Anyone who has worked on pneumatic circuit design has probably been through this: the board is laid out, the pump is selected, the air chamber structure is fixed, and then you get stuck on one solenoid valve. The datasheets all look similar. The price difference is only a few dollars. But after two days on the prototype, problems show up-exhaust is half a beat too slow, pressure holding drops too fast, or after three months the coil heat warps the plastic part.
SC0626DVG is discussed a lot in the industry, not because its specs are spectacular, but because it pins down several key metrics within a fairly narrow range. Two-way, normally closed, DC6V or DC12V, 350mmHg, 3-second exhaust, 3mmHg/min leakage, 200,000 cycles. Individually, none of these numbers is unusual. Put together, they become interesting.
This article is not going to repeat the datasheet-you can look that up yourself. What I want to discuss is what these parameters mean in real devices, when it fits, and when you should look at another solution.
Two-Way Normally Closed: What Does It Actually Save You?
First, the structure. Two-way means one inlet and one outlet, controlling only one path in the pneumatic circuit. Normally closed means the valve port is shut when power is off; the coil must be energized to open it.
This design is almost the default in medical and household devices. The reason is simple: when the device loses power, the air path should be closed, not open. If a blood pressure monitor loses power mid-measurement while the valve is still open, all the air escapes, and the user sees a strange error code. If a massage chair air cell leaks during standby, the next startup has to refill it, which directly hurts the experience.
Another hidden benefit of a normally closed valve is zero standby power. If the coil is not energized, it draws no power. For battery-powered portable devices, this is far more meaningful than saving a few milliamps of quiescent current.
SC0626DVG uses a two-way normally closed structure, which means it is suited to the role of "air only when needed." Exhaust valves, vent valves, and inflation control valves basically follow this logic.
DC6V and DC12V: Choosing Voltage Is Not Choosing a Number, It's Choosing a System
The datasheet lists two voltage versions:
DC6.0V: 353mA, 17Ω.
DC12.0V: 177mA, 68Ω.
Calculate the power, and both versions are around 2.1W. Same power, double the current difference. What does that mean?
If you are making a portable device with a 3.7V lithium battery boosted to 6V, the DC6V version can be used directly. But the 353mA peak current places demands on the boost IC and battery discharge capability, so you need enough margin in the design.
If you are working with a 12V system-car seats, massage chairs, industrial control cabinets-the DC12V version is more natural. The 177mA current places much lower demands on wire gauge and connectors, and PCB traces do not need to be as wide.
One detail is easy to overlook: the resistance difference between the two versions is threefold. A 17Ω coil operates at 6V, while a 68Ω coil operates at 12V; the turns and wire diameter are different. You cannot connect a 6V valve to 12V-the coil will overheat. Conversely, a 12V valve connected to 6V will not have enough pulling force; the valve may not open or may only partially open, making the pneumatic performance completely uncontrollable.
The essence of voltage selection is system architecture selection. Define the power supply first, then the valve-not the other way around.
350mmHg and 3-Second Exhaust: These Two Numbers Are Tied Together
Max pressure 350mmHg, exhaust time 3 seconds from 300mmHg down to 15mmHg, tested with a 100CC tank.
These two numbers must be read together.
350mmHg is about 0.46 atm, or 46kPa. This pressure level is typical in medical devices-inflating a blood pressure cuff to 280–300mmHg is routine, and therapy device air cells usually stay below 200mmHg. The margin at 350mmHg is not huge, but it is sufficient.
The 3-second exhaust spec is meaningful in blood pressure monitors. If the valve's flow capacity is insufficient, exhausting the cuff from 300mmHg to 15mmHg could drag on to 5 seconds or longer. Measurement time increases, the user's arm stays squeezed longer, and the experience gets worse. More troublesome, some measurement algorithms rely on the linearity of the exhaust rate; if the valve's flow characteristics are unstable, the algorithm has to correct repeatedly.
The 100CC tank is a standard test condition. The actual device's pneumatic volume may be smaller or larger. Smaller volume exhausts faster; larger volume exhausts slower. During selection, estimate using the actual pneumatic volume-do not simply apply the datasheet's 3 seconds.
One more point: exhaust time is measured at room temperature. If the device operates near 50°C, changes in air density and seal hardness may cause the exhaust time to drift by a few percentage points. When validating medical devices, the exhaust curve under high and low temperature conditions must be tested separately.
