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Replacing pen sacs

One of the easiest repairs to make to vintage pens is to fit them with new sacs. With a little study and a moderate amount of care and patience, even a beginner can manage this task. On this page, I provide an illustrated procedure for replacement of sacs on sac-fill pens.

What you need

A sac (of course!)

You can buy sacs in specific sizes or in assortments from Pendemonium. Generally, sacs cost between one and two dollars each, depending on where you get them and how many you buy at a time. If, like me, you are duffer, you might find one or two of the assortment packs to be the best bet.

If you want to go straight to the source, you can buy sacs individually or in bulk (or in assortments) directly from the makers; there are now two sac-manufacturing operations in North America:

  • The Pen Sac Company (http://www.pensacs.com/) was started by a couple of modern collector-entrepreneurs in the remains of White Rubber Company's Plant #2 in Ravenna, Ohio. They offer a wide range of sacs in both straight and "necked" design, plus tools and parts, and they accept telephone orders from the public.
  • Wood Bin of Simcoe, Ontario, recently entered the pen sac business and now sells translucent silicone rubber sacs alongside the traditional black latex (these silicone sacs are worth considering for your next resac job; they are impervious to damage from ink, plus they should not emit any gases that could discolor pen plastics, and they cost only a few cents more than the black sacs). Wood Bin also offers Vacumatic diaphragms in all the sizes, plus replacement pressure bars and tools.

What size do you need? Replacement sacs are sold by their diameter in 64ths of an inch (e.g., a #16 sac is 16/64ths or 1/4 inch across). They usually come longer than you need and can be trimmed to fit inside the pen. The Pen Sac Company's website includes a detailed listing of pen sac sizes by brand and model of pen, and also a formula for computing the sac size from the barrel's inner diameter. If you get an assortment of sacs, however, you will probably be able to find the right one by testing (see below).

Shellac (for sticking the sac onto the pen)

The preferred adhesive for sticking sacs to pens is old-fashioned alcohol-based orange shellac; it is easy to apply, dries quickly, seals well, and does not eat up plastic or rubber. Plus, it is easy to remove for the next resac job; you can just chip or flake it away with your fingernail or a blunt blade. You can get quart cans of shellac from your local hardware store, which should supply enough stickum for about 3,000,000,000 pens; or, you can buy a small bottle (with built-in applicator brush) from Pendemonium.

If you want to use other adhesives, bear in mind that aromatic-based adhesives (like airplane glue or nail polish) could eat up certain plastics. Plus, they might not be easily removable later on. While rubber cement is certainly not corrosive and is easily removed, it might not give an adequate seal. One expert restorer I know likes to use liquid cyanoacrylate ("super glue").

Talcum (for lubrication)

Plain talc or baby powder is usually applied to the finished sac to help it glide smoothly (er, like a baby's bottom) back into the pen barrel. Talc also helps keep sacs from sticking to the insides of the pen (and is particularly useful in the repair of Sheaffer Touchdown and Snorkel pens). A small bottle from the drug store should last you a good long while.


You may find a few basic and inexpensive tools to be of use during resacking:

  • Section removal pliers are big pliers with rubber-coated jaws that are just perfect for getting a grip on sections. You can get these from Pendemonium or Fountain Pen Hospital (psst...don't tell anyone I told you, but these are actually automotive spark plug removal pliers, and can also be found at your local auto parts house). Make sure that the rubber or plastic material on the jaws remains clean and free from tears or sharp edges that could scratch your pen.
  • Picks, long forceps, and tweezers are often useful for emptying the insides of pens to remove all the sac debris.
  • A few good sharp razor blades (of the kind that go in window scrapers) will enable you to trim sacs and even to help open recalcitrant sections (see below).
  • A sac spreader tool may be of help if the sac you're fitting is very small compared to the section nipple onto which it must fit. Pendemonium sells a very inexpensive spreader that works well.
  • If you intend to remove and reset the point and feed while you have the sac off, you'll want to look into a feed knockout block. This is simply a hard block of wood or metal with holes drilled into it, supplied with a number of dowels or pins of various diameters. You insert the section, point down, into one of the holes and use one of the dowels with a small mallet or hammer to tap (gently, please!) the feed out of the section. The steel versions are a bit expensive, but Pendemonium sells a very serviceable hardwood block (with steel top) for a bit less money.

