ScubaPro Mk10 assembly questions

[WhiteSands]

Have a question on the assembly sequence for the Mk10. As this is an old reg, I don't have the manual for it.

I'm guessing the correct sequence is to install the red/purple o-ring into the main body cavity, then install the piston with the help of the piston bullet, recheck the seating of the red/purple o-ring, remove bullet, then screw on the HP seat.

However, as the HP seat is screwed on, I was afraid the piston knife edge might cut a groove into the HP seat. I'm thinking if the knife edge is not perfect, that might not be a good idea.

However, if the seat is installed first, there will be no way to remove the bullet, so that can't be it.

 

[halocline]

The main spring keeps the piston off the seat until the reg is pressurized. That's the way all 1st stages work. (although with diaphragms the parts are different) So your sequence is right.

You won't be able to 'recheck' the HP piston o-ring unless you have x-ray vision, but if it's installed correctly in it's journal, it'll stay put. It's a tight fit, and getting the old one out can be a bit tricky. You'll want to take great care not to scratch the journal. I like those double hook o-ring picks from scubatools for that. I also like herman's o-ring installation tool for getting the new o-ring installed very quickly and easily.

One last thing, if you're using a kit that has color coded o-rings, they are pretty old. There's a good annotated schematic floating around that couv put together that has all the standard sizes marked in for the o-rings on the MK10. The HP o-ring is a 010, duro 85 or 90. It's important to use a stiffer (higher duro) o-ring for that spot. All the others can be duro 70, although I like to use a 90 for the seat seal; that one is a 013. Come to think of it, that might be purple in the old kits. The HP o-ring is amber, and I bet you don't even see it. That's the one that's protected by the bullet, it's hidden way in the journal. I'll try to attach the schematic if I can find it.

 

[halocline]

Here's the schematic

 

[redacted]

Have a question on the assembly sequence for the Mk10. As this is an old reg, I don't have the manual for it.

I'm guessing the correct sequence is to install the red/purple o-ring into the main body cavity, then install the piston with the help of the piston bullet, recheck the seating of the red/purple o-ring, remove bullet, then screw on the HP seat.

However, as the HP seat is screwed on, I was afraid the piston knife edge might cut a groove into the HP seat. I'm thinking if the knife edge is not perfect, that might not be a good idea.

However, if the seat is installed first, there will be no way to remove the bullet, so that can't be it.

You might want to spend more time learning how your regulators work.

 

[rx7diver]

Have a question on the assembly sequence for the Mk10. ... However, if the seat is installed first, there will be no way to remove the bullet, so that can't be it.

The main spring keeps the piston off the seat until the reg is pressurized.

Also, you don't *need* to use a "piston bullet." I've never used one (nor seen one in the flesh), and I've done a *lot* of Mk 10 rebuilds. In fact, the only specialized tools I use for a rebuild are (1) a brass "Scubapro Tool" (which has two little "spikes" used to unscrew the end cap which holds the HP seat, and two "knobs" used to unscrew the ambient pressure section) and (2) a short piece of brass rod (one end of which is shaped into a hook which is used to remove the piston's small active HP O-ring, and the other end of which is shaped into a slight "cradle" or "saddle" which is used to reinstall the piston's small active HP O-ring).

I purchased the brass "Scubapro Tool" a long time ago from a company called Peterbuilt, iirc, soon after I had tried to remove the ambient pressure section using a jerry-rigged/jerry-buit/jury-rigged "tool" and marred the chrome finish of my first Mk 10. #@%$#^&*!!! The tool also has a "wrench" that fits the Scubapro regulator hoses, so you won't mar them using channel locks, for example.

The brass rod "tool" was shaped by a friend from a piece of brass rod from the welding section of a hardware store. (Brass because, being softer, it's much less likely to mar the Mk 10's chrome finish, especially the groove the piston's small HP O-ring sits in.)

Hope this helps.

Safe Diving,

rx7diver

 

[halocline]

You absolutely do need to use a piston bullet or something equivalent to protect the HP o-ring from the piston knife edge. You don't need one on the MK20/25 or on the MK10+ because they have rounded piston edges. But the MK10 sharp piston edge will damage the HP o-ring, count on it.

rxdiver, I'd be curious to see a photo of the brass rod tool you mentioned.

 

[Bryan@Vintage Double Hose]

You absolutely do need to use a piston bullet or something equivalent to protect the HP o-ring from the piston knife edge.

This

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[rx7diver]

Also, you don't *need* to use a "piston bullet." I've never used one (nor seen one in the flesh), and I've done a *lot* of Mk 10 rebuilds.

You absolutely do need to use a piston bullet or something equivalent to protect the HP o-ring from the piston knife edge.

Hmmm. Ah just said ya don't. You said ya do. Ya callin' me a liah? Seems y'all spoilin' for a gunfight, padnah??!! (Apologies. I just watched "Open Range" again last night for the umpteenth time.)

My approach: Gently set the piston into the channel, so that it's resting on the small HP O-ring which earlier had been very lightly lubed and then slipped into its groove. Then *gently* "walk" your finger around the edge of the piston with slight pressure. You'll eventually feel the piston slip past the O-ring. It's how I was taught. It's how I've rebuilt countless Mk 5's, Mk 10's and Mk 7's. It's how I rebuild my own set of three Mk 10's. I've never damaged an O-ring yet ...

Safe Diving,

rx7diver

 

[Bryan@Vintage Double Hose]

BS...and impossible unless your finger is smaller in diameter than a pencil. ...

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[rx7diver]

BS...and impossible unless your finger is smaller in diameter than a pencil. ...

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Ummmm. Okay.