The Gillette PR-3500 is a 350-kilowatt prime-rated natural gas generator on PSI's 21.9L turbocharged V12 — the same engine as the SP-4000/5000 standby series. At 350 kW prime (550 bhp), the V12 runs at conservative loading for unlimited continuous duty. DSE 7420 controller, Stamford S4L1DG alternator.
The V12 at continuous duty — 12-cylinder maintenance reality#
12 cylinders under continuous operation means 12-cylinder ignition service every ~6 weeks (1000 hours). This is a multi-technician, planned maintenance event. The PSI 21.9L V12 at 350 kW prime operates at 550 bhp — 28% below its standby capability — providing excellent thermal margin for sustained operation.
The PSI V12 at prime duty requires rigorous scheduling discipline. We allocate dedicated service windows for the 12-cylinder ignition service, oil change (49 qt with filters), and air filter replacement at each 250/500/1000-hour interval. The engine is reliable at 350 kW continuous when maintained on schedule.
Tell us about the application — kW, voltage, application, install timeline — and we'll respond within one business day with budgetary pricing, lead time, and any sizing notes.
Adjust load percent and tank size to estimate runtime. Pre-filled with this model's spec where available.
Estimate runtime on this tank
Fuel demand at 75% load
3,675,000 BTU/hr≈ 3675.0 cf/min @ 1,000 BTU/cf
On utility natural gas the runtime is generally unlimited provided the supply line and meter can deliver this BTU/hr at the engine's required inlet pressure (typically 5–14" WC residential, up to 5 psi commercial). Confirm against the OEM's published fuel-pressure spec.
Service intervals
Manufacturer-recommended intervals for the Gillette PR-3500 under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.
Oil & filter
Every 250 hours or 6 months
Coolant change
Every 4000 hours
Air filter
Every 500 hours
Spark plugs
Every 1000 hours
Major overhaul
≈ 15,000 hours
Load bank test
Every 12 months
Common failure modes
What we've seen fail on this platform. Use as a service-planning reference, not a diagnostic — actual failure modes depend heavily on duty cycle and maintenance history.
Component
Symptom
Typical hours
Severity
Turbocharger
Power loss from continuous high-output duty
10,000+
moderate
Spark plugs / ignition
Misfire, rough running under sustained load
1,000+
moderate
Oil degradation
Accelerated valve train wear from continuous duty
250+
minor
Frequently Asked Questions
Is this the same 21.9L V12 as the SP-4000/5000 standby?
Yes — same PSI 21.9L V12 TCAC engine. The SP-4000 is 400 kW standby, SP-5000 is 500 kW standby. The PR-3500 at 350 kW prime is derated for unlimited continuous operation (550 bhp vs 684-764 bhp standby).
What fuel consumption at 350 kW prime?
4,623 ft3/hr NG at full load. At 75%: 3,556 ft3/hr. At 50%: 2,607 ft3/hr. At 24/7 operation, this requires a high-capacity commercial gas service — coordinate with your utility for sustained continuous supply.
540 kW prime-rated natural gas generator. PSI 31.8L V12 turbocharged, Stamford HCI534 alternator, DSE 7420. Continuous duty, 3-phase only. Gillette's largest prime gas unit.
