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How to Replace a Vacumatic Diaphragm

(This page revised March 23, 2015)

Reference Info Index | Glossopedia  ]

Fountain pen
Fountain pen

Although not terribly difficult, replacing a Vacumatic diaphragm is not so straightforward as replacing an ordinary 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 leak or otherwise malfunction, it can make further repair more difficult (if not impossible) for the next person, and it can also damage the pen. This article explains how to do it right.

Tools Required

Parts Required (see footnotes for more information)

Supplies Required (see footnotes for more information)

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

Diaphragm Pen Models

Oversize diaphragm     Oversize • Oversize (Lockdown)
• Senior Maxima (Speedline)
Standard diaphragm     Standard • Standard (Lockdown)
• Standard-girth Junior (Lockdown)
• Maxima (Speedline or plastic plunger)
Debutante diaphragm     Debutante • Everything not listed above

This information is also listed in Fountain Pen Sac Size Guide for Repairers.

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.

If a pellet actually does escape and you find yourself in need of a replacement, do not substitute any type of metal ball! Metal can corrode, and it can also cause the next repairer to destroy the pellet pocket while trying to extract your substitute.

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

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 below: the Vac wrench (left) and the Vac block (right). Vac wrenches, which are preferred by most professional repair people, come in two sizes; Oversize Lockdown and Speedline Senior 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. You can get Vac tools of both types from, which also offers an innovative dual-size wrench.

Vac wrench and Vac block

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 a pellet pusher like the ones offered by and Wood Bin Ltd:

Pellet pusher

Special Tools

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

Vacumatic filler pusher

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

Vacumatic filler pusher

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 2" (70 mm) long and the fixed tube is 4” (102 mm) long.

Filler Type Tubing Diameters

“51” (Deb filler) Fixed tube: " (4.76 mm)
Sleeve: " (5.56 mm)
Debutante Fixed tube: " (6.35 mm)
Sleeve: " (7.14 mm)
Standard Instead of a fixed tube and a sleeve, use a " tube
with a short length of " tube sweat-soldered into
the “business” end.
Oversize Use the Standard size. Pick out as much of the dia-
phragm as will come, then depress the plunger slightly
to guide the tool.

(The “51” requires a smaller ejector 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 " (13 mm) hardwood dowel. Using a drill of the same diameter as the fixed tube, drill a 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.

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


The key to seating the new diaphragm into the barrel completely, so the blind cap will line up when you’re done, is Vacumatic lubricant. Parker’s factory assemblers and field repairers used it. The Parker Vacumatic service manual calls for it. It’s the only way to get a diaphragm to seat properly in the pen. Without Vacumatic lubricant, friction keeps the replacement diaphragm from seating deeply enough in the barrel, and you can’t screw the threaded retaining collar all the way down without cranking so hard there’s a risk of damaging things.

As you follow the instructions in this page, refer to this diagram to identify the various parts:

Pen anatomy

Disassembly, Cleaning, and Diaphragm Removal

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

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 pump. 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 pump 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 pump 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.

Unscrewing the threaded collar

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.) For a heat source, I recommend the “embossing” gun that you can get at craft shops (illustrated below). It‘s inexpensive and reliable, and you can control how much heat it delivers by holding the pen nearer to or farther away from it, as necessary.

Heat gun
Despite what you might have read in various repair books (including Da Book), do not use an alcohol lamp or other open flame. Celluloid is highly flammable!
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 pump from the barrel. Sometimes, especially if the diaphragm has ossified and been shattered by a press of the plunger, the pump will just come out. But you frequently discover that the diaphragm has glued the pump in place. You can soak to loosen things, or you can wobble the pump gently (risking damage to the plunger), but these methods may not suffice. Now is the time to use your pump ejector.

To use the ejector, you need to remove the section from the pen. (On a “51” this calls for removing the shell and the collector/feed/nib assembly.) Nominally, the section on a Vacumatic is secured with a non-hardening thread sealant while the shell on a “51” is secured with shellac. In both cases, you’ll need to apply a little gentle heat. In general, you can follow the instructions for section removal in my article on sac replacement. Vacumatic sections and “51” shells are threaded: you cannot pull them free, you must unscrew them. This is your opportunity to do your pen a favor by giving it a thorough cleaning. Drop the section assembly into a bath of INDY’S IDEAL PEN FLUSH or diluted clear household ammonia (not sudsy ammonia, and most definitely not the lemon-scented variety!) for five or ten minutes. Make an ammonia solution by mixing 1 tablespoon (15 cc) of ammonia with cup (158 cc) of water. After soaking the parts, scrupulously clean off any ink residue and the cleaning solution. This means flushing water through the system, which you can do by using a rubber-bulb ear syringe to force water through the section from the sac end. (If you don’t have an ear syringe, you can use your mouth for this job.) When the assembly is clean, dry it thoroughly; blow some air through to dry the inside.

Removing the section also gives you the opportunity 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 ejector 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 pump’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 pump 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.

