Apeks DIN to yolk conversion question.

[Centrals]

I use a 19mm open head wrench to unscrew the Yoke clamp, nothing special.

 

[halocline]

My LDS guy tells me that he has actually seen parts fail (wear out) on regs such as my Apeks whose first stage
had been converted back and forth from DIN to Yoke many times. He didn't quantify how many times
it would take but he claims to have seen it.

Add this to the list of humorous dive-shop-pseudo-tech-guy statements. It's really a long list....

You gotta love these guys. Think about this, the DIN or yoke retainer must handle pressure in excess of 3000 PSI. Do you really think that assembling and disassembling it with a torque of maybe 20ft lbs could possibly weaken something made to handle that kind of pressure?

Maybe if the guy uses an air wrench.....

 

[Luis H]

Think about this, the DIN or yoke retainer must handle pressure in excess of 3000 PSI. Do you really think that assembling and disassembling it with a torque of maybe 20ft lbs could possibly weaken something made to handle that kind of pressure?

This statement implies that the pressure thrust is much higher than the force generated by the applied torque. That is an incorrect assumption.

Let me give you an example.

A typical yoke/ DIN retainer size can use a 5/8" thread diameter.

The pressure area under retainer is 0.307 inches square.

The pressure force is the pressure (3000 psi) times the area.
It comes out to be 920 pounds of force.

The same (5/8” threaded retainer) when it is torqued to 20 ft lbs the axial force that it generates is equal to 1920 pounds of force.

In this case, the pressure force is not even half the force created by the torque.




If you increase the threaded diameter to say 3/4” (using the same torque):

Then the pressure thrust will increase to 1325 lbs.
The axial force (for 20 ft lb) will not be as high. It will be 1600 lbs.
This is not a typical design, the torque would normally be higher with the larger thread diameter, but as you can see the force from the torque is still higher than the pressure force.




The typical fastener torque to force equation is:
F= T/K*d

Where :
F = axial force (lbs)
T = torque (in * lbs)
d = thread nominal diameter (in)
K = constant, typically 0.2 (typical K is between 0.15 and 0.3)

This is an approximate equation that works for non- lubricated typical threads. If threads are lubricated the force can be higher for the same torque (the value of K would be lower).
Note: any units can be used, but they have to be consistent.



The typical preload on a threaded connection is normally designed to be higher than any force that it is expected to ever see in service. Properly designed, it reduces the possibility of structural failure of the connection.

Thread wear from multiple screwing and unscrewing is a different subject. Any good mechanic should be able to keep the wear to a minimum, but it is something to be considered, not totally ignored.