Most central vacuum inlet valves made in the last twenty years (and some even older than that) have an industry standard configuration, with mounting screws four inches apart, vertically centered on 1.5” ID inlet neck. They connect to the tubing system via a mounting plate, shown below:
The mounting plate goes behind the drywall, and is held in place by the sandwiching action of the inlet valve. In new construction, the plate is nailed or screwed to a stud. While all-plastic mounting plates are most often used today because of their lower cost and greater ease of installation, in the past metal plates were common:
Beam Industries pioneered what was to become the industry standard form factor in the 1950s, and their first inlet valves looked like this:
These metal inlet valves were of excellent quality and lasted for decades, even in commercial use. In fact, they are still made today and are an excellent choice for heavy use or floor mount applications. Around thirty years ago, a less-expensive plastic version became available, and is still made today:
An advantage of this “round-door” type inlet is its easy-to-open design which provides a built-in alignment keyway for low- and dual-voltage hoses. Downsides are its rather obtrusive appearance on the wall, and the fact that the door, which only opens to 90 degrees, can be prone to breakage. For the sake of appearance, the screws should be painted to match the color of the inlet. Though painted screws are included, they are not long enough to work with most plastered or paneled walls.
In the late 1980s, Hayden Industries developed two new inlet styles, the so-called “square door” and “full door”, both shown below:
Both styles are arguably nicer-looking than the round-door type, with the full-door doing the best job of blending into the wall. The full-door also offers the benefit of opening all the way to the wall, reducing the potential for breakage. Until recently, neither had a provision for hose alignment, meaning that low- or dual-voltage hoses could twist during use, causing the switch to stop working. This annoyance has been remedied on current versions of these inlet valves.
All of the above are good, functional choices for your central vacuum. However, here at Just Central Vacuums we use the VacuValve, manufactured by Canplas Industries:
This is an attractive full-door design which has proven to be very durable over the 20+ years it has been on the market. The hinge design enables the door to open all the way to the wall, preventing failure. The valve features hose alignment tabs (visible in the open view above), and can be mounted up or down without revealing any unsightly gaps. Mounting as shown, with the hinge at the top, is our standard practice for several reasons. First, it allows the door to rest on the hose, rather than the hose on the door. This lessens wear on both. Second, it places the low voltage contacts at the top of the inlet neck, to prevent accidental activation from a metal object such as a coin resting inside the inlet valve. I once witnessed an example where liquid ingested into the system traveled down into a basement inlet and pooled on the contacts, shorting them and causing the power unit to run with all the inlets closed. An unusual example that nonetheless could have been avoided by mounting the inlet with the contacts at the top. Lastly, in the unlikely event that the door spring fails, the door will remain closed when the system is not running. Spring failure in a round- or square-door inlet (unless mounted upside-down) will cause the door to stay open, significantly reducing the suction at other inlets.
Stay tuned for Part Two of our fascinating discussion, which will cover non-standard inlets used in the past and present!