Help with a Ditmar

I was cleaning the lamp and I accidentally broke the mantle. Installed new but now the mantle kinda shrinked much smaller and curved a bit. I think it was much more difficult to light up the lamp this time. Do you think it is because of the twisted mantle or something else. Should the mantle be bigger model?

 

The earlier mantle should be fine. You can still use bigger ones without problems. They'd shrink during the preheat and burn-off period. It might shrink even further if the preheat period is longer and when the shrivelled up mantle is heated by the flame from the outside for too long. If the external preheat flame licking the mantle is a very hot one (during burn-off period), such as from a MAPP or propane torch, then it will also shrink more than normal.
How well they would re-expand and finally form depends on various factors. Some of them are: the quality uniformity of the make, whether or not there are creases/folds that was adhering together when it was tied/assembled earlier, the startup pressure and how well the fuel is heated and vaporized during preheat and release from the jet.
On many occasions, if the first start-up fuel release was well vaporized and ignited, there can be a 'whoomph' being heard when the mantle expands into bright ball of light. If the audible surge of expanding gases during ignition doesn't burst the mantle, you'd find that this would usually be the largest and best formed mantle, having nearly perfect symmetry.

 

Do you think that I should add some pressure before to the tank when I start fire on the pre-heat spirit cup or should I just gradually add more pressure during the process after the pre-heat has started when working with new mantle?

 

Pressurizing the Ditmar 520 before preheating wouldn't be a good idea since it has no fuel valve. The liquid fuel would spill around everywhere, causing heavy sooting and flaring after ignition.
In order to achieve the effect @MYN described it would be good to have the tank nearly full and start pumping quickly once preheating has been done properly. This way the pressure will rise much faster than with a rather empty tank.

 

As mention by @Martin K.
For lanterns without a shut off valve or footvalve, a soft start is safer and less damaging.
The mantle only need to burn off 'just-enough' before the fuel + air is channeled into the burner/mantles. Just enough to burn off volatile carbonaceous combustible matter to turn it to more or less an 'ash-sock'. You do not need to burn it any longer to remove all traces of leftover carbon during first start ups.
Burning it for too long from externally applied flames like the spirit preheat flame or gas torches won't serve any more purposes unless you intentionally want the mantle to shrink a little more than normal.
When we perform any extra preheat, what we want is to heat up the generator tube, instead of having the flames shooting too much towards the mantle or the ceramic burner. cap.
I've observed that using the same mantles on different lanterns(even of the same ratings) don't necessarily produce the same full-sized/well-formed mantle shapes. In fact you can just light the newly attached mantle with a lighter or match and allow it to burn off by itself without further assistance or sustained flames from any other sources. This way, the shrinkage is minimum.
Most of the re-expansion or forming effects come from how well the fuel is vaporized and premixed with air upon reaching the burner for ignition as well as how much the mantle has already shrunk before fuel ignition. You want the mantle to remain be as flexible as it can be and don't want the burnt-off mantle to 'harden' too much by heating it too long before re-expansion upon fuel ignition.
If fuel vaporization is 100% complete (fully gaseous), well premixed with air and already very hot, ignition will be instant, where gases would expand fast(often audible) and chances of it resulting in a well-formed mantle shape would be high.

 

Thanks for the answer. Perhaps initial heating of rise tube could be done with gas torch too?

 

Hi,

Does anyone know the thread size of the filling cap and pump cap?

Veikko

 

Of course you can - but the glass can get in the way..
Lots of lanterns and stoves have no "valve" - pre-heat with meths/spirit and once it is nearly all gone pump like a madman......