Solenoid Valves

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Offering advantages such as rapid and safe switching, a compact design, high reliability and typically long service life, solenoid valves are used in a wide range of industries; particularly, commercial, industrial, residential and appliance. Solenoid valves are mainly categorized in three ways: material being controlled; such as solenoid air valves and solenoid water valves; design, such as 3 way solenoid valves, proportional solenoid valves or plastic solenoid valves; or how they are being powered, such as pneumatic solenoid valves and 12 volt solenoid valves. Each type of solenoid valve is best suited for certain flow control applications. For example, miniature solenoid valves are commonly used in medical industries for applications such as gas analyzers, biotechnology equipment, and portable medical devices, while stainless steel solenoid valves are ideal for chemical processing applications due to high corrosion and abrasion resistance that allows for excellent control of acids, analytical reagents and bases. Additionally, high pressure solenoid valves allow flow control in areas in which other valves could not operate, such as potentially dangerous machinery or inaccessible lines.

The two main components of a solenoid valve are a solenoid coil and a valve. A solenoid coil is a magnetized wire coil that becomes activated through electrical charges, resulting in current flow. The current flow creates a magnetic field, thus converting the electrical energy to mechanical energy and moving the actuator. The actuator is attached to the valve, and causes valve movement. A spring returns both the actuator and the valve back to their un-activated state when the current flow is no longer present. Solenoid valves typically are configured in two main ways: normally open (NO) or normally closed (NC). In a normally closed (NC) valve, a plunging pin or rod within the valve is held in place by solenoid coil to block flow. In order for gas or fluid to flow through the valve, an electromagnetic charge is run through the solenoid coil, which becomes active and lifts the plunger out of the passage to allow flow. Normally open (NO) valves are the opposite; they remain open until the solenoid is activated and pushes down the plunger, blocking flow and creating pressure to keep the valve closed. In addition, solenoid valves can be direct-acting or pilot-operated. Direct-acting solenoid valves have a plunger that is in direct contact with the in-flow opening in the valve body, or orifice. This plunger is used to open and close the orifice, which permits or hinders flow. The pilot-operated solenoid valve, which is actually a combination of a pneumatic or hydraulic valve and a smaller solenoid valve, works with a diaphragm rather than a plunger, using differential pressure to control the flow of gases or fluids.

The many different types of solenoid valves have varied configurations and actuation methods. Pneumatic solenoid valves are one of the most common types, and are used to regulate the flow of air and other gases through the use of diaphragms and gas pressure. While some pneumatic valves regulate air or gas flow at relatively normal pressures, such as in home heating and cooling applications, other pneumatic valves are designed to output gas at extremely high pressures, such as in power tools. Pneumatic valves can also be referred to as gas solenoid valves, solenoid air valves, or just air valves. Another common type is a proportional solenoid valve, which functions by utilizing the same elements as a regular pneumatic or hydraulic solenoid valve but with more advanced flow control capabilities due to allow variable flow that is proportional to the electrical control signal. Solenoid water valves, or hydraulic solenoid valves, are less common than pneumatic solenoid valves but still vital to many applications. Solenoid water valves are typically NC as well as pilot-operated, as opposed to direct-acting. While most solenoid valves are 2-way, meaning that they have two connection areas and one orifice; however, 3-way solenoid valves are also available, with three connections and two orifices. Another highly common solenoid valve type is a12 volt solenoid valve. The 12 volt refers to the amount of voltages supplied by the direct current (DC) power source, which could also be 3v, 6v and 24 volt solenoid valves; however, 12 volt solenoid valves are the standard. All of these solenoid valve types can be constructed from a range of materials such as plastic solenoid valves, which can be PTFE, PVC, natural polypropylene, CPVC and PVD, or metal solenoid valves, such as stainless steel, bronze, aluminum and brass.

