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

[Zung]

... I did not do a full scale brake in, may be 5-6 times. I did not worry about the initial 3psi as my MK25s do the same and my diaphragms are creeping even a bit more before completely locking up....

What I do is to leave it on the tank for a few days to give the edge plenty of time to plow its way into the seat. Or just ignore it and it'll go away.

How does one tell about the Mk-20 versions? I know the latter ones have the larger holes but is there any way you can tell if it has a composite piston without disassembling it?

Hard to tell without opening it up. SP published it in EB #267 dated Feb 2000, and I have a MK20 with the big holes and a compsite piston I bought new in June 2000.

 

[redacted]

The early retainer that was recalled had 3 slots on each side of the plastic saddle. The replacement universal retainer came with a saddle with only two slots. But. even with two slots, it is worth a check next time you open it up. I ran into one shop that tried to explain to me that the fix was in the design of the new saddle and talked like that was all they changed.

 

[elan]

The early retainer that was recalled had 3 slots on each side of the plastic saddle. The replacement universal retainer came with a saddle with only two slots. But. even with two slots, it is worth a check next time you open it up. I ran into one shop that tried to explain to me that the fix was in the design of the new saddle and talked like that was all they changed.

Oh boy, that's not very good for that shop. If they believed that this plastic piece can stop from over-torquing....

Mine originally had a yoke that was under recall and it had this 3 holes saddle. I bought a new DIN assembly from LP that had the retainer with the lip - the one that stops the retainer from bottoming.

I use a torque wrench everywhere anyways so I would not over-torque it..



I just finished the rebuild of the MK5 that I already had clean.... What a nice regulator.. so simple and solid made. I put a new (concave?) seat, the one that Brian @VDH ships in his kits, put a polyurethane o-ring on the stem and EPDMs everywhere else. I also converted it to a DIN.

It seems to recover even faster than MK20/25 (less orings ?) Locks after moving about 3-5 psi and the IP drops a bit (no more than 5 psi) from 3k to 500psi.

Does it sound more or less right ?

Just like the Mk20 the IP drops a bit after sitting for 15-20 mins.

I like the look of the DID MK5 more than MK20/25 It looks like a tank. Solid brass thingy...

I just wanted to thank all the guys on the board that contributed into creating the diagrams with o-ring sizes. It helped a lot.

 

[redacted]

That Mk5 sounds good. My wife still dives her Mk20 but I put all except my Mk5/7s on retired reserves.

I am not absolutely sure the shop just did not want to be bothered with any "free" recall work; but....

 

[Couv]

Well done Elan,

Thank you for the updates.

BTW is that Lotus Elan or the antelope?

 

[halocline]

I just finished the rebuild of the MK5 that I already had clean.... I also converted it to a DIN.

It seems to recover even faster than MK20/25 (less orings ?)

Just like the Mk20 the IP drops a bit after sitting for 15-20 mins.

A few years ago I did some experimenting to try to test the IP drop and recovery of MK2, MK5, MK10, MK15, and a MK20 with the composite piston. Conventional wisdom would imply that as the flow capacity of the reg increases (in the order I listed) the IP drop would lessen. I found that was not the case with a single 2nd stage and an IP gauge on the LP inflator hose. The MK15 seemed to dip the most, and the MK10 dipped substantially more than the MK2 or MK5, almost the opposite of what you'd expect. I even spoke at length with Peter Wolfinger about it; surprisingly, he had not answer and not much interest in it.....

Then I tried connecting 2 and even 3 balanced adjustables, all with very strong purges, and putting all of them under full purge simultaneously. That changed the results; the MK15 and 20 initially dropped quite a bit then recovered and stayed around 10 PSI under IP, while the other regs really dropped....at least 25 PSI. But all of them had a big initial drop and then some recovery under continuous purge.

