Sp mk5 piston

[cbmech2]

awap kgault,
I wished I had a picture of them side by side. What I can say is that the older type piston stem is the same diameter all the way down to the base. The newer piston stem has a shoulder at the base which, limits the upward movement and prevents the seat from being cut into. Yes, the service kits are still available but, the pistons are not. I took the same expert tec seminar but, mine was this past July and that is what was said. I too am servicing MK5s, although I have not seen one in a few months. They are out of luck though if they have knife edge/piston problems. It's funny that what Rene said was pretty much 180 degrees out from what was said at the seminar I attended.

 

[kgault]

awap kgault,
I wished I had a picture of them side by side. What I can say is that the older type piston stem is the same diameter all the way down to the base. The newer piston stem has a shoulder at the base which, limits the upward movement and prevents the seat from being cut into. Yes, the service kits are still available but, the pistons are not. I took the same expert tec seminar but, mine was this past July and that is what was said. I too am servicing MK5s, although I have not seen one in a few months. They are out of luck though if they have knife edge/piston problems. It's funny that what Rene said was pretty much 180 degrees out from what was said at the seminar I attended.

Well given the year difference, Rene could have been turned down when trying to justify the re-running of parts.

I guess three of my customers are going to get free upgrades to MK25s in the next couple of years as the swivel retainers are going to become untorquable.

Keith

 

[redacted]

awap kgault,
I wished I had a picture of them side by side. What I can say is that the older type piston stem is the same diameter all the way down to the base. The newer piston stem has a shoulder at the base which, limits the upward movement and prevents the seat from being cut into. Yes, the service kits are still available but, the pistons are not. I took the same expert tec seminar but, mine was this past July and that is what was said. I too am servicing MK5s, although I have not seen one in a few months. They are out of luck though if they have knife edge/piston problems. It's funny that what Rene said was pretty much 180 degrees out from what was said at the seminar I attended.

OK, I went digging through my drawer of "reserve" 1st stages. (I try not to do that as it just makes it harder and harder to explain to my wife why I need another one.) I found 3 Mk5s. All have a small shoulder within about 1/2 inch of the piston head. Very similar to the large shoulder found in about the same place on the Mk10 pistons. I suspect this is just how they happened to machine them and that the shoulder is way too close to the piston head to have any effect on limiting piston travel. In fact, I can't see any benefit in limiting piston travel in any way that might prevent it from locking up. One of those pistons came out of a light yoked Mk7 so it is probably from fairly early production.

BTW, I'd be suspect of any Scubapro representative who suggested that shops should stop providing service for Mk5s. Even when you get to the point where new parts are not available (like the swivel retainer) there are plenty in the ebay junkyard at reasonable prices.

 

[cbmech2]

I have a MK5 with an AIR 1 and when I disassembled the 1st stage, voila! I now have pictures of the pistons I mentioned earlier in this thread. They are not the best pictures but, I am sure they will illustrate the point I was trying to make with respect to the differences.

 

[DA Aquamaster]

At a shop I previously worked for, the SP rep for that area got pissy because we used so many Mk 5 kits per year. He expressed that we should be selling new Mk25s rather than servicing Mk 5s. When we brought up the possibilty of providing original owners with free Mk 25s in exchange for their lifetime warranty covered MK 5s, oddly enough he seemed to be fine with sending more Mk 5 kits.

Some of the reps are no doubt all about sales rather than customer service but it does not hurt to remind them that the lifetime warranty and long term support are some of the major selling points that justify the price and in the long term those are two of the least expensive ways to add quality and value to the product.

I suspect that obligation, more than anything else, is what continues to drive Mk 5 service kit availability. If SP discontinued support for the Mk 5, they would have to replace all the Mk 5's still in service with their original owners and that will not happen until the cost of replacing them with Mk 25s is less than the cost of continuing to produce Mk 5 annual service kits. Due to SPs evolutionary and backward compatible design processes, the Mk 5 shares a seat with the Mk 10, a piston head o-ring with the Mk 25 and an HP piston stem o-ring with both of them. Since the remaining annual service parts are more or less generic o-rings, the point where SP can cost effectively discontinue support is a long way off and will be tied to the discontinuance of the Mk 10 - and there are still a ton of Mk 10s in service.

---

I suspect the shoulder on the "new" Mk 5 piston is there for piston centering as it is too short to contact the reg body before the spring is fully compressed. The Mk 15 is in a similar situation as pistons are no longer available for it either. We recently had a no longer available part fail on an orignal owner Mk 15 and SP replaced it with a Mk 25. The owner was delighted.

 

[redacted]

None of my 5 Mk5s or 2 Mk7s have that shouldered piston and all are working fine. I suspect that shoulder reduced manufacturing cost a little while improving cold water performance.

 

[cbmech2]

da / awap,
What Rene had said at the Expert Tech seminar was that the shoulder provided a postive stop so the knife edge could not cut into the seat too much. I have yet to see one that has done that but, I suppose that may be a remote possibility. Do either of you have good, clear schematics for an AIR 1? I have one but, the quality is not all that.

 

[redacted]

That reason makes no sense. The knife edge needs to cut into the seat as far as is necessary to stop the flow.

This Air1 schematic is pretty old: http://www.scubaproregulatormuseum.org/AIR_1.jpg

 

[DA Aquamaster]

I agree that expanation makes absolutely zero sense.

Look at the lenght of the shoulder and then look at the working range of the spring. If you compress the spring so much that the shoulder bottoms on the reg body, you have a lot bigger problem than the seat getting cut by the piston and the IP will be WAAAAYYYY out of the acceptable range.

An Air 1 Schematic won't help much. The critical elements are not to screw up the diaphragm if you remove ad re-install it as SP does not make them anymore and to adjust it properly. The diaphragm clip can poke a hole in the dipahragm if you are not real careful.

Adjustment wise, the upper portion of the valve and the the lever adjustment are more or less like the D400. The pone noteable difference is how parts 14 and 15 screw together. The length needs to be adjusted (by turning 14 after everything is assembled) so that you do not have excessive slack or inadequate distance between the diaphragm and lever.

 

[cbmech2]

I also handwrote a note after looking at the handouts I was given and it states that when the old pistons stabbed the seat it could possibly extract the seat from the cap. Another remote possibility I suppose.