TargetTalk

brent375hh wrote: ↑Wed Mar 10, 2021 8:40 pm It looks like you maybe ad libbed your directions instead of quoting the manual you referenced. My manual doesn't have anything about
" unscrew the cylinder one full turn", or "open the bleed valve". My manual just says " dismount compressed air cylinder from adapter ".

That second part is on the hand pump manual that I use. I'll see if I can find a copy of it...
I also thingten mine by hand, and don't need an wrench. That's very different from not thingtening all the way.

I've seen seals fail on adapters and cilinders, and it's not fun... I'm just trying to save you the experience!

And yes, if there is not bleed valve, you unscrew the cylinders until it hisses.
If you want a bleed valve on your tank, go for it. No one is stopping you.
But when you say not to screw the cylinder all the way in, that is wrong.

If you still want to do it, go ahead...

rmca wrote: ↑Thu Mar 11, 2021 12:21 pm

brent375hh wrote: ↑Wed Mar 10, 2021 8:40 pm It looks like you maybe ad libbed your directions instead of quoting the manual you referenced. My manual doesn't have anything about
" unscrew the cylinder one full turn", or "open the bleed valve". My manual just says " dismount compressed air cylinder from adapter ".

That second part is on the hand pump manual that I use. I'll see if I can find a copy of it...
I also thingten mine by hand, and don't need an wrench. That's very different from not thingtening all the way.

I've seen seals fail on adapters and cilinders, and it's not fun... I'm just trying to save you the experience!

And yes, if there is not bleed valve, you unscrew the cylinders until it hisses.
If you want a bleed valve on your tank, go for it. No one is stopping you.
But when you say not to screw the cylinder all the way in, that is wrong.

If you still want to do it, go ahead...

It takes 4 1/3 turns for my cylinder to go all the way on. .6 turns short of that, is where the valve hits the adapter to open it up. It takes another turn out to release the pressure. If turning the cylinder only to where the adapter hits the valve is "wrong" and assumed dangerous by you, how in the world do you turn yours yet another turn out from where the valve closes, under full pressure, to remove your cylinder? By adding a pressure release (that I admitted don't need) my cylinder will always have more threads engaged under pressure than yours.

brent375hh,

I really don't care how you do it... it's on you.
I would advise to screw it all the way in, to help align the cylinder with the adapter (removing the play in the treads) so the seal works as intended.
If you find an easier to do it, go for it, I really don't care... just be aware that there is a lot of energy in those little cylinders.

rmca,

When you can tell me how you unscrew your cylinder from the adapter, without turning past the point the valve has closed, under pressure, and then on out further until the seal releases, then I will listen to your point of all this danger. Until then, you are not really making any sense with your worrying about what you think I am doing wrong.

And if you don't really care, why keep telling me that I am wrong in a response?

The difference is that a fully seated cylinder is stronger than a thread that is not seated.
It then is only loosened after the tank valve is closed.
With your method the cylinder is not seated against the full capacity of the open tank.

Friggin wrote: ↑Thu Mar 11, 2021 9:19 pm The difference is that a fully seated cylinder is stronger than a thread that is not seated.
It then is only loosened after the tank valve is closed.
With your method the cylinder is not seated against the full capacity of the open tank.

When the tank valve gets closed, how much do you suggest that the pressure drops between the tank valve and cylinder? Zero.

When the cylinder gets filled, how many PSI do you think it takes before the threads are making the full contact with each other? Not very many.

When the tank valve gets closed, how much do you suggest that the pressure drops between the tank valve and cylinder? Zero.

It's not a matter of pressure, it's a matter of Volume.

When the cylinder gets filled, how many PSI do you think it takes before the threads are making the full contact with each other? Not very many.

I would rather have my cylinder fully seated and in it's strongest state before opening the valve, not relying on the pressure of the tank to move my threads into a seated position.

And as rmca said:

I really don't care how you do it... it's on you.
I would advise to screw it all the way in, to help align the cylinder with the adapter (removing the play in the treads) so the seal works as intended.
If you find an easier to do it, go for it, I really don't care... just be aware that there is a lot of energy in those little cylinders.

