Low on Excuses

The essence of vacuum bagging being, well, vacuum, and nearing the point in my own project at which the ability to apply atmospheric pressure in a coordinated fashion might well be a limiting factor, I dragged the Welch Duo Seal out of long retirement to see whether it might be coaxed into suction once again. I procured this pump through the largesse of Big George, who somehow had managed to come into two fifty dollar Duo Seals, but only needed one. So for $50 in 1999 US dollars (roughly equivalent to $400 of today's dollars, at least when it comes to purchasing anything from Australia) I became the proud owner of a somewhat dilapidated Welch Duo Seal 1400. Or I think that is the model anyway - can't really tell because IT DOESN'T HAVE A MODEL NUMBER. THAT'S HOW OLD IT IS. The serial number is 434; I saw one on eBay the other day with a serial number of 107,000 that was made in 1982! Anyway we are dealing with some seriously old machinery here - probably from the 1940s.

After procuring the pump from George in 1999, it sat in one storage facility or another, completely unused, until last week. I had plugged it in and watched it whirr, but had never tested it with a gauge to see exactly how badly - ahem - it sucked. George had replaced some seals on the thing when he bought it, and told me he could never get it to go much beyond 27"Hg, which is pretty poor vacuum from a pump that is theoretically capable of millitorr performance. So my expectations were pretty low.

All the oil had drained out, so after getting some mailed in from Grainger, and a trip to Culver City Industrial Hardware for some plumbing fittings and a vacuum gauge, we hit a balmy 17" of mercury. This was over ten inches Hg shy of where I had hoped I might be, and ten inches of mercury is a lot of mercury - 254mm worth, or a third of an atmosphere. Either aliens had sucked away a third of Earth's atmosphere, or my pump was in tough shape.

Being a pessimist and knowing the pump had not performed perfectly even before I bought it, I decided an inspection was in order. Mind you I had never performed any maintenance on a vacuum pump of any kind prior to this endeavor, but fools rush in as they say. Fortunately, vacuum in 1940 was a fairly straightforward affair, and three wrenches are all one needs to fully disassemble the thing - well, plus or minus.



There is a lot more to the pump than this photo indicates - namely another rotor/stator setup like this one further down the shaft, a bunch of seals, etc. But this is the heart of the matter - a rotor mounted eccentrically within a stator of larger radius, with spring loaded vanes sweeping varying radii as the rotor turns, effectively increasing the volume allocated to a particular number of air molecules 850 times per minute, with the intake rotor exhausting to the exhaust rotor, resulting in some serious vacuum if everything is functioning properly.

Unfortunately, visual inspection failed to demonstrate the source of my evils. So I phoned the repair desk at Capitol City Vacuum outside Washington, DC and basically pled ignorance in hopes that someone would take pity on me and tell me how to make my pump work. Fortunately Frank on the technical desk, aka Jedi Knight of Duo Seals, told me what to buy and what to do.

Basically he told me to get the basic repair kit (because my vanes are metal they don't wear out like the newer ones do) and a can of Vac Seal and put the pump back together. But the critical bit of information is that the stators are ADJUSTABLE. If they are too far from the rotors, the pump will not pump down. We are talking about 0.001" of clearance here, or less.

While I was in there I replaced the shaft ($40) so the seals would work and the pump would stop leaking oil everywhere, and then reassembled the thing. Unfortunately, an earlier "repairman" had overtightened one of the 5/16" bolts holding the intake side of the pump together, so it was not possible to get it tight. A trip to Auto Zone was required to procure the requisite Heli Coil, which worked like a proverbial charm - or at least allowed me to put the pump back together again.



What it did not do was get me enough vacuum. 25" was the fruit of all my labor. I assumed I would have to completely disassemble the pump yet again and readjust the stators, the thought of which made me look around for other projects, like finishing the wiring on the air compressor...

So I did that, fixing the pressure switch in the process, replacing the main tank valve, putting waterproof steel/plastic flexible conduit over the motor wires, and rewiring the mag start. Then I turned my attention back to the vacuum side of things.

In my zeal for applying Vac Seal, I had put perhaps a bit too much on the intake reservoir flanges, and decided to double check the gasket. Sure enough, it had moved out of position. Could this be the source of my troubles? Tracing the original gasket on some new gasket material and cutting on the lines gave me gasket number three, and without Vac Seal this time I reassembled the pump and plugged it in. The result? 30 inches! The atmosphere has returned, and we can breathe again!


I really don't know if I would recommend this course of action to anyone, but for $75 in parts I saved myself the cost of a different pump, or about $300 on eBay last time I checked. This fix was much less trouble than it might have been, and if it had been any more trouble I might have been better off sending the pump in to be overhauled by a professional.

What does this have to do with Moths, you might ask? I find myself asking the same question, and I have come up with the following answer:

Historically, mothing has been a class of do-it-yourselfers, experimenters, and development-minded individuals. Foiling seems to have brought an entire cadre of world-class sailors in, who have little interest in building boats or rebuilding vacuum pumps when they could be out there improving their boathandling. These guys will be super fast, as long as their boats remain competitive. And that is the point: when a new idea comes along, and proves faster than a current production boat, what will all these rock stars do? Will they get new Moths, or will they get grumpy and fork off into one design? Only time will tell whether the shifting sands of development sailing are too unsettling for their one-design taste.

For my part I will say that blogging is yet another time sink that the best builders and sailors seem to have little inclination toward. Sailing, building and blogging each compete with each other for time, to the extent that no one can really do all three at a high level simultaneously without becoming professional. Even then, people like Amac seem to have their hands full with the design, build and sail program, ignoring blogging completely. Rohan sails full time and manages to blog from events in real time, but he doesn't design or build his boats. So these activities are to a certain extent mutually exclusive. This seems like an argument to forget about the internet, and focus on building and sailing. But without blogs, the class loses cohesion, and we lose the ability to live vicariously through each others' experiences, which is a good deal of the fun.

At some point, each of us has to throw down and declare our loyalties. Personally, I like figuring out how things work, and how to build things myself. I also like the design process, and I like interacting with people who think about design. So it should be no surprise to find me smelling of acetone, covered in vacuum oil, swearing over the radio at myself for having forgotten yet again to install the shaft keys before bolting the stators on for the fifth time.

I have followed the Moth class for years because it seemed to be filled with other people who could have a good laugh at themselves and their tiny boats while moving design further down the track - people for whom a good stack is almost as much fun as winning a race, and who like to build boats almost as much as sailing them. I eventually bought a Moth and started sailing in the class for much the same reason, although the advent of foiling hastened that involvement. To the extent that recent trends seem to be moving the composition of the class more toward professional sailors, and away from designers and builders, the fleet becomes less attractive to people like me. But that is no fault of the class, and it certainly moves the sailing itself up several levels, which is great. In any event, the Moth continues to be a development boat, and develop it will - probably faster than many expect. Interesting times ahead!