Pump II: Exhausters

I described in a recent post how the exhausters function as a kind of “lungs” of the player mechanism, pumping out atmospheric air to keep the pressure low inside the system.

I also gave an overview of tearing down the pump for rebuilding, with a bit more detail about the reservoirs. The process for the exhausters begins essentially the same way.

The first thing you have to determine is if removing the whole exhauster bellow from the trunk is advisable or possible. Unless you want to make new boards from scratch consider this one carefully. If you think you can remove them prior to disassembly, do make sure you’ve located and removed all retaining screws which may be fastening the stationary board to the trunk.
If you try to pry off the exhauster with screws still holding it, you will cause needless damage and make a lot of extra work for yourself.

There are times when the stationary boards of the exhausters should stay in place, as removing them would ultimately cause more work than it would save.

Take measuremnts of the opening span (if you haven’t already) and also note where mounted hardware on the movable boards goes and how it is positioned. This will help you reconstruct, later – even if “later” is only next week! As an example, I recorded the following photo of the tension arm and spring:

Outer side view of one exhauster, with tension arm disconnected

What I ended up doing was putting a piece of painter’s tape on the outside (lacquered side) of the moveable board, which indexed the holes for future reference. This will save a heap of trouble later.

will need to mark both of these screw holes (including the one with screw eye still in place)

Getting the cloth off usually involves a combination of heat and/or moisture and elbow grease.
It can be a bear of a job, especially if the cloth had previously been glued with synthetic adhesive.
I found it helpful to get the cloth off as intact as possible, to aid in planning the layout of the replacement cloth.

Normally the process of removing cloth on the smaller pneumatics involves slitting the cloth along the crease and separating the halves, not worrying about damaging the hinge (as they will later be replaced).

However the exhauster hinges were generally made quite robustly, so examine them and if they appear to be in good shape, you may choose to reuse them. To check this, hold the “open” ends of each board next to each other, and gently try to move them in opposing directions, i.e. along the length of the hinge. There should be virtually no play or wobble. If the hinge is still well attached and not frayed or worn, you could reuse it.

If you do need to redo the hinge, be careful taking it apart so you can see exactly how it was installed in the first place, and copy it as faithfully as possible, using the same materials if possible (usually thick cotton/twill ticking).

Once the hinge is done you can turn your attention to the flap valves. Each exhauster generally has two flap valves, an inner and an outer. Again, check to determine the condition of what is currently in place. If the leather flap is still supple and whole, it may be fine. If, when you rub it with your fingertip or a fine brush, it starts to crumble or flake apart, it is afflicted with dry rot and should be replaced. Copy the type, size and shape of the leather in fabricating a new one.

Older flap valve leather: somewhat oxidized, but not rotten. I will reuse these.

To recover the bellows you will need a “heavy” fuzzy cloth. Mine was about .060″ thick.
The best kind to use is pure cotton backed rubber cloth, but at the time of this writing it is getting harder to source.

Cut the cloth with the right directionality {insert John Tuttle link} and then do a careful layout and measurements of how you will cut in preparation for recovering. You should cut with only a very slight overage margin, to make less work for the fitment. This is especially true if the bellows is still attached to the trunk and you must recover in situ. Make notes of where the center and corners of the bellows are, and mark them on the inside of the cloth with a soft pencil or marker.

An additional consideration here is the placement of stiffeners, which are used in many kinds of exhausters. If you were able to remove the original cloth largely intact and also remove the original stiffeners with minimal loss of material, the original cloth will help with layout and the original stiffeners may be reused.

A pair of new exhauster bellows cloths, with stiffeners already glued, ready to glue to bellows

Devise a method to clamp the exhauster open (will depend on style of bellow) at the correct span, and ready your cloth and glue (hot hide glue works best, as always). Check your setup carefully as mistakes during glueup will waste a fair amount of time and expensive cloth too. You may consider having a warm iron on standby and close at hand, as a gluing aid, if needed.

Using your marks and the stiffeners as a guide carefully but efficiently glue the cloth in place on the bellows. The glue sets up fairly quickly but you will have time to make one or two quick checks to verify that you have enough glue, where you need it, and not too much, where you don’t. An example of the latter would be a large glue bead forming inside between the front edge and the outer edge of the stiffener, which will cause the stiffener to bind and the bellows will not work as efficiently. Pay attention to the corners as the cloth can bunch a bit here, and may need a bit of finessing to sit properly.

If there were retaining tacks or staples used at the hinge end of the bellows, copy the original and be careful when tapping in the tacks to support the moveable board on the bench when you hammer that side. Otherwise you could damage the hinge, which you really don’t want to do at this point!

If the scenario was difficult and slowed down the gluing, you can use the iron (not too hot) to go around the perimeter to “reflow” the glue somewhat and really get it to soak into the cloth and wood. Don’t linger too long or you will flow out too much glue and rob the joint. When you start to see just a hint of glue coming out at the seam that is sufficient. Expert restorer Craig Brougher demonstrates his process in this video

At this juncture you’ve basically done the job, unless you had previously removed the bellows and now need to remount them to the trunk. A plus of having had to remove them for restoration is that you can check them for airtightness independently, before remounting them.

The two successful hallmarks of bellows restoration are that the bellows is sufficiently airtight in both the flap valves and the cloth around the perimeter, and also that the bellows opens and closes with minimal resistance in a straight and true fashion.

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