Shallow Pump¶

The shallow buoyancy pump is a single-stroke piston design that moves seawater directly into and out of a short port on the nose centerline (the stagnation point) to change the vehicle's displacement. It uses a 90-watt motor and a rolling-diaphragm (Bellofram) seal. On G3 gliders the pump is high-displacement (≥ ~960 cc).

Depth / gearbox variants¶

The shallow pump ships with different gearbox/motor combinations rated for different pressures (commonly 30 / 50 / 100 / 150 / 200 m). The mechanical gear drive is not the limiting factor — the limit is the energy that must be pulled from the battery on the return stroke. Pick the gearbox/motor for your working depth to get quick inflections (more important in shallow water) and to minimise return-stroke energy.

Vacuum requirement & back-drive brake¶

Top-inflection depth limits¶

Unlike the deep pump (which can retract at any depth), a shallow pump can only retract within its rated range — push it deeper and you risk an abort, and back-driving the pump at depth can over-volt the electronics (protection exists, but respect the limits). Operator rules of thumb for the deepest sustained top inflection:

Reducing drive for slow / efficient flight¶

The full drive is ±1000 cc, but the glider flies well on as little as ~300 cc of total drive. Reducing drive ("flying slow") is useful in shallow water or to save energy:

• Set b_arg: d_bpump_value(x) in your yo file (this bounds m_ballast_pumped).
• Or set it live, e.g. put c_dive_bpump -200 / put c_climb_bpump 200 with put c_autoballast_state 0, returning to ±1000 when full drive is needed.
• The autoballast software feature can set reduced drive automatically.

Maintenance — the Bellofram¶

The rolling diaphragm (Bellofram) is the part to watch: cracks or creases on a Bellofram are a death sentence for a shallow pump.

• While installed and retracted, rinse debris and grit out with a standard garden hose first.
• Then hand-clean with tap water and mild (dish) soap and a soft cloth. Do not use solvent-based cleaners.
• Apply a thin layer of Molykote 316 or 3M Silicone Lubricant (not a silicone spray containing acetone) to prevent stiction and stop debris sticking.
• Inspect: a healthy Bellofram is smooth and uniform under vacuum and slightly "wavy" with no vacuum. Creases can be felt with a finger and won't flatten against the cylinder wall; abrasion feels rough and looks like non-uniform cloth.

How to test¶

From lab_mode:

1. wiggle on
2. report ++ m_ballast_pumped
3. Confirm the pump completes a full extension (m_ballast_pumped = +400 cc) and full retraction (-400 cc) without errors.
4. wiggle off

To confirm the pump is even active: on every power-up the pump extends buoyancy to full displacement, and report ++ m_ballast_pumped shows the position moving.

With a properly ballasted glider, positive cc → positive buoyancy → climb; negative cc → dive.

Field troubleshooting¶

• MS_ABORT_DEVICE_ERROR / "buoyancy_pump device driver returned an error." Find the mission segment of the abort and inspect the .mlg plus the .sbd/ .dbd to see what the pump was doing. If it tripped at full throw or out of deadband, you can try explicitly setting limits (put c_dive_bpump -200, put c_climb_bpump 200, put c_autoballast_state 0) before putting the pump back in service.
• Stuck piston / potentiometer failure. A failed position potentiometer (the board that reads pump volume) can throw DRIVER_ODDITY: ... Buoyancy Pump is FAULTED! and a MOVE ERROR Error reading position, and the pump keeps taking itself back out of service even after use +. This usually needs a TWR rebuild, but as a field stopgap operators have set f_ballast_pumped_safety_max to the value the pump is stuck at, which can let you re-enable the pump (held at position) to run a thruster/bathtub mission toward recovery.
• A sudden pump fault accompanied by a slowly dropping leak-detect voltage can indicate water intrusion shorting the pump electronics — recover and inspect.