That said, I do like the idea of not having to unscrew the cylinder under pressure and the answer may be as simple as just using a correctly sized washer or spacer, then you would be fully seated and correctly spaced before opening the valve.

brent375hh wrote: ↑Thu Mar 11, 2021 7:18 pm And if you don't really care, why keep telling me that I am wrong in a response?

Because you asked... ;)

Friggin wrote: ↑Thu Mar 11, 2021 9:19 pm The difference is that a fully seated cylinder is stronger than a thread that is not seated.

He put it better than me. This is why.

Friggin wrote: ↑Fri Mar 12, 2021 7:35 am

When the tank valve gets closed, how much do you suggest that the pressure drops between the tank valve and cylinder? Zero.

It's not a matter of pressure, it's a matter of Volume.

Actually, if you are talking about STRENGTH, it is a matter of pressure, not volume. It's a simple pounds per square inch calculation -- the force on the threads is the same whether the cylinder is opened or closed.

Volume comes into play only if you want to look at the potential consequences of a failure. If the threads actually did fail (EXTREMELY UNLIKELY), the energy released with the cylinder closed would be significantly lower than with the cylinder open.

As for a fully seated cylinder being stringer than an unseated one -- yeah, probably, but does it matter? If one condition has a 5X safety factor and another condition has a 10X safety factor, the second is obviously "safer", but the first one is so over-engineered and safe that it is irrelevant in practical terms.

marky-d

Yes, I do believe that we are talking about the consequences of failure, at least I was.
The consideration of volume is not when the cylinder valve is open its when the tank valve is open.
Also, I think this entire discussion should be settled with one well placed washer.
I guess I would just rather be safe than sorry.

My apologies for the confusion, I was using the term "cylinder" to refer to the bulk fill "tank".

So just to clarify what you mean, you are saying adding a washer, so the cylinder cannot be screwed on as far, is going to provide the additional strength you are concerned about? I could see that providing more support to a side-load if the cylinder was dropped, but I fail to see how that will have any impact on the strength against the force of the internal pressure. The number of threads is the only thing resisting the force created by the internal pressure, so adding a washer is still going to technically reduce the strength (but not in a meaningful way).

You have me puzzled by your statement "relying on the pressure of the tank to move my threads into a seated position." Can you explain what you mean by that? You seem to want to suggest that adding some amount of mechanical axial load to the threaded joint (e.g. by screwing the cylinder down onto a solid shoulder) is going to improve its strength, but I may be misunderstanding what you are trying to communicate.

marky-d

I just talked to a mechanical engineer on this, and showed him the equipment. The o-ring is 8mm. The tank peak pressure is 3000psi. The surface area is .064 square inches, applying only 192 pounds of thrust on the cylinder.

An 8mm brass bolt has a shear strength of between 2000 and 3000 pounds.

So just to clarify what you mean, you are saying adding a washer, so the cylinder cannot be screwed on as far, is going to provide the additional strength you are concerned about? I could see that providing more support to a side-load if the cylinder was dropped, but I fail to see how that will have any impact on the strength against the force of the internal pressure. The number of threads is the only thing resisting the force created by the internal pressure, so adding a washer is still going to technically reduce the strength (but not in a meaningful way).

The reason for the washer is to keep the spacing required to allow the cylinder valve to not be physically pushed open but instead to be opened by pressure therefore allowing it to be bled. The added benefit is to have a tightened cylinder as recommended by the manufacturer. Seems better that just leaving it loose by a thread or so, a win win.

Here, for some reason your arguing against something that you already agreed with.

You seem to want to suggest that adding some amount of mechanical axial load to the threaded joint (e.g. by screwing the cylinder down onto a solid shoulder) is going to improve its strength

As for a fully seated cylinder being stringer than an unseated one -- yeah, probably,

To those that think the threads become stronger by screwing it hand tight, I ask some questions.

What torque value do you think you are applying to the cylinder by hand?

What is the the resulting thread load?

