Vacuum Gauge to Drafting Lift Readout
Reads the compound (vacuum) gauge during a draft.
Example
You enter
- Compound (vacuum) gauge reading (in Hg) 10
- Pump condition factor (0-1, default 0.667) 0.667
You get
- Total suction head 11.3
- Attainable ceiling (altitude-corrected) 22.6 ft
- Margin (ft) 11.3113
Details, formula, and sources
suction_head = vacuum_inHg x 1.13, against the altitude-corrected attainable ceiling (factor x (33.9 - elevation/1000)) with the margin left. 10 in Hg at sea level is 11.3 ft, only half the ~22.6 ft ceiling; 18 in Hg at 3,000 ft is 98% of the ceiling - the pump about to lose prime. Turns the gauge needle into feet and a cavitation warning. Pairs with the maximum draft lift, which is the ceiling. A readout aid, not incident command.
suction_head_ft = vacuum_inhg x 1.13; theoretical_ceiling = 33.9 - site_elevation / 1000; attainable_ceiling = pump_factor x theoretical_ceiling; margin = attainable_ceiling - suction_head_ft.
IFSTA / NWCG fire-pump drafting practice vacuum-to-lift conversion, by name.
The vacuum-to-lift conversion is public fire-service / wildland training material; incident command governs the actual draft.
Estimate. AHJ and licensed professional govern.
Field names used by the API: vacuum_inhg, pump_factor, suction_head_ft, attainable_ceiling_ft, margin_ft
- Vacuum-to-feet 1 in Hg of vacuum is about 1.13 ft of suction headIFSTA / NWCG
- Total suction head at flow the gauge reads lift plus suction-hose friction, checked against the ~2/3 attainable, altitude-corrected ceilingIFSTA / NWCG