Care and Feeding: How to Replace a Vacumatic Diaphragm

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(A portion of this article first appeared on Pentrace: The site for fountain pens that write.)

I’m in the business of repairing and restoring fountain pens; but, as I said in Care and Feeding: How to Replace a Pen Sac, I’d be silly to ignore the fact that some collectors want to repair their own pens. Although not terribly difficult, replacing a Vacumatic diaphragm is not so straightforward as replacing a sac. There are some definite pitfalls, and I see many pens with diaphragms that are incorrectly installed. Installing a diaphragm wrong can cause the filler to malfunction, and it can also damage the pen. This article explains how to do it right. (Revised May 31, 2008)

Tools and Supplies

First, you need a supply of diaphragms. My vendors of choice are the Pen Sac Company and Tryphon Enterprises. You can find contact information for all resources mentioned in this article at the end of Care and Feeding: How to Replace a Pen Sac. Shown here are the three sizes of diaphragms; from top to bottom, they are Debutante, Standard, and Oversize.

Here is a table indicating which models use which diaphragm sizes:

Note that every diaphragm comes with a pellet already installed, so you do not need to track down a supply of pellets. But do be careful when handling diaphragms, because sometimes a pellet can fall out. If this happens, the escaped pellet will obey the Law of Selective Gravitation, which states that a dropped object will roll to the location where it will be the most difficult to recover.

The first and most important tool is a “Vac tool,” which you must have in order to remove the pen’s filler assembly.

CAUTION   Do not even think about trying to remove the filler without a proper Vac tool. The only possible result is destruction!

The Vac tool screws onto the threads that are exposed when you remove the pen’s blind cap, and two styles are available as pictured here: the Vac wrench (left) and the Vac block (right). These tools are available from Fountain Pen Hospital, Wood Bin Ltd, and other dealers. Vac wrenches come in two sizes; Lockdown Maxima fillers need the oversize tool, while all others need the standard size. Most Vac blocks, like the one shown here, accommodate both filler styles.

To install the new diaphragm into the filler, you need something to push the pellet into the pellet pocket. The best tool I know for this task is Tryphon Enterprises’ magic pellet pusher:

There are two additional tools that can prove useful. These are tools that you can make yourself. The first is a tool that can push a stuck filler out from inside. The illustration below shows the tool that I made for this task.

This tool consists of three parts: a fixed tube, a sleeve (sliding tube), both of thinwall brass tubing, and a handle.

The tubing comes from a hobby shop that caters to model railroaders, and its wall thickness is 0.014” (0.36 mm). The following table shows the sizes you need for the various filler types; for all sizes, the sleeve is 2³/4" (70 mm) long and the fixed tube is 4” (102 mm) long.

(The “51” requires a smaller pusher because the “correct” size for a Deb filler does not fit through the collector opening in the front of the barrel.)

The handle is a 2” (51 mm) piece of ½" (13 mm) hardwood dowel. Drill a ¹/4" (6.35 mm) hole 1” (25 mm) deep in one end of the handle, and press the fixed tube in all the way. Slip the sleeve onto the fixed tube. Ta-da! A Vac filler pusher! When I actually need one for a Standard or a Maxima, I’ll figure out what the tubing sizes should be.

The last special tool is a probe. This is merely a 6” (152 mm) length of ³/32" (2.4 mm) brass rod with one end ground and polished to a hemispherical shape. The following illustration shows the “business end” of my probe.

You will also need a sharp X-acto knife, sac removal tools (among which I include dental scalers), and a bore light or otoscope for examining the inside of a pen barrel.

Disassembly, Cleaning, and Diaphragm Removal

The first step in replacing a diaphragm is to unscrew the filler’s threaded retaining collar from the barrel using your Vac tool.

CAUTION   If you are working on a Lockdown filler, extend the plunger before attempting to remove the threaded collar. If you don’t do this, and if the filler is stuck, you can pop the button from the end of the plunger. This can easily crack the plunger tubing, destroying the filler. If the plunger is stuck, you’ll need to work it free by soaking or removing an ossified diaphragm from inside the barrel, or both. (To remove the diaphragm while the filler is still in the pen, you must remove the section; see below.)

