Question Aqua lung core regulator hissing

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You all bring up good points. I will check the IP and see if it is in spec 138psi correct +or- 7psi. I will also make sure it's stable and doesn't creep up. Is the gauge I attached sufficient?
 

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You all bring up good points. I will check the IP and see if it is in spec 138psi correct +or- 7psi. Is the gauge I attached sufficient?
The lever doesn't seem to be low, but I will check it as well. If I barely touch the purge it purges.

I mean if I die I die, I saved 45 bucks though LOLOL Just kidding!
 
You all bring up good points. I will check the IP and see if it is in spec 138psi correct +or- 7psi. I will also make sure it's stable and doesn't creep up. Is the gauge I attached sufficient?
Keep in mind a 2-3% error margin for the gauge…
 
You all bring up good points. I will check the IP and see if it is in spec 138psi correct +or- 7psi. I will also make sure it's stable and doesn't creep up. Is the gauge I attached sufficient?

Yes, that gauge or one like it should be sufficient. After you check your 1st stage's IP and if it locks up (doesn't creep), then you should also check the cracking pressure of your 2nd stage. A magnehilic gauge is the industry standard, but many of us who do self service get by with doing an immersion test:
1. Fill a bucket with water.
2. Attached the reg set to a cylinder and fully open the valve.
3. Note the level where the diaphragm sits within the 2nd stage casing.
4. With mouthpiece up, slowly submerge the 2nd stage in the bucket until it just cracks and begins to release air.
5. Estimate/note how far below the surface, the top of the diaphragm is at the point noted in step 4.
6. Remove the 2nd stage from the bucket of water and then repeat a few times.

The 2nd stage should crack relatively within the range specified for it.

If IP is correct and stable, and cracking pressure is correct, and lever height is set properly, coupled with the adjustment you previously made to stop the hissing you can more safely assume the issue was with the 2nd stage seat and your set up is ok to dive.

Or you can just risk it and dive as you have adjusted it, but the above steps are less than 5 minutes to perform...in fact you will spend more time filling and emptying the bucket than you will doing anything else...but those steps can provide a good amount of info regarding the health of your regulator set.

I think everyone who has chimed in was earnestly trying to provide you helpful information but sometimes rudimentary details that are well known and routine get ommited during the explanation/discussions and often these little things are critical to the big picture and their ommission can lead beginners (to DIY service in this case) astray.

(Now I am keeping my fingers crossed that I didn't mistakenly leave anything out in the steps for the immersion test above.)

-Z
 
[...]Is the gauge I attached sufficient?
Borrowing from what I wrote elsewhere:

Pressure gauges get classed by how accurate they are. This precision is imprinted onto the scale of the gauge, e.g. here:

Gauge.png



This is a gauge that has a precision of 1.6%. This precision applies to the maximum value of the scale!

This gauge goes to a maximum of 16bar. 1.6% of 16bar is 0.256bar, which means the gauge can deviate 0.256bar (3.7psi) anywhere on it's whole scale. This is acceptable for the use we intend.

Precision's range from practically nothing, to 4%. The really expensive gauges go down to 0.1%. If you look at analogue gauges, anything above a precision of 1.0 is a gauge with a diameter larger than 100mm. If you think about it, that makes total sense, as these small scales on the small gauges can't represent anything accurately.
In general, the cheaper and smaller a gauge, the worse its precision.
A gauge that has no precision indicated automatically has one of 4% (I have seen way worse on some crappy ones...).

The gauge linked has no precision indicated, so it is assumed to have one of 4%. Furthermore, its scale goes up to 22bar. 4% of 22bar is 0.88bar (12.8psi). This gauge can deviate anywhere on it's scale nearly 0.9bar, which makes it completely useless for setting intermediate pressure accurately.

I should note, that these are maximum values. The gauge can deviate that much, but it does not automatically do so. The problem is that one has no real way to tell if it does, without another, more accurate gauge.

