BSP Parallel Thread Male x BSP Parallel Female Thread - Gas Fitting Sealing

[Len Ingalls]

Here is an opinion from the Left side.
Why don't mfgrs just stick with NPTaper or BSP Taper-tried & proven,simple & near idiot proof ?

Just venting Cheers/Len

 

[VicS]

To close out this thread,

Some points to note if you are in a similar situation: -

The Fulham Nozzle does not bottom out inside the female bushing so the fibre washer cannot be used, which is why the Dowty was recommended. I described the bottoming out wrongly in my OP. Subsequent measurement confirmed this is the case. I assumed that by design when the top touched the bottom touched as well, that assumption was clearly wrong.

Hamilton Gas Products describe the Fulham Nozzle as BSP Taper, but it is not, it is parallel, later in the item specific page on their website it is just described as BSP. Searching the web does identify tapered nozzles but not Fulham type. All the other nozzles that I could find which were BSP Taper Male had sharper serrations for gripping a hose; this is not correct for gas purposes. I understand that the Fulham is designed for gas hose and that the two round rings do not cut into the hose and thus reduce its wall thickness (pressure rating) and provide a double seal when the hose clamp compresses the hose.

The Dowty washer and Fibre washers are correctly described on ASAPs web page using the male and female designation, not anywhere else that I looked. The Dowty washers have stainless outer rims but most will be plain carbon steel, it took a bit of eBay work to find the stainless version.

Hope this helps anyone else. I have not pressure tested the assembly yet as the gas installation is still underway.

Once again many thanks for the advice given, it's much appreciated.

Fair Winds,

BlowingOldBoots

I am surprised you could not find Fulham nozzles with bspt male threads ........... Southampton Calor Centre list them in 1/4" 3/8" and 1/2" to 8mm


eg

BES also list both BSPT and BSPP Fulham nozzles


Wrongly maybe ???? but I think I would have looked for a fibre washer to fit where you have used the Dowty washer

The other type of nozzle you describe is I believe for high pressure connections. I dont remember what they are called though. I am sure its not Fulham nozzles

From BES website HP nozzles

 

[VicS]

Here is an opinion from the Left side.
Why don't mfgrs just stick with NPTaper or BSP Taper-tried & proven,simple & near idiot proof ?

Just venting Cheers/Len

I guess because for high pressures, hydraulics and high standard (eg aeronautical) engineering a seal made using jointing compound or tape between the threads would not be considered good enough. Parallel to parallel enables the seal to be made between two flat faces using the appropriate type of sealing washer.

 

[NorthUp]

https://farm1.staticflickr.com/623/20716083771_8cfdc5d01e_z.jpg

I suspect that dowty washer is not going to seal- the shoulder on the fittings should cover the rubber insert in the washer, needs a bigger shoulder diameter.

 

[Deleted member 36384]

https://farm1.staticflickr.com/623/20716083771_8cfdc5d01e_z.jpg

I suspect that dowty washer is not going to seal- the shoulder on the fittings should cover the rubber insert in the washer, needs a bigger shoulder diameter.

It is the correct Dowty Seal for the diameters. The fitting is undercut above the threads and the sealing face is not the shoulder directly below the nut but the lower shoulder in the picture. In my searching about both undercut and flush can be specified for blank plugs (which is where I noticed the difference), the fibre washer is used on the flush style as I guess this butts up against a flat face on the bushing. On the nozzle, the flat face at the undercut engages with a similar area in the bushing, which is slightly recessed. Close inspection shows a thin line of rubber just visible around this area after make up. The purpose of the steel ring on the Dowty washer is to prevent extrusion of the rubber so that it can all be contained in the sealing areas and compressed to make the seal. However, you may be right, we shall see when the pressure test is conducted.

 

[NorthUp]

Your points are noted, the explanation is clearer that the photo!
The dowtys are used in hydraulics with pressures of hundreds of bar, so gas at mbar ain't going to stress them (as you clearly know)

 

[Alfie168]

And that is why it saddens me when I see old time served artisans like me, not being replaced by the same. The old time skills and knowledge that is in our heads is slowly being lost as we peg it.
This is a typical thread, peeps dont know what to do. I do, because I learned it off a similar old gimmer when I was a lad. Silly things like when opening a wheel valve. open it all the way, then close it half a turn. It means the valve wheel is loose, a sure signal to the next guy that touches it that the valve is open. If it was opened all the way to the stop, it is then tight, then when someone tests it they dont know whether it is open or not! Learned on the first day as a bushy tailed apprentice!
S

It was still taught in 2001 and standard practice to back off a wheel valve/gate valve a quarter turn in all the places I worked. The reasoning was subtly different though. We were told that backing it off a quarter turn enabled you to ease it back and forth in the event it seized. Having it fully open meant you had only one way to force it, and were much more likely to damage it or break it.

Tim

 

[Heckler]

It was still taught in 2001 and standard practice to back off a wheel valve/gate valve a quarter turn in all the places I worked. The reasoning was subtly different though. We were told that backing it off a quarter turn enabled you to ease it back and forth in the event it seized. Having it fully open meant you had only one way to force it, and were much more likely to damage it or break it.

Tim

I met up with a fellow apprentice after 40 years! We talked and talked for hours. The fitter that taught us that was a god to us! That story came up and we both remembered it. Made perfect sense then and still does so I will stick with my version!

Stu