Making a case for the much maligned metal manifolds of the neon world.
The Townsend manifold and others like it are often looked down upon, but were they really that terrible? This, like many things, depends on your needs and the context by which you judge it.
Today we often use a borosilicate manifold that is put together using o-rings and compression fittings…the stopcocks are of a teflon and o-ring design and the main body is of a large diameter for maximum vacuum conductance. These are, in most of today’s neon shop environments, considered state of the art, and as good as can be had. And compared to the manifold types most of us started out with, this is certainly the case.
Many of the first manifolds we had from the 1920s onward were handmade, by ourselves, from glass tubing and used ground glass stopcocks. It was a right of passage for a bender to create their own manifold to process their tubing units. More often than not, the tubing used in these was the same tubing that got used in making the signs themselves–15 or 18mm for the main body, with 8 to 10mm tubing used for things like the U-gauge manometer and connections to gas flasks, blow hose/vent, etc. While this was a great expression of a bender’s glassworking skill and in many places marked the transition from apprentice to bender, many of them were not as well designed as they could have been. It was not at all uncommon to see glass manifolds that sprawled across a lot of workbench real estate. The long runs combined with small diameter tubing would conspire to create slower pump down speeds. Some of those manifolds had upwards of 8 feet of tubing in them…this is like pumping down an additional unit besides the one or two you are processing! In addition, the maintenance of taking one apart for cleaning was a true pain in the backside. As a result, more than a few shops would run and work with a less than ideally clean system and then depend upon aging or other tricks to deal with the effects of those impurities. Today’s easily disassembled large diameter types in a comparatively small footprint readily address both issues and this is why they are the favored type today.
While most still used the traditional hand made type, shortly before the o-ringed style began to become readily available, some metal manifolds were produced and sold. Most notable of these sold in the US was the Townsend.
These manifolds were made of copper and brass and while of a diameter comparable to most homemade glass units, they had a smaller footprint with shorter runs, often about a foot or so… so at least they had an advantage in that regard. In addition, they were quite rugged….a consideration not of significance to most, but if it was desired to have a portable setup for classroom use, this would not have been a bad way to go. The design was such that they used compression fittings that could be dismantled for cleaning and also were also among the first to popularize the option of having gases in pressurized metal tanks rather than the glass flasks commonly used. This meant that many more units could be filled before changing out a gas supply was needed, an advantage to the high volume production shop.
There are, however, a few problems inherent to any metal manifold used in neon work and a couple of problems specific to the Townsend:
First and foremost–flashback. This can occur with any system when conditions are such that the path of least resistance is not through the unit being processed but instead from the electrode closest to the manifold, through it and to ground by way of the vacuum pump. Obviously you never want flashback from a bombarder. Never. It is not only counter productive and can damage manifold parts (stopcocks primarily) but above all it is DANGEROUS. Even a glass manifold is not safe to touch during a flashback, but a metal one, by virtue of it being electrically conductive, is a sure fire way to be electrocuted if you have your hand on it and a flashback occurs. There are two simple ways to mitigate this hazard–ground the manifold, and never touch it while the bombarder it on. The latter is a good habit to be in regardless of the manifold type that you have. An additional way around this is with the use of an end ground bombarding transformer. (no mid-point ground as with most, instead one end of the HT winding is grounded, and the manifold grounded as well….this puts everything that the operator could contact at a zero potential with respect to ground……this is not always practical in every shop.) Of course, if you oven pump (heating the glass in an oven while evacuating and using an induction heater to convert the electrodes) and use no bombarding transformer at all, then this hazard is not applicable to you.
The other big issue with any metal manifold is leak finding. In a glass manifold, you can trace small leaks with a spark coil. But with metal, this is not an option as the conductive path grounds the arc and you never get to see it skate across the surface and enter where the pinhole is. The use of a small squirt bottle of acetone or a helium leak detector (expensive and beyond the scope of most neon shops) are pretty much the only options. While metal, usually stainless, is preferred in many industrial high vacuum applications, the leak tracing issue alone can put off many to the use of metal for a manifold in a neon shop environment. This is not to say it is a bad choice, only that other considerations must be taken into account and a metal manifold is not for everyone.
Another drawback was cleaning. These were built in such a way as to allow them to be cleaned out, but if you didn’t see dirt, you don’t clean it, right? Worse, and specific to the Townsend and the few others which also used brass and copper construction– Mercury contamination. Mercury in a manifold is always bad news. Aside of toxicity, the resultant contamination can make it difficult to process and fill good clean tubes that will live a long and happy life. The trouble with the Townsend in this area is that mercury can chemically bond with the materials used in the construction. The resultant mess can soften the metal, and the only good cleanup is with strong Nitric acid, which can erode the metal and leave additional porosity to trap further impurities later. So long as you were not doing repairs to mercury units (which tends to increase the risks of mercury entering a manifold) and were careful about debris traps to prevent most mercury from getting in there if a tube failed during processing, then the hazard of making a mess was reduced. More than a few sign shops were not always so careful, however.
But in spite of all that, during the 198os, while most of us had been using the glass manifolds we made from sign tubing, the prospect of a metal unit such as the Townsend looked pretty good. It was, however, beyond the budget for most of us….right around $2200 if I remember right! This put it out of reach to most smaller shops. I do not know how many were sold in their various forms, but they seemed to have stuck around and today they turn up more often than you’d expect-even when not still in active service; sign folks are hoarders and I am sure that many a shop would not dream of tossing something they paid 2 grand for, even if they stopped using it 30 years ago.
The Townsend, in good form, could achieve good vacuum and by virtue of its compact size (even though the body diameter wasn’t ideal) could do so quickly enough to compare favorably to many of the glass manifolds that people were using. The valves used were of high quality, borrowed from the refrigeration industry, and overall, if not abused and not contaminated with mercury, these manifolds tended to hold up well. It is easy for us now, with 40+ years of technological advances manifested in our scientifically designed borosilicate manifolds, to look down upon the Townsend and others like it, but taken in its historical context and compared to what was being done in most shops of the time, it really wasn’t so terrible.
Would I recommend a new bender go get a Townsend today? NO. Absolutely not. There are far better options available now and a newbie doesn’t need the added burden of dealing with the idiosyncrasies of a metal manifold while trying to learn everything else too. But if someone had one and wanted to make use of it, it would be possible, even if not desirable by today’s standards.
Having said that, I do have one, and it does work. I was fortunate in that it was kept clean and in good order by its previous caretaker. I use it on a portable bench in my home studio (and neon tool museum) in part because it is here and in part because it is rugged enough to present minimal difficulties when I want to move it or take the show on the road for others. In fact, during the M7.1 earthquake we had, it was under vacuum……after the violent shaking stopped, it was still under vacuum. I am pretty certain my old glass manifold would not have withstood that test. So while I do not consider the Townsend as tip-top as the new types, and I see several issues that one must understand and deal with accordingly in order to be safe and get good results, taken in its context of neon history, I do not think it deserves quite as bad a reputation as some have ascribed to it in recent years.