Choosing a pressure gauge should keep its accuracy, as well as its maximum scale in mind. An electronic pressure gauge that has a precision of 1.0, but goes up to 200bar would be of no use either, as it can deviate by up to 2bar.

The precision of a gauge must be kept as low as the wallet allows, while the range should be only slightly higher than the highest expected value.
 
How about a 0-160 psi that has this accuracy?

  • ASME B40.1 Grade A Accuracy Compliance ± 2-1-2 % of span
 
How about a 0-160 psi that has this accuracy?

  • ASME B40.1 Grade A Accuracy Compliance ± 2-1-2 % of span
11.0bar (160psi) is too close to your targeted working range of 9.0bar (130psi) to 10.0bar (145psi). In case you have a slight, or in unfortunate situations, not-so-slight, first-stage pressure creep, this gauge will likely be damaged.

Once you do the math, there really isn't all that much choice left for an analog gauge to measure intermediate pressure in SCUBA regulators. The use and misuse of intermediate pressure gauges are some of the most common mistakes I see when visiting dive centres or teaching students. Both the use of these gauges and the gauges themselves seem deceptively simple, yet there are crucial things that get overlooked almost constantly across the SCUBA industry.

Maximum Gauge Range​

  • Pressure gauges perform best when their operating pressure does not exceed 75% of the gauge range. Continuously using a pressure gauge past 75% of its range will eventually result in a gauge that is out of specification and shows faulty data. (On pulsating systems, it should be kept at 66%.) It is common industry practice to use a gauge with a range twice the expected operating pressure. However, this practice directly conflicts with the class and precision that we require, more on that further below. As we aim for around 10.0bar (145psi) maximum, the gauge should have a minimum working range of 13.5bar (195psi) (10.0bar/0.75). As a first estimate for the minimum gauge range, we end up with 13.5bar (195psi). We will refine this further.
  • The gauge must withstand a faulty first stage that has an intermediate pressure leak. Personally, I do not like gauges that do not have a built-in or in-line over-pressure valve. While you could argue that the second stages will vent excess gas, I have found myself multiple times using the gauge on a first stage with no second stages attached. This over-pressure valve must vent before the maximum gauge range is reached, as the gauge would get damaged otherwise. This, however, lowers the 13.5bar (195psi) from above, as we don't want our gauge to vent close to where we will be working. As these over-pressure valves are not always super accurate, it is wise to choose a gauge with a range of more than 13.5bar (195psi). An extra 2bar (30psi) or so should do nicely as a safety buffer, which puts us at 15.5bar (225psi) (13.5bar (195psi) + 2bar). This 15.5bar (225psi) is our definite minimum gauge range.

Accuracy Class​

  • The gauge must be suitably accurate. As explained earlier, the class of the gauge applies to the maximum value of the gauge, not the value that you are reading from the gauge. Most first stages have an intermediate pressure of 9.0bar (130psi) to 10.0bar (145psi). However, there are exceptions, such as Mares diaphragm models (with one exception), that have a much narrower intermediate pressure range of 9.8bar (142psi) to 10.2bar (148psi). If we were to work on one of those Mares models, our gauge must have a precision better than 0.2bar (3psi). This assumes we set the intermediate pressure at 10.0bar (145psi). As our gauge has a precision better than 0.2bar (3psi), neither upward nor downward deviations shall concern us, as we would still be within specification. Our earlier calculated minimum gauge range of 15.5bar (225psi) must have a minimum accuracy of 1.3% to still accurately work on this Mares regulator (15.5bar × 0.013 = 0.20bar). The 1.3% accuracy is our minimum required accuracy.
  • Nearly all small (63mm) gauges I have ever seen have a class unsuitable for our purpose. They are good enough to gauge when a regulator is cracking open by making the intermediate pressure drop visible. This means we end up with a 100mm gauge at minimum. Only these gauges can come with the required accuracy.

