3/8" to 9/16" HP Port Change?

[Akimbo]

This thread got be thinking about this: http://www.scubaboard.com/forums/ac...ed-accidentally-put-lp-hose-into-hp-port.html

Do any of you remember when and how the HP port size was changed? I didn’t notice until the early 1980s. Was it an industry-wide agreement or did one company make the change and others followed?

Edit: Corrected port size from 9/16 to 7/16.

 

[Nemrod]

I saw my Advanced NAUI instructor plug a LP hose into a HP port. Let's just say it was exciting. That was about 72, maybe 74, I think. The hose looked like a water mellon before it let loose and it did all of this in about 0.3 seconds, perhaps less. It left an indelible impression upon me. N

 

[herman]

I have no clue but early to mid 80s is my guess. I am guessing it's a type but the HP size is 7/16, not 9/16.

I got an old reg off ebay and as my normal procedure, I put it on a tank to assess it's condition....it's condition was some yoyo put a tilt valve second stage into the HP port...sounded like a big bore handgun going off in my shop. My ears rang for several days, luckily I was not otherwise hurt. My new procedure requires checking the HP port first before charging a reg.

 

[kwinter]

Been there, done that. I still have plenty of old Scubapro and Dacor first stages around with 3/8 HP ports. My guess is that the change happened in the early 80s. My bigger question has always been why the ports are 3/8, 7/16, 1/2 and 9/16 when almost all of them are manufactured in metric countries.

 

[Chugwhump]

Great post and follow on comments by old guys.

Chug
young at heart.

 

[Luis H]

Been there, done that. I still have plenty of old Scubapro and Dacor first stages around with 3/8 HP ports. My guess is that the change happened in the early 80s. My bigger question has always been why the ports are 3/8, 7/16, 1/2 and 9/16 when almost all of them are manufactured in metric countries.

Poseidon used to use metric threaded ports and there might have been other Europeans, but they never became standards.

Once the 3/8” became popular with US manufacturers, it just spread.

I don’t know if the 7/16” was a coordinated effort from several manufacturers (or involving DEMA) or if it was adopted by some manufacturers and others followed, but in either case it made sense to stay with the same standard.



BTW, the ports standard is more than just the threads. The ports loosely follow the MS16142 (Mil standard) and SAE J514 (Society of Automotive Engineer standards). Those are O-ring seal pneumatic/ hydraulic ports standards that specify all the interface dimensions, including O-rings groove and threads dimensions.

I say it loosely follows that standard because most manufactures design their own O-ring groove/ cavity slightly different than the standard, but they are compatible.

The US has often been a leader in the creation of standards and standardized interface drawings, so it makes sense to follow a well establish interface standards.
In the SAE J514 the 3/8” port is designated as a SAE-3 (with a 3/8”-24 threads) and the 7/16” port has a SAE-4 designation (with a 7/16”-20 threads).




---------- Post added January 3rd, 2015 at 08:58 AM ----------


I posted this last night in a related thread:

In the 60's and 70's both the HP and LP ports in US built regulators were commonly 3/8" threads. The LP ports kept the 3/8" thread size (for a little while some went to 1/2" thread, but I think that was short lived), but they changed the HP ports. I don't know the details of the HP port switch. It would be interesting to look at the catalogs from the 80's to see if any manufacturer mentions the switch.

I have plenty of vintage first stages and HP hoses with 3/8" threads.

In the old days we were very aware of it and were always very careful about it. As far as I remember the HP ports were always marked, but I still looked inside the port to double check. If you look carefully, it is normally easy to see the difference from the inside of an HP port and an LP port.

I still have the habit of looking inside the port (any size port). HP ports normally have a very small hole inside, while LP ports are designed for high flow with a noticeably large orifice. I am not suggesting to use this as an absolute rule, but it is one more piece of information to try to avoid a similar incident.

After more than 40 years servicing regulators, I still have a lot of respect for compressed air... maybe more... than I did in the 70's

 

[Akimbo]

Yeah 7/16, not 9/16... sorry for the typo.

