Scubapro Mark 10 question

[redacted]

This discussion and a newly acquired HP100 have made me go back and look at all 3 of my Mk10's. Two have about a 10 psi change in IP from high pressure to low pressure (3000 to 500) and one has about a 20 psi change. On the one with the 20 psi change, I've tried changing the HP piston o-ring from viton to polyurethane to nitrile, all with little effect. I also checked one of my Mk5's and it had about a 5 psi change of IP over the same range. So I brought a Mk20 out of retirement and found that supply pressure change had no effect on IP. I guess the Mk20 is back on duty and I'm going to have to relook all of my Mk10s.

 

[halocline]

Funny about the MK5 having less of an IP drop over the supply pressure range than the MK10s, maybe that has to do with the larger piston head. It could just be coincidence; maybe you should try all your MK5s. How many is that?

 

[Couv]

Matt may be on to something. The larger surface area of the MK 5 could be forcing the IP to lock up quicker. The MK 7 has the same piston, have you experimented with your honkers?

Here are a couple of other ideas. Is the IP correct at low tank pressure or perhaps near the low end? If low, try a couple of shims or a + HP soft seat and bring it up to the mid to high range and see what happens. If no help, perhaps a new spring is needed. No help, throw that NOS piston in. If still no help, I think I have some bushings that were engineered into the later model MK 10s. No help? You have my address.

c

 

[squidster]

Funny about the MK5 having less of an IP drop over the supply pressure range than the MK10s, maybe that has to do with the larger piston head. It could just be coincidence; maybe you should try all your MK5s. How many is that?

Hey Mattboy whats a good price for a mk10 in good shape?

 

[ageddiver]

When you boys start throwing them out let me know and I'll give you a few bucks

I've used the hell out of mine for eight years and on some very deep dives, and if the IP ever changed it sure didn't affect the performance. All maintenance by me (nothing special). IMO it's a workhorse, guys.

 

[halocline]

Hey Mattboy whats a good price for a mk10 in good shape?

I've seen them go from $30 to $70 on ebay. If you had one from a reliable source, where you knew the reg had been cared for and well serviced, and the seller could honestly tell you what the reg looked like inside, I think that would be worth more. I just paid $25 for a MK10 kit at my LDS, so getting one that you KNOW does not need an immediate rebuild is definitely worth something; if not, add the cost of a rebuild in.

Actually, this is a good question, and I hope lots of other people offer what they think they're worth. The easiest way to find out what a used one goes for is to bookmark, but don't bid on, several auctions over some time and average out the cost they sell for.

The short useless (yet correct) answer is "a good price to pay is as low as possible" and they're worth "whatever someone will pay."

 

[Couv]

I think AWAP has some you could get cheap. ;-) But to answer you question (Matt ain't here ) I just picked up a MK 10 along with a 109, both in good shape, for $57 and there were a few odds and ends thrown in for good measure.

Oddly enough, when a seller list it as a package, you are likely to pay the same price if it were sold alone. So, as a guesstimate, $40-$65 but I saw a beautiful one go for about $30 not long ago.


EDIT: Ooops, Matt is here and types faster.

c

 

[redacted]

Well, it's fixed. I was quite sure the problem was friction between the HP o-ring and the piston shaft. I really thought replacing the viton o-ring would do the trick so when ift failed it was time to think about it some more. I decided to take a closer look at the shafts. It looked like most others - stainless steel polished but still see mfgr production marks. Started to compare with some of my older Mk20 pistons and I noticed the current Mk25 composite piston looked similar but an older Mk20 piston had a chromed shaft. I had one more new Mk10 piston which also turned out to hav a highle polished shaft - perhaps chromed. I just installed it and now the IP change over the range of supply pressure is about 5 psi - about what I expected.

I took one of my other Mk10s out of service and replaced it with this one for use on an HP tank. Next project will be to see if a little polishing of the shaft on a problem Mk10 piston with good knife edge will help. I may even have to look into having one chromed. We'll see.

Looking for a good Mk10??? The problem is looks good and performs well are two different things. They can look real good on the outside but have slight damage or corrosion on the inside on any of the dynamic seating surfaces and not be able to achieve 'like new' performance or could even be unusable. And, unfortunately, there are folks who will try to dump their problem regs on ebay after they clean them up and make them as presentable as possible. Surprisingly, I've had good luck with just plain ugly looking regs that it was fairly clear the seller did not know that much about them and was just cleaning out someone's junk. I've bought about 2 dozen regulator stages on ebay and have not gotten burned yet. If you are not willing to take the chance on a bad one, you may want to look local so you can test it before you buy. Good luck.

 

[Couv]

Well done, Brother.

 

[DA Aquamaster]

So as long as the first stage is servisible i can trust it to work fine.
a scuba pro tech would most likely tell me if it cannot be serviced or if the reg is a little loose.

Crescent shaped cuts in the HP o-ring are a dead give away that pinching is occurring - but not all techs will catch that, or for that matter even inspect the o-ring. Having a Mk 10 not go the distance between annual services is another clue that it's time to get a new one.


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A change in IP of 5-6 psi from 3300-300 psi is expected with the Mk 5 and Mk 10 as it has a straight piston stem with less than perfect balancing for the seating edge itself. In contrast the Mk 20/25 with the slightly belled seating edge on the piston should have essentially 0 change in IP.