Leakage 3mmHg/min: The Quieter the Device, the More It Cares About Leakage
The leakage spec is 3mmHg/min, again at 300mmHg and a 100CC tank.
Converted, 3mmHg/min is about 0.4kPa per minute. In a 100CC volume, the equivalent orifice for this leakage rate is very small-it belongs to the level of "can hold pressure but cannot achieve absolute sealing."
Why not zero leakage? Because solenoid valve sealing relies on an elastomer pressed between the poppet and valve seat. Machining tolerances, surface roughness, and elastomer aging all cause trace amounts of gas permeation. Zero leakage is unrealistic in engineering and unnecessary.
3mmHg/min is enough for most intermittent-duty devices. During the holding phase, a blood pressure monitor usually maintains pressure for only a few seconds to a dozen seconds. At 3mmHg/min, the drop in 10 seconds is only 0.5mmHg, negligible for measurement results.
But for scenarios requiring long-term pressure holding-such as certain pressure-decay leak testers-this leakage rate may be too high. Leak testers often test at tens of kPa for several minutes; a 3mmHg/min leak could be misjudged as a workpiece leak. In such cases, choose a valve with lower leakage, or use a shut-off valve plus an independent sealing structure.
One more point worth mentioning: the leakage spec is measured under clean air conditions. If particles are present in the pneumatic circuit and scratch the sealing surface, leakage will rapidly worsen. Adding a 5μm filter upstream of the air source costs little but can significantly extend valve life.
200,000-Cycle Life: How to Understand This Number
Life test: 200,000 cycles. It sounds like a lot, but it depends on operating frequency.
If the device is a blood pressure monitor used three times a day, with the valve actuating twice per measurement (once for inflation and once for exhaust), that is 6 cycles a day, 2,190 a year. 200,000 cycles would last 90 years. Blood pressure monitors do not last that long in practice; valve life is not the bottleneck.
If it is a massage chair, one massage program may actuate the valve dozens of times. Used twice a day, that is tens of thousands of cycles a year. 200,000 cycles could be reached in two or three years. Of course, a massage chair usually has more than one valve; multiple valves share the actuation count, so the actual cycles per valve are lower.
The life test conditions are not detailed in the datasheet, but they are usually at rated voltage, room temperature, clean air, and intermittent duty. In real use, voltage fluctuations, temperature changes, and air supply quality all affect life. Coil insulation aging, spring fatigue, and seal wear are all gradual processes.
During selection, treat 200,000 cycles as a reference baseline, then discount it based on actual operating frequency and expected service life. If the margin is insufficient, either choose a valve with a higher life rating or reduce unnecessary valve actuations in the control strategy.
0–50°C, 75% RH: The Environmental Boundary Is Not a Suggestion, It's a Red Line
Operating environment: 0–50°C, 75% RH.
This range covers most indoor and in-vehicle scenarios. But there are two boundaries to note.
Low-temperature end, 0°C: If the device is used outdoors in winter or in a cold storage environment, the temperature may fall below 0°C. At low temperatures, seals harden, valve response slows, and exhaust time may lengthen. More troublesome, if there is moisture in the pneumatic circuit, freezing at low temperature can block the valve port. For such scenarios, choose a low-temperature version or add drying measures to the pneumatic design.
High-temperature end, 50°C: If the valve is installed in a sealed enclosure with pumps, motors, and power supplies generating heat nearby, the local temperature may exceed 50°C. The coil itself also generates heat; 2.1W is not small in a compact valve body. High temperatures accelerate insulation aging and seal aging, shortening life. Leave a heat dissipation path in the design, or choose a valve with a higher temperature rating.
75% RH is an upper limit, not a target. In high-humidity environments, coil insulation resistance drops. If the valve body is not well sealed and moisture enters the coil area, a short circuit may occur over time. Outdoor or high-humidity scenarios require a version with a higher protection rating.
What This Valve Is Good For-and What It Is Not
Good for:
Blood pressure monitor cuff exhaust control. 3-second exhaust, 3mmHg/min leakage, and normally closed structure-these specs sit right at the typical requirements of a blood pressure monitor. The DC6V version suits portable models; the DC12V version suits desktop or in-vehicle models.
Massage device air cell control. Massage chairs, leg massagers, neck massagers-many air cells, each valve responsible for one cell or a group of cells. The two-way structure is simple and reliable, and 200,000 cycles is enough.