Pushing out the filler

One problem you’ll run into is that your ejector 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” ejector may also give you cause for concern, as its smaller tubes don’t fit against the shoulder and collar as they should. The ejector still works, but it calls for a little more care to avoid shattering the pellet pocket.

With the pump 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; the spoon-shaped dental scaler is a very effective tool for this. 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 reassemble 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 bur, grinding the pellet out. Be very careful not to cut into the pellet pocket itself. If you run the rotary tool at high speed and do not apply any more pressure than is necessary to hold the bur against the pellet, the bur will melt its way into the pellet, and the pellet will form itself around the bur shaft; this makes the pellet very easy to remove.

Diaphragm Preparation and Installation

The first step in installing the diaphragm is to cut it to length as described in this CAUTION block:

To prepare the diaphragm, you must cut it to the correct length. Parker bought its diaphragms already cut to length, and Parker’s repair manual does not acknowledge 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 pump parts without being able to displace enough air to work effectively.

Marshall and Oldfield say to cut to a maximum of 30 mm, but this is 1" and is really a little longer than ideal. They give no minimum, potentially leaving you to cut the diaphragm too short.

The correct length to cut the diaphragm is 1" to 1" (26.2 mm to 27.0 mm).

Next, you must ensure that the hole in the pellet pocket is large enough to allow installation of the diaphragm. (The reason for this is that plastic pellet pockets were made with their ends essentially cylindrical, not curved inward. The hole was much bigger than necessary to clinch the diaphragm in place. Parker installed the diaphragm by inserting the two parts into a fixture that positioned them correctly and then swaged the pocket closed around the diaphragm by applying heat and pressure. The final hole size is not the same in every pen.) Use the rounded end of the brass probe to test the hole size. If the probe slips freely into the end of the pellet pocket, you’re home free. If not, use the probe and the heat gun to enlarge the hole very slightly.

The pellet pocket is made of celluloid or a celluloid-like material that can catch fire very easily. Apply heat with extreme care!

To enlarge the pellet-pocket hole, place the rounded end of the probe into the opening. Heat the pellet pocket gently over the heat gun, spinning it so all sides are warmed evenly. Push gently on the probe; as the pellet pocket softens, it will return to its original shape, and the hole will grow larger. As soon as the probe slips in, stop!

Insert the pellet pusher into the open end of the diaphragm and position the pellet on the end of the pusher. Stretch the diaphragm backward along the tool to thin the rubber over the pellet. Lick the stretched diaphragm to provide a little lubrication, and insert the pellet into the pellet pocket. (Depending on the exact diameter of the pellet-pocket hole and the thickness of the rubber in the diaphragm, that little dab of saliva can make insertion easier.) I don’t recommend using Vacumatic lubricant here.

Installing the diaphragm

Now cover the diaphragm with a thin coat of talcum powder (or graphite). This will make it easier to turn the diaphragm inside out, and it’ll also help the pump to function smoothly.

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.

Inverting the diaphragm

Use the probe to continue inverting the diaphragm until it extends over the pump’s tapered inner collar. Holding the diaphragm in place on the tapered collar, operate the pump to make sure there are no twists or other problems and to see that the diaphragm everts so that it is just exactly fitted over the plunger. The following cutaway illustration shows more clearly how the diaphragm should fit after it’s installed.

Diaphragm installed and cut to correct length
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.

Filler Installation

You are now ready to reinstall the pump into the barrel. Lubricate the diaphragm with Vacumatic lubricant as shown here, and insert it into the barrel.

Lubricating diaphragm

Wiggle the diaphragm a little if necessary to slip its end past the tapered seat in the barrel and then insert the pump until it stops. Make sure the diaphragm is not twisted in the barrel. Use your Vac tool to screw the threaded collar down onto the tapered collar; if you have used Vacumatic lubricant, the collar should screw down until it comes to a firm stop. This is where it was when the pen was new. If you have not used Vacumatic lubricant, the diaphragm may not seat as far into the tapered seat, and in this case you should screw the collar down firmly but not overly tight; 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 tighten the collar; 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.

Parker’s Vacumatic repair manual instructed the repairer to cement the threaded retaining collar in place using Vacumatic cement, which supposedly never hardened, and said further that no other adhesive should be used. Unfortunately, given a few decades, Vacumatic cement did harden into a pinkish-white chalklike substance. I find a surprising number of fillers that appear to have had it applied between the two collars, virtually transforming them into a single chunk of metal. It’s a ticklish proposition to separate the collars without damaging one or both of them.

It turns out that no adhesive at all is actually necessary, although some modern repairers recommend securing the threaded collar with shellac. I do not recommend this practice; it just makes things harder for the next person who will work on the pen, and that person could be you.

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!

  1. Diaphragms are available from several online sources.

The information in this article is as accurate as possible, but you should not take it as absolutely authoritative or complete. If you have additions or corrections to this page, please consider sharing them with us to improve the accuracy of our information.

This article is also available as a chapter in The RichardsPens Guide to Fountain Pens, Volume 2, in either of two printed versions or as an ebook for your computer or mobile device.

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