Extra Bits​

  • I strongly suggest getting a glycerin-dampened gauge. Glycerin-filled gauges have the advantage of dampening shocks. If you were to use your intermediate pressure gauge properly, this would negate the need for a glycerin-dampened gauge. Proper use means attaching the gauge before pressurizing the first stage. This allows the pressure to gradually build up within the gauge, and no undue stress is introduced. However, this is the part that almost all technicians will get wrong at some stage, me included. Furthermore, almost all technicians don't even realize that they got this part wrong. We oftentimes attach our intermediate gauge while the first stage is pressurized. This introduces a pressure shock within the gauge. The gauge won't be damaged by doing this once, or twice, or thrice. But every time this is done, the internal mechanics are subjected to undue forces, and there will come a time when the accuracy of the gauge will start to suffer. When I check old gauges in dive centres used in this way, almost all are out of original specifications after a while.
  • I would suggest getting an analog gauge. I must admit that this is personal preference, and quality digital gauges do exist. The most accurate gauges, for that matter, are digital. But digital gauges have the downside of suffering from a sampling rate. Digital gauges do not update instantaneously, but only do so at certain time intervals, their sampling rate. Analog gauges, on the other hand, always update instantly. This will be of significant interest when checking cracking pressure. Again, digital gauges are not in themselves unsuitable for this task, but extra care must be taken to get a gauge with a sufficiently quick sampling rate. On a side note, I personally find it easier to see a swinging needle out of the corner of my eye than a changing digit.
There Are a Few Caveats for the Above Mentioned:
  • Nothing stops you from buying a super-expensive digital gauge that goes to 200bar with an accuracy of 0.1%. This is perfectly suitable for the job but may be overkill.
  • I took the extremely tight intermediate pressure range of some Mares first stages. Most other regulators require a less accurate gauge, as their intermediate pressure range is usually between 9.0bar (130psi) and 10.0bar (145psi). If you set the intermediate pressure at 9.5bar (138psi), the gauge only needs to be accurate to 0.5bar (7psi). This would mean an accuracy of at least 3% on a 15.5bar (225psi) gauge.
  • As with so many things, it comes down to your personal choice. Are you sure you always attach your gauge the right way? If yes, skip the glycerin, as it would add an unnecessary cost you can avoid. Are you not required to set the pressure of certain tight-fitting intermediate pressure first stages? If yes, you can go for a gauge with lower precision than the 1.3%. Are you not bothered when the pressure is slightly off? While not ideal, even an intermediate pressure ever so slightly above or below the specifications of the manufacturers will work just fine. This means a less accurate gauge may still be OK for you.

My go-to gauge in the workshop is this. I apologize for the German link, but I'm sure translation tools can make it work for you. You may notice that this is a gauge with an accuracy of 1.6%, not 1.3% as earlier suggested. This is because nearly all regulators can be accurately set with this gauge, and I keep a more accurate gauge in a drawer for when the need arises.

Buy a gauge that is right for you while keeping the above things in mind. It doesn't have to be a super fancy, expensive one, but you should know which trade-offs you make and choose wisely which corners you may want to cut.
 
I was only planning on using it once really. Just to check to make sure it was ok to dive my last trip before it goes in for service. My local shop sends them out so I can’t just stop by and have them check it. @Tanks A Lot if I got that same gauge but in the 200psi version would that be ok?
 
I was only planning on using it once really. Just to check to make sure it was ok to dive my last trip before it goes in for service. My local shop sends them out so I can’t just stop by and have them check it.

I use my pressure gauges to regularly check the IP on the regulators I’m diving. If I’m diving daily, I check at least weekly. If diving infrequently, before every dive trip.

During the initial period after service the seat will take a set (small groove from the impact on the orifice) and this will affect the IP.

With unsealed diaphragm regulators it’s easy to adjust the IP without having to open it. Some of the higher end modern pistons can be adjusted too.
 

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