Scubapro balanced adjustable second stage freeflowing
- Thread starter MarkH
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Tanks A Lot
Contributor
I'm fairly sure the source of the problem has already been pointed out: most likely the spring, or how it interacts with the surrounding parts.
Springs are relatively easy to check, even though manufacturers tend not to publish detailed mechanical properties. For us, two factors are of interest:
k = Spring constant (N/m)
F = Applied force (N)
x = Displacement (m)
A practical example:
Suppose the spring in the picture measures 23.00 mm in its relaxed state. I have locked the caliper at 16.00 mm. Place the spring on the scale, put the caliper needle into it and push down until you just touch the scale. The reading shows roughly 1.6 Kg.
Plugging the numbers into the formula requires some unit conversions, such as weight to force and mm to m, but we can do these on the fly:
k = (1.6 kg * 9.8067 m/s2) / (23 mm / 1000 − 16 mm / 1000)
k = 2242 N/m
Here, the numerator is the applied force (converted from weight), while the denominator is the displacement in metres (converted from millimetres). That’s really all there is to it. If you can find someone with a known good spring, they can measure theirs and you can compare results.
What I usually do is take several measurements of force and displacement, then average the calculated values of k. For example:
20 mm → ?? kg
19 mm → ?? kg
18 mm → ?? kg
…
The attached spreadsheet might help if you’d rather not crunch the numbers manually and are lazy, like me.
If my notes are correct, your spring should measure 23.00 mm in the relaxed state, with a constant k of about 2300 N/m. I’d be very interested to hear what your measurements show.
Maybe someone with better mechanical skills than me, such as @Mobulai or @axxel57, could measure what they find for Scubapro’s 01.020.216 spring. My own measurements are a little dated and my notes may not be perfect.
Springs like to deform over time under stress relaxation. That simply means that the spring is shorter in its uncompressed state than it originally was. I would not be surprised if this is exactly what happened here.
I also second @axxel57’s observation that the seat may have developed an uneven impression. A bit of a clearer picture would be awesome.
Some other checks worth making:
Springs are relatively easy to check, even though manufacturers tend not to publish detailed mechanical properties. For us, two factors are of interest:
- The spring’s relaxed length: This is very easy to measure with a caliper.
- The spring constant (stiffness), in newtons per metre (N/m): This is less straightforward to measure, but still easier than most might expect.
- Measure the length of the relaxed spring as accurately as possible with a caliper. This step is crucial, since the value goes into the formula for the spring constant. I usually repeat the measurement a few times to be confident of the result.
- Next, set your caliper to the spring’s length minus 1 mm (or another convenient offset that you record) and lock the caliper.
- Place the spring on the kitchen scale and zero it.
- Insert the “needle” of the caliper inside the spring and slowly push down until the caliper contacts the scale. Record the weight at that point. Again, I repeat this a few times to get the most reliable reading possible.
k = Spring constant (N/m)
F = Applied force (N)
x = Displacement (m)
A practical example:
Suppose the spring in the picture measures 23.00 mm in its relaxed state. I have locked the caliper at 16.00 mm. Place the spring on the scale, put the caliper needle into it and push down until you just touch the scale. The reading shows roughly 1.6 Kg.
Plugging the numbers into the formula requires some unit conversions, such as weight to force and mm to m, but we can do these on the fly:
k = (1.6 kg * 9.8067 m/s2) / (23 mm / 1000 − 16 mm / 1000)
k = 2242 N/m
Here, the numerator is the applied force (converted from weight), while the denominator is the displacement in metres (converted from millimetres). That’s really all there is to it. If you can find someone with a known good spring, they can measure theirs and you can compare results.
What I usually do is take several measurements of force and displacement, then average the calculated values of k. For example:
20 mm → ?? kg
19 mm → ?? kg
18 mm → ?? kg
…
The attached spreadsheet might help if you’d rather not crunch the numbers manually and are lazy, like me.
If my notes are correct, your spring should measure 23.00 mm in the relaxed state, with a constant k of about 2300 N/m. I’d be very interested to hear what your measurements show.
Maybe someone with better mechanical skills than me, such as @Mobulai or @axxel57, could measure what they find for Scubapro’s 01.020.216 spring. My own measurements are a little dated and my notes may not be perfect.
