Swivel nut question

[guruboy]

Just picked up <u>Regulator Saavy</u> and enjoying the read.

Have a question about p32. There is a diagram of an air balanced flow-through piston first stage with a LP swivel.

Looks like the swivel is kept on by a swivel nut which sandwiches the spring retainer between the swivel and the swivel nut.

I assume the swivel nut rotates with the swivel.

What keeps the swivel from unscrewing from the swivel nut? Just the washer? Any thread lock on there?

Sorry if this is a remedial question. I'm a EE, not a ME.

 

[OkByMe]

The nut/bolt is torqued in place. The torque value is specific to the diameter of the nut/bolt, thread pitch and material. Each specific regulator using that config has detailed instructions on whether to use thread lock or a lubricant and the torque value. Some regulators use a shoulder bolt and others may use a bottoming bolt and others may have threaded boss that accepts a nut and others a boss which accepts a thrust washer and snap ring.

 

[Zung]

+1
In case of Scubapro, the washer is Teflon, and the torque spec is barely above finger tight: 4N.m/35lb.in for a brass bolt and double that for stainless steel, no thread lock. It appears a bit scary at first, but I've yet to see a single mishap out of my dozen or so regs over 20+ years. You do need a small torque wrench to do it properly though.

Edit
Luis H, who's the resident guru/ME, posted an analysis here, but it's about the tensile strength of the bolt itself: its head snaps off easily if over-torqued, especially the brass one.

 

[Couv]

If you have a MK 5 and you're concerned about having a brass swivel retainer, you can purchase a stainless steel retainer from VDH Shop Online

 

[halocline]

Looks like the swivel is kept on by a swivel nut which sandwiches the spring retainer between the swivel and the swivel nut.

If you're describing a MK5 or MK10, the swivel retainer is a hollow bolt that fits into a threaded fitting in the swivel. Underneath the head of the bolt there's a plastic spacer/washer. I don't understand what you mean by "spring retainer" in this context. Am I missing something?

The bolt is kept in place by tightening to a specific torque as indicated. I have never heard of a case in which the bolt comes loose and falls out on it's own; rather it's not unheard of for this bolt to sheer off from being severely over torqued. That's why SP went to the steel bolts and discontinued the brass ones.

The early MK5s didn't use a bolt, the swivel had a flanged fitting and there was a washer and circlip that held the swivel in place. So there's evidently not much force pulling the swivel off the main body while pressurized.

 

[Candiru]

Can a swivel bolt on a mk10 be either brass or stainless steel? Any idea how to tell the difference, (weight, magnet, scratch the chrome off?)

 

[rsingler]

Yes, they are still chrome-plated brass for the Mk10. Don't know if/when a switch was made to SS. But a careful inspection under loupes or a microscope will tell you most of what you need to know in a used purchase. Some deformation of the threads will be evident in bolts that have been over-torqued. If they haven't, there's absolutely nothing wrong with the brass in either the Mk5 or Mk10. By the time the Mk10 was introduced, the issue of turret bolt separation had become well-enough known that techs (for the most part), were more careful at reassembly. More important, the dimensions of the Mk5 and Mk10 turret bolt are different, with the Mk10 having a much more substantial shoulder to the load-bearing turret portion than the Mk5. If you look, or ask your tech to look at the threads, you can reassure yourself as to prior mistreatment of the bolt. Of course, you can't see the stress that might have been imposed, but since the load in threaded elements like this is commonly resting on less than 3 threads, some deformation can usually be seen. For the Mk10, the issue is not the turret, but over-torquing of the yoke assembly on some reg bodies. But even here, we're talking less than a dozen cases (from what I hear) among literally thousands and thousands of regulators.

To answer your question: yes, take the upper edge of the turret (with no load-bearing responsibility), and rub the corner against some 3000 grit Micro-mesh. You'll see the brass underneath. There's a look to chromed metal that you may recognize that may make this unnecessary. SS parts have a finer machining pattern because the metal is harder.

 

[Candiru]

So my follow up question is whether the mk5 aftermarket SS bolt will fit in a mk10?

 

[Zung]

No, it won't.

 

[halocline]

I've never seen a brass/chrome swivel retainer for a MK10, they're all stainless on the ones I've had apart. I think they switched to stainless during the late model MK5, I don't know why they would go back to brass for the MK10. Maybe there was some overlap where they started producing MK10s, but still were making MK5s, and if so, maybe that happened before the switch to ss. That could mean some very early MK10s had brass retainers, but as I mentioned I've never seen one. I do have an early MK10 that I've never had apart.