damaged my mk10?

[Candiru]

I was messing around with my mk10 g250's setup today. Measuring my ip I was locking at 135 with a drop of 10 with a breath. For some reason I wanted to see what the the ip would do if I pushed the purge on both regulators at the same time. It caused the ip to rapidly pulse around 100 to 120. The crazy thing is that after I turned the tank off and on again the ip reads 110. I'm pretty sure that my ip gauge is ok as my mk2 still reads 140. Any thoughts as to what might has gotten destroyed. I assume that its rebuild time now?

Also the 017 oring at the piston should be duro 70 or 90?

Thanks!

 

[halocline]

You probably did not destroy anything. I'm not sure what you mean by "pulse" but I've found when measuring IP drop on a cheap gauge on the LP inflator hose there are seemingly lots of variables. Like, for example, my MK15, a very high flow reg, seemingly drops more than my MK2, with the same gauge, same 2nd stage. It makes no sense because there absolutely is an inverse relationship between pressure drop and flow rate. My best guess is that there is a corresponding venturi effect somewhere in the turret that causes increased pressure drop in the LP inflator hose as air flows out a different port to the 2nd stage. So I would not worry if your MK10 IP seems to jump around during extreme flow; it's probably due to turbulence in the turret and inaccuracy in the needle response of the gauge.

Now, why your IP is reading so much lower, who knows, but you might have knocked some crud off the HP piston o-ring and reduced friction. I doubt it, I'd bet it will come back up if you reconnect the MK10, purge a few more times, and let it sit for a while. If it doesn't come back to where it was, the main spring would be suspect.

The piston head o-ring should be duro 70; it only experiences IP/ambient pressure gradient.

 

[Candiru]

I purged and reconnected and now it locks up at 120 no creep. I think I'll rebuild (aftermarket from vintage double hose) and add 1 of the SS shims I got from mcmaster carr. If its already maxed out on shims I'll start looking for a new spring

 

[Couv]

Edit: Apparently we were typing over each other. But if you don't know how many shims are in place already, you probably aren't the last person to rebuild this reg. As a good DIYer....you should do that as a matter of course.
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Except for the fact your MK2 IP remained the same, I would suspect the IP gage. If you have access to another one, try that first. When was the last time your MK 10 was rebuilt? Usually, ip tends to go up over time due to the hp seat being engraved deeper. Also, as the lubricant on the piston stem o-ring erodes away slowing the piston down.

If there is really an issue with the first stage and not the gauge, I would be concerned with a 25 psi IP drop. The spring could be broken, the hp seat may have come loose and then jammed short in the retainerl-but that would mean something else is not correct such as the hp seat spacer (orange washer or -013 o-ring)

My vote is to open it up. What if you get a stable ip at 110, tune your second stages to the new ip, then it suddenly jumps back up to 135? Good God Man! Your life support equipment is nothing to trifle with.

Pardon the hyperbole but I'd be interested in your findings...pictures would be cool too.

 

[halocline]

I'm pretty confident that his MK10 did not actually drop 25 PSI under full purge, even with 2 second stages. (Assuming he has a good supply pressure and flow) As I mentioned, I believe there's a venturi effect that causes extra drop in the LP inflator hose as air rushes into the other ports to the 2nd stages. I also would be skeptical that the needle swing on a $25 gauge can be trusted to actually reflect immediate pressure swings; once its steady I'm sure it's reasonably accurate.

And, if by some chance his IP did raise 20-25 PSI during a dive, I bet the G250 2nd stages could handle it fine. Most of the IP increase would just get routed to the balance chamber.

 

[redacted]

I am not one to do unnecessary rebuilds. That is, I don't replace an HP seat until I am pretty sure that is the problem. Also, I tend to set IP fairly low and see nothing automatically wrong with an IP of 120 especially with an HP 2nd stage. Plus, with more use, there is only one direction that IP will head

I suggest you let it sit under pressure for an hour or so with an occasional purge and watch what the IP does. Include a couple more cycles of tank pressure off and on. The fact that it locks up nice and stable suggests the seat is OK. But, you still might want to pull the seat retainer and verify that all looks good and no sign of anything (crud) that should not be there.

On problem that could explain the behavior you saw was some contaminant in the ambient chamber that was missed during cleaning and assembly and is now being dislodged and pushed away. At this point, it is unlikely to even be visually detectable.

It is my understanding that when springs get old (wear out) the associated changes in the metal properties will make IP rise rather than lower.

Also, an easy way to change the IP on a Mk20 about 5psi is to make an adjustment by adding or removing a washer between the body and the seat retainer. For a while, Mk20s had a problem with leaking through the seat retainer and removing that washer changed the HP seat o-ring seating just a bit and often cured the leak. I have tried adding a washer (IP adjusting washer) to a Mk5/7/10 in a similar manner to raise IP about 5psi with pretty good success. One problem is the added washer may compromise the o-ring seal between the retainer and the body resulting in a leak. I suspect that is caused by the washer not being perfectly centered as loosening and re-tightening stopped it. Once it does made a good seal, I have not had the leak reappear.

 

[Couv]

I'm not sure we are all reading the OP the same. If I understand his complaint correctly, IP initially locked up at 135. Then after some hard purges the IP locked up at 110 ...a 25psi difference. Now, it locks at 120.

Additionally, I think Candriru just bought this reg and it's last rebuild date and place of service is unknown.

 

[Candiru]

I am the original owner early 90's mk spec bootable with a pair of g250's non-hp. I am getting a big order from scubatools this week including another ip guage to check against the dive rite bc ip. I guess my gut feeling is the bourdon tube in the ip gauge is wonky.
I have some oem mk10 kits coming and a couple of the VDH aftermarket kits as well. I will post autopsy pics as I proceed. Last annual was feb by scuba toys.com

 

[Texfrazer]

Excellent! We all love pretty pictures of regs that have strange and unknown issues. Thanks for sharing!

 

[Candiru]

Still waiting for tools, I will post pics ASAP.