Electric Pumps

Each hydraulic system carries one electric pump — Green, Blue, and Yellow. All three are mechanically identical: a single three-segment assembly comprising an electric motor, an inlet boost pump, and a variable-displacement hydraulic pump. Output is approximately 18% of an engine-driven pump, sufficient for surface retraction and the specific automatic triggers documented in Hydraulic Generation Overview, but not for sustained substitution of an EDP.

The electric pump assembly is more complex than the EDP in one respect: it carries its own electrical protection chain — a temperature switch, a current-unbalance detector, and a remote-controlled circuit breaker. The protection logic is what makes the electric pump a one-event component: an overheat or phase imbalance trips the pump immediately, and resetting requires ground access to the circuit breaker.

1. The three-segment assembly

                ┌─────────────────────────────────────────┐
                │      Electric Pump Assembly             │
                │                                          │
                │   ┌────────────────────────────────┐    │
   3-phase ─────┼──►│  Electric motor                │    │
   115/200 V    │   │  - 7600 (Vickers) / 7700 rpm   │    │
   400 Hz       │   │    (Parker) under load         │    │
                │   │  - 45 A max running            │    │
                │   │  - 194 A max start-up          │    │
                │   │  - Fan-cooled exterior         │    │
                │   │  - Hollow-shaft fluid cooling  │    │
                │   │  - OVHT switch at ~193 °C      │    │
                │   └──────────────┬─────────────────┘    │
                │                  │                       │
                │                  ▼                       │
                │   ┌────────────────────────────────┐    │
                │   │  Boost pump (impeller)         │    │
                │   │  - Raises fluid by 2.7–3 bar   │    │
                │   │  - Feeds hydraulic pump inlet  │    │
                │   └──────────────┬─────────────────┘    │
                │                  │                       │
                │                  ▼                       │
                │   ┌────────────────────────────────┐    │
                │   │  Hydraulic pump                 │    │
                │   │  - 7 pistons, in-line type      │    │
                │   │  - Variable displacement        │    │
                │   │  - Yoke + spool compensator     │    │
                │   │  - 32 L/min @ 150 bar full flow │    │
                │   │  - 206 bar @ zero flow          │    │
                │   └──────────────┬─────────────────┘    │
                │                  │                       │
                └──────────────────┼───────────────────────┘
                                   │
                                   ▼
                              System manifold
                                   │
                                   │
                Outputs/feedback signals:
                  • Pressure switch (100/120 bar hysteresis) → HSMU
                  • CUDU (Current Unbalance Detector Unit)   → HSMU
                  • Temperature switch in motor               → relay → RCCB
                  • RCCB (Remote-Controlled Circuit Breaker) → power gate

The three systems use the same design with different part numbers:

• Green electric pump: 1JV
• Blue electric pump: 1JC
• Yellow electric pump: 1JJ

All three have the same performance characteristics. The maintenance documentation describes the Green pump and references the same description for Blue and Yellow.

2. The electric motor

Power supply and demand characteristics:

The start-up surge of 194 A — roughly 4.3 times the running current — is a meaningful electrical event. Two implications:

• Multiple electric pumps should not start simultaneously in normal operation. The HSMU manages the automatic triggers to avoid co-incident starts; in practice the Green and Yellow triggers are mutually exclusive on the same bus.
• The pump's HSMU triggers always include a settling assumption — for example, the Green ELEC PUMP 25-second window starts from steady state, after the surge has subsided.

Cooling — two parallel paths

The motor is cooled by both air and fluid:

• A blower attached to the motor shaft draws air through the motor housing; the heated air exits through a flexible hose to outside the aircraft.
• A small flow of hydraulic fluid is routed through the hollow drive shaft, cooling the main bearings and the rotor from inside.

The dual-path cooling is what allows the motor to sustain its 45 A running current at 7,600 rpm without thermal runaway. Either path failing alone — air blocked or fluid cooling lost — would shift the thermal balance toward the OVHT threshold.

