Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

if none of them were from CNG then why do you quote them ? CNG tanks have a service life of 15 years which may be extended with proper inspection to 20.  biannual inspection is mandatory.
I had a petrol car ( Audi)) explode from under me, barely made it out. no LPG or CNG car has done this to me.

None of the BLEVEs are from CNG because you can't get a BLEVE from CNG. The L in BLEVE is LIQUID. CNG is not liquid.
LPG BLEVEs are pretty impressive though...

EDIT. You can of course get a BLEVE with petrol or Diesel if it is heated in a sealed container.
One advantage of CNG and Hydrogen is that leaks dissipate naturally. They don't collect in low lying areas waiting to catch you out and in the case of petrol and diesel contaminating the ground, killing flora and fauna.

Yeah... with all the dismissive attitude being bandied about regarding the fundamental hazards of the pressures involved, the Boiling Liquid Expanding Vapor Explosion nit certainly did not seem worth picking at the time. 

But you're absolutely right... the core different is those pressures. A BLEVE is by definition only propelled by a smallish multiple of atmospheric pressure; much less than a pressurized tank, or even the head pressure of a PRV when venting. The resultant explosion/fireball of course is much more energetic than that pressure.

mnem
 

[Saskia]

wait until you see an N2O tank explode ..
explosions are detrimental to your health, that part is undisputed ...

[mnementh]

well, the training you need for pumping cng is about the same as lift handle, put gizmo over filling gizmo, turn lock push button.the filling stations are unsupervised credit card driven terminals without any staff.if lifting the handle and putting it over the nozzle plus pushing a button is too complicated the folks in  question should not be driving.

I had 80 l of petrol explode in that Audi I was referring to.  ai don't t see the point you are trying to make. there are more petrol cars burning than lpg/cng cars burning  so what is the hubbub about ?

Come on Valkyrie... you know exactly what I'm talking about:



It's THAT factor I'm talking about. And you and I both know that at least a quarter of the motoring public, probably more, is so mentally defective for one reason or another that they really should not be allowed to drive. Or vote, for that matter.

From a safety standpoint, we have to prepare for the Lowest Common Denominator. Right now, CNG/LPG has a built-in limiting factor: the kind of people who are interested in these alternative fuels are by definition a bit smarter and more observant than the average citizen.

If you were to make CNG/LPG the standard motor fuel due to shortages of oil liquid coal slurry with that attitude towards the refueling station, there would be LPG/CNG fireballs on every street corner in America^* and probably where you live too.   

mnem
I give up. 

*slight exaggeration for dramatic effect

[mnementh]

wait until you see an N2O tank explode .. explosions are detrimental to your health, that part is undisputed ...

N₂0 tank is ~750PSIG (for comparison to the pressures we've been discussing). As to how potent it is being fuel/oxidizer in one as compared to say compressed O₂,  that's a question for the chemistry wonks. I expect the surrounding fuel materials will make a big difference in that analysis.

I just know it can make you giggly if it leaks, and if you let a gasoline engine breathe it things get really interesting. 

mnem
That use case really makes me giggle... 

[Saskia]

oh, we converted the N2O tanks to TNT equivalents ...
a 10kg container was something like 6.whatever kg of TNT

[Kosmic]

No whoosh here. Fell with a thud. I know posi not phillips not JIS.   

And then the Canucks are fond of their Robertson.   

We are!  I showed one of my American friends the Sears Kenmore dryer that came with my house and he coudn't get over the Robertsons on it.  It would've been made here by Camco or Inglis, probably Inglis.

Then there's the story of the Canadian Westinghouse Ltd. motor generator set that nobody was expecting to see down in Baltimore...

What, Robertson screw is a Canadian thing ? I naively thought they were pretty standard at least in North America. To my defense, I rarely need to go to the hardware store when I'm on vacation.

[mnementh]

Nope; most common screw head south of the border is #2 Philips. More likely to be Torx than Robertson in the good ol' Hew-Hess-Hay... 

Honestly, Robertson still look just wrong to me, even after spending a couple years up there. 

mnem
*screw'd*

[Kosmic]

Nope; most common screw head south of the border is #2 Philips. More likely to be Torx than Robertson in the good ol' Hew-Hess-Hay... 

Honestly, Robertson still look just wrong to me, even after spending a couple years up there. 

mnem
*screw'd*

They are working pretty well on wood when building a deck. And can be found in most electrical installation over here for some reason.

[mnementh]

Nope; most common screw head south of the border is #2 Philips. More likely to be Torx than Robertson in the good ol' Hew-Hess-Hay... 

Honestly, Robertson still look just wrong to me, even after spending a couple years up there. 

mnem
*screw'd*

They are working pretty well on wood when building a deck. And can be found in most electrical installation over here for some reason.

I found that in drill/driver use cases the bits tend to wear dull/round out on the corners quickly, then start to strip out screw heads. Much more so than Torx (what we use for TapCon and Deck screws down here) for sure, and IMO also faster than #2 Philips in appropriate general-purpose low-driving-load use cases.   



mnem
*screw'd²*

[AVGresponding]

Because I can!



