16mm IDRIS

Hi Neil.

Thanks​ for the tip and I see your logic.

Didn't work but could have. The tube ends expanded and I ended up losing the tube inside.

To STEAMBUFF please ... your reply on the 22nd. concerning gas tank pressures ... you seem to be suggesting that ROUNDHOUSE use a working pressure of 245 PSI in their tanks... I do not understand such a high figure ... to me that is not a working pressure, it is a worst-case scenario ... I do not know how they would use 245 PSI and feed it through a single -stage pressure reducer ( i. e. the gas valve ) to get about 10 or 20 PSI into the burner ... many years ago I conducted several experiments on a small gas tank 2/3 full of gas to see what happened if the temperature was raised or lowered ... I have just repeated that test and achieved virtually the same results.

All the tests were done outdoors using pre-heated water from an electric kettle ... definitely no flames involved !!

My figures are typical because nowadays the gas bottles I buy no longer state the ratio of butane and propane ... they just say it is a "mix"

The pressure in the tank is about 40 PSI at 22 degrees C. ... to achieve approx. 245 PSI needs the tank to be at a temperature of 100 degrees i. e. boiling water.

Are you saying that ROUNDHOUSE allow their tanks to run at that temperature ... mine tend to run at about 30 -50 PSI so the temperature is "hand-warm" ... once upon a time I was told never to heat canisters above 55 degrees C.

martin

Hi Martin,

Thanks for your reply.

The pressure figures quoted for Roundhouse were taken from their Gas Test Certificate that was supplied with my loco. (Cheddar quoted a test pressure of 375psi

On their website Roundhouse quote that their gas tanks are suitable for mixed gasses up to 60% butane/40% Propane, with a 70/30 mix being most common, they also say that the Gas Tank is rated for 65 degrees Centigrade and should not achieve this.

Some points to bear in mind.

1/Roundhouse gas tanks are used for External and Internal fired boilers and supplied for home-builds.

2/ The location of the gas tank varies from in a tender to in the side tanks right next to the boiler.

3/ They ship loco's world wide.

So if the ambient temperature is 35 degree's (Yes that is even possible in the UK), since the tank is Black, it could exceed this temperature if the loco is sat in full sunlight. (You will know this if you have a dark coloured car), so it could easily reach 50 degree's.

After a run, the boiler will be hot and some of its heat will be passed to the gas tank (if it is next to the boiler) raising its temperature even further, especially if it is sat in the sun.

Saying that we also have to bear in mind that when the liquid gas in the tank becomes a gas it will expand and the temperature will drop. (Hence why the cylinder you use to fill the tank with feels cold)

I have experienced situations where when refilling the gas tank after a run, it is too hot to touch, so well in excess of the 22 degrees you quote. (I suspect it is between 35 and 50 degrees - I have not measured it)

I have never measures the pressure in a gas tank nor its temperature.

I am sure Roundhouse allow a safety margin.

Dave

Just seen Dave's post - my guess was they were allowing for pure propane, but no they are allowing for elevated temperatures.

Neil

Edited By Neil Wyatt on 25/08/2015 10:17:33

To Mr. STEAMBUFF please ... looking at Neil Wyatt`s post just above, it seems you are Dave ?????? . thank you for your prompt reply ... that answers some of my questions ... possibly the tank has not been tested to 490 PSI ... maybe it has only been tested to 375 PSI, this is still very high, but yes, it does give a wide safety margin allowing for mis-use ... my concern has always been that we could be over-testing some designs of tank.

The other thing I have never managed to get an answer to, is the test temperature for all the sets of figures quoted on the MPBA information kindly supplied by Neil Wyatt on 22nd of August ... these appear to be the same readings I was aware of many years ago ... I tried to find the ambient temperature for those sets of figures ... I even went to an Annual general meeting of the MPBA armed with a small gas tank fitted with a pressure gauge ... after lots of phone calls and letters, I could never find anyone willing to answer the question of gas temperature for those figures.

Do you know anone who would know what the temperature was please ?? ... my guess would be 60 - 80 degrees ... to me, the figures do not mean much without a quoted temperature, because the pressure goes up and down like a yoyo with change in temperature.

Regards, martin

Hi Martin

Yes I am Dave (Steambuff) as per my signature at the bottom of my message

My Cheddar gas tank test certificate states "We certify that this refillable Gas Tank has been tested to a pressure of 375psi (25 bar) - Propane content not to exceed 30%"

My Roundhouse gas tank certificate states "Vessel for Group 1 gasses and associated pipework and fittings : Test pressure 34 bar, maximum permissible working pressure : 17 bar, Maximum working temperature 65 degrees C"

34 bar = 493psi : 17 bar = 246psi

So Roundhouse will have tested at 493psi.

Sorry I cannot help you on the question regarding the temperature as to which the tests in the article that Neil supplied.

Regards Dave

Hello Martin and everyone,

Just reading the latest installment and I have to admit to being a little confused.

"7BA can be tapped onto 3/32 diameter rod but the resulting thread will need to be reduced with a file or machined back down to 3/32 diameter" (page 372, last paragraph).