Opening the pen

We are now ready for the scariest, most sphincter-tightening portion of the job: removing the section from the barrel.

Your pen likely has been closed for many years; it may have a very tight friction fit that will take a bit of carefully applied muscle to break. Then, there is also the possibility that a previous "restorer" has glued the section in place; even here, you may still be able to open the pen but you must proceed carefully. You should start out using your hands, and move to tools only if you need them.

Also, bear in mind that most pens used friction or press fits for the joint between section and barrel, but that some sections actually screwed into the barrel on threads (the early Parker Duofolds are the principal example).

Still here? Good! Let's get started.

Remove the cap and the blind cap (if any) and set them aside. If your pen has a removable point (like an Esterbrook), you can also remove it and set it aside.

Now we will remove the section from the barrel. First, try your hands: grasp the barrel tightly (point upwards) in your weaker hand; then, place your stronger hand on top, grasping the section between the thumb and the crook of the index finger (something like a golf grip). While holding onto the barrel, wiggle and pull the section very slightly until it begins to loosen. Ease your grip and work the section out of the barrel. Most of the time, this should do the trick. Do not get agressive when twisting or shifting the section in the barrel; this could open cracks in the barrel (which is pretty fragile at this location).

If you can't get the section loose with your hands, here's a trick taught me by Bert Heiserman which may help break any glue used in a previous repair: lay the pen flat on a table, on top of a soft cloth or paper pad. Take a razor blade and lay its edige in the seam between section and barrel. Bear down slightly on the razor blade, then turn the barrel slightly and repeat. Work your way around the seam with the razor blade, and with any luck you will crack the glue (and not the pen!).

You can also apply some heat to help loosen the section; use a low-temperature alcohol flame or an industrial heat gun (or, if you don't have these, use a high-wattage hair dryer). Don't use matches, cigarette lighters, or candles (these are too hot), and don't boil, broil, or microwave the pen (these could destroy the finish or melt the pen). Apply just a bit of heat all around the joint, then try the hand trick again; if it still doesn't work, try a bit more heat. Be patient!

If you still have trouble, break out your section pliers and have a go. If you don't have section pliers, you can improvise with a pair of channel-lock or adjustable pliers (needlenose pliers aren't a good bet, since they can't grasp more than a small area of the section).

Now, hold the barrel in one hand and the pliers in the other, and gently twist in either direction (twist carefully, and with the minimum pressure on the pliers). Once you feel the section loosen up, you can drop the pliers and use your hands to remove the section.

Cleaning the pen

Now that you've got the pen open, you can breathe a sigh of relief. Now, it's time to remove all of the debris of the old sac. Start with the section: if you're lucky, the frozen sac has come out intact on the section. You should be able to snap most of it off without much force.

Examine the section to see where the end of the glued-on sac begins; you can usually find a little seam into which you can introduce your fingernail or a blunt blade (like a bread knife, nail file, etc.). Scrape or chip away the remnants of the sac from around the section nipple. If you need to, use a razor blade to carefully scrape any more stubborn bits (once you loosen them, they tend to flake off pretty readily). You need not get the nipple clean and shiny (actually a bit of roughness will help the new sac adhere), but you should remove as much of the old sac and shellac as you can. In particular, you want the new sac to fit flat around the section nipple without any bulges that could make reassembly difficult.

Now, we turn to the barrel. Often, you can get most or all of the sac out simply by tipping the barrel and shaking it a bit. You can also hold the barrel in your fist (with the open end somewhere near the middle of your palm) and pound on a table. Use a long pick or probe to feel around inside the pen and loosen up any stuck bits of sac. Use tweezers or thin needlenose pliers to find and withdraw the pressure bar; work gently so you don't foul it on the lever mechanism.

Once you've removed the sac remnants and the pressure bar, you should be left with just the naked plastic barrel and the lever or button that operates the filler. If the barrel had ink leaked into it, you can rinse it out under cool tap water. If the pen is of common celluloid (or a modern plastic like acrylic), you can soak it or put it in an ultrasonic tank. Do not soak rubber or casein pen barrels. Once you've gotten the barrel clean, set it aside to dry overnight (you can hit it inside with a shot of canned air to drive out most of the water and speed up the drying).

