Is this the simplest form of Automatic Ventilators Ever ?

Building an Emergency Ventilator with Linear Actuators: A Practical Engineering Solution

During the COVID-19 pandemic, healthcare systems worldwide faced critical shortages of mechanical ventilators — devices that typically cost $25,000 to $50,000 and require months of production time. This crisis sparked a global engineering response: could emergency ventilation systems be built quickly, simply, and affordably using readily available components? At FIRGELLI Automations, we explored this question by designing and building a functional automatic ventilator system using electric linear actuators as the core mechanical component.

What emerged from this project was a proof-of-concept system that could be assembled for approximately $300 using off-the-shelf components. While not intended to replace certified medical equipment, this design demonstrates the fundamental principles of automated bag valve ventilation and shows how electric linear actuation technology can be applied to critical healthcare challenges. The system uses a simple mechanical approach: a linear actuator compresses a medical ventilator bag at controlled intervals, delivering measured breaths to a patient.

This article documents our complete build process, component selection rationale, and lessons learned. Whether you're an engineer interested in emergency medical device design, a maker exploring healthcare applications, or simply curious about how linear actuators can solve real-world problems, this project illustrates the intersection of accessible motion control technology and critical medical needs.

Understanding Bag Valve Ventilation and Automation Requirements

Before diving into the build, it's essential to understand what we're automating. Bag valve mask (BVM) ventilation is a manual technique used by emergency medical personnel to provide positive pressure ventilation to patients who cannot breathe adequately on their own. A medical professional squeezes a self-inflating bag, which pushes air through a one-way valve into the patient's airway.

Manual BVM ventilation works well for short-term emergency care, but prolonged use presents significant challenges. Healthcare workers can maintain proper compression for only 15-20 minutes before fatigue affects their ability to deliver consistent tidal volumes and respiratory rates. During a mass casualty event or pandemic surge, this limitation becomes critical when the number of patients requiring ventilation exceeds available medical staff.

Automating this process requires several key mechanical capabilities:

• Controlled stroke length: The actuator must compress the bag through a specific distance to deliver appropriate tidal volumes (typically 400-600ml for adults)
• Adjustable cycle timing: Respiratory rates must be controllable, typically ranging from 10-20 breaths per minute
• Consistent force application: Each compression must be uniform to ensure reliable air delivery
• Continuous operation: The system must run reliably for extended periods without overheating or mechanical failure
• Fail-safe considerations: Any automation must include provisions for immediate manual override

Electric linear actuators are uniquely suited to this application because they provide precise, controllable linear motion with adjustable force, stroke length, and cycle timing. Unlike pneumatic or hydraulic alternatives, electric actuators require only a power supply and simple control electronics — no compressed air systems or hydraulic fluid handling.

Component Selection and Bill of Materials

Our design philosophy prioritized simplicity, accessibility, and cost-effectiveness while maintaining functional reliability. Every component selected had to be readily available, require minimal technical expertise to install, and work together without custom fabrication or specialized tools.

Primary Motion Component: FA-35 Linear Actuator

The heart of this system is the FA-35-12-2" electric linear actuator with a 2-inch stroke length. This specific model was chosen for several technical reasons:

• Stroke length compatibility: A 2-inch (50mm) stroke provides sufficient compression distance to evacuate the ventilator bag while maintaining a safety margin to prevent over-compression
• Force capacity: The FA-35 series delivers adequate force to compress medical-grade ventilator bags, which require consistent pressure to overcome airway resistance
• 12V DC operation: Standard voltage simplifies power supply selection and allows for potential battery backup systems
• Duty cycle rating: Because the load on the actuator is relatively low (compressing an air-filled bag), continuous operation doesn't approach the actuator's thermal limits
• Built-in limit switches: Internal switches automatically stop the actuator at full extension and retraction, eliminating the need for external position sensing

For applications requiring position feedback for more sophisticated control algorithms, feedback actuators with integrated potentiometers or Hall effect sensors would be the next logical upgrade.

