The Difference Between Normally Closed Valves and Normally Open Valves
Normally closed and normally open are often used to describe various types of valves, specifically two-port valves. Based on each term, it’s easy to understand that the biggest difference between normally closed valves and normally open valves is how they operate. However, what are the applications for each type of valve and what benefits do they present?
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Normally Closed Valves
Normally closed valves are designed to block flow through the valve and are commonly used for emergency safety. During usual operation, these devices use a spring to remain closed. The valve will open when the system begins to experience overpressure to ensure safety. Once pressure begins to normalize, it will automatically close.
Solenoid valves can also be normally closed. A solenoid valve is an electromechanical device that controls the flow of liquid or gas through a system. Normally closed solenoid valves include a plunger that remains in a closed position when the system is running smoothly, like pressure relief valves.
Normally closed solenoid valves also include a coil that, when powered, will cause the plunger to open and allow liquid or gas to pass through the valve.
Normally Open Valves
Normally open valves are also used as safety devices. However, unlike normally closed valves, these parts work to maintain low pressure in a system. Normally open valves are designed to allow liquid or gas to flow through in usual circumstances. As the system builds pressure, they will begin to shut in order reduce and regulate pressure levels. In some extreme overpressure situations, they will close almost entirely.
There are normally open solenoid valves as well. These devices will remain open until power is sent to the coil and signals the plunger to close.
Normally closed and normally open valves are available in 3-port configurations as well. These contain a pressure port, an exhaust port, and a cylinder port and work differently than the two-port valves listed above.
For example, when the coil in a normally closed 3-port solenoid valve is not energized, the pressure port remains closed, preventing flow through the valve, and the exhaust port stays connected to the cylinder port. However, when it is powered, the pressure port opens and connects to the cylinder port while the exhaust port closes.
Normally open solenoid valves are the opposite. In usual operation, the pressure port connects to the cylinder port and the exhaust port is closed. When energized, the exhaust port connects to the cylinder port and the pressure port closes.
The difference between normally closed valves and normally open valves is not just in how they operate. Each type also has different applications and benefits that you must consider to ensure that you choose the right valve.
Comparison of Normally Open Solenoid Valve and Normally Closed Solenoid Valve
The solenoid valve refers to the actuator for flow control. According to the state of the solenoid valve, we can divide solenoid valve into two types include normally open solenoid valve and normally closed solenoid valve. The “open” and “closed” refers to the state of solenoid valve when the solenoid coil is not powered. For some special functions, the self-retaining solenoid valve is a typical type, and it is known as normally open (closed) solenoid valve.
Normally open solenoid valve
Normally open solenoid valve is closed when the solenoid coil is powered, and the normally closed solenoid valve is open when the solenoid coil is off. If the solenoid valve is required long-term opening, the normally open solenoid valve will be the ideal choice. If the solenoid valve is required long-term opening or close, the bistable solenoid valve is more suitable. As for the voltage, AC (380V, 240V, 220V, 24V) and DC (110V, 24V) is applicable for the normally open solenoid valve.
Normally open solenoid valve applies to the actuator that using steam as heat medium and automatically control temperature. normally open solenoid valve can make two-position automaticcontrol and remote control to the steam heater, radiator, dryer and other steaming plants. Normally open solenoid valve has wide applications, including dyeing, textile, printing anddyeing, food, medicine, tobacco, cementproduct, petrochemicalindustry, metallurgy and etc.
Normally closed solenoid valve
Normally closed solenoid valve means closed when the solenoid coil is powered, and the solenoid valve is open when the solenoid coil is off. Normally closed solenoid valve apply for international standard voltage include AC 380V, 240v, 220v, 24v or DC 110V, 24V.
Difference between normally open solenoid valve and normally closed solenoid valve
How to distinguish normally open solenoid valve and normally closed solenoid valve on the model? The model usually consist of different letters, they have different meanings.
- K for normally open, while the normally closed type doesn’t need letters.
