Thread on Faber tank?

[scubaalblake]

Ok - just been given an old UK Faber Steel tank in Aus.
Looks ok but will obviously have to be tested and probably need a rumble inside. LDS can do that.

I know that there has been issues with the mismatching of M25 and 3/4 NPSM threads on tanks.
Question - how can I tell for sure which thread is on the tank?
I have a brand new 3/4 NPSM valve which *seems* to fit perfectly......but does it really?
Tanks markings are:
PZ Faber 90/9500/054 -manufacturer, year, batch, number
TP 348BAR 03 90 - test pressure, month and year of first test
BS5045/1/CM/S - UK manufacturing standard
CP232BAR 15C 10.0L 11.2KG - working pressure, capacity, weight
2030/12 - ? serial number?

As you can see there is no indication of the thread. Does anyone know?

My understanding is that the M25 thread is slightly smaller than the 3/4. There was an incident in Aus where M25 valves blew out of a 3/4 tank under pressure due to that mismatch. (the M25 screws in but is not a proper fit) So my thinking is that *if* this tank was M25, my 3/4 valve would not screw into it..so the fact that the 3/4 seems to screw in correctly means the tank is 3/4..........but can someone confirm that?
Al

 

[krawlings]

I would say your thinking is correct .If the larger thread (3/4"valve )gos on with limited resistance . then it is correct, as it is the larger of the two threads . You can all so call Faber and get a little info from them to give your self more comfort in your analysis.

 

[elan]

If I remember correctly from my PSI class there should be a marking saying M25 x 2 somewhere on the top line on the neck if it's M25 tank. But I would contact Faber directly and give them the serial number to be sure.

 

[scubaalblake]

Ok I'm trying to contact Faber as others have suggested but no reply yet. However it may be even more confusing because apparently UK tanks *used* to use 3/4 BSP valves which is NOT the same as 3/4 NPSM as used by the US....argh....why do these things have to be so difficult
Apparently its virtually impossible to tell the difference unless you a) have $$$$$ worth of professional thread gauges OR blow your brains out by fitting the wrong valve
Hoping Faber can tell me.........

 

[Hickdive]

Eek!

It WILL be a 3/4" BSP neck thread. The old BS5045/1 ONLY allowed for 3/4" BSP or M25.

DO NOT use a 3/4" NPSM!

Although the diameter is the same so a 3/4" NPSM will apparently screw in properly the thread pitch is different and you run a significant risk of having the valve blow out under pressure.

I didn't think UK spec cylinders could be tested in Australia but apparently there is one test station will do them. I can't remember off the top of my head who it is.

If you can get it tested then you'll need to get a 3/4" BSP valve to use the cylinder safely. You can still buy these in the UK;

A.P.Valves Direct

 

[Scared Silly]

Apparently its virtually impossible to tell the difference unless you a) have $$$$$ worth of professional thread gauges

My suggestion would be to find a machine shop and take the cylinder along with a 6 pack of beer. Any decent machine shop will have a thread gauges of various standards. However, that may still leave you with questions.

 

[scubaalblake]

Thanks all. Faber have replied and confirm that the thread is indeed G 3/4 BS 2779:1986 (ie NOT NPSM 3/4). Good job I checked.

Interestingly I have another BS5045 UK tank that I have had in test in australia for 20 years now and have no difficulty getting filled or tested at all. It has a UK valve. Apparently if you had the tank in Aus and being tested (ie has an existing Aus test stamp) before the rules changed then that is taken as confirmation that it met the standard and it can carry on being tested. Issues only arise with one that has never previously been tested here before.

---------- Post added February 20th, 2013 at 12:25 AM ----------

>Eek!

>It WILL be a 3/4" BSP neck thread. The old BS5045/1 ONLY allowed for 3/4" BSP or M25.

Faber have confirmed its G 3/BSP based on the serial number but I dont think its correct that BS5045 only allowed metric or G 3/4.
Tanks made by Faber for the Australian market used to be marked BS5045 (prior to the Australian standard) and definately had 3/4 NPSM fitted - I have three of them!
Thats why there is so much confusion between very similar threads - the tank standard does not definatively confirm which thread it is.

---------- Post added February 20th, 2013 at 12:31 AM ----------

Yep,
Just chcked on a current Ad for Faber cylinders in Aus right now and they are (I quote):
- Made to BS5045 Part 1
- Comply to all Australian Standards
- Have a 3/4 inch NPSM thread

so BS5045 does not imply G 3/4 (if only it were that easy!)