Be careful when threading the tool onto the collar; cross-threading will damage the filler severely. Exercise care also as you clamp the tool onto the collar; a Vac block can exert far more pressure than is actually necessary, and you can squeeze the collar hard enough to damage it, especially if it’s a wartime plastic one.

Once you have the tool in place, the collar usually comes loose easily; but sometimes you’ll find one that is stuck because the plastic has shrunk or because a previous repairer has glued it in place. The best recourse is to apply gentle heat in order to loosen the bond. (If the plastic has shrunk, heat expands it slightly, usually enough to break it loose from the collar.) I recommend using a professional-quality variable heat gun; but a hair dryer may work.

CAUTION   Celluloid begins to soften at about 165° F (74° C), so go carefully. Shellac softens at about 140° F (60° C), so that if shellac has been used, you can free the adhesive bond safely. If heat doesn’t do the trick at first, soak the filler end of the pen overnight in cold water and try again the next day.

After you’ve unscrewed the collar, remove the filler from the barrel. Sometimes, especially if the diaphragm has ossified and been shattered by a press of the plunger, the filler will just come out. But you frequently discover that the diaphragm has glued the filler in place. You can soak to loosen things, or you can wobble the filler gently (risking damage to the plunger), but these methods may not suffice. Now is the time to use your filler pusher.

To use the pusher, you need to remove the section from the pen. (On a “51” this calls for removing the shell and collector/feed/nib assembly.) I always remove the section even if the filler came right out; this gives me an opportunity to run the section assembly through my ultrasonic cleaner and to clean residual ink from the inside wall of the barrel.

Remove all of the old diaphragm that you can get from inside, using dental picks bent into hooks, your set of Father Terry Koch sac removers, or other appropriate tools. Ideally, you’d like to remove all of it, leaving a clear field to insert your pusher tool. But there will usually be some bits left, such as the center part where the pellet goes into the plunger’s pellet pocket.

Now insert the pusher into the barrel, bringing the sleeve into contact with the shoulder of the barrel’s tapered seat. This guides the fixed tube so that it will slip perfectly over the pellet pocket and bear against the end of the filler’s tapered collar. Hold the barrel in your “weaker” hand and use the palm of your ”stronger” hand to push on the pusher’s handle and pop the filler loose. This may take a little force, but I’ve never yet had the tool fail, even with a diaphragm that had been shellacked in and required a little heat to encourage it.

One problem you’ll run into is that your pusher won’t fit into a Deb or Sub-deb Vacumatic. No problem. Just slide the sleeve off, and be careful when you insert the tool so that it seats properly. The “51” tool may also give you cause for concern, as its smaller tubes don’t fit against the shoulder and collar as they should. The tool still works, but it calls for a little more care to avoid shattering the pellet pocket.

With the filler out, you can remove the remaining bits of diaphragm. You will often need to scrape these bits from the surface of the tapered seat and from the inside of the barrel. I find a crescent-shaped dental scaler very effective here. Go carefully to avoid digging into the plastic! When you have all of the diaphragm’s remains out, clean inside the barrel with water and a soft test-tube brush. Too hard a brush will scratch the plastic.

If there is any foreign substance on the threads of the retaining collar, remove it. A brass brush may work, or you may need to scrape the threads turn by turn with an X-acto knife. Ideally, when you reasssemble the pen later, the collar should screw into the barrel without resistance (and therefore without the assistance of the Vac tool) until it begins to push on the inner parts.

The final step in cleaning is to remove the pellet and the remains of the diaphragm from the pellet pocket on the end of the filler plunger. Do not simply try to pull the pellet out, and do not insert a dental pick or other tool to lever it out! The pellet pocket on a plastic plunger is sometimes brittle and easy to break, so be very careful. You can use the tip of a very sharp No. 11 X-acto knife to cut the pellet out in little bits. Another method is to use a rotary tool with a small spherical burr, grinding the pellet out. Be very careful not to cut into the pellet pocket itself. If you run the rotary tool at high speed, the burr will melt its way into the pellet, and the pellet will form itself around the burr shaft; this makes the pellet very easy to remove.

