Can't get the valves off my steel tanks

[Still Kicking]

Valves get stuck all the time ......

Lubricant should also not be used when installing valves per the manufacturers installation manuals.

Maybe this is why valves get stuck....

Here's the relevant page from the Luxfer manual. Lubrication is "essential."

 

[34109411]

I am on vacation in Mexico and I brought my own gear - including 2 e7-100 steel tanks. They had a hydro and visual in January 2022. The dive shop I went to here says he can't get the valves off the tanks. He seems like a nice / competent kind of guy. Does anyone have any suggestions that may help us ? Thanks [He said he tried a mallot and something else]

go with the wrench, put a towel around the valve so you don't damage it. Dont fo crazy on it, it should get loose. It happen to me this spring on my 30 CF but it was bit different but same thing.

Where are tou exactly in mexico i was there 3 years could tell you where to go to get help.

Be safe.

 

[tbone1004]

Maybe this is why valves get stuck....

Here's the relevant page from the Luxfer manual. Lubrication is "essential."

it was unclear whether it was steel or aluminum

 

[Tanks A Lot]

Maybe this is why valves get stuck....

Here's the relevant page from the Luxfer manual. Lubrication is "essential."

The thoughts on this diverge quite substantially, and there are good reasons for lubricating the valve threads, just as there are good reasons not to. I personally do not lubricate the threads and teach to avoid using any lubricant, as I feel that the downsides of doing so outweigh the positives lubrication would provide.

Reasons to use lubrication are generally attributed to:

• Easier removal of the valve
• Protection against galvanic corrosion

Both points are flawed in my experience and share the same thought process. The belief is that lubrication protects the cylinder from corrosion should moisture enter.

Galvanic corrosion occurs where brass and aluminum/steel are in contact with each other and an electrolyte, mainly water for our purposes, is present. This is always present on the face of the cylinder and the shoulder of the valve, and no one ever lubricates this area. This is also the area mainly affected by galvanic corrosion, not the threads.

The thread area is subjected to galvanic corrosion in the case of water ingestion. I see two flaws with the idea that lubrication would protect the cylinder threads:

• Experience has shown that lubrication can trap water droplets in the thread area. This trapped water does not drain from the thread area and leads to pits in the threads of the cylinder. I have never seen a pit in the threads of a non-lubricated cylinder, but I have seen many pits where lubrication was used. Without lubrication, the moisture can drain from the threads. While it is true that, in this case, the threads overall get damaged, it is usually only slightly. The concentrated water droplet trapped by lubrication leads to a concentrated point of failure.
• Lubrication would only be effective in preventing galvanic corrosion if it were to electrically isolate the brass and aluminum/steel from each other. I highly doubt that this could be achieved in our scenario. Most lubricants used in SCUBA are not fully dielectric, and while they may provide some electric barrier, they won't isolate the two parts. Molykote 111, suggested by Luxfer, for example, is not a dielectric. Furthermore, due to the extreme forces exerted onto the valve, 1150 Kgf, most of this grease will be squeezed out from between the two mating threads. We are left, if at all, with an extremely thin film of lubricant which isn't dielectric to begin with.

Additionally, lubrication greatly distorts torque specs. Torque for an M25x2 6g thread on an aluminum cylinder should be 95 Nm according to BS EN ISO 13341-2010 + A1-2015. This torque is specified without lubrication. If one were to lubricate the threads and torque to 95 Nm, one would greatly overtorque the valve. Now, I'm the first to admit that I do not fully agree with the torque specs given by ISO and the EN. I feel that they are way too high.

You can find much literature advocating for using lubricant, as well as not using it. BS EN ISO 13341-2010 + A1-2015, for example, advises against it.

Valving procedure for parallel threaded valves
[...]
6.2 No lubricant, sealant, or tape shall be applied to the threads.

The case for or against lubrication is certainly not as clear-cut as some portray it to be. The issue is very nuanced. I must admit that in the past I wish I did lubricate the threads, but that was a very specific scenario which involved substantial saltwater ingestion in a fleet of cylinders; several litres each.

 

[Pavao]

:

• Experience has shown that lubrication can trap water droplets in the thread area. This trapped water does not drain from the thread area and leads to pits in the threads of the cylinder.

• 
  Can you elaborate on how this water got there in the first place, please.
  The first thought is, if lubricant is trapping water in, why is it not trapping water out?
  
