Which piston reg is the best to practice rebuilding on? Preferably an SP reg.

[halocline]

It also would not surprise me if the gauge itself moves a little. These are cheap gauges after all.

IP includes seating force, which in the real world has got to be somewhat dependent on the pressure gradient. This is, I believe, a contributor to the drop in IP with tank pressure on balanced piston regs, but I'd have no idea how to measure it. I bet Luis does.... I could see seating force dropping after a few minutes of contact between the piston/seat; the seat is plastic and somewhat malleable. But, that still doesn't explain where the air in the IP chamber goes. So, either the hoses expand, or a bit of air gets past a seal, or it cools significantly, or the gauge is inaccurate over time. There are no other possibilities I can think of.

 

[Couv]

It also would not surprise me if the gauge itself moves a little....

This is my guess too. The mechanism, most likely a bourdon tube, uncoils and then recoils a little.

Have a look at the guts of an spg:

 

[elan]

So I had a chance to rebuild 5 piston regs in total, 2x MK5, 1xMK10, 2xMK20.

They all seems to be pleasure to work on. I liked MK5 the most, then MK20 and I did not like the MK10. MK20 seems to be taking more time to rebuild and it seems to be more complicated but still looks like thought out design.
I was astonished by the simplicity of the MK5, it seems to be a great reg.

I have noticed that IP lock depended directly on how nice the piston edge is. One MK5 has a very tiny scratch and the lock is a bit mushy. The last MK20 that I have bought of one of the board members turned out to be the best, I have reused the seat after checking the state of the piston and the seat, the piston edge was clean like brand new and the reg locks and recovers just as good as my new MK25.

I do not know if it makes sense or not but I have noticed that on those regs where I used Poly o-rings duro 90 on the piston head the recovery is slower. I used duro 70 on the piston head of the last MK20 rebuilt and it recovers and locks just like the MK25 I got new.

It will be interesting to see how the MK5s will behave in the cold water, as well as how they will withstand the usage overtime.

The MK10 was a total disaster, the pressure drops about 30 psi on inhalation but then recovers and locks. I do not know if this is my poor rebuilding or those regs just drop the IP that much. I tried with 2 different seats and it looks the same. Overall I did not like the MK10, especially putting the HP o-ring into the body
I will stick to MK5 and MK20 for the future if I get any more regs.

I want to thank again the guys who has annotated the diagrams.

So far I feel comfortable to rebuild my existing MK25s when the time comes

Given the pistons are so sensitive to the damage as well as reading some reported cases of the creep after servicing I really hesitate now to give the regs to any fresh of the mill technician to rebuild. I have seen how many techs treat the customers regs in a few of the local LDS . At least in the case when I screw up I'm the only one to blame.

 

[Slamfire]

...and I did not like the MK10.
The MK10 was a total disaster...
...Overall I did not like the MK10

They are a POS. I volunteer my services for proper disposal. Seriously, if the price is attractive enough I might be persuaded to buy it from you. And since I'm in Canada, there are no convolutions about that funny US money, or any border entanglements.

I have 4 Mk10's and while I agree that the body oring can be a pain (one time I tried to put in a new oring for half an hour only to discover that I had not taken out the old oring in the first place), I do like them. Others can correct me if I'm wrong but I believe the Mk10 will deliver less volume of gas than the Mk20 or Mk25. I was under the impression that this was one of the improvements engineered into the Mk20(5). That could be an explanation as to why you would see more of a drop in the IP on inhalation. All I can say is that I've never been able to out-breath a Mk10, thus any "improvements" in flow quantity are moot for my particular case. Besides, it would be really cool if I could do a 4 gas deco dive with all Mk10s. No more having the degrade those dives by having to carry one unbalanced piston in the O2 bottle.

Given the pistons are so sensitive to the damage as well as reading some reported cases of the creep after servicing I really hesitate now to give the regs to any fresh of the mill technician to rebuild. I have seen how many techs treat the customers regs in a few of the local LDS . At least in the case when I screw up I'm the only one to blame.

Once you get a taste for rebuilding your own regs it's hard to get that same level of confidence in a reg that somebody else has worked on. Particularly after you find some unpleasant surprises on regs that came in from "legit" technicians. There much to say about knowing exactly what's inside your regs and in what condition they are. Now you don't have to do any more trust-me-dives with your equipment.

 

[elan]

@Slamfire
I think I will still keep the existing MK10 and use it as a backup reg for the double hose diving... I will not probably buy more of them.. though Since you are in the cold region did you try MK10 in cold water ? low 40 - high 30 , I only had a chance to try MK25s in the 40f area and they were working properly....

What do you use for the O2 ? MK2 ? I have acquired an MK2 for that purpose but I have not had a chance to dive it yet, it's still in the box...

 

[Eric Sedletzky]

I thought if you used cristolube and Viton O-rings you would be OK to use a regular MK2 with pure O2, no?

---------- Post Merged at 08:33 PM ---------- Previous Post was at 08:32 PM ----------

I have a MK20 I need to rebuild too.
First I need to find a kit.

 

[elan]

I got a brand new MK2 plus which many people say is great for O2. Im still trying to figure out what is different in the plus version. According to some its a new seat which is more o2 compatible and the TIS.
For the orings my undestanding is that EPDM rings which are used by SP are O2 compatible.

A week ago I have bought a kit for MK20 fot 20USD off ebay mostly for the seat bushings and the filter. That serms to be a good price.

 

[Slamfire]

Since you are in the cold region did you try MK10 in cold water ? low 40 - high 30 , I only had a chance to try MK25s in the 40f area and they were working properly....

I don't think I've ever taken them in to 30's range. We dive year round here, but the water only gets down to mid 40s. I've been on lake dives that take the temp down to the low 40s. So far no probs whatsoever and I do not pack the ambient pressure chamber with grease or christo.

What do you use for the O2 ? MK2 ? I have acquired an MK2 for that purpose but I have not had a chance to dive it yet, it's still in the box...

Close. I use a Sherwood Brut or a Zeagle Rezort which is a very similar design to the Mk2. With the Sherwood you have to educate buddies before doing a bubble check so that they become aware that the trickle of bubbles should be there by design (dry bleed ambient pressure).