MK2 overhaul question

[BIGJACK]

I just rebuilt my MK2 and it still works! It took a lot of cycling but the IP settled down at about 127. My question is about the two washers shown in the schematics at either end of the spring and the washer under the yoke. My reg didn't have them when I opened it up. I bought it on ebay and the kit from VDH. Are these washers needed? This is my first successful rebuild.

 

[bl6394]

A MK2 - when properly assembled and tuned should crisply lock up with an IP of 145 psi - when exposed to a supply pressure of 3000 psi. The "washers" you refer to are shims. A repair technician would place appropriate shims in the unit to achieve a pressure of 145 psi IP with 3000 psi input. These shims would be available from Scubapro.

A repair technician would then verify that when the supply pressure is dropped to 500 psi - the IP is still within the range of 125 -145psi.

NOTE: This reply is NOT instruction on regulator repair - and the information is provided without warranty - simply as a description of the optimal behavior of a properly tuned scubapro MK2 when supplied with various pressures. It may be incomplete or wrong. If you are uncertain about the condition of your regulator - please consider having it serviced by a qualified technician.

 

[tstormdiver]

Another thing to keep in mind, Scubapro recommends not using more than 3 shims. Each shim brings the IP up about 5 psi. If the IP can not be reached with 3 shims added, then the spring needs to be replaced.

 

[BIGJACK]

Thanks for the replies. What about the washer listed in the schematics under the yoke?

 

[Wayward Son]

I have a Mk2, taking notes...

 

[axxel57]

A MK2 - when properly assembled and tuned should crisply lock up with an IP of 145 psi - when exposed to a supply pressure of 3000 psi. The "washers" you refer to are shims. A repair technician would place appropriate shims in the unit to achieve a pressure of 145 psi IP with 3000 psi input. These shims would be available from Scubapro.

A repair technician would then verify that when the supply pressure is dropped to 500 psi - the IP is still within the range of 125 -145psi.

NOTE: This reply is NOT instruction on regulator repair - and the information is provided without warranty - simply as a description of the optimal behavior of a properly tuned scubapro MK2 when supplied with various pressures. It may be incomplete or wrong. If you are uncertain about the condition of your regulator - please consider having it serviced by a qualified technician.

Interesting, and how do you properly tune a MK2 to crisp 145PSI?

The shims nowadays add or lower 3-5PSI IP.

When you have rebuilt a MK2 and your your IP at 3000PSI is 143, then you start changing shims until you have your crisp 145PSI?

Are you going to charge for the changed shims?

What do you think you would achieve with crisp 145PSI instead of for example 143PSI?

If somebody would do real cold water diving, do you think you would do him a favor with your crisp145PSI?

For me that sounds a bit as if somebody has attended a Scubapro Master Technician Course............

 

[rhwestfall]

For me that sounds a bit as if somebody has attended a Scubapro Master Technician Course............

To me, the disclaimer was the first clue.....

 

[bl6394]

Interesting, and how do you properly tune a MK2 to crisp 145PSI?

The shims nowadays add or lower 3-5PSI IP.

When you have rebuilt a MK2 and your your IP at 3000PSI is 143, then you start changing shims until you have your crisp 145PSI?

Are you going to charge for the changed shims?

What do you think you would achieve with crisp 145PSI instead of for example 143PSI?

If somebody would do real cold water diving, do you think you would do him a favor with your crisp145PSI?

For me that sounds a bit as if somebody has attended a Scubapro Master Technician Course............

You seem to misunderstand how shims work - they only raise the IP - not lower it. The mfg makes a variety of shims available to adjust the IP from the base value resulting from spring tension. If the IP can't be properly adjusted with shims - we'd replace the spring. Factory spec for a Scubapro first stages is 145 - not 143 - or 147.

I'd charge for any parts and time. Assuming you're running a business or value your time - perhaps you charge for your time and materials too. If you don't charge - let me know - I'll send you some work.

Your suggestions that the IP be dropped to make the regs more reliable for use in cold water is not recommended by the manufacturer. Nor would they suggest detuning the second stage. Their trainer compared that to trying to run with a sock in your mouth. Not saying that doesn't work for you, but if someone was diving in cold fresh water - I'd caution him that a non-environmentally sealed piston reg would be more likely to freeflow - particularly if they had poor technique or air consumption. I've seen students free flow in 38 - 42 degree water in MK25's - but never in MK17's. The MK2 EVO's have features to make them more tolerant to cold water - but I prefer diaphragms regs.

You are correct - I have attended the manufacturer's training. For the money ($200) it was a two day course well spent.

You're kind of an odd duck... But please don't take offense! You seem to know more about the Regs than the manufacturer. Perhaps you'll tell us more?

 

[bl6394]

To me, the disclaimer was the first clue.....

Absolutely. Professional Liability is a ... non-PG-word. When you work with members of the public - some capable / some less so - and there is a chance that things will not go well - well I do what I can to limit my liability.

 

[bl6394]

Thanks for the replies. What about the washer listed in the schematics under the yoke?

Not sure what version of the MK2 you own - or what version of the schematic you're referring to .

Assuming a recent MK2, the plastic piece immediately behind the yoke is called a spacer in the MK2 Plus or a Saddle in the Mk2 EVO - a largely cosmetic part that would not affect the IP. That would be part 8 "spacer" 10044021 or part 8 saddle 10063021.

The parts that will affect your IP are the washers or part 2 in my schematic. These shims increase the force the spring applies to the piston. Regarding the shims: scubapro used to only offer 2 different thicknesses that resulted in roughly 5 and 8 psi increases respectively. The 8 psi black washer is no longer available (obsolete) - instead the factory is installing up to 6 shims - Up to 3 at the piston head sight and up to 3 behind the main body and sleeve. If more than 6 shims are required - then replacing the spring may be necessary.

The greater the force applied by the spring against the piston - the higher the resulting IP. Visualize the spring pushing against the IP in the chamber above the piston - when the IP is high enough to overpower the spring - the knife edge in the body of the reg will contact the HP seat and prevent additional gas from flowing - limiting the IP.

Two great resource to understand this further - and more generally learn about regulator function and repair are:

Pete Wolfinger's SCUBA Regulator Savy and Vince Harlow's SCUBA Regulator Maintenance and Repair.

And yes - as that wit above mentioned - the manufacturer's classes can be a great resource as well.