Jockey (Pressure-Maintenance) Pump Sizing (NFPA 20)
The jockey pump flow and the staggered pressure-switch settings for a fire-pump system, per NFPA 20 practice.
Example
You enter
- Fire pump rated flow (gpm) 750
- Fire pump churn / shutoff pressure (psi) 120
- Minimum static supply pressure (psi) 50
You get
- Jockey pump flow 7.5 gpm
- Jockey stop (psi) 170
- Fire pump start (psi) 155
Details, formula, and sources
Jockey flow is small (about 1% of the fire pump's rated flow, at least 1 gpm) so it makes up leakage without the fire pump starting on every drop -- a 750 gpm fire pump takes about a 7.5 gpm jockey. The switches stagger so the jockey acts first: jockey stop = fire-pump churn (shutoff) pressure + minimum static supply (170 psi for a 120 psi churn and 50 psi static); jockey start = stop - 10 (160); fire-pump start = jockey start - 5 (155). A too-large jockey masks a real flow and fails to start the fire pump on a fire. A settings guide; NFPA 20, the pressure switches, and the AHJ / stamped fire-pump design govern.
jockey_gpm = max(0.01 x fire_pump_gpm, 1); jockey_stop_psi = churn_psi + min_static_psi; jockey_start_psi = jockey_stop_psi - 10; fire_pump_start_psi = jockey_start_psi - 5.
NFPA 20 (Standard for the Installation of Stationary Pumps for Fire Protection) pressure-maintenance (jockey) pump practice, by name; the pressure-switch settings and the AHJ govern.
The jockey-flow rule of thumb and the staggered pressure-switch offsets are public NFPA 20 practice; the fire-pump rating, churn pressure, and static supply come from the pump data and the water supply.
Estimate. AHJ and licensed professional govern.
Field names used by the API: fire_pump_gpm, churn_psi, min_static_psi, jockey_gpm, jockey_stop_psi, fire_pump_start_psi
- Jockey flow ~1% of the fire pump's rated flow, minimum 1 gpm; head above the system max pressureNFPA 20 practice
- Staggered settings jockey stop = churn + min static; jockey start = stop - ~10; fire-pump start = jockey start - ~5NFPA 20 practice