This is also a good time to give the point and feed a good cleaning. You can soak the unit overnight in a cup of cool tap water, or run it through a couple of cycles in an ultrasonic tank (but NOT if it is hard rubber or casein). Otherwise, you can rinse it under cool running water, and use an otic syringe or pipette to force water through the feed channels on back of the feed. If you are up to the task, you can also knock out the feed and point and clean them individually; this means you'll have to reinsert and reset them later on (if the pen writes well, I'd recommend not trying to fix what isn't broken).

Inspect the pressure bar: if it is bent or corroded, it might be a good idea to replace it. Pendemonium, Fountain Pen Hospital, and Wood Bin carry an assortment of pressure bars that should fit most pens.

When the barrel is clean and dry, reinstall the pressure bar. In lever fillers, the blade portion of the bar should fit right under the lever (so that it comes between the sac and the lever. For button fillers, the pointy end of the bar should fit all the way down into the filler button so that it will keep the button in the up position when the pen is closed again.

Fitting and trimming the sac

Now, you will select a sac and trim it to fit your pen. If you want to be precise, you can consult Pen Sac Company's size charts to find the proper size of sac to fit in your pen, or use their sizing formulas if your pen isn't listed. Otherwise, get an assortment of sacs and try them out by dropping them into the pen.

The sac should go in for pretty much the full length of the barrel (save for a quarter or half inch or so, needed to clear the button or pressure bar). Insert the sac as far as it will go, mark the spot by pinching it between thumb and finger at the mouth of the barrel, then pull it out and lay it beside the barrel to see how far inside it went.

You may use the largest sac that will fit inside the pen without binding, crimping, or pinching on the pressure bar (a sac that is partially deformed when it rests in the barrel won't fill efficiently). In general, it is better to use a sac that's a bit too small rather than one that is too large. Believe it or not, a small but properly-fitted sac will hold more ink than a large sac that's been crammed into the pen.

Once you've selected the right sac, and verified that it will fit all the way into the pen, you can now trim it. I use a three-step procedure:

  • Put the sac all the way into the barrel; use scissors to snip it off even with the mouth of the barrel. Remove the sac (with tweezers, if needed).
  • Lay the sac beside the section, so that the open mouth of the sac is even with the spot where the section joins with the barrel; find the top of the section nipple and mark this spot on the sac with a pencil.
  • Back off from this mark a few millimeters (to allow for sloppy measurement), then use a sharp razor blade to chop off the sac. Cut the sac so that it's new mouth will be straight and even; it's best not to use scissors for this step because they will inevitably cut on a bit of an angle.

Attaching the sac

Here's where that applicator brush in the little Pendemonium shellac bottle comes in handy; open the bottle and daub some shellac around the section nipple. I like to daub a bit more inside the mouth of the sac, but I'm careful not to use too much (so that it won't get into the feed channels and clog the pen).

Attaching the sac takes a bit of patience. You might find a sac spreader tool to be of use, but I generally don't find them helpful. I usually "sneak up" on the nipple by placing the sac over one side of it, at an angle, then, I pull the sac over the rest of the nipple and gently work it so that it lines up straight and reaches the top of the nipple. The liquid shellac helps to lubricate a bit. Then, I twist the sac on the nipple by a half-turn or so either way to spread around the shellac for a good seal.

After the sac is in place, you can wipe up any excess shellac with your fingers. Be careful not to use too much shellac; as I said, excess shellac could get into the feed and clog it.

Once you're satisfied with the fit, you may set aside the assembly to dry (allow a few hours). Try to master your impatience and allow the sac to dry fully before starting reassembly; otherwise, you could shift the sac or lose it altogether.

Reassembling the pen

Coat the sac in talc or baby powder so that it will not stick or bind on the pressure bar or the sides of the barrel (I usually pop the top off the talc bottle and simply dip the sac inside, up to the end of the section). Then, simply reinsert the sac and press the section straight into the barrel (lining the lever up with the point is optional).

If you have an old Parker button filler (or similar), you'll proably be screwing the section back in. The job is slightly complicated by the fact that the end of the pressure bar must fit into a small notch in the side of the section's threads. Find this notch and make sure the pressure bar fits into it; the screwing-in will feel a bit balky (since you're spinning the metal bar against the barrel), but go slowly and all should be well.

You're now officially done, and can enjoy filling your newly-refurbished pen with your choice of ink for a bit of writing. If you like, you can test the filler first using water (so there isn't so much of a mess should you have to redo the resac job). It's also OK simply to put the pen away without filling it (with no ink inside, it won't get "sac-rot" while it waits for you to use it).