the vac filler to the aerometric, and that's because the aerometric is an improvement over the vac system.

I've never used a pen to the point where ink capacity is an issue, and I think between the two capacity has to be very similar, and certainly more than adequate for normal usage.

It depends on how you feel after you have written with both pens. The Aero feels lighter in my hands. I think it is injected moulded plastic as opposed to the hand lathing of rod stock used to make the Vacs. The vac seems heavier and more substantial in my hands. I love the shape of the Vacs, and I love the double Jewels. So I prefer my Vacs for user pens. Yet I do rotate them and use my aeros, also.
I agree on the ink situation. The Vac holds more, but unless you are isolated from your ink supply, writing the next Great American Novel, I doubt the difference in capacities between the two makes much difference in actual real world use.
As far as the filling systems, my restored vacs are just as reliable as the Aeros. And I understand the diaphragm now lasts at least 10 to 30 years, now that many of the repair folks are using silicone diaphragms instead of rubber. As far as Aeros, I have had my first Aero 51 since 1973, bought new for me for a Christmas present when we lived in England. Other than flushing it now and then, it has had no repairs or adjustments, and still writes and fills great. I don't think it has ever had anything in it other than Quink Black or Blue-Black.
So it really boils down to your individual preference after you have handled and tried each pen. If I were you, and you could swing it, get one of each, one with a fine, and one with a medium nib. Prices are not coming down anytime soon. Aeros are also going up in price, and "first year" (1948) aeros will get expensive sooner or later.

Oh, and let me let you in on a little fact as far as ink supply checking. Sometimes the Aero's ink supply is just as hard to determine because the ink coats the pliglass, and it is hard to see the "bubble" in there.
For Vacs, just give them a gentle shake with the cap on. If you hear "sloshing", it is time to fill up. I have never run dry using this technique, and 51's are hard to shake ink out of anyway.
I personally don't think the process of filling and flushing a vac is really any big deal. Filling a Vac is as easy as can be, and no more difficult than filling an aero, actually.

Thank you for your help and advice. I guess I'll go for both, but first the vacumatic (a christmas present to myself )
and then the aerometric. I'll let you know my impression writing whit this pen. It is blue and gold. thank you again and every piece of advice is welcome. Thank you.