Servicing my own gear

[redacted]

Regarding the bullet tool on the MK 25 - scubapro recommends it's use to protect the knife edge and piston end. It ensures everything stays aligned when inserting the piston into the assembly. I can't speak to the alternative procees that Awap may use.

For $7.00 - I recommend its use.

When SP first came out with the Mk20 (Mk25 with no external adjustment) the recommended assembly procedure used the assembly tool to install the o-ring and both bushings without use of the bullet tool. The bullet tool was used with earlier BP models that actually have a sharp knife edge that could cut the o-ring. If the tech was not careful, it was possible to dislodge the o-ring from its bushing sandwich. It was easy enough the feel the unusual resistance this would cause but if the tech just applied more force the o-ring could be damaged. I suppose this is the situation that is avoided by using the bullet tool.

 

[Jim Lapenta]

I got my mag gauge from eBay, brand new in the box for 15.00. Tubing from the aquarium store for 5 bucks. cut a lexan mounting plate at work on the water jet. Spare mouthpiece with a hole punched in the side to run the tubing into. Less than 30 bucks for a magnahelic.

 

[halocline]

first stage HP seat, not the second stage

Of course, but you do understand that IP is the force that closes the HP seat, not tank pressure, don't you? The HP seat is never subjected to tank pressure.

 

[tbone1004]

Of course, but you do understand that IP is the force that closes the HP seat, not tank pressure, don't you? The HP seat is never subjected to tank pressure.

yes, and the smaller the delta between IP and supply pressure, the easier everything is going to come together because it is much less violent inside of the chamber until the grooves are cut. At least as explained to me in the reg courses

 

[wizbangdoodle]

Yes, for $7, that is cheap insurance. I'll definitely buy the bullet tool. I remember the knife edge on the piston and having to be careful and using that bullet tool. Correct me if I'm wrong, but didn't manufacturers move away from knife edges on the piston setups because it would cause whistling during a dive?

Keep the discussion going, I'm picking up lots of good tidbits.

 

[halocline]

yes, and the smaller the delta between IP and supply pressure, the easier everything is going to come together because it is much less violent inside of the chamber until the grooves are cut.

That's highly doubtful. IP is the force required to shut the valve. There's no more pressure on the seat than whatever IP is, by design. If higher tank pressure resulted in more pressure on the seat, it would be reflected in higher IP. There seems to be a lot of misunderstanding about this. For instance, there's an often-repeated statement about higher pressure tanks being tougher on HP seats, but this is absolutely not true. Tougher on o-rings that retain HP, like the piston o-ring in a MK25 or the balance chamber o-ring in a diaphragm reg, sure. But not the seat. If the larger pressure gradient across the seat resulted in more seating force, this would absolutely result in higher IP.

Certainly the first time you pressurize a reg its a good idea to turn on the valve slowly (it's a good idea all the time). But other than that, there's no reason to think that there's any problem at all with putting a freshly serviced regulator on a full tank.

 

[halocline]

For the Mk 25 - the manufacturer 's service procedure involves cycling the purge several times to ensure lockup without drift or creep at 500psi Followed by a test at 3000 to ensure stable ip at full supply pressure.

In the shop - we use a hp regulator - in the field - you'll find two tanks make this easier

I believe you, but I don't think doing this is necessary or even helpful for the seat. It's probably more as a precaution in case something isn't right and you get an IP spike. Having only a few hundred PSI get past the seat is one thing, 3K PSI is another. So that's a valid reason to try a newly serviced reg on a near-empty tank first. But IMO it's easy to just keep your hand on the tank valve, watch the IP gauge, and be ready to shut it off and purge if necessary.

I've never had an IP spike on a 1st stage that I've serviced, and I bet you haven't either.

 

[halocline]

Correct me if I'm wrong, but didn't manufacturers move away from knife edges on the piston setups because it would cause whistling during a dive?

You are correct that SP went away from the knife edge, and the MK20/25 pistons have rounded edges. There's not the same need for a piston bullet that there is in the earlier MK5/10/15. Now I don't doubt that SP still recommends using one, or maybe there was a period of time when they said you didn't need one on the rounded pistons, then went back to it, who knows. I know from personal experience that it's easy to assemble a MK25 without the bullet. The bushing tool is so helpful in seating the bushings that it's almost mandatory, but I have done them without it. I would not recommend that. It's really important that those bushings are installed correctly.

The reason SP went away from the knife edge was probably more about flow rates than anything else. The rounded piston edge has better aerodynamic properties and IP drop under high demand is impressively low with the MK25 piston. SP can boast of a flow rate on the MK25 of around 300 cfm, or the equivalent of emptying an AL80 in about 15 seconds. It's a little silly, like having a car that can go 1000 mph.

Both the older MK5/10 and the later MK20/25 can whistle; it seems to be a bit of a crapshoot involving the spring, lubrication on the HP o-ring, and maybe the stars aligning. The only one of my regulators that has ever whistled is my MK2; a completely different design.

 

[bl6394]

Yes, for $7, that is cheap insurance. I'll definitely buy the bullet tool. I remember the knife edge on the piston and having to be careful and using that bullet tool. Correct me if I'm wrong, but didn't manufacturers move away from knife edges on the piston setups because it would cause whistling during a dive?

Keep the discussion going, I'm picking up lots of good tidbits.

I call it a knife edge - but yes - under magnification it is clearly rounded.

 

[bl6394]

...
I've never had an IP spike on a 1st stage that I've serviced, and I bet you haven't either.

If you do enough regs, it happens - albeit infrequently. One of our customers also had a Mk17 that shattered it's load transmitter and cracked the diaphragm retaining ring... Still not sure how that happened...

ALWAYS - having a downstream second stage attached (or similar OPV) mitigates the risk of the burst LP hose leading to the IP gauge when initially charging the 1st stage. Exploding LP hoses are no fun.

Otherwise - the process previously described relates more towards the initial tuning of the IP - than protection against IP spikes. For balanced (Mk25) or over-blanced (Mk11 / 17) regulators - the initial IP tuning occurs at 500psi. The subsequent test at 3000 verifies that the IP has the desired characteristics (model dependent) across a range of supply pressures. For the Mk25 - you may see a 1-5psi variance between 500 and 3000 psi.