A coaxial solenoid valve is a direct-acting solenoid valve with a relatively unobstructed flow path designed for highly viscous fluids or high pressure applications. The unique design of this solenoid valve makes them suitable for systems with high flow rates where the minimum pressure lost on the valve is desired. They are usually called just a coaxial milk.
In general, systems with thick liquids with a viscosity of more than 50 ° C (square millimeters per second) require special solenoid valves for their control function. General solenoid valves cannot be used to regulate concentrated liquids such as heavy oils, greases, syrups or other sticky media. A thick environment can block the passage or cause too much force to open / close the valve and deactivate it. Most solenoid valves, when opened, direct liquids 90 degrees up and over the orifice, then 180 degrees down and under the seal, and another 90 degrees toward the outlet. In addition, indirect solenoid valves use small pilot ports with fine paths. While this design works perfectly with low viscosity environments (eg water, air or light oils), if used with concentrated liquids, it can cause a very high system pressure drop.
The invention of coaxial solenoid valves made it possible to control highly viscous liquids by removing obstacles in the liquid path. Coaxial solenoid valves are used to handle liquids with a maximum viscosity of 500 or 600 cc (CST).
Is coaxial solenoid valve suitable for your application?
A coax valve has several advantages over general solenoid valves. These valves may be a good option for your program if:
- Your system needs high flow and low pressure drop.
- Your media is very sticky (over 50 CST).
- Your environment is an aggressive, abrasive, slightly polluted or sensitive gas or liquid.
- You have high back pressure (up to 400 bar) or pressure fluctuations.
- Your system needs fast response time.
- Your environment is vacuum up to 10-4 mbar.
- Your system will experience a zero pressure differential.
Design and operation
In a coaxial solenoid valve, the concentric solenoid valve is mounted to an internal moving inner tube through which fluid flows (Figure below). This inner tube is connected directly to a magnetic piston, which moves parallel to the direction of flow when the coil is activated. This lateral movement opens or closes the valve mode regardless of the system pressure. In a normal valve, when the coil is activated, the tube moves against a return spring (not shown in the figure below) and moves away from the valve seat (the tube moves to the left in the figure below). ), Which causes fluid to flow. Due to the lack of coil energy, the pipe is pushed back to the valve seat by a back spring (the pipe moves correctly in the figure below). To prevent fluid from coming into contact with other internal parts of the valve, the tube is sealed and secured in place with O-rings.
Types of coaxial solenoid valves
All coaxial solenoid valves operate principally straight, allowing them to operate at zero differential pressure. These valves can be 2/2 way or 2/3 way and are normally closed or normally open.
In a 2/2-way configuration, depending on whether it is normally closed or normally open, the coaxial solenoid valve can power the output coil when it is energized or disconnected.
As shown in the figure below, a 3/2-way configuration can be used to direct the fluid to a second output. In this setting, outlet 1 is placed before the pipe that is fed from the inlet by default. When the coil is discharged, the inlet fluid exits from the inlet to the outlet 1 and the outlet path 2 is blocked by the valve seat. When the coil is activated, the tube moves away from the opening outlet of the valve seat 2 while sealing the outlet 1 at the same time.
Free flow path
Because the flow path is relatively unobstructed, coaxial valves are intended for highly viscous liquids. They can also withstand low flow with low pressure due to their simple design.
Not affected by pressure
Coaxial solenoid valves can withstand pressures up to 400 bar and at the same time are not affected by pressure fluctuations at the inlet or outlet. They can also work in zero pressure differentials or in vacuum applications.
Compared to a coaxial valve with other valves for highly viscous media (ball hub, gate, butterfly and globe valves), they act very quickly. Stimulation of other solutions may take several seconds.
Optional position signaling devices can be added during the milk production process to send open or closed position feedback.
Coax valves have a long life cycle, are durable and require minimal maintenance. But for easy installation and maintenance, they can be equipped with manual replacement.
The main application of coaxial solenoid valves is for highly viscous liquids, so systems containing the following fluids are excellent applications for their implementation:
Most mineral and vegetable oils such as corn oil, olive oil, castor oil, coconut oil, sesame oil, palm oil, flaxseed oil and so on.
Butter such as peanut butter, almond butter, hazelnut butter and…
The fast response time of these valves, as well as their availability in the 2/3 way functional configuration, make them suitable for precise mixing / dispersing applications.
The main criteria for selecting coaxial solenoid valves are the differential pressure characteristics at the ports, the amount of KV and the valve hole. Ingredients, ie body materials and seals, must also be considered to be environmentally friendly to prevent corrosion and the proper life of the milk.
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