- ZC stand for the solenoid valve,
- F for explosion proof,
- X for pilot-operated type,
- Numbers generally stand for the size of the valve.
- Normally closed solenoid valve: turn on the solenoid coil, the pipeline will be open; turn off the solenoid coil, the pipeline will be closed, we call this process inching.
- Normally open solenoid valve: turn on the solenoid coil, the pipeline will be closed; turn off the solenoid coil, the pipeline will be open, we also call this inching.
How to choose normally open or closed solenoid valve?
In general, we select solenoid valve type according to the continuous working period. Common types include normally open, normally closed and self-retaining type. Specific rules as blows:
- When the solenoid valve has prolonged on state, and the opening time is much longer than the closing time, we choose normally open solenoid valve.
- When the solenoid valve has long-term off state, and the closing time is much longer than the opening time, we should choose normally closed solenoid valve.
- When the solenoid valve requires same time on the opening and closing, we should choose self-retaining type solenoid valve, also called double acting type.
- For some working conditions used for safety protection, such as the furnace flame detecting and other conditions, normally open solenoid valve is not applicable; we should choose long-term electricity type.
- For gas leak alarm device system, we should choose normally open type gas emergency shut-off solenoid valve. After closing, the solenoid valve should be started up manually.
Kaidi is a solenoid manufacturer who has rich experience in providing on-off solenoid, proportional solenoid, explosion-proof solenoid and solenoid coil. We are the regular supplier of Rexroth, Yuken, Vickers, Parker solenoid. Besides, we also supply customization service based on the particular requirements of different clients.
How Does a 2-Way Normally Open Solenoid Valve Work?
Have you ever wondered how fluid and gas can be contained and directed through equipment without any leaks? Solenoid valves are important parts of any equipment that uses fluid or gas. This part allows operators to turn the flow of the fluid or gas on and off without fear of leaks. This promotes safe and efficient use of the equipment.
Because solenoid valves are so important to the automation of fluid and gas control, it's vital that the right solenoid valve be used for a certain function. One commonly used solenoid valve is one that is normally open. This valve works slightly different than a valve that is normally closed.
The basic function of the normally open solenoid valve is the same. A normally open solenoid valve controls the flow of gas or liquid. This valve differs in the way that the flow is started or stopped. When a normally open solenoid valve is not powered, the plunger is down, which means that a flow is allowed through the valve. Once the coil on the plunger is energized, however, the magnetic field causes the plunger to rise. This effectively seals the valve, preventing the gas or liquid from flowing through.
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2-way Normally Open Solenoid Valves
2-way, normally open, solenoid valve has 2 pipe connections, an inlet called the cavity port and an outlet called the stop port.In its natural de-energized state the stop port is open and media flows into the cavity port and out the stop port.When the valve is energized the plunger seals the orifice stopping flow through the valve.Turn off the power. The orifice opens and flow through the valve resumes.
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5 Tips For Choosing Between NC Solenoid Valve & NO Solenoid Valve
Solenoid valves are generally classified into two types: normally open type and normally closed type. The normally open solenoid valve means that when the coil is de-energized, the solenoid valve is opened; when the coil is energized, the solenoid valve is closed. A normally closed solenoid valve means that when the coil is de-energized, the solenoid valve is closed; when the coil is energized, the solenoid valve is opened.
We can choose the normally closed or normally open type according to the length of the continuous working time.
1. When the solenoid valve needs to be closed for a long time, and the closing time is longer than the opening time, and the continuous opening time is not very long, you can choose the normally closed type.
2. When it is necessary to open for a long time, and the opening time is longer than closing time. We recommend the normally open solenoid valve for you.
3. For gas alarm system, it is necessary to use the normally open type gas emergency cut-off solenoid valve with manual opening.
4. However, some conditions that need to be applied to safety protection, such as furnace and kiln fire monitoring, cannot be selected as normally open, and should be selected for long-term energization type.
If you still confuse about it, please contact us directly and we will recommend the best product for you.
Open solenoid normally
.What is a Solenoid Valve?
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