Zung
Contributor
Scope: Scubapro MK10Plus, MK20 & MK25 only
In 2 "Engineering Bulletins", SP stated:
EB #242: "Both 1st stages should be lubricated with CHRISTO-LUBE * lubricant versus the standard silicone which has been used in the past. If silicone grease is used, you will find in general, that the intermediate pressure range will be higher than what we recommend."
EB #248: "The MK10plus and MK20 1st stages are assembled using Christo-Lube® lubricant, p/n 41-047-000. Your choice of lubricant will affect the intermediate pressure. If standard silicone grease is used, the intermediate pressure could increase by as much as 20 psi. SCUBAPRO recommends using Christo-Lube for these two first stages."
I raised the question in another thread, and the responses were largely negative.
Just now, I've the opportunity to do some experimenting. I've scored yet another MK20 on eBay (I know, I don't need it, but you know how it goes), older generation with the small ambient holes, advertized as "150 dives", which I assume to be 150 dives since last service.
Initial testing gives an IP of 10 bar/145 PSI, rock steady, no creep.
After much head scratching, I decided to take it apart for a service. To my surprise, everything is shiny new inside, so I shoot a "complain" to the seller, who says it's 150 dives in its whole life, serviced a year ago, and very few dives since. Oh well...
Since it's apart anyway, I take a closer look: there's a very slight scratch at the edge of the piston stem, and the lubricant is silicon grease (transparent instead of white). So I clean everything in the ultrasonic, lube with Christo 129 and reassemble.
After settling, the IP is 9 bar/130.5 PSI, creeping to 9.2 bar/133 PSI!
There's absolutely no part substitution, I use the exact same piston o-rings, seat, and the single shim at the seat retainer. Net difference is .8 bar/11.6 PSI, within range of what SP says in EB 248.
I'll wait a while to see if the creeping stops. If it doesn't, maybe I'll give it the mattmagic treatment and report back.
Meanwhile, any comments?
Edit/epilog
The creep is bugging me, so I substitute a spare piston I previously applied the mattmagic on. Initially the IP is a little low, as I thought it would be, so I add a shim at the bottom of the spring. Now the final result is 9.0 bar/130.5 PSI, no creep.
In 2 "Engineering Bulletins", SP stated:
EB #242: "Both 1st stages should be lubricated with CHRISTO-LUBE * lubricant versus the standard silicone which has been used in the past. If silicone grease is used, you will find in general, that the intermediate pressure range will be higher than what we recommend."
EB #248: "The MK10plus and MK20 1st stages are assembled using Christo-Lube® lubricant, p/n 41-047-000. Your choice of lubricant will affect the intermediate pressure. If standard silicone grease is used, the intermediate pressure could increase by as much as 20 psi. SCUBAPRO recommends using Christo-Lube for these two first stages."
I raised the question in another thread, and the responses were largely negative.
Just now, I've the opportunity to do some experimenting. I've scored yet another MK20 on eBay (I know, I don't need it, but you know how it goes), older generation with the small ambient holes, advertized as "150 dives", which I assume to be 150 dives since last service.
Initial testing gives an IP of 10 bar/145 PSI, rock steady, no creep.
After much head scratching, I decided to take it apart for a service. To my surprise, everything is shiny new inside, so I shoot a "complain" to the seller, who says it's 150 dives in its whole life, serviced a year ago, and very few dives since. Oh well...
Since it's apart anyway, I take a closer look: there's a very slight scratch at the edge of the piston stem, and the lubricant is silicon grease (transparent instead of white). So I clean everything in the ultrasonic, lube with Christo 129 and reassemble.
After settling, the IP is 9 bar/130.5 PSI, creeping to 9.2 bar/133 PSI!
There's absolutely no part substitution, I use the exact same piston o-rings, seat, and the single shim at the seat retainer. Net difference is .8 bar/11.6 PSI, within range of what SP says in EB 248.
I'll wait a while to see if the creeping stops. If it doesn't, maybe I'll give it the mattmagic treatment and report back.
Meanwhile, any comments?
Edit/epilog
The creep is bugging me, so I substitute a spare piston I previously applied the mattmagic on. Initially the IP is a little low, as I thought it would be, so I add a shim at the bottom of the spring. Now the final result is 9.0 bar/130.5 PSI, no creep.
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