The VELA platform: turbine, blender, exhalation system, safety valves, power and the user interface
Identify which VELA generation is in front of you, follow the gas path from intake and oxygen inlet to the exhalation port, and name the assembly that carries each function before you open the covers.
What kind of machine this is
The VELA is a turbine ventilator built for intensive care and step-down use with paediatric and adult patients. It needs no compressed air: room air is drawn in through filters, mixed with oxygen inside the machine and pushed to the patient by a small high-speed blower. Oxygen comes from a high-pressure wall or cylinder supply, or at very low pressure from a flowmeter into a separate low-pressure inlet. Everything else, the timing of breaths, the PEEP, the oxygen mix and the monitoring, is done by one main board behind the screen.
The family went through three hardware generations. The first used a main board derived from the older Bird T-series ventilators with a separate video board. The next two, called ColdFire 1 and ColdFire 2, put video and oxygen monitoring on one main board. ColdFire 2 begins at a serial-number break given in the service manual, and from that point the front panel is supplied without the main board, the main board has a different part number, and the serial number of the ventilator lives on a small board at the rear. Before you order anything, read the serial number from the rear label and write down which generation you have.
Option level matters too. The manual lists Basic, Plus and Comprehensive front panels with domestic and icon overlays. Modes and features beyond the basic set are enabled by the manufacturer after purchase, not by the engineer. When a user says a mode is missing, that is usually a configuration question, not a fault.
Flow delivery: the turbine and how it is controlled
The turbine is a brushless three-phase DC motor driving a blower. The main board converts the required flow into a drive command; a motor driver turns that command into three phase currents. An optical speed sensor on the turbine sends a pulse train back to the processor, and a differential pressure transducer measures the pressure rise across the turbine. Speed and pressure difference together let the software know how much flow is leaving, even when the patient's lungs push back harder or softer from breath to breath.
Two consequences follow for the engineer. First, the turbine has its own characterisation data. The relation between speed, pressure difference and flow is measured at the factory and stored with the turbine, on an EEPROM in the ColdFire generations. A turbine that no longer matches its data delivers the wrong volume even though it spins smoothly. Second, the differential transducer must stay honest. Two small auto-zero valves periodically connect both sides of that transducer to ambient so the software can measure and subtract the offset. If a zero valve sticks or its tubing is swapped, the volume error appears without any obvious noise or alarm.
The turbine sits in a muffler housing. The right-hand muffler carries a filter core, the left one is acoustic only. A dirty filter core raises the pressure the turbine has to work against and is one of the listed causes of low delivered volume. Between the turbine and the patient an inspiratory check valve and an electrically driven inspiratory hold valve sit in the manifold. The hold valve closes the path from the turbine during inspiratory hold and maximum inspiratory pressure manoeuvres.
Oxygen: a blender without a pressurised reservoir
The VELA mixes oxygen on the low-pressure side. Filtered room air flows into an accumulator from which the turbine draws. High-pressure oxygen passes an inlet filter and check valve, a safety solenoid, a regulator and an inlet pressure transducer, then a bank of solenoid valves, each feeding a fixed orifice, plus a separate nebuliser path. The software opens and closes the solenoids breath by breath to add the right amount of oxygen for the set concentration and the current flow demand. The pressure transducer lets it compensate for supply variations. The safety solenoid shuts off oxygen when the ventilator is switched off or has stopped working.
Because the accumulator is not a pressurised tank, the oxygen inlet pressure reading dips with every inspiration at high oxygen settings. The manual describes this as normal. The low oxygen inlet alarm uses a pressure threshold and a time delay, so short dips do not trigger it. A wall supply that sags under load, a partly closed zone valve or a long thin hose can still pull the pressure down for long enough to alarm, and that is a site problem, not a blender fault.
Two needle valves on the blender block are used to trim delivered oxygen at a low and a high setting during calibration. The jam nuts on them should never be touched outside that procedure. The low-pressure inlet bypasses the blender completely: oxygen from a flowmeter is added to the gas output, and the delivered concentration then depends on the flowmeter and the patient's minute volume, not on the O2 control.
Exhalation, sensing and the mechanical safety system
The exhalation valve is a linear electromagnetic actuator pushing a poppet against a seat through a silicone diaphragm. The board drives it with a controlled current, and the force on the poppet sets the pressure at which gas escapes, which is how PEEP and pressure limits are produced. The removable parts at the front, valve body and diaphragm, are cleaned and sterilised between patients; the actuator behind them is not.
Downstream of the valve sits the variable-orifice flow sensor. A flexible flap opens in proportion to flow, the pressure drop across it travels down two small tubes to a differential transducer on the main board, and the software turns it into exhaled flow and volume and uses it for flow triggering. An airway pressure transducer on the exhalation side gives the feedback signal for PEEP, pressure control and pressure support. Three auto-zero solenoids serve the exhalation transducers in the same way as on the turbine side.
The safety system is purely mechanical. A spring-loaded relief valve, adjustable by the user, limits the maximum pressure if the electronics fail, and a sub-ambient valve lets the patient breathe room air if no breath is delivered. You will meet the relief valve again in the checks: it must be seated for the leak test and the exhalation valve calibration, and returned to the clinical setting afterwards.