  But most importantly I’m trying to understand how water is getting in in the first place. You have an oring sitting above the threads, water must pass this oring to get to the threads, if water is passing by the oring, then gas is also passing by the oring, you have a valve not sealing then, this tank leaks.
  
  A second point you made said lubricant is ineffective in creating a barrier between the thread of the valve and the thread of the tank because the lubricant would be squeezed out due to the extreme force between the threads, leaving only a thin layer of lubricant. Yet you state water is trapped in the threads, in the very place where lubricant is squeezed out, and the lubricant itself is what is trapping water there, although according to you, there’s no room for the lubricant to be there.
  
  I’m not really trying to make a point for or against lubricant here, just trying to understand how those statements you made make any sense

 

[Still Kicking]

it was unclear whether it was steel or aluminum

Lube or dont lube ...your choice. But don't spread misinformation that the manufacturers recommend against it.

 

[Boarderguy]

Lube or dont lube ...your choice. But don't spread misinformation that the manufacturers recommend against it.

Same to you. It is recommended by luxfer for their aluminum tanks. Nothing about Catalina, PST, or Faber.

 

[Tanks A Lot]

[...]
Can you elaborate on how this water got there in the first place, please.
[...]

The water ingested by cylinders always comes from two sources. One scenario is that the cylinder was emptied completely and the valve left open. This happened to the fleet of cylinders I briefly mentioned in my last sentence.

The other scenario involves a malfunctioning compressor. The compressor's last filter, the one with the molecular sieve, only filters out a tiny amount of moisture from the air. The vast majority of moisture is expelled earlier in the cyclone separators and the clever implementation of a PMV. In the tropics at 35°C, you will get around 150 mL of water per S80 filled. If the PMV and cyclone separators are malfunctioning, the final filter and molecular sieve are overwhelmed after filling just a handful of cylinders. This last example is extremely common in dive centers in the tropics.

The first thought is, if lubricant is trapping water in, why is it not trapping water out?

Absolutely fair point, and I guess it does to some degree. Unfortunately, the lubricant is not static and will move around ever so slightly. Think about a diver making a back-roll from a boat with a cylinder having half a liter of water inside. That water will come rushing down towards the valve and hit the lubricant, ever so slightly dislodging it.
Or it may not, but the point is that it can. While most lubricants are awesome at being very hydrophobic, some people use whatever they have at hand. This can result in the lubricant "catching" the water. Even hydrophobic lubricant can in unfortunate situations create a barrier or obstruction that the moisture has a hard time to escape.

Furthermore, the valve is the part that sees the highest temperature swings when using or filling a cylinder. Moisture is suspended in the gas that you are filling. This suspended air of course penetrates between the threads, up to the O-Ring. On temperature changes, this suspended water can condense between the threads.

A second point you made said lubricant is ineffective in creating a barrier between the thread of the valve and the thread of the tank because the lubricant would be squeezed out due to the extreme force between the threads, leaving only a thin layer of lubricant. Yet you state water is trapped in the threads, in the very place where lubricant is squeezed out, and the lubricant itself is what is trapping water there, although according to you, there’s no room for the lubricant to be there.

I guess I worded this poorly, apologies. Think about two threads meeting each other, with the male threads getting pushed extremely hard into one direction, parallel to the female thread, not perpendicular to it. Let us assume that the crests of the male thread will be pushed upwards. That upward pushed crest will leave a small gap underneath itself and the lower female thread. Maybe this picture can convey better what my poor wording can't.

Note that I have drawn this extremely exaggerated. Tolerances on a real M25x2 6g thread are fairly small, but they still do leave a small gap underneath the crests as shown in the picture.

I’m not really trying to make a point for or against lubricant here, just trying to understand how those statements you made make any sense

I'm absolutely with you here, lubrication of cylinder threads is a delicate thing. One seems to loose whether you do or whether you don't. I can easily see the arguments on both sides of the aisle, but from personal experience I made the choice mentioned above.

 

[Still Kicking]

Same to you. It is recommended by luxfer for their aluminum tanks. Nothing about Catalina, PST, or Faber.

Ok here you go....this information is not classified. Lol

But what do these manufacturers know? They probably havent done a lick of metallurgy research.

 

[Boarderguy]

Ok here you go....this information is not classified. Lol

But what do these manufacturers know? They probably havent done a lick of metallurgy research.

Reading is hard for you. They're saying to lube the o-ring, not the threads of the valve or tank.

"Remove the large inlet o-ring from the base of each valve and apply a thin layer of lubricant to each"