MK10 vs MK5

[Ken abucs]

I was looking for recomendations on whether to use my MK5 or my MK10 for my primary regulator. The MK5 has a cold water kit installed. I've seen some threads that indicate the MK10 might not be the best choice for 3500PSI tanks. Is this true? Does the MK5 cause the same concerns.

Most of my diving is done in cold salt water. Bottom temps in the mid 40s are common, I've been as cold as 38F. Most of my diving is to 40ft depths, but 100 - 120 ft depths on occasion.

 

[Isaac-1]

Both the Mk 5 and Mk 10 had several revisions, although I can't think of any Mk 5 revisions that would effect its cold water performance. (In fact I can't remember a cold water kit for the Mk 5 at all (it is possible SP offered a retrofit one though), although the SPEC kit was included with the Mk 10 in certain later years, therefore we need to identify which Mk 10 you have.

There are 3 variations of the Mk 10 body: (note yoke screw may have been changed)

variation 1, had a flat yoke screw and small (1/16 inch or so vent holes drilled in the side of the body)

variation 2, may have either flat or round printed yoke screw and counter sunk looking vent holes (about 3/8 inch upper part with 1/16th inch hole in the bottom)

variation 3, added a machined groove about 1/4 inch wide to retain a black rubber band above the vent holes, (I think holes had slightly larger bore) black rubber band may be missing from early examples.

Which one do you have?

As to 3500 psi usage, both the Mk 5 and Mk 10 were designed in a era of 3000 psi max pressure tanks, the problem at higher pressure is o-ring extrusion, thre are differences in the pistons of the Mk 5 vs the Mk 10 that may make one better than the other.

Ike

p.s. On a personal note I used a Mk 10 with 3200- 3300 psi tanks for a number of years with no problems

 

[redacted]

A number of Mk5s pictured with enviro kit: MK 5

I've had more trouble with the HP piston o-rings on my Mk10s than on my MK5s. I use a Mk10 din on my HP100. I don't see either the Mk5 or Mk10 having a problem with higher preassures.

BTW, if you need any filters for the Mk5 enviro chamber, let me know. I picked up a few in a lot of SP parts and don't have much call for them in TX.

 

[redacted]

A number of Mk5s pictured with enviro kit: MK 5

I've had more trouble with the HP piston o-rings on my Mk10s than on my MK5s. I use a Mk10 din on my HP100. I don't see either the Mk5 or Mk10 having a problem with higher preassures.

BTW, if you need any filters for the Mk5 enviro chamber, let me know. I picked up a few in a lot of SP parts and don't have much call for them in TX.

 

[halocline]

I recently bought some duro 90 polyurethane o-rings specifically for the HP piston in my MK5s and MK10s. They are really stiff o-rings. I put one in a MK10 and it worked great, but just today I tried one in a MK5 and it leaked like a sieve. I have no idea why, and maybe someday I'll try to figure it out. But, my thinking is that since at one time SP claimed they were using "hyperthane" o-rings which were supposedly higher duro polyurethane for HP piston use, these true 90 duro P.U. o-rings would be ideal for resisting extrusion. They are definitely more difficult to get in there. It's worth looking into if you are interested in using a MK5/10 for higher pressures.

 

[Wayward Son]

no idea what O rings George put in my Mk5 when he serviced it, but I've used it on 3442 fills several times without issue & once had a shop pump 3950psi into my 330 aluminum 100 (that tank often ends up around 3500 too) and have never had an issue with it.

 

[Isaac-1]

I recently bought some duro 90 polyurethane o-rings specifically for the HP piston in my MK5s and MK10s. .

May I ask where you found these o-rings?

 

[halocline]

May I ask where you found these o-rings?

I think it was oringsusa.com. When I said "specifically...hp piston" I meant that I bought them for that purpose, not that they were made specifically for that.