Hi all.....yes BarryM...I have a French ANTON V71 gas regulator & when supplied, Fabrice also included a replacement seal kit which comprised two small nitrile [NBR] o-rings & a 20 diameter x 1.5 mm thick nitrile [NBR] diaphragm
I questioned the diaphragm material with Fabrice....& his explanation after translation via Babble Fish to the best of my ability
was .......
The pilot pressure from the boiler is not steam from the top of the boiler but water from a lower boiler tapping @ ~~~~~ may well be @ 140 PSI, but only @ approx 100 degrees C - it is important not to lag this pilot line to the regulator so as to get further surface cooling & hence further water temperature reduction
On the other side of the diaphragm we have LP 70/30 gas - the nitrile [NBR] elastomer has total compatability with this gas & so a section from a bicycle tube would appear OK....
just make sure that it is not perished
It is important to be able to bleed the trapped air from the water pilot line as close to the regulator as possible...otherwise the air acts as an accumulator & can cause a fluttering effect on the diaphragm & hence irregular gas supply to the burner...........Derek