Electronics and power
The user interface module is one assembly at the front: a 10.4-inch colour LCD with a resistive touch overlay, a backlight inverter, membrane keys with built-in LEDs, an optical data dial and the main system board. The main board carries the pressure transducers, the analogue-to-digital and digital-to-analogue converters, the solenoid drivers, the motor and exhalation valve drivers, a watchdog and monitors of the supply rails. If the processor stops refreshing the watchdog or a supply rail leaves its window, the hardware forces the ventilator to a safe state and it will not restart until the cause is removed. The main board also has a 3 V coin cell that is replaced at the yearly PM.
The power PCB sits on the right-hand panel. It accepts mains through the power cord, charges the internal batteries and produces the low-voltage rails for the main board. The internal batteries are a set of nickel-metal hydride packs in a tray under the top cover, with a large capacitor assembly attached to the same tray. The internal battery fuse is on the power PCB. When the batteries are disconnected, the charge controller resets its memory and starts a long recharge cycle on reconnection; the DC status lamp tells you how that cycle is going. The operator's symbols also refer to an external battery; how it connects and is charged on your units must be taken from the manufacturer's documentation.
Treat the inside as live even with the switch off. Mains enters the power PCB as long as the cord is connected, the backlight inverter generates high-frequency high voltage for the lamp, the capacitor on the battery tray stores energy and the battery packs can deliver a large current into a short. The manual's rule is simple and worth following every time: pull the mains cord before the cover comes off, and disconnect the battery connector as soon as the tray is accessible. Work on an ESD mat with a wrist strap; the boards are static-sensitive.
On the rear panel you find the oxygen inlets, the air intake and fan filters, the mains inlet and switch, a nurse call jack, printer and video connectors, analogue input and output, and an RJ-45 jack that is used with an adaptor for software loading. One serial port is marked as non-operational in the manual; leave it unconnected.
| Part | What it does | How it fails | |
|---|---|---|---|
| 01 | Front panel with main PCB, LCD, touch screen, inverter, keypad and data dial | Control, monitoring, display, transducers, drivers, watchdog, coin-cell backed memory | Dead keys or LEDs, touch offset, dim or blank screen, transducer drift, watchdog shutdown |
| 02 | Turbine and muffler assembly with speed encoder and characterisation EEPROM | Generates all inspiratory flow; speed feedback to the main board | Noise, low delivered volume, characterisation no longer valid, encoder or driver faults |
| 03 | Blender assembly with solenoids, orifices, needle valves and O2 inlet transducer | Adds oxygen to the accumulator to match the set concentration and flow | Oxygen out of range, inlet pressure errors, leaking or sticking solenoids |
| 04 | Exhalation valve assembly with removable valve body and diaphragm | Controls PEEP and pressure limits through a current-driven poppet | Leak from a wrinkled diaphragm or cracked body, failed characterisation, PEEP errors |
| 05 | Variable-orifice flow sensor and flow sensor receptacle | Measures exhaled flow and volume, provides the flow trigger | Wrong monitored volume, leaking receptacle O-rings, kinked internal tubes, worn flap |
| 06 | Manifold base with inspiratory check valve, hold solenoid, relief and sub-ambient valves | Routes gas, holds inspiration, limits pressure, allows spontaneous breathing | Leak test failure, humming check valve, cracked manifold or damaged O-rings |
| 07 | Power PCB on the right panel with internal battery fuse | Mains input, charging and low-voltage rails | No mains operation, no charging, blown battery fuse, connector faults |
| 08 | Battery tray with NiMH packs and capacitor assembly | Internal backup power | Short run time, battery low messages, charge controller losing its memory |
| 09 | Oxygen sensor cell in the manifold | FiO2 monitoring and closed-loop correction of the blender | Monitor shows no value, drift, Check O2 Cal or range alarms |
| 10 | Rear panel with fan, filters, O2 fittings and rear peripheral PCB | Cooling, air intake, gas inlets, external ports; holds the serial number on ColdFire 2 | Clogged filters, worn inlet check valves, invalid serial number events |
Typical scenario: the mode that never was
Typical scenario, not a recorded case. A ward asked for an engineer because a VELA would not offer a ventilation mode the clinicians had used on another unit. The engineer first wrote down the serial number, the generation and the front panel version, then compared them with the second ventilator. The second unit had a higher option level and newer software. Nothing was broken; the first ventilator had simply never been configured with that mode. The engineer documented both configurations, explained to the ward that enabling features is done by the manufacturer after purchase, and passed the request to the department that handles contracts instead of opening the covers.
Identify generation, panel level and software before calling anything a fault. Missing modes and features are a configuration question for the manufacturer, not a repair.
Noisy turbine that calibration could not fix
Engineers discussed a turbine ventilator, model not recorded, whose blower made an unusual noise and would not pass its turbine calibration. Repeating the calibration changed nothing. Colleagues who had seen the same symptom said that in their experience two such turbines had to be replaced; calibration does not cure a mechanical problem. Their advice was to command a fixed flow in the test mode, listen to and watch the turbine behaviour, and, where possible, fit a known-good turbine to confirm the diagnosis before ordering.
A noisy turbine that fails calibration is usually a mechanical fault, not a data problem. On a VELA confirm with the manufacturer's test screens and the delivered volume test, and remember that a new turbine brings its own characterisation data.
On-site checklist
- Serial number, generation (T-2, ColdFire 1 or ColdFire 2) and front panel level recorded
- Software version and turbine and machine hours read from the extended functions screens
- Turbine serial number recorded if accessible from the records
- Oxygen supply type checked: high-pressure inlet, low-pressure inlet or both
- Mains cord, cord guard and plug inspected before any work
- ESD mat and wrist strap ready before the cover comes off