Woodward 8901-037 Booster Servomotor

Woodward 8901-037 Booster Servomotor

The Woodward 8901-037 is a single-cylinder pneumatic-hydraulic booster servomotor designed to provide instantaneous hydraulic working pressure to mechanical-hydraulic governors during prime mover startup. On medium- and slow-speed marine propulsion diesel engines, heavy power generation gensets, and large gas engines, rotary gear pumps driven by the governor drive shaft cannot produce sufficient hydraulic pressure at cranking RPM. The 8901-037 utilizes compressed starting air admitted concurrently with engine roll to drive an internal displacement piston, instantly priming the governor power cylinder and pushing fuel racks to the start-fuel index without rotational delay.

Model Details

• Manufacturer: Woodward Inc.
• Part Number (MPN): 8901-037
• Configuration: Single-Cylinder, Spring-Return Hydraulic Booster
• Pressure Ratio (Hydraulic Oil Out to Air In): 1:1
• Technical Manual Reference: Woodward Product Manual 36684 / Supplement 26904

Technical Specifications

Key Features

1. Zero-Lag Hydraulic Priming: Delivers instant oil pressure to the governor power piston at the exact millisecond starting air is admitted to the engine, bypassing the gear pump spin-up lag.
2. Integrated Dual Discharge Routing: Configured with an unrestricted discharge port (Outlet No. 1) directly feeding the main accumulator/work system and a restricted orifice port (Outlet No. 2) for metered actuator stabilization.
3. Adjustable Stroke Fuel Limiting: Features an external mechanical stroke-limit setting screw with locknut to calibrate the precise volume of displacement oil injected per starting cycle.
4. Automatic Sump Refill Cycle: Internal heavy-duty coil return spring and integrated suction check valve automatically draw fresh oil from the governor sump once air pressure vents to atmosphere.
5. Cast Construction for Marine Duty: Heavy ductile iron housing engineered to withstand continuous engine-block vibration, cyclic hydraulic spikes up to 35 bar (500 psi), and saline ambient environments.

Compatible Woodward Governors & Actuators

• Woodward PG Series: PGA, PG-PL, PGG, PG-200, PG-500, PGTM.
• Woodward UG Series: UG-8, UG-40, UG-8PL, UG-Dial.
• Woodward EGB Series: EGB-10P, EGB-29P, EGB-35P, EGB-50P, EGB-500P.

Applications

• Direct-Reversible Marine Main Engines: Provides instantaneous throttle positioning for rapid ahead-to-astern crash maneuvers where starting air capacity and reaction time are safety-critical.
• Standby Marine Auxiliary Generating Sets: Accelerates dead-ship and blackout recovery starts to meet strict SOLAS emergency bus load acceptance timelines.
• Continuous Mechanical Fuel Control Priming: Displaces governor terminal shafts out of low-idle stop locks before mechanical gear pump delivery establishes nominal pilot stage pressure.
• Pneumatically Controlled Industrial Compressors: Interfaces engine starting sequence logics with governor boost assist during heavy backpressure starting conditions.

Frequently Asked Questions

What does the Woodward 8901-037 Booster Servomotor do?

The Woodward 8901-037 uses compressed starting air to instantly pump a measured volume of hydraulic oil into the engine governor during startup. This immediately overcomes the governor’s power piston inertia and positions the fuel racks for firing without waiting for the engine-driven gear pump to build pressure.

What is the pressure ratio of model 8901-037?

The 8901-037 features a 1:1 air-to-oil pressure ratio. For every 1 bar (or psi) of compressed starting air admitted to the pneumatic port, the booster delivers approximately 1 bar (or psi) of hydraulic oil pressure out of its discharge port to the governor circuit.

How do I adjust the amount of start-fuel oil injected by the booster?

Oil volume is adjusted via the external stroke limit screw located on the end cover of the booster. Loosen the locking nut and turn the screw clockwise to decrease displacement volume, or counterclockwise to increase volume. Retighten the locknut securely before starting the engine.

Can the 8901-037 replace a tandem booster model?

No. The 8901-037 is a single-cylinder model with one displacement volume. Tandem boosters (such as 8901-065 or 8901-067) have two distinct cylinders designed to feed both the power piston and speed setting servo simultaneously on complex multi-fluid governor architectures. Verify your engine arrangement drawing and governor model before substitution.

Why is my engine governor hunting or sluggish after installing the booster?

The most common cause is entrained air in the booster oil chamber or interconnecting lines. If the booster was mounted horizontally, mounted above the governor oil level, or piping loops trapped air during initial installation, the booster will inject compressed air bubbles into the governor accumulator, causing severe control instability. Re-check line slopes and execute the manual air-bleeding procedure.