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

[Fishpie]

.......as far as servicing is concerned nothing. O rings and seat are in the same place and accessed the same way.

 

[halocline]

In my possession I now have new MK25s which I plan to rebuild myself not sooner than in a couple of years from now. MK2 is in plans of purchasing for an O2 deco later this year.

So far I have been rebuilding diaphragm regs including Apeks, Zeagle and USD DH regs.

I have ordered some SP tools already, and Im planning to stay with SP for the pistons.
Thanks a lot in advance.

I'd just rebuild the regs you own; if you are planning on buying a used MK2 for O2 use (it's considered an ideal O2 reg) then why not start with that one? You really couldn't get an easier reg to work on. As far as the balanced piston, I feel that the MK20/25 is a bit easier than the MK5/10 even though there are more parts. It's easier because you don't have to deal with the HP piston o-ring removal and seating in the reg body. Just remove the bushings and the o-ring will come out, and you just stack everything in place, hold it in with the special tool, and push the piston in; no bullet tool needed. You don't even need the MK20/25 bushing tool; I don't have one, although I'd get it if I worked on those regs frequently. I just put everything in place, including the seat carrier, and then push the piston in. So far no disasters.....

Once you start buying regs specifically to work on, it's a slippery slope.

---------- Post added May 9th, 2012 at 10:10 PM ----------

What is the difference between an mk5 and a mk10?

There are some differences; the MK10 uses a smaller piston and the body fits together differently. The cap/body connection is in the IP chamber, that's why there's that big o-ring. Apparently SP did that to correct some alignment issues with the MK5; the MK10 basically has a piston channel that's machined out of one piece of brass. The yoke (or DIN) retainer o-ring is in the end of the MK10 retainer, but on the shaft of the MK5. It's a different o-ring. The turret retainer is different; on the MK5 it's a brass hexagonal-head bolt; on the MK10 it's SS with an allen wrench fitting and round head. This means you need an allen socket for a torque wrench to properly install the MK10 turret, although I think awap has a work-around.

The MK10's ambient chamber is a little harder to fully pack with grease if you're into that sort of thing (I am) but you can find SPEC boots for them; it makes them look remarkably like atomic 1st stages.

 

[Zung]

... I feel that the MK20/25 is a bit easier than the MK5/10 even though there are more parts. It's easier because you don't have to deal with the HP piston o-ring removal and seating in the reg body...

I refrained from calling this one out: every time I did, I got my butts heavily kicked by the gurus here. It was my worst nightmare, and, after half a dozen tries, still worthy of a good assortment of tasty words...

 

[elan]

Thanks guys, I happened to get the bushing tool as well as the bullet from ST some time ago. So it looks like it's a good idea to get a used MK20/25 and practice

 

[ams511]

The MK10's use the standard DIN kit. The MK5's are special.

If I remember correctly wasn't there a thread several months back about using a Sherwood DIN kit to convert a MK-5?

 

[elan]

So I finally got a used MK20 to practice rebuilding... It looks like it was a later version of MK20 with the wide ambient chamber windows, TIS and a composite piston.

The original owner claimed that it was only used a few times after it was rebuilt 3 years ago.

Initial examination of the seat and bushings have kind of confirmed that - the seat literally looked as if it was replaced a couple of dives ago. The previous technician did not take the piston bushing off and did not clean underneath so that was the only ugly dirty place in the whole reg - which was not hard to clean

I have rebuilt it today, reused the seat and the bushings, but replaced all 0-rings with new - I used polyurethane ones in for dynamic (except the second big o-ring on the piston) + DIN, and EPDM for the rest.

I also converted the reg to DIN so the filter got replaced too.

So far the reg works well, it locks up instantly and then creeps for about 3 psi and locks completely.

A funny thing that I have noticed which I have also seen on my diaphragms, after the IP locks at say 133 it moves back to 130 after sitting without purging for 15-20 mins.

Another interesting thing that I have noticed is when you inhale the IP does not flatten down at a lower level and stays there during the inhale as it does on my diaphragms but rather reacts quicker to the breath changes and if I slow down inhaling the IP catches up quickly and I can only bring it down when I inhale fast.

Having the tools it does not look like it is more difficult to rebuilt than a diaphragm reg, I had only to be paranoid with not damaging the piston edge.

An MK5 is now waiting for a rebuild

 

[Scott L]

Any regulator not owned by me.

 

[Zung]

... I have rebuilt it today, reused the seat and the bushings, but replaced all 0-rings with new - I used polyurethane ones in for dynamic (except the second big o-ring on the piston) + DIN, and EPDM for the rest.

I also converted the reg to DIN so the filter got replaced too.

So far the reg works well, it locks up instantly and then creeps for about 3 psi and locks completely.

A funny thing that I have noticed which I have also seen on my diaphragms, after the IP locks at say 133 it moves back to 130 after sitting without purging for 15-20 mins.
...

Congrats!

The 3 PSI creep is probably due to the fact the seat has been disturbed from its original position. Hopefully it'll disapear with use, after the edge grinds through the previous sitting area.

The 7 PSI drop, if the air is off, is due to a leak somewhere, possibly the 2nd stage, or any hose that might be around. You can safely ignore it, or drop the whole thing in your bathtub to investigate. If it happens with the air on, it's likely because the edge is finding its way to a new home. Have you broke the thing in? If not, purge 20 times and see what's up.

 

[ams511]

So did your Mk-20 have a new retainer installed or did it have the old one? 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?

 

[elan]

Congrats!

The 3 PSI creep is probably due to the fact the seat has been disturbed from its original position. Hopefully it'll disapear with use, after the edge grinds through the previous sitting area.

The 7 PSI drop, if the air is off, is due to a leak somewhere, possibly the 2nd stage, or any hose that might be around. You can safely ignore it, or drop the whole thing in your bathtub to investigate. If it happens with the air on, it's likely because the edge is finding its way to a new home. Have you broke the thing in? If not, purge 20 times and see what's up.

Zung, that drop is with the air on. After the rebuilt I put it in the bathtub with the tank and had no leaks

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.

---------- Post added ----------

So did your Mk-20 have a new retainer installed or did it have the old one?

I have got the new DIN kit that has the newer retainer with that lip that prevents it from bottoming.. I don no how you can tell them apart without reassembling, my understanding is that you cannot as the pistons can be retrofitted