The nominal diameter of 7BA is 0.0985"; 3/32" is 0.09375" so smaller than 7BA. Why would you need to reduce a 3/32" rod to...3/32"?

Actually, just doing the maths, the thread form would be full at 95% so a good fit for something like a piston which could work itself loose inside the cylinder.

Andy

Edited By AndyB on 08/09/2015 22:53:06

The metal can get extruded into the thread form, a bit like thread rolling. If the rod needs to be passed through an accurate 3/32" hole then the crests need to be removed.

But in this case as its onto the reduced ends of an 1/8" rod I can't see why you would need to 1) reduce the end to 3/32" instead of proper size, 2) need to take the crests off as it will pass through the gland and is going into tapped holes?

Hello Andy ... nice to hear from you ... Jason has answered the question perfectly ... the thread gets squeezed outwards in diameter.

martin

Hi Martin and Jason,

Terribly sorry, I missed the bit where the thread was rolled, I assumed cutting with a die.

You know what they say about ASSUME...

Andy

To anyone building the IDRIS loco ... I have happily spent most of this summer running the loco round the small track in our back garden ... managed to keep SWMBO happy by mowing the grass with one eye on the loco ... I have discovered several things that may be useful ... the Roundhouse safety valve slowly dropped its blow-off pressure as the O-ring got squashed ... instead of 40 PSI it was lifting at 30 PSI ... this had to be reset. Needed a tiny bit of brute force !

I found the best way to run the boiler was NOT to allow the safety valve to lift ... pity, it looked good ... I tried to run it at a maximum of 35 PSI ... the steam valve ended up at about 1/4 turn open ... I used the gas valve to set the boiler pressure with the engine continously running.

The water pump drawings further in the series show a ram of 3/16 diameter ... now I have got everything running better I have swapped the ram for a smaller size of 5/32 diameter ... this also takes less power from the engine ... possibly even 9/64 would do the job ... when using the water pump I started with the boiler water gauge half way up the glass ... not filled to the top.

My small track has lots of tight radius curves ... the engine ran much, much happier when I made the wheels on the wagons loose on their axles ... with 2 wheels fixed on each axle the engine slowed right down ... so much so that I ended up always pulling a bogie wagon (from SWIFT SIXTEEN) with a large steel bar as a ballast load ... without any load to pull the engine was likely to fall off sideways on the first bend.

hope this is useful ... martin

Having purchased the latest issue of ME, there are no further instalments of Idris....

Has this article concluded and Ive missed something?

I have to say that I was wondering the same John.

The Weather has been far to nice lately to sit in the workshop so progress has been somewhat stationary the past few weeks.

I'll get back to my build soon......​

To John and Alex ... as far as I know the next part of the IDRIS series is coming up in issue 4520 ... that should be around the 29th. of October.

P. S. to my entry on the 2nd. of October ... something else that may be useful ... I discovered that the check valve on the side of the boiler needed to have a lift of no more than about 0. 028 inches ... also the spring pushing the ball onto its seat needs to have a minimum pressure exerted on the ball when the valve is shut.

When everything has worked as per plan I have managed to get a run time of 30 minutes from the gas tank.

martin

Martin,

Indebted to you for the update on the next part.

To anyone building the IDRIS ... there is an error in the sketch shown on page 661 in the latest copy of M.E. ...

In the middle at the top, there are 2 joints shown using high temp. silver solder ... only the end-ring joint on the left hand side needs to be high temp. silver solder ( SF 24 ) ... the smaller tube on the right hand side can be fastened with ordinary silver solder ( SF 55 )

A request for help please ... in part 5 of the IDRIS article, on page 218, I showed a photo of a commercial gas valve ... very neat and very tiny ... it is a combined fill and vent valve all in one... whenever I try to use it to fill a gas tank the flow of liquid gas slows right down ... it takes 4 or 5 tries to fill the gas tank with a maximum volume of 54 cc ... has anyone any ideas how to speed up the process please ? judging by the amount of condensation on the valve body I assume it is starting to freeze up ... my old method which I have used for more than 20 years uses 3 separate valves for fill, vent and supply ... they take up a lot of space and need a lot of work to produce them ... however, they will reliably fill a gas tank to the correct level in one operation.

Has anyone any suggestions for what I am doing wrong please ??

martin.

Martin,

Is the gas valve on the top of the gas tank and pointing vertically upwards?

When filling the tank the cylinder you are filling from must be vertical and upside down (Filler at bottom)

Dave

To Steambuff ... thanks for your reply ... "Yes" to both of your suggestions ... I`m afraid it is not that.

To anyone building IDRIS ... in part 8 of the series, on page 829, there are 2 errors ... at the top of fig 34 there are 2 7 BA clearance holes shown ... their distance from the top edge is given as 0. 350 inches ... this measurement of 0. 350 should refer to the vertical support distance from the top edge of the plate as shown ... the 2 holes are placed roughly between the 2 so as to straddle the centre of the 1/4 x 1/2 brass bar shown in part 3, fig 12, page 746.

The other error is also shown on page 829 just above the top of fig 35 ... the melting temperature of Silver flo 24 is obviously not 8000 degrees ... it is 800 degrees.

martin