Parts of a Medical Ventilator

All 15 parts on the diagram

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The ventilator 7

Display It shows the settings, the measured values and any alarm messages.
Control knob Turned to change the value of a setting chosen on the screen. The change is then confirmed.
Alarm indicator It lights when the machine raises an alarm. One maker uses red for the most urgent alarms and yellow for the rest.
Gas inlets A hose from the air supply goes on one. A hose from the oxygen supply goes on the other. The supply can be a wall outlet or a cylinder.
Exhalation valve Some makers call it the expiratory valve.
Backup battery The machine normally runs from the mains. It charges the battery as it does.
Cart Some makers call it a trolley.

The breathing circuit 8

Inspiratory filter Makers say to fit a filter on both ports of the machine.
Humidifier It sits between the inspiratory filter and the inspiratory limb.
Inspiratory limb Limb is the makers' word for each of the circuit's two hoses.
Y-piece (wye) Its third opening is the patient end of the circuit. One maker writes Y-piece, another wye.
Test lung It goes on the patient end of the Y-piece.
Expiratory limb The water trap is fitted in this limb.
Water trap It is fitted upright, hanging below the hose.
Expiratory filter The last thing the gas passes before going back into the machine.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two of three makers' manuals use it: an operator's manual, full text at https://archive.org/details/manuallib-id-2587394; a second maker's instructions for use, https://archive.org/details/manual_medical_Drager_Evita_XL_Intensive_Care_Ventilator_Software_6.n_User_Manual; and a third maker's pocket guide, https://archive.org/details/manualzilla-id-6038408. Wikipedia (Ventilator, Heat and moisture exchanger) was read as well, text only. The detail lines are in our own words and say what a part is and where it sits, nothing about its use on a patient. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's machine, nothing traced. Licence: own work

How it works

Two drawings name the parts of a medical ventilator. The first is the machine on its cart. The second is the breathing circuit, the set of hoses that joins it, shown ending at a test lung.

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Go round the circuit

Gas leaves the machine through the inspiratory filter and passes through the humidifier into the inspiratory limb. The two limbs meet at the Y-piece, which here carries a test lung. The expiratory limb runs back past the water trap and the expiratory filter to the exhalation valve. On the machine itself, find the display, the control knob, the alarm indicator, the gas inlets, the backup battery and the cart.

Inspiratory means on the way out of the machine; expiratory means on the way back to it.
This page names parts only. How a ventilator is set up and used is taught by its maker and by clinical training.

Questions and answers

What are the main parts of a ventilator?

The machine, with its display, controls, alarm indicator, gas inlets, exhalation valve and backup battery, and the breathing circuit: two hoses called limbs, a Y-piece where they join, filters, a humidifier and a water trap.

What is a ventilator circuit?

The set of hoses and fittings between the machine and the patient end. Makers call it the patient circuit or breathing circuit. It has an inspiratory limb, an expiratory limb and a Y-piece that joins them.

What is the Y-piece on a ventilator?

The Y-shaped connector, also called the wye, where the inspiratory limb and the expiratory limb meet. Its third opening is the patient end of the circuit. For a machine check, makers put a test lung or a cap on it.

What is a test lung?

A rubber breathing bag that is put on the Y-piece in place of a patient, so the machine and its circuit can be checked. It is what this drawing shows on the end of the circuit.