Pneumatic therapy devices. DVT pumps, anti-bedsore air mattresses-these require cyclic inflation and deflation. A normally closed valve maintains air cell pressure when power is off, improving safety.
Smart toilet pneumatic control. Water-air mixing, drying air path switching; the DC12V version can be powered directly from a car or adapter.
Industrial gas sampling. The two-way structure suits gas path switching, but pay attention to air supply cleanliness and pressure range.
Not ideal for:
Applications requiring proportional control. SC0626DVG is an on/off valve with only open and closed states. If precise flow or pressure control is needed, use a proportional valve or PWM plus sensor closed-loop control.
High-pressure scenarios. 350mmHg is the upper limit; beyond that, seals and structure may fail. Industrial pneumatic systems usually operate above 0.5MPa, and this valve cannot be used there.
Liquid media. The datasheet says Air. Do not use it with water or oil. Liquid density and viscosity differ greatly from air, and both flow characteristics and sealing will suffer.
Continuous high-frequency actuation. 200,000 cycles is based on intermittent duty. If the valve must actuate several times per second for hours continuously, coil heating and seal wear will accelerate.
Several Common Pitfalls in Selection
Pitfall 1: Looking only at voltage, not current. The DC6V version draws 353mA. If your power IC outputs a maximum of 300mA, the valve will cause a brownout reset as soon as it opens. Include the valve's peak current in your selection.
Pitfall 2: Ignoring the test conditions for exhaust time. The datasheet uses a 100CC tank; your device's pneumatic volume may be 30CC or 200CC. Different volumes make a big difference in exhaust time. It is best to test with the actual pneumatic circuit.
Pitfall 3: Not treating the air supply. Dust, oil mist, and moisture in the air are the biggest killers of solenoid valves. Add a filter and oil-water separator. They cost only a few dollars and can save a lot of after-sales problems.
Pitfall 4: Cutting corners on the drive circuit. The coil is an inductive load and generates back EMF when power is removed. Without a flyback diode, the drive transistor can be damaged. This may not show up on the prototype, but it will fail in batches after mass production.
Pitfall 5: Ignoring mounting orientation. Some solenoid valves have requirements for mounting angle because the poppet resets by gravity. SC0626DVG is normally closed and spring-reset, so mounting orientation is relatively flexible, but it is still best to follow the datasheet's recommended orientation.
FAQ
Can SC0626DVG be used in blood pressure monitors?
Yes. 3-second exhaust, 3mmHg/min leakage, and normally closed structure meet the basic requirements for blood pressure cuff control. The specific suitability depends on your pneumatic volume and the measurement algorithm's requirements for the exhaust curve.
Can the DC6V and DC12V versions be interchanged?
No. The coil resistances differ. A 6V version connected to 12V will overheat; a 12V version connected to 6V will not have enough pulling force. The system voltage must be determined during selection.
Is 3mmHg/min leakage high?
It depends on the application. It is sufficient for intermittent-duty devices. For leak test equipment requiring long-term pressure holding, it may be too high. Calculate based on actual holding time and allowable pressure drop.
Under what conditions is the 200,000-cycle life tested?
Usually at rated voltage, room temperature, clean air, and intermittent duty. Actual life is affected by temperature, air supply quality, and operating frequency, so leave margin during selection.
Can it pass water?
The datasheet says Air. It is not recommended for water or other liquids; sealing and flow characteristics do not match.
Do I need a filter?
Yes, recommended. A 5μm filter can block most particles and significantly extend valve life. The cost is low, and the benefit is high.
Final Thoughts
SC0626DVG is not a universal valve. Its parameter boundaries are clear: low-pressure air, intermittent duty, normally closed safety, and small-to-medium flow. Within these boundaries, it is a reliable, inexpensive, easy-to-drive valve. Outside them, you need to look at other solutions.
The core of selection is not comparing which parameter is higher or lower, but breaking down the device's real operating conditions-pneumatic volume, working pressure, required exhaust time, allowable leakage, actuations per day, ambient temperature and humidity-and matching them against the datasheet. The one that matches is the right one.
If you are working on a blood pressure monitor, massage device, pneumatic therapy device, or similar pneumatic product, get samples of SC0626DVG and run them in your actual pneumatic circuit. The datasheet is a reference; measured results are the answer.