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malicious_bloke, dunno if you know, but you can right-click a steam line with the angular transducer to see the amount of steam inside. This can be useful for determining how many turbines you can add.
If you have a single turbine, and you check the steam level on the pipe entering the grate, and that level is rising, you know you can probably stand to add another turbine.
Couple other notes: I'd keep my grates a bit closer to the turbine (they're pretty far below). This is for a couple reasons:
1) the less time steam blocks exist, the better fps/block update performance you'll get
2) less steam is likely to "miss" the turbine altogether.
Also, unless you plan on using ammonia at some point, you can consider killing output steam altogether by placing a block (of your choice) directly under the output space (underneath where one might put a CVT to monitor power output). This again helps mitigate the steam block performance issues.
Really there's not much reason to do an ammonia loop these days; its more sensible to try to generate enough steam to warrant an HP turbine.