So, my best guess is that the results are influenced by venturi effect in the LP chamber; the MK2 seems to have far less of this than do the others. That's probably due to the turret in which all the LP ports are connected on the other regs. IOW, fast flow out some of the ports to the 2nd stages causes a drop in pressure in the other ports, i.e. LP inflator hose. It would be good to get an inline IP gauge that could be installed right at the 2nd stage hose connection and see if the results are different; my guess is that they would be. What this implies is that the later SP balanced piston regs have an air path that results in greater venturi effect, and I wouldn't doubt that. Putting the LP inflator hose on the end LP port (where an occasional knucklehead will insist that you get "20% better breathing") made no difference on any of the regs.

Did you have a MK5 DIN retainer, and if so, where did you get it? It's different than the retainer for the others I believe. Awap has figured out some arrangement with steel washers that seems to work well.

I am not sure what exactly the slight drop in IP is after the reg sits pressurized, but my guess is that there is an initial seating force that slightly lowers as the piston/seat surface mate more fully. I notice this with all my MK5s and 10s. I wish it could be explained by something clever like cooling of the air in the IP path, but if anything, the air should warm up in there, so I don't know where that couple of PSI goes unless it leaks out someplace. There are lots of places it could do so, and we're only talking about a very small quantity of air. It's definitely nothing to worry about.

 

[ams511]

The early retainer that was recalled had 3 slots on each side of the plastic saddle. The replacement universal retainer came with a saddle with only two slots. But. even with two slots, it is worth a check next time you open it up. I ran into one shop that tried to explain to me that the fix was in the design of the new saddle and talked like that was all they changed.

I have two MK-20's that were ebay purchases one has the small holes in the ambient chamber while the other has the large. Neither has had the recall work done. I have not disassembled either of them to see what is inside. Is there anyway to disassemble and reassemble them keeping the alignment of the seat the same? If the regs do not have the composite piston I am probably better off rebaying them and looking for something more recent.

 

[Zung]

Check for the retainer is easy: remove it, check if there's the extra ring as per the pic, put it back and torque it to 30 N.m/266 lb.in.



Check for the piston requires complete dissassembly and the IP may creep a bit afterward.

Edit:

I've got a few MK20's that lived a long time before I "upgraded" the retainers. Never had any problem before, or any after. As long as you torque them properly, you should be OK.

Regarding the piston, maybe you can try going after the symptoms: purge hard, release: if the IP swings back to nominal in a second or less and stays there, there's no cause for worry.

 

[halocline]

Actually you don't need to completely disassemble to check the piston, just partially. You can remove the HP seat retainer with a spanner and look at the piston edge. If it's brass tipped, that's the old (middle) style piston and you're done. Usually if you don't disturb the seat, when you put the retainer back in it will line up well. If the piston tip is stainless steel, and you want to see if its the early style or the later composite, replace the HP seat retainer, making sure the spring is in place, then carefully take apart the body with a different spanner and hope that you don't pull out the piston with the ambient chamber; usually if you're careful you can work the reg apart leaving the piston in place. Then you can see if the head is metal (it will still have a plastic part at the base of the stem) or plastic, in which case it's the composite piston. Personally I would only ditch the regs if they have the brass-tipped piston, the first style seems to work well.

But, in order to remove the seat retainer and/or the ambient chamber, you do need the spanners or something that will catch the holes and turn the part. I bet I could tell ninety percent of the time which piston it is just by purging with an IP gauge in place; the composite piston has much quicker recovery and lock up. If you have someone who can service the regs well and has access to the new piston, it's probably around $50 which IMO is well worth it, then you'd have two MK25s without the pesky external IP adjustment. I have a friend with a mid-series MK20 that I serviced and replaced the piston on about 3 years ago; I was going to service it for her a month or so ago but it was working so perfectly I just left it alone. MK20s with the new piston are VERY IP stable over the long run. It would not surprise me if they lasted over 400 dives well cared for. That's a nice feature in a 1st stage.

 

[ams511]

Zung and Halo thanks for your help. I will check through the old posts for the pictures of the pistons. Both regs appear to be in excellent shape and seemed ok when I tested the IP, so I would hate to screw them up. I will double check but I think I have a MK-20 kit so I can rebuild it.