IP on MK20

[Jens Bölte]

Hello

I have a MK20 1-stage here which I just serviced. The problem is that the IP is too high, around 11 - 11.5 bar, after service. I did not measure the IP before service. So, I can't tell how high it was before service. Any idea how I could get it down to 9.5 bar? Even removing all plastic rings (a white one and a black one sitting on each side of the spring) brought down the IP only to 11 bar. It is not an IP creep. IP just goes up to 11 bar and stays there.

Best wishes Jens

 

[lexvil]

With no spacers it is out of adjustment range, I would try doing some quick cycling, like 100 quick hits with the purge button, leave it under pressure over night and see what happens.

assuming the piston is in good condition it may just need some cycles to help it seat properly.

 

[axxel57]

Your IP Meter is okay?
How long do you have and use that Mk20 1st?
Does it has the T.I.S. system installed or was converted to T.I.S.?
With time and use sometimes the main spring gets a bit shorter and stiffer.
So if you have an old Mk20 model with the old main spring, it is possible that it shows higher IP than normal.
In that case you should try a newer main spring.
You could also try to lower the IP by lubricating the piston o-rings with a 'thicker' lube like Molykote 111.
In any case I wouldn't bother too much about the 11bars IP, unless diving in very cold conditions.
For me it is more important that the IP is stable.

 

[halocline]

If I'm not too stupid to get this right, 11 bar is just about 160PSI. That's too high for my tastes, and if that's what it is with no shims on the spring, something is wrong. Are you sure you have the right seat? Does your piston have a brass tip? (That's an important one because if it does, you should replace it regardless with the composite piston).

Basically there are only three things that can cause this; problem with the seat, the piston, or the main spring. So you'll have to start replacing those parts one at a time. It would be great if you had another M20 (or 25) you could borrow parts from to test. But seat and piston problems usually cause creep, not this.

A long shot would be poor lubrication and/or excessive extrusion at the HP piston o-ring. You can try testing IP at very low tank pressure. Just turn off the tank valve and tap the purge a few times until the SPG reads 25-30 bar. If the IP is back in line, maybe 9 bar, that indicates a HP o-ring problem.

 

[Jens Bölte]

Hi,

Ok, here is what I did. I took out one of the plastic-rings, attached the regulator to our measuring bench which has a quick-set feature for about 10 minutes. Over this time-period, the IP slowly dropped to 9.6 bar, max 9.9.bar, min 9.3 bar. Seems that it took a little bit longer than usual to set piston and seat properly. I was too impatient.

best wishes Jens