How Do You Achieve A Good Seal On A Parker 51 Sac?

[Venemo]

I have a few Parker 51 pens that I've taken apart, cleaned out, and now it's time to replace their sacs, so I thoroughly removed any gunk and residue from the sac nipple, then shellac'd the new sac and left it to dry for a day or so.

 

The result: after the shellac dries, it seems that it doesn't provide a good air seal. There seem to be "bubbles" under the sac between the "ridges" of the sac nipple, and as I apply some pressure on the sac, it starts to separate from the sac nipple very easily. For this reason, I'm too afraid to put this in a pen, because even though it sold of holds, I'm afraid it would come loose and start to leak soon. It also seems that the shellac is weak, if I apply very little force the sac comes off easily.

 

I've now repeated the process 3 times, tried 2 different kinds of shellac, each time cleaning out the gunk and residue from the previous attempt carefully. But I always get the same result. What am I doing wrong? Is there a trick that I'm missing here?

 

This feels very silly because I was able to do this successfully in the past but for some reason I can't get it right this time.

[gyasko]

You have that many with failed sacs?

[gweimer1]

Why kind of sacs are you using? How old is the shellac?

[eachan]

The Pliglass sacs that are in Aerometric Parker 51s rarely fail and on the odd occasions when they do it's usually as a result of damage. They do become discoloured but that's not a reason for replacement. None of the sacs produced today will last as long as the original. It is well known that shellac is not a suitable adhesive in this situation. Unfortunately I don't know what is used but a search of this site should provide the answer. It's one of the araldites, I think.

Edited October 28, 2020 by eachan

[gweimer1]

One thing to check - how is the nipple underneath the sac? Is it hard, or has it gotten soft?

[gweimer1]

I was always taught that shellac was the adhesive to use on the pli-glass sacs, and I've never had any issues with it to date. The Marshall-Oldfield book also mentions that nail varnish is a good adhesive for these.

[Ron Z]

The 51 uses a #15 sac, which is what David Nishimura's are... they're really identical to the originals. They also don't need to be trimmed at all. You can also use a #16 PVC sac. I find that they are a pretty snug fit on the 51 sac nipple, which is long enough that they don't pull off. I haven't had a 51 sac come loose. But having said that, there are a couple of things that I do.

 

1 - I always clean the inside of a PVC sac with a Q-tip soaked with denatured alcohol, then dry it with the other end, especially at the opening. This cleans out any of the mold release compound that may have been left behind, so the ink flows properly and the sac sticks better.

 

2- I scuff up the sac nipple with just a couple of turns of 220 grit sand paper. This also helps the sac to stick better.

 

3- I use shellac. Since the sac nipple is plastic, I don't feel comfortable using a solvent based cement. Put a good coating on (don't be stingy), slide the sac on and twist it a bit so that it is distributed inside. You should end up with a bead or fillet at the forward end of the sac. Leave it there and let it harden, then put the sac guard on after it dries. Note that the pressure on the sac from the pressure bar is back a ways, not near the nipple, so it should not disturb the seal at all.

 

"nail varnish" = nail polish, which contains acetone. This is one of the few areas where I disagree with my friends and colleagues in the UK.

[pajaro]

Thank you Ron Z.

[Venemo]

You have that many with failed sacs?

 

Yes, these are used from ebay.

 

Why kind of sacs are you using? How old is the shellac?

 

The sacs are brand new from the Pendragons.

I tried two types of shellac, one I bought from the Pendragons about 2 years ago, the other I got in a local store brand new.

 

The Pliglass sacs that are in Aerometric Parker 51s rarely fail and on the odd occasions when they do it's usually as a result of damage. They do become discoloured but that's not a reason for replacement. None of the sacs produced today will last as long as the original. It is well known that shellac is not a suitable adhesive in this situation. Unfortunately I don't know what is used but a search of this site should provide the answer. It's one of the araldites, I think.

 

The sacs are brand new from the Pendragons. The originals were severly discolored, twisted, some of them already came off.

 

One thing to check - how is the nipple underneath the sac? Is it hard, or has it gotten soft?

 

It is hard.