I glanced through a few catalogs and the earliest 3/8-7/16" adapter I noticed was in 1980 Scubapro. I didn't see any mention of the thread change on the regulators but may have missed it. That is far from conclusive but is a good starting point for looking at catalogs.

---------- Post added January 3rd, 2015 at 09:41 AM ----------

…BTW, the ports standard is more than just the threads. The ports loosely follow the MS16142 (Mil standard) and SAE J514 (Society of Automotive Engineer standards). Those are O-ring seal pneumatic/ hydraulic ports standards that specify all the interface dimensions, including O-rings groove and threads dimensions…

We made a lot of custom manifolds and valve blocks with straight thread ports when I was designing saturation diving systems. Machine shops would buy a special cutter that bored out a pre-drilled hole to the tap drill size, cut the O-ring seat, and cut the spot-face for the hex landing in one pass. It’s not ideal, but I have used these small cutters with a large drill press on soft materials like brass and aluminum.

Carbide Tipped Straight Shank SAE Port Contour Cutters for Roll Threads On Form Relief Tool Co.

As Luis mentioned, straight thread ports are very common in hydraulics. The majority of components like valves, pumps, and motors come with them.

Cool Trick
You can take the compression fitting like Swagelok for ¼" tubing, discard the nut and ferrules, slip a standard LP O-ring past the threads up to the hex, and screw it right into a standard LP port on a Scuba regulator. The other end of the fitting can be a tubing or pipe thread for most any size. That is useful to adapt a Scuba first stage for another purpose in a shop or a bench fixture.

…I say it loosely follows that standard because most manufactures design their own O-ring groove/ cavity slightly different than the standard, but they are compatible…

That is probably because the standard hex landing is a bit large.

…The LP ports kept the 3/8" thread size (for a little while some went to 1/2" thread, but I think that was short lived), but they changed the HP ports……

That “might” have been because the Navy and US Divers discovered that the standard LP hose on the Band Mask was a flow restriction for deep sat operations. USD purchased the Band Mask from Kirby Morgan in the early 1970s. They solved the problem by replacing the 3 to 4" long LP hose from the free-flow and bailout manifold to the second stage with thin-wall rigid tubing. The USN Experimental Diving Unit had one of the very few breathing machines of their own design in those days so it wasn’t as easy for companies to do their own R&D like today. Every regulator manufacturer has at least one Ansti breathing machine now — not as large as the old one at EDU or the one at Dive Lab, but big enough for Scuba regulators.

The first regulator I noticed the 7/16" HP and 1/2" LP port on was the original Oceanic Omega (not the first, just the first I noticed). Bob Hollis told me that the larger LP hose and single 1/2" LP port on the end of the first stage turret was to provide the flow that the second stage was capable of. The rest of the LP ports around the turret were 3/8". Bob chose the end port because it was in-line with the flow-through piston.

It may well be that they discovered that the restriction on a 3-4" hose like on the old Band Masks was negated by the longer, thus higher volume, hose. It may also be that the restriction doesn’t matter unless you are below 600' on HeO2.

---------- Post added January 3rd, 2015 at 10:05 AM ----------

… My bigger question has always been why the ports are 3/8, 7/16, 1/2 and 9/16 when almost all of them are manufactured in metric countries.

I wondered that myself. I know the Calypso was introduced in Europe in 1957 but didn’t use the same hose connections. I asked in an old thread where the current “standard” hose connections at both ends came from but never got an answer.

 

[Mike Lev]

They made adapters that go from one size to the other. They are hard to come by. I have some.

 

[Akimbo]

They made adapters that go from one size to the other. They are hard to come by. I have some.

Dive Gear Express has most any adapter you can think of.
https://www.divegearexpress.com/regulators/adapters/hose.shtml

 

[ams511]

My guess is that the change happened in the early 80s. My bigger question has always been why the ports are 3/8, 7/16, 1/2 and 9/16 when almost all of them are manufactured in metric countries.

Could the hose manufacturer have driven the port size decision?