Mechanical Mounting System

Proper mechanical mounting is critical for efficient force transfer and system longevity. We used two standard FIRGELLI mounting brackets:

• MB1 Bracket: Attached to the actuator's rear mounting point, this bracket secures the actuator body to the base frame structure
• MB6 Bracket: Connected to the actuator's extending rod, this bracket interfaces with the compression plate that contacts the ventilator bag

These standardized brackets eliminate the need for custom fabrication or welding. The mounting system must be rigid enough to prevent flexing during compression cycles, as any deflection reduces compression efficiency and can introduce timing inconsistencies.

Power and Control Electronics

The electrical system consists of two primary components:

12VDC Power Supply: A standard wall-adapter style power supply converts AC mains voltage to the 12V DC required by the actuator. For a production or emergency deployment system, battery backup capability would be essential to ensure continued operation during power interruptions.

Timer Relay Module: This is the system's control brain, albeit a simple one. The timer relay alternates power to the actuator in forward and reverse directions at user-adjustable intervals. The adjustment dial controls both the extension and retraction timing, effectively setting the respiratory rate. This approach trades sophisticated control for absolute simplicity and reliability — there are no complex circuits or microcontrollers to fail.

Medical Component: Ventilator Bag Assembly

We purchased a certified medical ventilator bag assembly from an established medical supply vendor. This component includes the self-inflating bag, one-way valves, oxygen reservoir, and patient connection port. Using a proper medical-grade bag is non-negotiable — these bags are specifically designed with appropriate valve characteristics, material biocompatibility, and reliability standards that cannot be improvised with consumer products.

Assembly and Operational Principles

The mechanical operation of this system is deliberately straightforward. The ventilator bag is positioned between a rigid back plate and a compression plate attached to the actuator's extending rod. When the timer relay energizes the actuator to extend, the rod pushes the compression plate forward, squeezing the bag against the back plate. This compression forces air through the bag's one-way valve system and into the patient circuit.

When the timer interval completes, the relay reverses polarity to the actuator, causing it to retract. As the compression plate withdraws, the bag's self-inflating mechanism draws in fresh air (potentially supplemented with oxygen through the reservoir), preparing for the next compression cycle. This creates a continuous breathing pattern with adjustable rate and volume.

Timing and Respiratory Rate Control

The timer relay's adjustment dial controls the duration of each phase — both compression and relaxation. For typical adult ventilation, target respiratory rates range from 10 to 20 breaths per minute, corresponding to cycle times of 6 seconds to 3 seconds. The inspiratory-to-expiratory (I:E) ratio, typically around 1:2, must be considered when setting the timer intervals to ensure adequate exhalation time.

In our basic configuration, both the compression and relaxation phases use the same duration, creating a 1:1 I:E ratio. While not ideal from a respiratory physiology perspective, this simplified approach demonstrates the core concept and could be easily refined with more sophisticated control electronics.

Duty Cycle Considerations and Continuous Operation

One critical advantage of this application is the minimal mechanical load during operation. The actuator compresses only an air-filled bag, not a heavy mechanical load. This light duty cycle means the actuator generates minimal heat and can operate continuously without approaching its thermal limits. Standard linear actuators often have duty cycle ratings (the percentage of time they can operate in a given period), but bag compression falls well below these thresholds.

For comparison, applications like TV lifts or standing desks involve moving substantial weight over longer strokes, generating significant heat. The ventilator application's short stroke, low force requirement, and intermittent duty cycle create an ideal match for continuous operation.

System Demonstration and Performance

The video below shows our completed ventilator system in operation. You can observe the consistent compression cycle, the bag's refill behavior, and the overall mechanical reliability of the linear actuator-based approach.

During testing, several performance characteristics became apparent:

• Consistency: The actuator delivered remarkably uniform compression cycles, with minimal variation in stroke timing or force application
• Adjustability: The timer relay dial provided intuitive control over respiratory rate, though incremental adjustments required a screwdriver and some trial-and-error
• Reliability: Extended test runs showed no signs of mechanical wear, overheating, or performance degradation
• Noise level: The actuator and relay produced minimal acoustic noise, substantially quieter than the pneumatic compression systems used in some commercial emergency ventilators

The total material cost for this build was approximately $300, including the actuator, brackets, control electronics, power supply, and mounting materials. The medical ventilator bag represents about half this cost, while the motion control components account for the remainder. This compares favorably to emergency ventilator systems that were developed during the pandemic crisis, many of which cost several thousand dollars while offering similar basic functionality.

