A bit of dress grinding around the firebox was required, to get the ashpan to fit a little better. The sides of the firebox were trimmed down until the ashpan bolted up with a minimal gap. Next time on a wide firebox I will set it up in the mill and take a cut, would save some time and effort.
The stay and rivet heads on the throatplate were dress ground to give some room for cladding. It's close to the rear driving wheels so space is precious.
The 1/4" ball valve regulator and steam circuit is the next subject of review. The existing ball valve was reviewed and the bore looked between 4 and 5mm which is the smallest part of the pipework. I had another 1/4" ball valve with a 7.5mm bore and same overall dimensions so it was swapped out.
The steam circuit plumbing seems to fit OK, a hydro test should reveal any leaks between the valve and the header flange...there are some aluminum washers there that may or may not give a seal. Certainly a workshop essential to have a hydro test pump!
I will make some 1 in 3 & 1 in 6 tapered test pieces to see how the blast pipe sits, and where the steam is meeting the petticoat. The 1 in 3 taper should meet the petticoat at the bottom radius close to where it meets the chimney bore, and the 1 in 6 somewhere below the top of the chimney. That way we can have some confidence the steam isn't billowing in the smokebox and also not sucking air down the chimney, for good smokebox vacuum. Short large diameter chimneys can be a challenge to get this to work.
I will also check the blast orifice diameter (Martin Evans' formula has worked for me before as a quick check). Locomotive draughting is a science in itself, and everyone has a different and sometimes conflicting viewpoint! Rule #1 is the exhaust must be able to get out the chimney!
Large grate areas (wide firebox) for the same size piston and blastpipe arrangement will have lower primary air velocity through the grates than a narrow firebox loco. According to the textbooks I have there is a formula and relationship of grate area to piston diameter, so they must be equally matched for efficiency. One outcome of low air velocity through the firebox is the tendency to clinker and a low steaming rate of the boiler. Interesting facts!
Happy steaming!
Nigel
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