When did most regulator sets become fail-open?

[CharlieDontDive]

As I understand it, nearly all commercially available regulators in the modern day will fail open (that is, a freeflow) rather than failing closed (no air at all). As I recall, there are only a couple of regulators on the market which fail closed and both are for tech diving use.

I was curious to know at what point the average non-technical, recreational diver had access to fail-open models (thinking of the 1950's through the 1980's). Was this always the case? Or was there a time when your Average Joe diver used a fail-closed reg. If so, when did fail-open become the near-universal standard?

 

[lowwall]

The fail-closed seconds were tilt-type upstream valves. They had pretty much disappeared on new designs by the middle of the '60s, although a few existing models soldiered on for another decade.

There's an excellent thread on this at https://vintagescuba.proboards.com/thread/4282/healthways-single-hose-regulators?page=1. I borrowed the following picture from the second post on the thread.

 

[Bigbella]

As I understand it, nearly all commercially available regulators in the modern day will fail open (that is, a freeflow) rather than failing closed (no air at all). As I recall, there are only a couple of regulators on the market which fail closed and both are for tech diving use.

The bulk of Poseidon regulators are upstream-servo in design; but incorporate, out of that necessity, an OPV, formerly, on a specially-designed hose; or, in the case of newer models, one on the first stage. In the event of a first stage failure, “normal” breathing from the second stage is still possible, thanks to that venting of the OPV and the design of the LP valve housing and its rubber insert (one of which I had once seen, after an over-pressure event, partially extruded through the valve housing vents, like strands of vermicelli). The models also far less likely to free-flow.

There are no modern “failed-closed” upstream designs, intended for diving; that is an all-too persistent myth; nor, in their use, would there ever be a sudden, massive free-flow to the mouth and face, like many downstream designs, in the unlikely event of a failure . . .

 

[Akimbo]

The tilt valve design was very common in World War II military aircraft for high altitude Oxygen systems (before I was born). Some of the early Scuba pioneers in the US tried adapting them for underwater because they were available in military surplus stores pretty cheap. Many (most, all???) were made by Scott Aviation. I still saw some in surplus stores in the early 1960s.

Scott still sells them attached to an oral-nasal mask for BIBS (Built-In Breathing System) regulators to deliver Oxygen in chambers used in commercial diving and HBOT (HyperBaric Oxygen Treatment). This image includes demand supply (inhalation) and exhaust (exhalation) tilt-valve regulators.

The primary disadvantage of tilt-valve upstream demand regulators is first stage failure — IP pressure creeping high enough to pressure-seat the tilt valve with more force than the diaphragm can overcome. This is MUCH less of an issue with BIBS because people can breathe the chamber atmosphere in all but the most unusual contaminated gas emergencies. First stage regulator used in BIBS are also much more robust and are hand-loaded so that risk is far less than with small individual Scuba regulators.

Scott also made an early FFM for the Scuba market in the 1950s. I never saw one taken apart so I can't say if it was a tilt-valve or not... but it likely was. @Sam Miller III might have direct personal knowledge.

Tilt-valve demand regulators are very simple and inexpensive to manufacture. The parts in the Sportsways (defunct 1950-60s manufacturer) tilt-valve regulators looked suspiciously similar to Scott's, to me. anyway. Sam also knew many of the people at Sportsways.

 

[Yawana-Dive]

I’ve got a 60s Sportsways tilt valve 2nd in mint condition I picked up on EBay. It’s hooked up to a Healthways 1st with the over pressure release valve. I often dive it just for fun.
You can’t adjust the cranking pressure of the tilt valve but it’s a beautiful breather anyway.

 

[Akimbo]

I’ve got a 60s Sportsways tilt valve 2nd in mint condition I picked up on EBay. It’s hooked up to a Healthways 1st with the over pressure release valve.

Nice find. An equally problematic issue that you brought up is a first stage failure can burst the hose without a relief valve or OPV (Over Pressure Valve), which are the same thing. A relief valve between the tilt-valve and hose that vents into the 2nd stage housing would make it a pretty acceptable design and still be low cost. Basically the same thing as a free-flowing modern regulator.