BevanThanks for that comprehensive answer, it does indeed help.
In regular service the garratts in general did not have the gauges as found on 29 now. By my time when gualified for them in early 1965 I can remember few having the original ones that were enclosed in the single casing. Possibly as they were a bit more labour intensive when needing to change just one of the gauges at a time.
In the main the two round gauges the independent being the smaller, showing the amounts of the pressure applied and again IIRC a steady 100psi as per the main reservoir setting this gauge was to the left of the main larger gauge. The large round gauge showed the BP usually 70psi and the constant MR pressure of 100psi. Being an A6et BV, this was designed to allow a minimum reduction of 7psi when the handle was lapped, that also allowed the high pressure controller on the pump to cut in and charge the supplementary reservoir to 125psi to assist in BP and auxiliary recharges.
Some, and not many did get the duplex gauges but it generally only was for a stop gap measure when waiting on the normal gauges as needed. I personally never saw a duplex on a garratt for the independent brake, that is not to say there were none.
You mention an exhaust steam pressure gauge, are you talking about something along the lines of the 36cl podgers gauge, certainly that was never on them in regular service and unnecessary. I have noticed an external valve on the outside firemans side of the smokebox below the pumps line and towards the rear, again that is something new.
Having a multi Valve regulator fitting for the regulator the garratts also had a continual blow down pipe located under the firemens side step just to the rear of it, same as the pigs and 38's also I believe on the 57 and 58cl.
I personally cannot understand why duplex gauges are used instead of the originals, if its a spare parts thing, I would think that the round types which were interchangeable with those on diesels would be much more able to be sourced than the duplex gauges.
On old engines that only had the single BV, especially the #4's descending heavy grades such as the Blue Mountains, Illawarra Mountain, and long descending grades of 1:40 or steeper, the regulations provided for the driver to increase the BP pressure, and on those old BV's the handle was put in full release making the BP pressure 100psi. It meant as you got nearer the bottom of the grade, you had to slowly bring the BP pressure back to its normal setting of 70psi, this was done by bringing the train to a stand 3 times and adjusting the slide valve feed valve down 10psi at a time. In a sense it was the same with diesels on those grades but it was also different as far as how much air adjustment was made as it usually meant the BP was only set at around 85 rather than the 100psi of the MR.
I hope this helps
I've just had a close look at that wonderful cab ride footage filmed by Roger MCkenzie when he did a trip on a Garratt working from Newstan to Port Waratah, and there are a couple of brief glimpses of the gauge set up. The loco he was on did indeed have two large six inch duplex gauges, just like 6029 now has, so my recollections are not as reliable as they used to be!