Most blood pressure monitors on the market today adopt a normally open micro Electric Solenoid Valve, while the use of a normally closed micro Electric Solenoid Valve is extremely rare. The reasons can be explained from the following perspectives:
If a normally closed micro Electric Solenoid Valve is used, in the event of a power failure or malfunction, the valve defaults to a closed state. This means the high pressure in the cuff cannot be released automatically, leaving the arm under prolonged compression. Therefore, the selection of this specific micro solenoid valve is a critical design choice with direct consequences for user safety. This may cause numbness, impaired blood circulation, and poses a safety risk—especially for elderly users and patients with hypertension.
In contrast, a normally open micro Electric Solenoid Valve defaults to an open state (vented to the atmosphere) when not powered. This allows cuff pressure to be released freely, even in the case of power loss or malfunction. Such a feature prevents "continuous compression" caused by device failure during inflation, and complies with the mandatory safety requirements of blood pressure monitor standards.
With a normally closed micro Electric Solenoid Valve, the micro Electric Solenoid Valve remains shut during inflation and requires precise control of power-on timing and exhaust rate to fully release air from the cuff after inflation.
With a normally open micro Electric Solenoid Valve, the micro Electric Solenoid Valve closes synchronously with pump inflation (powered state) and automatically opens to exhaust air when power is cut off. This design minimizes residual cuff pressure, simplifies circuit design, and reduces the likelihood of failure.
Most home blood pressure monitor users are everyday consumers, especially seniors, for whom ease of operation is critical.
If a normally closed micro Electric Solenoid Valve is used, incomplete exhaust may require users to manually deflate the cuff before the next measurement, adding unnecessary steps.
A normally open micro Electric Solenoid Valve, however, automatically releases air after measurement (power-off state), keeping the cuff relaxed and ready for immediate reuse, greatly enhancing user convenience.
The preference for a normally open micro Electric Solenoid Valve in blood pressure monitors is primarily driven by safety (avoiding sustained compression risks), while also ensuring simplified control and greater user convenience. This design is not a technical compromise but a well-established industry solution aligned with medical device safety standards and user experience requirements.
