Atmosphere encompasses a few areas critical to valve selection. These areas are ambient temperature, ingress protection and environment.
Ambient temperature ratings really need close attention to maximize the life of the solenoid valve. The minimum temperature rating depends on the mechanical operation of the valve as far as what elastomers are used in static and dynamic sealing areas. The maximum temperature rating of a solenoid valve is usually limited by the coil. The higher the ambient temperature, the more difficult it is for the coil to dissipate heat, and the more inefficient the coil becomes. Remember that temperature of the media will affect the heat dissipation ability of the coil as well.
Ingress protection is a term that defines a coil's ability to withstand external ingression of dust and water. The most common coil ingress protection rating is Type 4, 4X in North America or
IP-65 in Europe. Type 4, 4X means the coil or coil enclosure is watertight, dust-tight and corrosion-resistant. IP-65 means dust-tight and able to withstand 6.3 mm nozzle water jets from any direction. These ratings are given not only to coils, but to electrical enclosures.
Environment of a solenoid valve can refer to the media in the environment that may affect the external parts, such as the humid, salty air present on the gulf coast of the United States. In the case of the gulf coast air, the valve body material would most likely be a series of stainless steel such as 316L.
A common mistake in solenoid specifications is choosing an internal elastomer based on external environmental conditions. Most of the time, a valve’s elastomers are internal only and are only affected by the media inside the valve. In other words, if 316L stainless steel is chosen for a valve in a salt-laden environment, choosing a fluoropolymer elastomer when the valve is used for instrument air may not be needed. The fluoropolymer might typically be specified because of a user’s perceptions regarding corrosion resistance, but it might be an unnecessary expense.
Environment can also mean media in the atmosphere such as acetylene that may cause an explosion if ignited by a spark or heat. This area could be addressed in an entirely different article because hazardous environment requirements are truly a place where “the devil is in the details.” An abridged version is given in Table 1.
There are so many nuances and details in making sure the correct agency approvals are obtained that even the most experienced people make mistakes. Such decisions, however, are usually part of the user specification. The plant in which the user is installing the equipment will already have received designations of the required approvals and methods of protection. Some users have multiple areas designated within each plant with different approval requirements depending on the media that could or would be present in those areas of the plant. These decisions have to be made when the plant is designed, and they are reviewed by the appropriate safety officials and insurance companies. However, hazardous environment considerations are an area of major expense for end users and for solenoid manufacturers. The initial cost to get approvals is just the beginning of that cost. Next come regular plant inspections, file fees and paperwork change charges.
Voltage is a simple, but still vital part of the specification process. It merely is the voltage of the system to which the valve is wired. Most coils are designed per UL requirements to operate at +10% to -15% of the rated voltage because of normal voltage fluctuations in the line or from the source. However, care is needed with voltage range tolerances, because all coils are not designed this way. The information needed to determine coil design is in the valve manufacturer's installation and maintenance sheets or catalog information. When specifying voltage do not assume that the manufacturer knows whether voltage requirements are AC or DC. When specifying DC voltage, the letters DC should be written out after the voltage value: as in 24/DC. When specifying AC voltage, the frequency should be included (For example: 120/60 or 230/50).
The extras category in specification points can mean just about anything. For example, if something like extra-long lead wires, manual operator, mounting bracket, manual reset, functional safety data, certificates of compliance, low power or bus system compatibility is added, it can be mentioned under “extras.” Many extra features are possible, but not always available on every solenoid valve. Those specifying solenoid valves need to use this category to list what’s not listed in the other categories.
Many areas must be considered when selecting solenoid valves. A catalog cannot answer all the questions because there are many optional features that may not be included. To be sure the right valve is selected, list specific considerations along with quantities and needed lead times. What is not optional needs to be outlined. If some flexibility in the specification exists, options can be recommended, which is especially helpful when lead times are crucial. A good technical support representative can not only find a valve that meets specification needs, but be able to find one that can be delivered in desired time frames.
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