Part-number variants

Two designs are in service depending on the airframe build:

• Vickers (FSN 401-450): 7,600 rpm under load, OVHT at 193 °C ± 5, boost pressure 2.7 ± 0.34 bar.
• Parker/Abex (FSN 003-050 etc.): 7,700 rpm under load, OVHT at 200 °C ± 10, boost pressure 3 bar. Includes an additional gerotor-type hydraulic pump dedicated to cooling-fluid flow through the hollow shaft.

The differences are minor and functionally equivalent for the crew. Maintenance distinguishes; the cockpit does not.

3. Boost pump

A small impeller-type pump sits on the opposite end of the motor shaft from the motor. It raises fluid pressure by 2.7 ± 0.34 bar (40 ± 5 psi) before the fluid enters the main hydraulic pump.

The boost pump is functionally similar to the EDP's inlet boost impeller — it raises pump-inlet pressure to keep the piston-pump section out of cavitation. The combined upstream pressure at the hydraulic pump inlet is approximately:

• 4.5 bar absolute (reservoir cushion) +
• 2.7 bar absolute (boost pump rise) =
• ~7.2 bar absolute at the hydraulic pump inlet.

This is well above the vapour pressure of phosphate-ester fluid at operating temperature, providing a large margin against cavitation.

4. Hydraulic pump segment

The hydraulic-pump section is a variable-displacement, in-line, 7-piston unit. Compared with the EDP's 9-piston design, the smaller piston count and lower nominal output reflect the electric pump's role as a backup rather than a primary source.

Performance:

Compared with EDP performance:

The flow ratio (32/175 ≈ 18%) is the documented value behind the operational rule that an electric pump is not a sustained EDP substitute. The pressure differential between full flow (150 bar) and zero flow (206 bar) is larger than the EDP's (175 vs 206 bar), meaning the electric pump's output pressure droops more under load.

5. Pressure switch — 100/120 bar hysteresis

The electric pump's delivery-line pressure switch is set differently from the EDP's:

The electric pump's lower trigger (100 bar instead of 120) reflects its lower full-flow pressure (150 bar). If the trigger were set to 120 bar, normal full-flow operation would be too close to the threshold and could produce spurious LO PR indications. The hysteresis between 100 and 120 bar prevents oscillation when pump output is near the threshold.

The signal goes to the HSMU. The HSMU does not extinguish the ELEC PUMP FAULT light when the LO PR signal clears under all conditions — see §7 for the FAULT-light latch behaviour after thermal events.

6. Overheat protection — 193 °C / 200 °C switch

Each electric pump motor has an internal temperature switch. When the motor housing temperature reaches the threshold (193 °C ± 5 on Vickers, 200 °C ± 10 on Parker), the switch operates and triggers a chain that cuts off power to the pump.

The chain:

Motor temperature reaches threshold
            │
            ▼
   Temperature switch operates (opens contact)
            │
            ▼
   Sends signal to:
            │
       ┌────┴────────────────────────────┐
       ▼                                  ▼
   ECAM HYD page                  Local relay
   "OVHT" indication              (21JV / 11JC / 12JJ)
                                          │
                                          ▼
                                  Energises relay → closes contact
                                          │
                                          ▼
                                  Cuts off RCCB supply circuit
                                          │
                                          ▼
                                  RCCB opens → pump power cut

A useful consequence: the electric pump's overheat shutdown is automatic and immediate — the architecture removes power without waiting for crew action. This contrasts with the EDP's overheat case, where the crew is expected to follow the ECAM procedure to switch off the pump.

Hysteresis — 16 °C window

The temperature switch resets at 177 °C ± 5 (rising at 193 ± 5, falling at 177 ± 5). The 16 °C window prevents oscillation around the trigger and ensures that a recovery requires actual cooling, not just a fluctuation.

Package skin temperature limits

The fluid temperature anywhere inside the pump assembly must stay below 110 °C during and after operation. The pump-assembly skin temperature must stay below 200 °C even in failure conditions (dry running, loss of Green system, etc.). These are design limits maintained by the cooling architecture; the crew has no direct interface with them, but the limits are why the package can survive a brief dry-run window without external intervention.

