MK10 IP Creep

[halocline]

Mine was definitely due to something specific wrong and not general wear and tear; the reg had exactly one 30 minute dive on it. I bet I just missed a tiny piece of crud when I was cleaning it during the rebuild and that got caught in the seat. Unlike my mentor AWAP, I don't have a fancy ultrasonic cleaner and am forced to use maggots and leaches to clean my regs.

I'd still like to figure out why the IP drop during inhalation is considerably greater with the MK10 than the MK5. I'm sure it makes no difference in performance, but I'm a curious dude. From my way of thinking about it, with a given supply pressure and a given 2nd stage flow capacity and purge flow, there should be an inverse relationship between flow rate and IP drop, at least theoretically, right?

 

[superstar]

I had nothing to do for for a few hours so I did IP checks on my regs.
very old mk5 132# 3 sec creap to 135#
newer mk 5 130# 1 sec creap to 132#
older mk 10 137# steady
mk 15 140# steady
Mk 2 135# 1 min creap to 140#

 

[superstar]

The mk 2 drops 10# when purging the 2nd stage all others drop 20#
I had 800# in the cylinder when I checked them.

 

[Couv]

Mine was definitely due to something specific wrong and not general wear and tear; the reg had exactly one 30 minute dive on it. I bet I just missed a tiny piece of crud when I was cleaning it during the rebuild and that got caught in the seat. Unlike my mentor AWAP, I don't have a fancy ultrasonic cleaner and am forced to use maggots and leaches to clean my regs.

I'd still like to figure out why the IP drop during inhalation is considerably greater with the MK10 than the MK5. I'm sure it makes no difference in performance, but I'm a curious dude. From my way of thinking about it, with a given supply pressure and a given 2nd stage flow capacity and purge flow, there should be an inverse relationship between flow rate and IP drop, at least theoretically, right?

Different Strokes

OK, let's try another stab at your question. If the flow rate for a MK 10 and MK 5 are approximately equal, then my first guess would be wrong. But as others have pointed out, the piston length of the MK 5 is longer than the MK10. That being the case, the 5 may have a longer stroke. A longer stroke and larger diameter would mean more volume at the same pressure.

Now go change that piston stem o-ring…..and never you mind if I have any dangling participles.

c

 

[DA Aquamaster]

I don't think the stroke is any longer given that the area where the piston head o-ring bears in the swivel cap is about the same depth. I am not real sure why the Mk 5 piston stem was longer but it was probably driven by something like the lenght of an off the shelf spring that was suitable for the design.

 

[halocline]

The mk 2 drops 10# when purging the 2nd stage all others drop 20#
I had 800# in the cylinder when I checked them.

This might have something to do with the 2nd stages. If your MK2 has a downstream unbalanced 2nd like the R190, and the others have higher flow 2nds, you could be flowing more air with the purge on the BP 1sts. This is why, when I was comparing my 1st stages, I used the same B/A 2nd for all the tests. I'm assuming the 2nd stage purge flow rate is the limiting factor; i.e. all the 1st stages could flow more air than the 2nd. If that's right, and the flow on purge is consistent, then IP drop should inversely mirror actual flow through the reg, because if you have the same limitation at output, higher pressure will equal more flow. One thing that has occurred to me is the possibility of a venturi effect at the LP ports. Since the IP gauge is on a LP inflator hose, I suppose it's at least theoretically possible that fast moving air through the turret into the 2nd stage port might create a pressure loss in the surrounding area, which could lower pressure in the LP inflator hose. Or is that a stretch?

Couv, the piston stem o-ring is fine, I just changed it. BTW, you missed a nice looking 5 LP port MK5 for $30 recently. hehe

 

[Couv]

From DA:

"I don't think the stroke is any longer given that the area where the piston head o-ring bears in the swivel cap is about the same depth. I am not real sure why the Mk 5 piston stem was longer but it was probably driven by something like the lenght of an off the shelf spring that was suitable for the design."

OK, but the bore is larger which means more volume at the same pressure.


Why are a giraffe's legs so long? ....so they will reach the ground.


Matt, you may be on to something. If you are using different turret arrangements on the MK5 than the MK 10 that could be part of the explanation. One engineering aspect of designing engines, carburetors etc. is volumetric efficiency; porting plays an important role in that regard. I'm not an engineer, where are Luis and Pesky when you need them?

Incidentally, I just finished getting rid of my MK 5s...next, the MK 2 and the honker....I'm on a mission to standardize my gear.

Thanks for checking that o-ring, I was beginning to lose sleep.

c

 

[redacted]

Couv - I prefer my Mk5's over my Mk10's but I'm sure hard parts for the 10 are easier to come by than for the 5. My Mk10's seem to give me more IP stability problems than any of my other older regs. But I don't think I can beat my Mk2 for carefree reliable, if mediocre, performance. And I really think my Mk7 is my favorite as I tend to be a bit leg heavy in warm water dives with an S80. Plus I enjoy diving with a regulator that is older than most of the "professional" divers I run into.

 

[DA Aquamaster]

Larger volume in the IP pressure areas gives you a bit more of a reserve to draw off air to the second stage, so more internal volume should soften the hit on the IP drop.

Also the diameter of the hole in LP port swivel retainer is a possible candidate for flow rate differences. I have some Mk 5 retainers in the parts bin so I will compare one with a Mk 10 next time I have one open.

I think another difference in the pistons is the degree to which the flow passage opens up near the head. Things seem to have gotten wider and deeper from Mk 5 through the Mk 20/25.

 

[coldstroke]

If you have the schematic Items # 22 and 36 (I think that is the numbers) is where I would look first. The piston #22 has two things that can happen. First salt build up on the shaft will nick the o-ring # 36, second a nick, scratch, or corrosion on the end will create a short HP seat life.

That is generally a solid unit. It may be time for a new piston and spring to extend the life.

Are you looking for a schematic?

I would like to get a copy of the schematics; I could use it.