Springs like to deform over time under stress relaxation. That simply means that the spring is shorter in its uncompressed state than it originally was. I would not be surprised if this is exactly what happened here.
I also second @axxel57’s observation that the seat may have developed an uneven impression. A bit of a clearer picture would be awesome.
Some other checks worth making:
- Are the short lever feet in good shape, or is one slightly bent? This would put uneven forces onto the poppet, potentially skewing it inside the barrel.
- Does the spring cause uneven pressure? Roll it on a flat surface, does it wobble?
- Are the threads for the orifice in good condition, especially inside the barrel? A crooked orifice in its seating could cause problems, though it’s difficult to verify without cutting the barrel open.
I have new replacement .216 springs (supposedly manufactured last year) that I can measure once my caliper is back from a “loan”
I also have the stiffer .218 (A700 and g250V) that I could measure subsequently
Speaking of interacting parts, wasn’t there a compatibility “chart” for levers and poppets; IIRC the latest Swing poppet is preferable with the newer .141 levers as their curly feet engages with it better
But I doubt this is the source of troubles here
I also have the stiffer .218 (A700 and g250V) that I could measure subsequently
Speaking of interacting parts, wasn’t there a compatibility “chart” for levers and poppets; IIRC the latest Swing poppet is preferable with the newer .141 levers as their curly feet engages with it better
But I doubt this is the source of troubles here
OP
MarkH
Contributor
It seems like this is an almost dangerously quirky reg engineering-wise compared to other ones I've worked on. I'm not sure I should bother spending a couple hundred dollars for a new orifice/spring/maybe lever, when everything might still not work together. With my conshelf, you can almost rebuild the second stage using a broken paper clip and some scraps of rubber (semi-exaggerating) and it works fine every time, but with this one, if something is just slightly out of spec, to the point of me not even being able to visually see it, the reg will fail and maybe kill me 100' deep. If I can find a single source of parts, I might still give it a try out of stubbornness.
I totally understand your position on it being worth it or not as an inventment, but alas it can work quite beautifully with some cheap workarounds
I previously got the exact "upgrade" set (lever, poppet, spring) from @buddhasummer for relatively cheap; and you can always dress an orifice with a micromesh
You might even be able to skip on the spring and keep the original and simplly shim it (a 1$ washer from McMaster can do the trick) if it has hardened over the years
The poppet and the lever are the key ones; new poppets need the curly foot lever to properly engage; the old ones (blue and grey) don't mind both (but have been designed with the old lever in mind)
And bent levers also can be extremely problmatic (but that applies to all regs)
It’s not worth it, go to Deep6 and buy a second stage and after you learn the joy of actually breathing underwater, but another one and toss these clunkers into a box and forget about them.
You can continue along this path where you will learn that an old second can be bought for $20 and after you put $150 worth of parts into them you can sell it for $20
You can continue along this path where you will learn that an old second can be bought for $20 and after you put $150 worth of parts into them you can sell it for $20
OP
MarkH
Contributor
Well this is a vintage gear forum so presumably there are a few people on here that like the old metal stuff. I drive 40 year old cars and my house is 115 years old because I like it that way. I could go get a new car with much more horsepower, driving comfort, a big screen on the dash and the ability to control it from a phone, but I drive my old economy cars because they're cool. Many people don't get it. My house isn't even Smart. I have to turn on the lights with a switch on the wall and I can't even see what my fridge temperature is remotely from my phone, but I call it "character" and I like it that way.It’s not worth it, go to Deep6 and buy a second stage and after you learn the joy of actually breathing underwater, but another one and toss these clunkers into a box and forget about them.
You can continue along this path where you will learn that an old second can be bought for $20 and after you put $150 worth of parts into them you can sell it for $20
And sometimes clinging to past can be silly, why have a switch for the kitchen lights at all just wait for the sun to come up. I’m from the past, the 109/ba was the hottest thing available when I started diving, they can still hold their own when the work right but for far less money you can get vastly better performance from many sources. I have two very nice 109’s on the verge of going in the trash because they just aren’t with the bother, nostalgia has its place but at least get some decent breathers for actual diving.
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