Significance of Parameters for IVD Instrument Fluid Path Micro Solenoid Valve

The solenoid valve is an important automation control component that can be classified into various types based on its control methods. Each type of solenoid valve has its specific application scenarios and functions, capable of meeting the fluid control needs of different industries and fields. This article will introduce some specification concepts of micro solenoid valves in IVD instrument fluid systems.

Working Pressure

If the pressure exceeds the pressure that micro solenoid valves can withstand during operation, the valve may leak or even be damaged.

Cv Value

The definition of the Cv value: When the valve is fully open, and the pressure difference ΔP between the two ends of the valve is 1 psi (6.895 kPa), the amount of 60°F (15.56°C) water that can flow through the valve per minute, measured in gallons per minute (GPM).

The greater the flow of liquid under the same pressure difference, the larger the Cv value, indicating a wider internal flow path of the valve and greater fluid flow capacity.

Response Time

This refers to the time required for the valve to fully open or close from the moment power is supplied. In some applications, the response time requirement for the valve may be high. Some applications require high consistency in response time between individual valves. For example, in liquid distribution using multiple needles, the liquid amount is controlled by the opening and closing times of the valves. If high consistency in the liquid amount distributed by multiple needles is required, high consistency in the response time of the valves is necessary.  

Internal Cavity Volume and Dead Volume

Internal cavity volume refers to the volume of the area inside the valve that stores liquid. Dead volume refers to the area within the valve where the liquid cannot flow effectively.

Pump Action Volume of the Valve

Pump action volume refers to the volume change in the internal cavity as the valve switches from open to closed, or from closed to open, due to the movement of action components, resulting in suction or discharge effects on the liquid. As shown in the shaded red area in the image below, this volume difference between opening and closing will produce suction or discharge effects during the switching, similar to a pump.  

Leakage Rate

This refers to the amount of liquid leakage under a specific pressure when the micro solenoid valve is in a closed state. For example, an airtightness test can be conducted to evaluate the leakage rate using the pressure decay rate. Not all micro solenoid valves can guarantee zero leakage when closed. For instance, valves with PTFE seals may leak due to the relative hardness of PTFE. Valves used in needle cleaning control pipelines, if leaking, may cause water droplets to seep from the needle tip.  

Operating Temperature

This includes the ambient temperature in which the valve can operate and the temperature of the medium flowing through the valve.

Sealing Materials

Common sealing materials include FKM, EPDM, FFKM, PTFE, etc. Sealing materials come into direct contact with the liquid passing through the valve and often require a chemical compatibility assessment. PTFE generally has better chemical compatibility.

Filtration Requirements  

Micro solenoid valves form a seal through the fitting of seals and mechanical parts. If foreign objects enter and get caught in the sealing area, it will cause leakage. Foreign objects might also scratch certain PTFE sealing rings, also causing leakage. Therefore, liquids entering the mini solenoid valve usually need to pass through a filter. The specific filtration precision required should be based on the requirements in the micro solenoid valve manual.

Interface Types

Interfaces can be chosen according to demand, such as barbed connections, 1/4-28UNF, M5, M6, G1/8 threaded interfaces, etc.

Life

Micro solenoid valves can operate a certain number of times before failure or damage, for example, a lifespan of 1 million or 5 million cycles.

Electrical Parameters, such as Power Consumption and Voltage

For power supply, some valves recommend distinguishing between the operating voltage and holding voltage. When the micro solenoid valve needs to operate, increasing the supply voltage ensures normal operation of the valve and increases the micro solenoid valve response speed. After the operation is completed and the valve is in a stable open or closed state, lowering the voltage reduces power consumption and prevents the coil from overheating. Long-term overheating of the coil may cause excessive response delays.