Advanced Control Systems and Future Enhancements

While our timer relay-based system demonstrates the fundamental concept effectively, real-world medical applications demand more sophisticated control capabilities. The next logical evolution would incorporate microcontroller-based control, offering several significant advantages.

Arduino-Based Microcontroller Integration

An Arduino or similar microcontroller platform could provide programmable control over multiple ventilation parameters:

• Independent I:E ratio control: Separate timing for inspiration and expiration phases, allowing proper respiratory physiology
• Variable tidal volume: Adjustable stroke length to deliver different air volumes based on patient size and clinical requirements
• Pressure limiting: Integration with pressure sensors to prevent barotrauma from excessive airway pressures
• Alarm systems: Monitoring for disconnections, pressure anomalies, or power failures with audible and visual alerts
• Data logging: Recording ventilation parameters for clinical documentation and quality assurance

Using feedback actuators with position sensing would enable closed-loop control, where the microcontroller actively monitors and adjusts the actuator's position in real-time. This approach allows for adaptive responses to changing airway resistance or compliance, more closely mimicking the behavior of sophisticated medical ventilators.

Patient-Responsive Ventilation

Advanced systems could incorporate patient monitoring inputs to create truly responsive ventilation. For example, integrating a pulse oximeter or heart rate monitor would allow the system to adjust respiratory rate based on the patient's oxygenation status. Pressure sensors in the patient circuit could detect spontaneous breathing efforts and synchronize mechanical breaths accordingly — a feature called assist-control ventilation in medical terminology.

These enhancements require not just additional sensors and control systems, but also sophisticated programming to implement safe, clinically appropriate control algorithms. The mechanical simplicity of the linear actuator-based compression system remains unchanged, but the intelligence layer adds substantial capability.

Design Limitations and Important Medical Considerations

It's crucial to address this project's limitations explicitly. This system was built as an engineering demonstration and proof-of-concept, not as a certified medical device. Several critical factors would need to be addressed before any such system could be used in actual patient care:

• Regulatory compliance: Medical ventilators must meet stringent FDA (or equivalent international) regulatory standards for safety, efficacy, and reliability. This requires extensive testing, clinical validation, and quality system compliance.
• Fail-safe mechanisms: Medical devices require redundant safety systems to detect and respond to failure modes. At minimum, this includes pressure relief valves, battery backup, disconnect alarms, and immediate manual override capability.
• Clinical monitoring: Proper mechanical ventilation requires continuous monitoring of multiple parameters including tidal volume, airway pressure, oxygen concentration, and patient vital signs. Our demonstration system lacks these essential monitoring capabilities.
• Sterility and infection control: Medical devices that contact the patient circuit must meet biocompatibility standards and support proper sterilization or single-use protocols.
• Clinical expertise: Mechanical ventilation is a complex medical intervention requiring trained professionals to set appropriate parameters, monitor patient response, and manage complications.

This project should be viewed as an exploration of how motion control technology can address medical challenges, not as instructions for building actual medical equipment. The engineering principles demonstrated here have value for understanding automated bag valve systems, but the path from prototype to approved medical device involves substantial additional development, testing, and validation.

Applications of Linear Actuators Beyond Emergency Ventilation

While this project focused on emergency medical applications, the core technology — precise electric linear actuation with simple control systems — has broad applicability across healthcare and laboratory environments. Linear actuators are increasingly common in medical device design because they offer clean, quiet, controllable motion without hydraulic fluids or complex pneumatic systems.

Similar actuation approaches appear in hospital bed positioning systems, patient lift mechanisms, automated CPR devices, and laboratory automation equipment. The same attributes that made linear actuators suitable for this ventilator project — precise stroke control, reliable continuous operation, and simple integration — apply across numerous medical and life science applications.

For engineers and makers working on healthcare projects, industrial actuators offer the robustness and reliability required for demanding applications, while micro linear actuators suit compact medical devices and laboratory instruments where space constraints dominate.

Conclusion: Accessible Technology for Critical Needs

This project demonstrates that sophisticated medical device functions — in this case, automated mechanical ventilation — can be achieved using accessible, readily available motion control components. The total system cost of approximately $300 and the straightforward assembly process show how electric linear actuator technology can be rapidly deployed when critical needs arise.

