ITW magnetic valve

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ITW magnetic valve
Manufacturer ITW, Devlin
Introduced Possibly ca. 1974
Discontinued 2005
Switch type Linear, tactile
Sense method Magnetic valve
Switch mount Plate mount
Patents US4099176 (1974)
US4017850 (1976)
US4227163 (1979)

ITW magnetic valve is a provisional name which refers to a type of electromagnetic switch patented by ITW and manufactured by ITW and Devlin.

History

ITW filed a patent for their magnetic valve switch in 1974. The tooling was later sold to Devlin; these Devlin-made switches are reported to have been very popular in the newspaper editing industry, with most European and North American newspapers specifying them across their operations.[1] Devlin ended production of them in 2005, choosing to use only Cherry MX switches.

Devlin referred to these switches as "Cortron" switches. No further details are known, as all documentation was disposed of (along with the tooling) at the termination of production.

Variants

Full-height

One variant of these switches uses a helical return spring, and appears to be linear.[2] The switch has a fairly typical late 1970s design, similar to contemporary metal contact switches.

These have been sighted with both cruciform keystems.[2] and with a keycap mount that appears to be compatible with Honeywell keycaps.[3] Options include alternate action and mechanical shift lock.[3]

Patents for these switches were filed in 1974 and 1976.

Intermediate

This design has a lot more in common with the low-profile design than the earlier designs. The switches are branded "itw".[4] A patent for this switch was filed in 1979. The patent notes that the shell and slider are designed to hold either a contactless analogue sensing arrangement (magnetic valve) or a "mechanical" contact arrangement using a separator bar to hold the contacts apart.

  • Dummy switch, used as a stabiliser

  • Dummy switch opened; note the lack of magnet and ferrite core

Low-profile

The most common variant of this switch is the low-profile version with an open shell. The switch should not be be confused with the RAFI RS 76 C Hall effect switch, with which it bears more than a passing resemblance, in particular the open low-profile shell, slider, and keycap mount.

The low-profile version has no spring under the slider; consequently, a buckling rubber sleeve is placed within the keycap to act as the return spring. These switches are tactile, with around 60 cN force.[5]

The switch contains a circular recess for an LED.[6]

Comparing the switches in the Devlin KMX-144 and Decision Data keyboards, it's clear that at least two subtle variations of this switch were made, evident by examining the LED recess.

Low-height Keyboards

  • Some Aydin keyboards (low-profile, white)[7]
  • Decision Data Computer Corporation keyboard (low-profile, white)[8]
  • Devlin KMX-144 (low-profile, white)
  • Some Gilbarco Marconi gas terminal keyboards, made by Cortron (low-profile, white)[9]
  • Some Symbolics 365407 (low-profile, white)
  • Some Texas Instruments Low Profile 2230528-0001 (low-profile, grey)[10]
  • Xerox 820 II keyboard (low-profile, red)

Intermediate-height Keyboards

Full-height Keyboards

References

  1. ↑ Private correspondence with Devlin employee
  2. ↑ 2.0 2.1 2.2 Google+ — HP 02645-60023 Dated 2012-04-26. Retrieved 2015-07-28.
  3. ↑ 3.0 3.1 3.2 Deskthority — Xerox X998
  4. ↑ 4.0 4.1 Deskthority — Pr1me PST100 (ITW magnetic valve)
  5. ↑ Geekhack — Devlin KMX-144 find - thread reload.... Dated 2012-02-06. Retrieved 2015-07-28.
  6. ↑ Deskthority — Reverse Rubber Dome Switch?
  7. ↑ Google+ — Misc Aydin Keyboards Dated 2012-02-23. Retrieved 2015-07-28.
  8. ↑ Kaineko2 — Decision Data Computer Corporation keyboard (Japanese only) Retrieved 2015-07-28.
  9. ↑ Imgur of Gilbarco switches and label on ebay — [1] [2] Retrieved 2015-07-28.
  10. ↑ Imgur — TI - ITW Mag Valve Low Profile Retrieved 2022-02-02.
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