by David Halfpenny (1802)
My article in NL&J 258, about undeclared Propane in ‘Butane’ canisters, caused some to query the robustness of homebuilt tanks designed for Butane Only. To get a feel for the issue, the Committee tasked me ‘To test a gas tank to an existing design to ascertain the pressures it is able to withstand’.
I chose Dick Moger’s elegant 80ml design from the G1MRA ARM1G book. Barrel: 20-gauge copper tube 1.75” diameter by 65mm long. Endplates: 16-gauge un-flanged copper plate. Central Stay: 1/8” diameter unthreaded bronze. Filler Bush: Ronson-fit M4.5mm x 0.5mm with O-ring recess. Feed Bush: 1/4” x 40tpi. Silver-brazed throughout. The builder had tested to 300psi which had domed the endplates slightly.
Inspector, Fred Roberts, G1MRA Technical Secretary, with myself – Deputy Yorkshire Group Inspector – as witness, checked my gauge against the G1MRA Master. A cheap and simple test rig sufficed to make the test. We filled the tank with water and pressed it by stages to 180psi (Butane Only test), then to 300psi (the builder’s test) and then to 400psi (2018 Code test). Neither increased the doming. At 500psi (Roundhouse test) there was some slight extra doming. Finally, we took the pressure to 600psi (Accucraft test). The shape of the increased doming showed the stay to be effective.
That pressure is roughly three times the maximum pressure of canister gas at domestic hot water temperature. The tank itself remains completely serviceable.
Tank, filler and pipework, after sustaining 600psi. Photo David Halfpenny