Question for Scuba Pro Techs

[Couv]

I was in the process of upgrading a 109 to a BA when I noticed the new balance chambers I have look different than the ones I have seen before. Here is a picture of the new one (on the left) next to the old one. It a bit longer than the old one. The chamber itself is just a tiny bit tighter than the old one too, but when compared to the spring pressure not noticeable. Could one of you SP techs confirm that this is a SP replacement part, or did someone goof on the order?

Question two: I have recently rebuilt a couple of MK 7 first stages and they work great except they do give an aural warning at low tank pressure. Everything from the oscillator to the stem pin and springs look pristine, but no honk. Any ideas?

Thank you.

Couv

 

[Luis H]

I have two balancing chambers that look like the left one and at least one that looks like the right one, but it is as long as the other two.

The hexagonal looking one came in an upgrade kit that I have had for a few years (I am falling behind in upgrading some of my 109). The two newer ones were bought as individual parts (they are not available in full kits anymore). They are less than a year old.

I think some of my BA's do have shorter balancing chambers like the one on the left, but I can remember for sure.


IMHO a honker that doesn’t honk is probably not a bad thing. I guess an audio alarm is not a bad idea… it is just not for me.

 

[Couv]

I have two balancing chambers that look like the left one and at least one that looks like the right one, but it is as long as the other two.

The hexagonal looking one came in an upgrade kit that I have had for a few years (I am falling behind in upgrading some of my 109). The two newer ones were bought as individual parts (they are not available in full kits anymore). They are less than a year old.

I think some of my BA's do have shorter balancing chambers like the one on the left, but I can remember for sure.


IMHO a honker that doesn’t honk is probably not a bad thing. I guess an audio alarm is not a bad idea… it is just not for me.

Hello Luis,

OK….if the chamber tube length is ok, that is probably the main thing. If fact, when I assemble the newer S-wing poppet with the newer chamber, it looks like a better fit. Now that you mention it, I suspect the shorter chamber was for the old blue poppet that has only one o-ring on the stem that goes into the chamber.

Re: the Honker, yeah….I agree, it's just that when you rebuild something, you want everything on it to work as advertized. Everything looks good inside, so it may be a matter of a worn spring. If you have any ideas, please let me know.

Cheers,

Couv

 

[DA Aquamaster]

The newer ones are a bit longer - but remember the overall lenght of the poppet assembly is what counts. The longer cylinder portion of the balance chamber is not really relevent as the o-rings on the stem bear deeper in the cylinder - the same place they would in terms of distance from the back of the balance chamber as the would with a shorter one.

What it does accomplish is make the balance chamber long enough to engage the poppet with the spring in place, which makes it easier to assemble and install. (But it is not real hard to install in the first place.)

Or at least it did. SP has since added the lower piston bushing from a Mk 25 to the assembly, placing it on the balance chamber prior to the spring, essentially using it as a spacer to increase spring pressure on the assembled poppet. Viewed optimistically, it creates a way to increase the cracking effort with a weak spring on a G250, etc without turning the orifice too far in and restricting the working range. Viewed pessimistically, if you leave it on, the increased (and now excessive) spring pressure increases the cracking effort so that the "old" R156s and G250s do not breathe better than the current G250HPs and S600s.

I suspect the latter more than the former and 95% of the time I leave the spacer off.

I have seen the short black balance chambers, short white balance chambers, longer white balance chambers and the current balance chamber that looks sort of like a soviet rocket.

-----

I am not sure who knows how to get the honking side of a Mk 7 to work. I suspect those techs are all retired or dead and I frequently hear complaints of otherwise pristine Mk 7's that don't honk.

 

[redacted]

I have 2 new chambers that I ordered separately from kits that look like the one on the left. I have one new chamber (white in color) in an older kit with a current s-wing poppet that is the same length as the one on the right. My stash of older chambers that I have removed from older SP BP 2nds with the metal stems all look like the one on the right. I also opened up one of my rebuilt 156s and found yet a slightly different style black chamber with the thick part looking like the one on the right but with a longer stem like the one on the left.

My Mk7 starts honking in the 350 to 400 psi range and then effectively stops honking (and stops delivering useful air) somewhere in the 150 to 200 psi range. You do have to take a pretty good breath to make it honk. If you just sip, it might not get to oscillating. If you try it at a real low tank pressure (150psi) and it does not stop delivering air while the alt will still deliver, the stem may not be pulling back enough due to a weak spring. But I would start with the 2 o-rings and sealing surfaces on the oscillator. If they are not sealing correctly, that would prevent effective oscillation.

 

[Couv]

Balance chamber…ok, so no worries there. I was concerned that perhaps I ended up with a few balance chambers from an Apex or some other brand X company.

Honker.....now I feel like a real idiot, thanks to your post, I now realize that I must have my test hose plugged into the wrong port. I thought it would honk no matter which port I had it plugged into. I drained my tank down to test this thing and when the primary did not give out sufficient air, I moved it over to the alt port. So that could very well be all it is. I used to sell these darn things, it's a good thing I never tried to demonstrate one plugged in the wrong hole. I'll have to check that out when I have time, hopefully this evening when I get home from work.

Never underestimate the power of a stupid person by himself.

Thanks,
Couv

 

[Couv]

Honk, honk.....Awap, you're the man. Both my heavy yoke and light yoke MK7's are working as advertised.....thanks

Couv