Diaphragm Preparation and Installation

CAUTION   To prepare the diaphragm, you must cut it to the correct length. Parker bought its diaphragms already cut to length, and neither Parker’s repair manual nor any other existing documentation I have seen acknowledges the need for cutting. This is why so many “restored” Vacs have diaphragms that are not cut. An uncut diaphragm will eventually jam and refuse to function, and a diaphragm that is too short puts undue stress on the filler parts without being able to displace enough air to work effectively.

To determine the correct length for the diaphragm, install it into the filler. The easiest way to do this is with two tools: the pellet pusher and your homemade probe.

The probe serves a double purpose. First, you can use it to determine whether the new diaphragm will install easily. If the probe slips freely into the end of the pellet pocket, you’re home free. If not, use your X-acto knife to shave around the edge of the opening in the pellet pocket until the probe slips in. Take off only as much material as you must; if the opening is too big, the pellet can pop out again later.

Use your fingernails to turn the open end of the diaphragm inside out like the cuff on a trouser leg. Now use the probe’s rounded end to push more of the diaphragm into the inverted end. Work around as needed, until the diaphragm is halfway inverted.

Now insert the pellet pusher into the open end and position the pellet on the end of the pusher. Stretch the diaphragm backward along the tool to thin the rubber over the pellet, and insert the pellet into the pellet pocket.

With the pellet installed, you can use the probe to continue inverting the diaphragm until it extends over the filler’s tapered inner collar. Slide the threaded collar into position against the inner collar. Now, using your fingernails for purchase, pull the diaphragm farther over, keeping it even all around, until it covers the threaded collar. Check it for length by depressing the plunger all the way. See that the diaphragm everts so that it is just exactly fitted over the plunger. It should not stretch, and there should be only the absolute minimum of extra rubber if there is any extra at all. You can now cut the diaphragm off, using a sharp X-acto knife, right at the point where it passes over the flange on the tapered inner collar, as shown here:

The following cutaway illustration shows more clearly how long the diaphragm should be.

CAUTION   The diaphragm must not ride up over the flange on the retaining collar. If it does, it can put excess strain on the barrel, eventually causing a permanent bulge and preventing a correctly installed diaphragm from seating tightly.

If you repair Vacs frequently, you can save time later by cutting a set of diaphragms for the various pen models and using the cut diaphragms to gauge the length for future cutting. You cannot cut just one diaphragm for a universal gauge; different filler models require diaphragms of different lengths.

Filler Installation

You are now ready to reinstall the filler into the barrel. Wet the diaphragm to lubricate it (saliva is handy), and insert it into the barrel. Turn it a little if necessary to push it past the tapered seat in the barrel and then insert the filler until it stops. Make sure the diaphragm is not twisted in the barrel. Use your Vac tool to screw the threaded collar firmly down onto the tapered collar; it should squeeze the rubber against the tapered seat enough to seal it but no more than is necessary. Do not allow the plunger to turn as you do this; if it turns, it will twist the diaphragm. Do not apply “brutal” force, but the collar must also seat far enough in that you can screw the blind cap down until it touches the barrel. If the blind cap does not line up evenly with the barrel, you can usually push it sidewise until it does. (Pushing the blind cap moves the filler slightly; if the filler won't move, it may be too tight.)

Note   Parker’s Vacumatic repair manual instructs the repairer to cement the threaded retaining collar in place using Vacumatic cement, which never hardens. No other adhesive should be used. It turns out that no adhesive at all is actually necessary, although some modern repairers recommend securing the threaded collar with shellac.)

Use a bore light or an otoscope to examine the diaphragm from the open end of the barrel, checking to see that it is not twisted. If it is twisted, unscrew the threaded collar, untwist the diaphragm, and reinstall the threaded collar. Test the plunger action to be sure that it is smooth and that the plunger travels to the full extension in both directions. Test the seal by putting the open end of the barrel in your mouth and sucking. Stick your tongue against the open end and release the suction. The partial vacuum in the barrel should hold the barrel to your tongue.

Reassemble the pen, ink it, and use it!

The information in this article is as accurate as possible, but you should not take it as absolutely authoritative.

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