MK25 question

[Genesis]

its still tapered and you could consider it a "knife-edge" (it won't cut you, but its still the same basic design - just not actually sharp.)

The seat is tapered to "accept" it.

There's a lot of force on that small contact point when the seat and piston are "closed"; if you rotate the adjuster while pressurized, you are grinding one against the other, and apparently SP has had regs lock up after adjusting the IP while pressurized.

 

[oxyhacker]

Its not the same basic design at all - while the piston is similar in look and function, the dynamics of how the seal is achieved are very different - the knife edge piston is made so that the sharp edge on the piston scores and pentrates the seat material to make a seal. The newer blunt piston has a rounded end that fits into a matching recess in the seat, with minimal deformation - actually, it has more in common with the conical seats being used on many newer diaphragm regs than with the classic knife edge.

Anyhow Scubapro says the Mk20/25 doesn't have a knife edge piston, and that's good enough for me. Since there are differences in how the two patterns are serviced, its important to preserver the verbal distinctions.

Genesis once bubbled...
its still tapered and you could consider it a "knife-edge" (it won't cut you, but its still the same basic design - just not actually sharp.)

 

[SeaCobra]

oxyhacker once bubbled...
Actually the Mk20/25 doesn't have a knife edge piston. After the probs with the Mk15, which did, SP switched to a blunt piston with rounded edges, which fits into a matching recess in the seat.

You will find several different piston configurations in the MK20 and yes it did have a "knife-edge". It went knife then to blunt and then back to knife. Sorry to say I no longer work for a SP location since the intro of the MK25, so I have no info there.

Jeff

 

[oxyhacker]

Over the years the rounded edge has gotten less rounded, but it still supposedly relies on wedging in rather than digging in, and so is technically not a knife-edge piston according to SP (much as many old timers would like to see the Mk25 devolve back into the Mk5!) I don't mean to be picky, but since the knife edge and rounded edge pistons must be treated somewhat differently in servicing, It makes sense not to blurr the distinction by casual misuse of terminology.

Genesis's main point, BTW, that the Mk25 should not have the IP adjusted while pressurized, remains correct, and well worth noting if you own one of these regs. I was always puzzled why they went to the external adjustment on the Mk25 after the problems with the Mk15.

SeaCobra once bubbled...


You will find several different piston configurations in the MK20 and yes it did have a "knife-edge". It went knife then to blunt and then back to knife. Sorry to say I no longer work for a SP location since the intro of the MK25, so I have no info there.

Jeff

 

[rknazik]

There was a problem last summer with the high pressure O ring in the MK20-25 parts kits. They were too soft and would leak. Scubapro shipped new high pressure O rings as replacements, but I don't think they formally "recalled" the regulators that had the bad ones.
A couple of the kits I bought even last winter had the "bad" O rings in them, so you might have gotten one of these.

 

[ElectricZombie]

sylvester once bubbled...
My wifes MK25 has a leak from where you insert the allen wrench to adjust the IP. This is a new reg 8 dives on it, what could cause that ? I will take it to the LDS next week when he opens but for my knowledge Id like to know the possable source of the leak.

Could be a bad o-ring.

I have also noticed that people who push their Mk25's past an IP of 145 or so will often have this problem.

Have it checked out by a professional ScubaPro tech.