 

[mnementh]

I knew most of those things. Y'all been beating me over the head with them for ages... I still think they're just a overrated back-stab connector. 

mnem
*stickin' muh pecker in hornet's nests for fun & profit since nineteen-mumblety-mumble*

[Neper]

LPG is dangerous enough; it is low-pressure, just enough to keep it in a liquid state, but CNG is exponentially more dangerous because of the pressures involved. I certainly don't trust the average motorist to safely handle either.

There are thousands of unattended self-service filling stations offering CNG and/or LPG, all across Western Europe. So, why aren't people blowing themselves up all the time, over here?

[mnementh]

Answered in painfully excruciating detail in the 4th post on this page.

mnem
 

[Neper]

Answered in painfully excruciating detail in the 4th post on this page.

There was a time, years ago, when over a third of all vehicles in the Netherlands were running on LPG because their government had drastically increased taxes on petrol. Still no mushroom clouds all over the place. Surely, the drivers of these cars can't all have been Nobel prize winners.

[mnementh]

Bet you they had attended filling stations then. We still don't have unattended LPG filling stations over here; in fact, it is very rare that the average citizen even gets a LPG tank refilled. 

20-pounders as commonly used for space heaters and BBQs are most often "refilled" by an "exchange" company that has locked cages at the local gas station, grocery or hardware store. To get around having to do hydro-expansion testing on every out-of-date tank they handle, these companies typically only refill to 15lbs; that way they get away with just a visual inspection, new valve as needed, then printed-stamp on the tank and a new shrink-wrap sleeve.

mnem
 

[Robert763]

if none of them were from CNG then why do you quote them ? CNG tanks have a service life of 15 years which may be extended with proper inspection to 20.  biannual inspection is mandatory.
I had a petrol car ( Audi)) explode from under me, barely made it out. no LPG or CNG car has done this to me.

None of the BLEVEs are from CNG because you can't get a BLEVE from CNG. The L in BLEVE is LIQUID. CNG is not liquid.
LPG BLEVEs are pretty impressive though...

EDIT. You can of course get a BLEVE with petrol or Diesel if it is heated in a sealed container.
One advantage of CNG and Hydrogen is that leaks dissipate naturally. They don't collect in low lying areas waiting to catch you out and in the case of petrol and diesel contaminating the ground, killing flora and fauna.

Technically, you are right, it is the liquid that in a fire situation could possibly boil (this would to a large extent depend on where the fire was in relation to tank position) and release more gas as a result of boiling, increasing the pressure to such an extent that it could rupture the tank, thus spilling out high pressure gas and hot liquid fuel, making air-fuel bomb which explodes with tremendous force. I suppose you could consider it similar to the Thermobaric bombs (vacuum bombs) that Russia is said to have been using in its war with Ukraine.

But equally nobody would want to in the way of the blast of fire that comes from the pressure release valve when it happens to open to reduce the internal pressure, it becomes a high pressure flamethrower as witnessed in the first video posted earlier and is capable of destroying anyone or thing in its path.

Petrol (gas for the Americans) and diesel are not contained in a sealed container on a vehicle as there are special vapour locks / vents to allow a certain amount of breathing, plus there is on all the fuel systems I have ever soon some plastic / rubber flexible tubing in the pipeline and filler neck which would melt and vent long before the tank would rupture. Added into this, most fuel filler caps these days also made of plastic and would melt as well. So a Bleve from a petrol or diesel powered vehicle's fuel tank I should think are extremely unlikely. Fuel carried in a steel unvented can is of course is another thing, but who in their right mind would keep cans of fuel in their vehicle these days.

Not quite. A BLEVE does not need an ignition. For that matter it does not even need a flammable liquid. The classic BLEVE is a water boiler explosion. The requirements are that the liquid is heated well beyond it's atmospheric pressure boiling point and the only thing stopping it boiling is the increased pressure  in the containment. Once the containment fails the liquid boils instantly and the expansion of the resulting gas is the explosion. For instance water expands 1600 time when it turns to steam. If it happens to be flammable with an ignotion source that increases the expansion but that bit is not part of the BLEVE.

[AVGresponding]

Indeed, steam boiler explosions were are no joke.

[mnementh]

*unconsciously edges a little further away from the wall of the dwagon-cave with our NG boiler immediately on the other side*

mnem
perhaps now's a good time to toddle off and fix another lawnmower... and maybe some bicycles...

[AVGresponding]

Shirley that's not a high pressure boiler?

Closest most people get to HPS these days is while they are chatting to their barista. I've yet to see any news stories about mass hipster fatalities in espresso machine explosions, but one lives on in hope...

[AVGresponding]

And now for something completely discord

[Specmaster]

I'll only make this one comment on the subject...

The "flamethrower" bus demonstrated a properly functioning safety feature: the pressure relief valve.  This is to ensure overheated vessels release their contents in a controlled manner - not explosively.  You get a flamethrower, not a mushroom cloud.  Comparisons to completely sealed containers is completely irrelevant.

