Embraer E-Jet Hydraulic System

The Embraer E190 and E190-E2 each have three independent hydraulic systems, numbered 1, 2 and 3. On the E190-E2 each works at a nominal 3,000 psi. There, systems 1 and 2 are each pressurised by a pump driven by their own engine, backed by an AC electric pump, while system 3 has no engine-driven pump at all; two electric pumps and an accumulator keep it going, and in an electrical emergency its main pump runs from the AC essential bus. A power transfer unit (PTU) lets system 1 pressurise system 2 after an engine 2 failure.

The design tolerates multiple failures: the E190-E2 can still be operated safely with two of its three systems failed. Like the electrical and fuel systems, it changed between the generations: the first-generation E190 also has three systems, but some of the automatic pump logic described here came with the E2. This article follows the E190-E2 and states where the E190 differs; other models are introduced in E-Jet family and flight deck. The general principles are covered in hydraulic pumps and power sources.

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Three hydraulic systems

On the E190-E2 the pumps are arranged as follows:

The three systems never exchange fluid, a point they share with the A320: the PTU transfers pressure only. System 3 also resembles the A320's blue system in having no engine-driven pump, but where the A320's blue system can be pressurised by a pump on the ram air turbine, the E190-E2's system 3 keeps its electric pump ACMP 3A, fed from the AC essential bus, which the RAT generator then powers (see E-Jet electrical system).

Engine-driven and electric pumps

On the E190-E2, the engine-driven pump (EDP) of systems 1 and 2 cannot be stopped or disconnected from the engine gearbox. The only way to take it out of its system is to close its shutoff valve, and the pump keeps turning. The valve closes when the engine fire handle is actuated (see E-Jet fire protection and oxygen), and closes automatically if system 1 or system 2 fluid exceeds 125 °C.

The E190-E2 has four AC motor pumps (ACMP), at least one in each system: ACMP 1B, ACMP 2B, ACMP 3A and ACMP 3B. They follow different logics:

• ACMP 1B and 2B (ELEC PUMP 1 and 2), in AUTO in flight, come on if an EDP or an engine fails, or when the flaps are extended beyond 0. They switch off at flaps 0, or 1 min after touchdown.
• ELEC PUMP 2 also has ground logic. In AUTO it runs when engine 1 is running and the parking brake is released, so that system 2, which serves the nosewheel steering and the inboard brakes, is pressurised for taxiing without engine 2. It also comes on during the engine 1 start, at 40 % N2, if the parking brake has been applied within the last 6 min, making system 2 available for the flight control check.
• ACMP 3A is the main pump of system 3. It is not left in AUTO: it is switched ON after engine start (the operator's checklist does so when start-up clearance is received) and OFF at shutdown.
• ACMP 3B, in AUTO, comes on when ACMP 3A fails. It is powered from AC bus 2.

The first-generation E190 lacks some of this automation. Before shutting down engine 1 for a single-engine taxi-in on engine 2, its crew select ELEC PUMP 1 ON (HYD PUMP 1 ON in the checklist), check for the HYD PUMP NOT AUTO message and only then stop engine 1. Automatic operation of the system 1 electric pump while taxiing on engine 2 alone came with the E2.

System users

The users that matter most in failures are these:

• System 2 supplies the landing gear, the nosewheel steering and the inboard brakes on the E190-E2. On the first-generation E190 it also drives the inboard power control unit (PCU) of each aileron, and on the E190-E2 it drives the multifunction spoiler pair added with the E2.
• System 3 supplies flight controls. In an electrical emergency on the E190-E2 its accumulator, and then ACMP 3A, keep it powering them. On the first-generation E190 it drives the outboard PCU of each aileron and the lower rudder PCU.
• System 1 drives the upper rudder PCU on the first-generation E190 and, on the E190-E2, supplies the outboard brakes and is the source for the PTU.

The first-generation figures show the logic. Each E190 aileron has one PCU on system 2 and one on system 3: losing one PCU halves the aileron's force authority, and the aileron becomes inoperable only if both systems fail. The E190 rudder's two PCUs, on systems 1 and 3, work as active and standby, each able to give full control (see E-Jet flight controls). The E2 changed the way the actuators share the work: on the E190-E2 they are all active in normal mode, where the E1 used an active and standby arrangement whose channels swap roles after the first ground power-up of each day.

On the E190-E2 a priority valve protects the flight controls when pressure is low: it isolates the landing gear and nosewheel steering, so that the flight controls keep priority.

Power transfer unit

The E190-E2's power transfer unit (PTU) transfers pressure from system 1 to system 2. Its purpose is narrow: with the engine 2 driven pump failed, it keeps the landing gear and nosewheel steering available during take-off and landing. It moves no fluid between the systems and does not serve the flight controls.

With its selector in AUTO, the PTU runs when engine 2 or EDP 2 has failed and all of these conditions are met:

• the flaps are extended;
• EDP 1 is operating;
• system 2 quantity is above 12 %.

The comparison with other types is instructive:

The E190-E2's PTU, like the 737's, serves one purpose, here the gear and nosewheel steering of system 2.

Indications and controls

The hydraulic panel carries the ELEC PUMP selectors for ACMP 1B, 2B, 3A and 3B and the PTU selector. Before engine start on the E190-E2 the PTU and ELEC PUMPs 1, 2 and 3B are set to AUTO while ELEC PUMP 3A stays off. Each system's fluid quantity is given as a percentage, and the reservoir temperature decides whether the fluid must be warmed before engine start.

On the E190-E2, rising fluid temperature brings protections in a fixed order:

In very cold weather the hydraulic fluid is warmed before engine start. On the E190-E2, at a reservoir temperature of -18 °C or below, the crew follow the HYD warm-up procedure (QRH NP16): all four ACMPs on, nosewheel steering engaged and the flight controls checked until all three systems are above -10 °C. ELEC PUMP 2 is then switched off and the PTU allowed to run for 30 s, after which the panel returns to AUTO with ELEC PUMP 3A off.

On the first-generation E190, a hydraulic built-in test (PBIT) of the flight control actuators runs on the ground whenever all three systems are pressurised and the fluid is above 10 °C. It takes about 1 min, stays valid for 50 h and is interrupted if the controls are moved.

Failure cases

On the E190-E2 the failure cases follow from the pump logic and the users above:

• Engine 2 or EDP 2 failure. In flight ACMP 2B comes on automatically in AUTO. For take-off and landing, the PTU keeps system 2's gear and nosewheel steering available from system 1.
• Engine 1 or EDP 1 failure. ACMP 1B comes on. The PTU plays no part: it is triggered by the loss of engine 2 or EDP 2.
• Overheat. At 125 °C the affected pump is isolated, and the HYD OVERHEAT warning comes at 145 °C. The crew stay in the HYD OVERHEAT checklist and complete it even if the warning goes out.
• Low pressure. The priority valve isolates the landing gear and nosewheel steering in favour of the flight controls.
• Electrical emergency. With no AC bus powered, the RAT deploys. The system 3 accumulator supplies the flight controls until the AC ESS bus powers ACMP 3A again. A pump unloader valve acts while the RAT is deploying and a flow limiter valve while it is operating, both to avoid overloading the RAT, and the system 3 overheat protection, with its caution and warning, is inhibited so that the pump is not switched off for temperature while it powers the flight controls.

The landing gear, brakes and steering themselves are covered in E-Jet landing gear, brakes and steering.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.