The heavy-hydraulics research programme compares three buildable excavator circuits by pump-shaft energy: fixed open-centre, load-sensing, and ideal independent metering. Earlier steps used random pressures and found load-sensing saving a third to a half. This step ties pressures to loads (a digging-force model) and pins the margins to opened sources: a 25 bar differential-pressure limiter from a Politecnico di Torino thesis simulating a midi excavator, and a measured 6 bar open-centre block and 0.883 pump efficiency from Juza and Hermanek (2023).
Result over 20,000 cycles: load-sensing uses a median 1.04 times the energy of open-centre and loses in 61% of cycles. Sweeping the margin puts the break-even near 23 bar; at 14 bar load-sensing wins in 93%. Independent metering beats load-sensing in every cycle (median 0.66).
Caveats: the two margins come from different machines, the pressures are an assumed force model, and no measured pressure trace was reachable (two candidate sources were blocked). It is a sensitivity result, not an energy figure. Details and code: research/heavy-hydraulics/LOG.md. Written with AI assistance.