I've been searching the forums for information on which sac I should use in a Conway Stewart "28," and I'm hoping someone in this forum will be able to help? I have the pen apart and the old sac removed--it came out in one piece except for the part that was attached to the nipple (which I've removed). The sac looks like it's pretty good-sized, but I've only got size 16 and 16T here, and it's quite a bit wider than those in diameter. Does anyone know which sac is the best fit for this pen?
Thanks.
Larry Hartsfield

Hello Larry,

I suggest using a size 16 sac on the CS 28. I don't have one open and in front of me, but if you were to measure the diameter of the feed/ink sac nipple in 64ths of an inch, I do believe that you will come up with 16/64" (1/4") or just slightly more.

I have always used a sac at the size of the feed/ink sac nipple or just one size smaller. You do not want the sac to fill and touch wall of the pen body. As one holds the pen, the pen warms to body heat. If the ink sac is touching the inside wall of the pen body, it, too, increases in temerature. This heat is transfered to the ink, which in turn expands as the ink moecules are excited by the increase in temperature. The result of this is a pen that will suddenly leak a blob (technical term) of ink onto the paper, your hand, or clothes.

Peace,

Phroneo

Thanks, Phroneo,
I ended up experimenting. My first thought was to use a 20, but that was a bit snug, so I tried an 18 and that was perfect. The 16 was just a bit small. With the 18 I have space all around the sac and nothing is touching the pen body. I'm going to let it dry overnight, and I'll give it a run in a couple of days. Thanks again.
Larry

So is the sac sizing is related to the diameter in 16ths of an inch? A size 20 will be 20/16"?

I must say I put a sac of the largest possible size at the longest possible length for the greatest possible capacity. As a result 'friend' the CS45 has an enormous capacity, I suppose like an eyedropper.

The only problems I've encountered was in a Burnham which was button fill and with their screwed section. The twisting meant a smaller than normal sac as it kept catching on the button mechanism when screwed in. I can understand the interesting warming principle you describe but have never knowingly experienced it (but that's certainly not to say I never will and I hate it when pens 'blob'!).

Many thanks

Greg

Hello Greg,

Yes, 20/64" or 5/16" for the ink sac nipple on the nib section would use a 20 ink sac. I believe that I got this information from several sources - "Da Book" (not 100% certain) from "The Pen Sac Co.", a manufacturer of ink sacs in Califonia, from Martin at "The Wood Bin," a fountain pen supply company based in Canada, and, I think if one does a search on this forum, from the FPN. It's just that I learned it so long ago and from so many different sources that I cannot give you a pinpoint reference.

I've never had the pleasure of owning a CS45, and now in reflection I find that strange because I have a ton of vintage CS fps and mps, so I don't know its relative size. But it seems to me as if you don't have to fill the pen too many times.

Peace,

Phroneo

Hi Phroneo.

Thanks for the info, always happy to learn from others.

The CS45 doesn't come up very often and is almost identical to the CS55 but the body is ~3mm longer and the lever set 2-3mm nearer the section. Nib, girth, cap etc are all identical except the cap rings and, in my case, the material. It is a wonderfully reliable pen (never blobs, always starts first time etc) and the best writer I have (if you don't want flex). I use it a lot and it gets through a lot of ink!

Th CS45 was a pleasant surprise when it arrived in that it is shiny BHR, I have never known a CS55 in this material. I think there were more colour options etc for the CS55 which was made in the usual marbles etc (the only one I have is boring black!). I have a regret in that I let Jonathan's 'Autumn Leaves' 45 get away from me when he flogged it. It actually went for way above my budget, but maybe I should have made an exception for this unusual and beautiful pen. Ah well.

Greg