One type of valve that is particularly comparable to solenoid valves is an actuated ball valve. An actuated ball valve is mostly used to shut flow off or turn flow on, not necessarily for flow control. A ball valve contains a ball with a small hole in the middle that helps to control the flow of materials through the pipe, and an actuator that rotates the ball to start or stop flow. While there are many applications in which solenoid valves should be used instead of ball valves, such as low flow and high speed cycles, there are also applications in which a ball valve should be used instead of a solenoid valve, such as high flow and applications requiring a manual override option. However, there are many beneficial characteristics of solenoid valves that give them advantages over other valve types. For example, since solenoid valves are powered by natural pressure and electromagnetic force, they generally have fewer moving parts than other valves. This is widely considered to be a good design, since moving parts require maintenance. In addition, solenoid valves can be easily operated by remote devices that activate the solenoid coil, making solenoid valves extremely useful for hazardous applications. Also, solenoid valves can use either hydraulic or pneumatic power because both can be activated or piloted by solenoids. However, pneumatic power is more commonly used because it considered cleaner and lower maintenance than hydraulic power, due to the absence of degrading fluids which produce waste and must be maintained.

Solenoid Valve Types

• 3 way solenoid valves are for hydraulic and pneumatic applications. 3-Way solenoid valves have three ports, one being the pressure port, one the tank and the last, the service port.

• 12 volt solenoid valves are the standard amount of voltages supplied by the direct current (DC) power source.

• Air valves regulate the release of air.

• Gas solenoid valves are one of the most common flow control valves that that handle and control the flow of gaseous media.

• Hydraulic solenoid valves use fluid pressure and are ported through the return line to the reservoir.
  

• Miniature solenoid valves fit easily into a small area and also measure or dispense small amounts of material. Mini solenoid valves are particularly useful in medical applications.
  

• Plastic solenoid valves are primarily used in applications that involve corrosion or chemicals.
  

• Pneumatic solenoid valves are similar to the hydraulic version in that they both use pressure. However, the return port of a pneumatic valve, which uses air, is exhausted to the atmosphere.

• High pressure solenoid valves are solenoid valves that control the flow of fluids or gases in high pressure applications.

• Proportional solenoid valves have direct-acting control valves with linear characteristics. Proportional solenoid valves control accuracy, hysteresis and repeatability within close tolerances.
  

• Rotary solenoids valves have three bearing balls that ride on an inclined plane and turn linear motion into rotary motion. The magnetic arrangement permits direct rotational motion.

• Solenoid air valves control are electrical valves that regulate the flow of air.

• Solenoid water valves are electrical devices that control water flow.
  

• Stainless steel solenoid valves are electromechanical valves that are used to control the flow of liquids or gases; they are ideal for chemical processing applications due to the high corrosion and abrasion resistant properties of stainless steel that allow for excellent control of acids, analytical reagents and bases.
  

Solenoid Valve Terms

Analog Position Sensor - Position sensor whose voltage output differs through various values.

Bubble-Tight Sealing - A circumstance in which there is no leakage of air from between the internal sealed ports of the valve, whether in the energized position or not, in a five second time period. Soap bubbles are used to detect leakage.

Closed State - A situation in which the tubing is pinched in the valve.

Coil Voltage - The maximum voltage to which the coil must be energized for the valve to achieve its highest specified capacity.

Continuous Duty - Energizing a solenoid valve at a constant level of power for its entire on-time.

Current Drain - The quantity of current in amperes flowing through a solenoid valve coil when it is energized.

Cycle - The normal opening and closing of a valve.

Cycle Rate - The measure of how many times a valve is able to open and close within a set period of time.

Duty Cycle - Proportion of time that the solenoid receives power.

Flow Control - A feature that allows for the manual reducing or controlling of flow.

Flux Plate - Magnetic steel plate that helps transmit magnetic flux in the magnetic circuit of a solenoid valve from the enclosure to the sleeve construction. A flux plate is necessary on valves with a body construction consisting of a non-metallic body.

Frequency Response - Changes with the output variable in steady-state conditions, caused by a sinusoidal input variable.

Gain - Association of input to output or the sensitivity of a device.

Hysteresis - The variation between up-scale and down-scale outcomes in equipment response, when exposed to the same input from the opposite direction.

Normally Closed - A term that refers to a valve that is closed when unenergized.

Normally Open - A term that refers to a valve that is open when unenergized.

Open Loop - A system in which direct feedback is not supplied to gauge the response.

Position Sensing - Employing electronic sensors to watch the position of the valve and provide electronic feedback.

Pulse and Hold - Increases function of solenoid valves by reducing power consumption and heat generation. The valve is opened and held open at decreased power.

Pulse Width Modulation (PWM) - A technique that utilizes a modulated wave function to control analog devices.

Repeatability - The ability of the equipment to generate consistent results on successive tests.

Stroke - The space the plunger covers during a state change.