7. FAULT-light latch

After a thermal trip on a Green or Yellow electric pump, the FAULT light on the corresponding pushbutton does not extinguish when the crew selects the pump OFF. The light remains illuminated until both of the following are true:

• Motor temperature has dropped below the reset threshold (177 °C).
• The circuit breaker has been reset on the ground.

For the crew in flight, the practical consequence: an electric pump that has tripped on OVHT stays "marked" by the FAULT light for the remainder of the flight. There is no in-flight recovery action. The pump is not available again until ground maintenance resets the circuit breaker.

This is documented behaviour and is not a second failure. The architecture deliberately latches the indication so that the overheat event is not forgotten in the cockpit workflow.

8. Current Unbalance Detector Unit (CUDU)

The CUDU (designator 2JV on Green; equivalents on Blue and Yellow) monitors the three-phase current supplying the electric pump. It is housed in the avionics compartment and operates on 28 VDC — independent of the AC supply it is protecting.

What CUDU detects

A three-phase induction motor can continue to rotate with one or two phases lost ("running on residual phases"), but the surviving phases carry disproportionate current and the motor windings overheat rapidly. Conventional over-current protection on the total current may not catch this because the total current can actually decrease in a single-phase loss while individual phase currents spike.

CUDU monitors the balance between the three phase currents. An unbalance condition triggers the protection.

What CUDU does

When unbalance is detected:

• CUDU signals the HSMU.
• HSMU commands the contactor to cut off the electric pump's three-phase supply.
• The pump stops; FAULT light illuminates.

CUDU reset

CUDU reset requires interrupting its own 28 VDC supply on the ground. The architecture is intentional: a fault detected by CUDU should not silently self-clear; a maintenance action is required to acknowledge and reset, ensuring the underlying cause is investigated.

9. Remote-Controlled Circuit Breaker (RCCB)

The RCCB (designator 3JV1 on Green, equivalents on Blue and Yellow) is installed on the 717VU panel and is the final electrical gate between the AC supply bus and the electric pump motor.

The RCCB is "remote-controlled" because the HSMU can open it via a control signal, not just by manual action. Triggers that cause the RCCB to open:

After an RCCB trip due to overcurrent or HSMU command, reset is by pressing the R button on the rear of the RCCB. This is a ground-access action; the crew cannot reset an RCCB from the cockpit.

10. The full protection chain

The five-layer protection chain summarises everything that can shut the electric pump down:

Any single layer is sufficient to stop the pump. The crew sees the result (FAULT light, ECAM caution); the underlying chain is invisible in flight.

11. Automatic triggers — the system-specific recap

The full table for which conditions automatically run each electric pump in AUTO:

The detailed reasoning behind each trigger is in the individual system-pump articles (Hydraulic Generation Overview gives the architectural picture).

12. Maintenance interfaces — task references

Electric-pump-related maintenance tasks documented in AMM 29-21 (Green), AMM 29-22 (Blue), and AMM 29-23 (Yellow):

Operational details visible to the crew during maintenance:

• After an RCCB trip, the technician presses the R button on the rear of the RCCB on panel 717VU to reset.
• After a CUDU detection, the technician interrupts and restores the 28 V DC supply to the CUDU itself to clear the latched fault — designed to ensure the trigger is investigated rather than silently self-clearing.
• A failed temperature switch within the electric pump body cannot be replaced as a standalone component; the entire pump assembly is replaced as a unit. The temperature switch's behaviour is verified during the post-replacement functional test.

13. Cross-references and chapter interfaces

The electric pump touches several other chapters:

The electric pump is an integration point between hydraulic, electrical, and flight-control logic — more so than the EDP, which has a simpler upstream-dependency profile.

14. Boundary of the documented detail

What the AMM and FCOM document about the electric pump:

• The three-segment construction (motor + boost + hydraulic pump) is detailed in §5.B of the relevant ATA-29 chapter.
• The performance numbers (rpm, flow, pressure, current) are tabulated.
• The OVHT thresholds and hysteresis are specified.
• The CUDU and RCCB logic is documented at the protection-chain level.

What is not documented at crew level:

• The internal hydraulic-pump compensator details (similar to the EDP compensator but specific to the 7-piston unit).
• The exact algorithm by which CUDU determines "unbalance" (proprietary protection-circuit logic).
• The RCCB's internal trip-curve characteristics.
• The temperature switch's exact response time and contact rating.