The COVID-19 pandemic highlighted vulnerabilities in medical supply chains and the value of engineering communities' ability to innovate under pressure. While this specific design served primarily as a proof-of-concept and learning tool, the principles explored here contributed to broader discussions about emergency medical device development and the role of open-source engineering in healthcare crises.

For those interested in motion control applications — whether in medical devices, home automation, industrial equipment, or robotics — this project illustrates fundamental principles of actuator selection, control system design, and mechanical integration. The simplicity of the timer relay approach proves that sophisticated functionality doesn't always require complex control systems, though the path forward involves adding intelligence while maintaining reliability.

Frequently Asked Questions

Can this system safely replace commercial medical ventilators?

No, this system is a proof-of-concept demonstration, not a certified medical device. Commercial medical ventilators must meet stringent regulatory standards including FDA approval, extensive safety testing, clinical validation, and quality system compliance. They incorporate sophisticated monitoring systems, alarm capabilities, pressure limiting, and fail-safe mechanisms that this basic design lacks. This project demonstrates engineering principles and shows how linear actuators can automate bag valve ventilation, but it should not be used for actual patient care without substantial additional development, testing, and regulatory approval.

Why use electric linear actuators instead of pneumatic systems or servo motors?

Electric linear actuators offer several advantages for this application. They provide direct linear motion without requiring rotary-to-linear conversion mechanisms, operate from simple DC power without compressed air systems, generate minimal noise, and integrate easily with basic control electronics. Pneumatic systems require air compressors and pressure regulation, while servo motors need additional mechanical components to convert rotation to linear compression. Linear actuators deliver the precise, controllable, repeatable motion needed for bag compression in a compact, self-contained package that requires only electrical power.

What stroke length is appropriate for ventilator bag compression?

A 2-inch (50mm) stroke length is generally appropriate for adult ventilator bag compression, providing sufficient travel to deliver tidal volumes in the 400-600ml range typical for adult ventilation. The actual volume delivered depends on several factors including bag size, compression plate area, and the percentage of bag volume evacuated during compression. Shorter strokes may be suitable for pediatric applications with smaller tidal volumes, while adjusting the compression depth (rather than using longer stroke actuators) typically provides adequate volume control. The key is ensuring complete bag refill between compressions while avoiding over-compression that might damage the bag or valves.

How do you control respiratory rate and inspiratory-expiratory ratio?

In the basic timer relay configuration, the adjustment dial controls the duration of both extension and retraction cycles, effectively setting the respiratory rate. This creates a 1:1 inspiratory-to-expiratory ratio, which is simpler but not physiologically ideal. For more sophisticated control including proper I:E ratios (typically 1:2 for adults), a microcontroller-based system using an Arduino or similar platform would allow independent timing control for inspiration and expiration phases. The microcontroller could also adjust these parameters dynamically based on patient monitoring inputs, though implementing such systems requires programming expertise and careful validation of control algorithms.

What power backup systems should be included for reliability?

While our demonstration used a standard wall-adapter power supply, any system intended for actual use would require battery backup to ensure continued operation during power outages. A 12V sealed lead-acid or lithium battery system with automatic switchover circuitry would provide redundancy. The relatively low power consumption of the actuator during bag compression means a modest battery pack could provide hours of backup operation. Medical-grade implementations would also include low-battery alarms and dual-battery redundancy. The actuator's 12V DC operation simplifies battery integration compared to systems requiring AC power or higher voltages.

What maintenance does the linear actuator require for continuous operation?

Electric linear actuators in this low-load application require minimal maintenance. The sealed construction protects internal components from contamination, and the light duty cycle (compressing an air-filled bag) generates minimal wear on mechanical components. Periodic inspection of mounting brackets for tightness, visual inspection of the actuator rod for damage or contamination, and verification of smooth operation would constitute basic preventive maintenance. Unlike pneumatic or hydraulic systems, there are no fluids to monitor, seals to replace regularly, or filters to service. The actuator's internal limit switches and motor brushes represent the primary wear items, though in this application they would typically provide thousands of hours of reliable operation before requiring service.