[Dave1000]

Let me describe a “typical” rotary exhaust machine for small (internal) volume valves and lamps from back prior to the 1970’s (which still run to this day, I am absolutely sure), bear in mind it is a while since I worked on one, and I did not take detailed notes when I did.
The machine itself is roughly mushroom-shaped. The stem/stalk/column of the mushroom is hollow and carries all the connections/services to the valve-plate or, in the case of electrical connections, to sprung electrical connections in principle, akin to a commutator/carbon brushes. The valve-plate is attached to the top of the column. (A valve-plate is actually two lapped plates, on a 20 position head around 30cm diameter, on a 50 head machine something like 70cm). On a traditional 20 head machine the column will have an ID probably of less than 30cm, on a 50 head something like 60cm or a bit more.
On top of the lower half of the valve-plate sits the upper half, which is attached to the indexing drive and the wheel-like turret assembly that carries the compression heads etc..
Pumps and all other ancillary kit generally have to be located remote to the machine, for what I hope are very obvious reasons, although I have seen some machines with a small final “polishing” diff’ pump sat on top of the machine, above the valve-plate, but which must still be connected via the valve-plate, and I have seen one comparatively modern, HUGE, rotary exhaust machine with diff’ pumps mounted in the centre of the turret. Typically though, on older and certainly small machines, pumps will be 2-3m from the base of the column. I have never seen any pump connected with anything significantly larger than 75mm s/s tube. To fit all of the pump lines etc. through the inside of the column, some have to be reasonably small – typically 10-20mm.
The valve-plate will be a total of something like 70-100mm thick and each position will have a port of around 10-15mm diameter, through the plate. The top of the plate will be connected to the heads via rigid stubs attached to the plate and flexi or rubber vacuum hose. The compression head will have a small internal chamber and this attaches to the 10cm or so long, 3-4mm ID tubulation.
So between pump and lamp/valve, ignoring all the connections, twists and turns, each of them producing a pressure drop, there will be (roughly, probably conservatively) something like 3-4m of 75mm pipe, 2-3m of 10-20mm pipe/hose, 70-100mm of 10-15mm “orifice”, and 10cm of 3-4mm tubulation.
People may be familiar with CONVERT.exe by Josh Maddison? There is or was a similar file available as a free download that calculates pressure drops for you – long since lost by me, but if anyone wants to try to find it and plumb that lot in and see what sort of pressure drop you get between lamp/valve jacket and pump with an index time of umpteen seconds…….
As to operation of the actual machine, conventionally there would be, given in no particular order here, rough vacuum (in my experience, from a factory-wide system – “factory vac’”), leak check, purge (with dry nitrogen in the case of vacuum and most other jackets), ideally a station where the lamp (or valve) is lit to some degree to outgas things, plus the actual pumping to achieve evacuation of the jacket. Ideally there would be heat applied to the outside of the jacket as well, to outgas the glass. (Without a leak check station to find gross leaks, you are taking serious risks – it will let down your high vacuum lines, at worst blowing the oil out of diff’ pumps, or at least ensuring that the next 2-3-more indexes are making scrap as it will take that long to get even close to recovering the vacuum. Any leak detected would lead to that head/position being shut (clipped-off in the terminology familiar to me), upstream of the compression head.)

Assume that you have a 50ml jacket at 0.01 Torr, attached a compression head at 0.001, or 0.0001 Torr, through a 10cm, 3mm ID tubulation. That is a pressure differential of 0.009, or 0.0099 Torr between head and jacket - how long to get the jacket to 0.001 or 0.0001 Torr? Yes, I know, in theory it is for ever, but you get my drift.