How exactly does adding a tension load by torquing the cylinder by hand become additive to the the strength of the joint prior to it being subjected to the 192 pounds of thrust load provided by air pressure?

I for one am not a mechanical engineer so I don’t have answers to your questions.
I do know that the manufacturer probably put extensive man hours into the design of this product and if they recommend it be tight then that’s good enough for me. Common sense tells me that if the cylinder is properly seated the seal would be properly aligned and the play would be taken out of the threads.
I for one would rather err on the side of caution, the ER is full of people that were certain that they had all their bases covered.
Murphys Law can be a real bitch.

As I said, but perhaps not clearly enough, was that "stronger" can be irrelevant. Whether I drive a Ferrari that will do 200mph or a Honda that will do 120mph, it doesn't really matter if I'm only trying to go 25mph. Instead, I'll choose to drive the car based on other factors, such as comfort or convenience. I COULD wear a belt AND suspenders to hold my pants up, but I don't really feel the need, since only the belt does just fine.

As a mechanical engineer, and someone with fairly extensive experience working with high pressure air, hydraulics, and consumer products, I can tell you that often the contents of a user's manual is dictated more by legal concerns than technical. Does that mean warnings aren't valid? No, but it does mean that it is usually much safer and easier to assume an ignorant (and litigious) consumer base and make extremely conservative blanket statements, than to explain the finer technical details of, for example, thread loading or seal design.

In my opinion, the OP asked some pretty reasonable questions and showed a basic understanding of the engineering and physics involved. I find it frustrating when that is met with dire warning from people based solely on a statement in a user's manual rather than science.

But to each his or her own. I'm not going to tell anyone how they have to do anything, but I will try to provide technical help where I can.

I'm just surprised I haven't seen 'anyone' pipe up to say "throw away your PCP and get a SSP instead". :)

marky-d

Ok, I have looked at this, and I am impressed by the overthink.
Yes, a purge valve is a great idea.
Yes, completely screwing the tank onto the adapter is better than not, because you protect the threads from bending damage if you bump into it.

If your tank will unseat and fill partially screwed on AND you buy a purge valve. Why dont you Just grind off the fill tit or drill a pin valve clearance in the adapter...... Less axial loads on the threads with better protection from bumps and bruises and the valve will close when bled......

spektr wrote: ↑Sat Mar 13, 2021 11:30 am Ok, I have looked at this, and I am impressed by the overthink.
Yes, a purge valve is a great idea.
Yes, completely screwing the tank onto the adapter is better than not, because you protect the threads from bending damage if you bump into it.

If your tank will unseat and fill partially screwed on AND you buy a purge valve. Why dont you Just grind off the fill tit or drill a pin valve clearance in the adapter...... Less axial loads on the threads with better protection from bumps and bruises and the valve will close when bled......

If I grind off the end (for zero valid reasons) I can no longer use my adapter to bleed the cylinders if I ever need to for travel or shipping.

Friggin wrote: ↑Sat Mar 13, 2021 10:07 am I for one am not a mechanical engineer so I don’t have answers to your questions.
I do know that the manufacturer probably put extensive man hours into the design of this product and if they recommend it be tight then that’s good enough for me. Common sense tells me that if the cylinder is properly seated the seal would be properly aligned and the play would be taken out of the threads.
I for one would rather err on the side of caution, the ER is full of people that were certain that they had all their bases covered.
Murphys Law can be a real bitch.

They probably put extensive man hours in advising to install the adapter with a 27mm wrench as well. Do you own/use one?

Not a Dire Warning (let’s not get dramatic) just one guys opinion about being safe. Pretty sure I’m still entitled to my opinion in this country. That said, glad to here that you are a mechanical engineer and approve of leaving the cylinder back a little.
Still not really sure why you guys are jumping down my throat about it being better to have the cylinder seated before opening the tank valve. Anyway I already built this and it works great.
Had all the parts needed on hand. My cylinder starts releasing air at 1-1/4 turns out so I made a 1.3mm Delrin washer to space it out. Tested it several times, works great. Only weak link is that it uses a Kwik connect but I use them when filling the tank from my compressor and never had any issues.