These items belong to the manufacturer's internal documentation and are not part of operator-side maintenance literature. For the pilot and line technician, the documented level is sufficient for operational understanding and routine maintenance.

Self-test

[!note]- Q1. The Green ELEC PUMP FAULT light is on. The crew selects OFF on the pushbutton. The light does not extinguish. Diagnosis?

This is consistent with an OVHT-related trip rather than a low-pressure trip. After an electric pump overheat, the FAULT light is latched and stays illuminated until both the motor cools below the 177 °C reset threshold and the corresponding RCCB is reset on the ground. The pump itself has accepted the OFF command and is no longer running. The persistent light is the indication of the latched overheat memory, not a refusal to switch off. No in-flight action recovers the pump; the crew accepts the loss and reports for ground reset.

[!note]- Q2. The electric pump's pressure switch triggers at 100 bar (decreasing) and resets at 120 bar (increasing). Why is this trigger set lower than the EDP's 120 bar trigger?

Because the electric pump's full-flow output pressure is only 150 bar (vs the EDP's 196 bar). If the electric pump's trigger were set at 120 bar, the threshold would sit too close to normal full-flow operation and would produce spurious LO PR cautions whenever the pump operated against high demand. Setting the trigger 50 bar below full-flow pressure gives a working margin for normal pump operation while still catching a meaningful pressure loss. The 100/120 hysteresis prevents oscillation between the two states.

[!note]- Q3. The electric pump motor draws 194 A at start-up versus 45 A in running mode. What architectural consequence follows?

The 4.3:1 start-up surge means electric pumps should not be started simultaneously on the same electrical bus. The HSMU manages the automatic triggers such that Green and Yellow electric pump activations are mutually exclusive (the Yellow trigger explicitly checks that the Green ELEC PUMP is not running for gear retraction before activating). Beyond that, the surge is a transient that the bus accommodates; it does not cause supply problems in normal operation. The 194 A figure matters as an engineering datum rather than as a crew action item.

[!note]- Q4. What does CUDU detect that conventional overcurrent protection does not, and why does this matter?

CUDU detects current unbalance between the three phases of the AC supply. A three-phase motor can continue to rotate with one or two phases lost; the surviving phases carry disproportionate current, while the total current may actually decrease, evading overcurrent protection. The motor windings overheat rapidly in this condition. CUDU monitors phase-to-phase balance directly, catching the failure mode that overcurrent protection misses. The output cuts the pump's RCCB to prevent winding damage. The architecture treats phase loss as a distinct failure class deserving dedicated detection.

[!note]- Q5. The electric pump produces 32 L/min vs the EDP's 175 L/min. Why is this 18% figure operationally significant rather than just a maintenance reference?

Because it sets the boundary on what the electric pump can sustain. At 18% of EDP flow, the electric pump can move a surface (retract spoilers, complete a gear cycle, drive a flap motor briefly) but cannot maintain a system against continuous heavy demand. This is the engineering basis for the standard caution: "do not select a HYD ELEC PUMP ON for sustained operation after a hydraulic failure." Running the pump continuously after an EDP loss does not restore a meaningful margin — there is not enough flow to drive the consumers, and the pump itself is stressed by the prolonged operation. The 18% figure is why the rule exists.

References

Per FCOM DSC-29-10-20 (electric pump descriptions, automatic-trigger conditions, the general note on not running ELEC PUMP for sustained substitution); AMM 29-21 (Green electric pump 1JV — full description of motor, boost pump, hydraulic pump, pressure switch 5JV, CUDU 2JV, RCCB 3JV1; performance parameters, OVHT thresholds, hysteresis, Vickers and Parker variants); AMM 29-22 (Blue 1JC, reference to 29-21); AMM 29-23 (Yellow 1JJ, reference to 29-21); AMM 29-31 (FAULT light latch behaviour, motor overheat switch).

Independent study material, not an Airbus publication. Refer to current operator FCOM, FCTM, AMM, and QRH for operational use.