Motor vehicle LPG tanks in Australia also have such a valve, for exactly the same reason.  I know - I've worked on them.

Agreed but the valve on the bus, did its job perfectly, if anybody was standing in that position would coped the lot full on, or indeed if there was building etc in the way, then that would also have been torched. Surely the valve should have been pointing upwards that way the fire services etc could be a bit more certain how they could approach the fire for their own safety and others around them?

[Specmaster]

And now for something completely discord

Just got back from North Weald and getting something to eat, so I may be on later....

[Cerebus]

LPG is dangerous enough; it is low-pressure, just enough to keep it in a liquid state, but CNG is exponentially more dangerous because of the pressures involved. I certainly don't trust the average motorist to safely handle either.

There are thousands of unattended self-service filling stations offering CNG and/or LPG, all across Western Europe. So, why aren't people blowing themselves up all the time, over here?

Don't forget Iran, Pakistan, Argentina, Brazil and China - who are the top 5 countries by numbers of CNG vehicles (12 million in total). It would be unkind to make a comparison of the intellectual capacity of the average Iranian/Pakistani/Argentinian/Brazilian/Chinese/European versus the average American based solely on the opinions of one self-identifying dragon.

[factory]

Some pictures of the fine tuning mech from the hp 3310A function generator, also used on 3310B, the shaft has the plastic disc moulded on to it, the same as the control knobs and was probably made the same way.





The top surface is angled, the one spec pictured has worn down quite a bit to have a flat on the edge.


For comparison, the shaft with moulded disc from 3310A on the left and the larger one from the 200CD tube oscillator on the right.


A failure mode of these (200CD), it has cracked, will probably fall apart same as the controls do.


And finally, the complete fine tuning spring mech from the 207A sweep oscillator.


David

[khs]

HP 120B update

So I stole a 6AQ5 and 12AU7 from on of the type 515.

Result : no HV ! I used my HV probe and probed directly at the connector that plugs at the back of the CRT. I get ZERO. No HV-ing going on, not a sausage 

Bad tubes ? As I said it's not like I have a zillion to try out ! 

So that's were I am now, trying to probe on that HV board to see if I can troubleshoot it, hoping my tubes are good and there is something else wrong with it... hopefully not a burned HV transformer 
Problem is that access to that board is not ideal. I can get to its bottom because of the way it's installed in the chassis. I can only probe the top, and that's not easy as most interesting components are by the read panel. Hard to get probes down there, or see what you are doing really. Also, the caps mostly can't be probed as they sit flush on the board, their terminals are not exposed 

You could swap the HV control tube with one of the others in the 120B, the other might be a problem as it's the oscillator tube. Also check the solder joints on the tube sockets, had many bad joints from thermal cycling, more of a problem with the higher power tubes.

David

Swapped the contorl tube / 12AU7 no luck.

Swapped the oscillator tube / 6AQ5 ... well no I can't. Both the one in my second type 515 and my type 310A which I resorted to opening up out of desperation, are cooked... 100% black inside. I tried them anyway, no luck.

So basically the 6AQ5 I pulled from my first 515 is the ONLY such tube I have here that's not black... it's crystal clear and I can see that at the very least, it lights up. Better than nothing I guess.

So I will or a new tube or two very soon but of course that will take time to get to me. So in the mean time I will pretend that my tube works and try trouble shooting the board.

- I checked all power supply going to that board, board does get all the supplies it needs, so that's good. That includes the unregulated 420V that goes to the primary of the HV tranny. Yes tranny again, transformer this time not transistor 

- Zero oscillation going on : HV probe says zero volts on the secondary side, and when I scope the board, I see only DC voltages, zero sign of activity.

- I measured DC voltages as indicated on the schematic below, around the 2 tubes, i.e 3 elements : pentode and x2 triodes.  DC levels are 100% completely wrong. See measured levels indicated in red. So if we look at the two triodes : both are fed with 300V, and both are supposed to have about 90V on their anode. But, in my case not at all. Get near zero (2.8V) and the other near B+ (300V and the rail is at 304V).
So one Triode is conducting like mad, and the other is not conducting at all, and it sits like that, stable.
As for the Pentode / oscillator tube, it's control grid sees 0.8V instead of negative 123V !
so no wonder it does not work... now the problem of course is that it's a close-loop system, so no way to know what element in the loop is causing the entire loop to fail.


So now what to do...

Checking solder joints yes but not easy as pulling the board from the chassis looks like it will be a major tear down, looks quite involved....

Short of having another oscillator tube to swap, I will make the hypothesis that it's either bad joint as you said, or some passive component that just died.
One thing that might point in that direction is that now I think of it, the brightness control used to have bugger all effect on bruightness. It had as I said effect on the pitch and loudness of the arcing sound if that's what it was, but it did not have much effect on brightness.. it was always very bright.
So right there, we can say that some component or joint in the HV board was not good...

Wish me luck.....

Grid of V301 pin 2 should be at a lower voltage.
So you may check R313/R312/R310/R309/R308.
(Take care and discharge the 2.5 KV before touching the resistors!!)