Help identifying a Scubapro 1st stage

[Couv]

Tamas,

I would have no objections to using that yoke on a 3000 psi tank. In fact, I use one on my 3475 psi tank with no issues. You can get a service kit for your MK 5 & 109's from Vintage Double Hose. Shop Online

However, note the 109 duro poppet kit will require that you have a "duro poppet" which can be found on eBay. Initially, it's not the cheapest way to go as you can purchase a poppet with the seat attached, but the next time you need to replace the seat you're right back where you started. One other small issue that bears mentioning is the duro poppet is sometimes not compatible with the old large foot levers. See this thread:
http://www.scubaboard.com/forums/re...ew-s-wing-lever-issues-threads-continued.html

 

[DA Aquamaster]

Just for clarity to the OP, the Mk V was produced in a single end port version as well as with 2, 4 and 5 port swivel caps.

The first stage body also had a single 3/8" HP port, then a single 7/16" HP port and then finally two 7/16" HP ports.

The yokes came in an early thin 2250 psi yoke, a slightly later and slightly thicker 3000 psi yoke and finally the late style heavy yoke with a 9/16" yoke screw. Yoke knobs were flat and all metal and later used a plastic knob with a Mk V decal on the end.

Pistons also differed with an early straight piston and later stepped piston that was designed to prevent "cookie cuttering" of the seat.

The seats also changed over the years from a flippable, flat, white nylon 66 seat to a concave grey seat.

The major issue with the Mk 5 and high pressures is that the tolerances between the piston stem and first stage reg body can be large enough to cause problems with "pinching" of the piston stem o-ring. The current piston stem o-rings are 90 duro EPDM and are less prone to this issue than the older, softer o-rings, but it can still be an issue on some Mk Vs, especially if they've got some heavy use and wear on them. What will happen is that the o-ring will get pinched and develop either feathers or missing crescent shaped bits on the o-ring that cause the o-ring to leak and eventually fail. On average, the Mk V tends to do fine at 3000 psi, but the number of Mk Vs that will do well at 3300 psi, 3442 psi, 3600 psi, etc decreases rapidly.

 

[redacted]

The first stage body also had a single 3/8" HP port, then a single 7/16" HP port and then finally two 7/16" HP ports.

I have a Mk5 with two 3/8th inch HP ports.

 

[Luis H]

Just for clarity to the OP, the Mk V was produced in a single end port version as well as with 2, 4 and 5 port swivel caps.

I may be wrong, but the only single port version I remember was actually called the MK-1. It did not have a swivel. The port was at the end of the piston cap.

It was first offered with the 108 second stage (mid 60's), but when the 109 adjustable second stage was introduce (around 1967 or 1968) the Mk-1 and the Mk-5 were then switched to the new second stage.

 

[tamas970]

Thanks for all the help. Unfortunately time is pressing, I won't be able to finish the vintage-repair project before my next diving trip and got myself an mk19+G250V set from a local store's afterchristmas-sale.
I'll definitely look back, because I am not much fun of the plastic-toy look of the G250v and the weight of the mk19. They will do as reliable backups anyway.