These small components, when specified and maintained properly, are reliable and durable workhorses. However, because they operate differently from larger control valves, there is often confusion about what they do and how they should be maintaine…
These small components, when specified and maintained properly, are reliable and durable workhorses. However, because they operate differently from larger control valves, there is often confusion about what they do and how they should be maintained. This article will explain what solenoid valves are, how they are used within the pulp and paper industry, how to decide whether to repair or replace, and how to properly maintain them.
Solenoid valves — a primer
Solenoid valves use electricity to open and close an orifice in the valve body, allowing or preventing a medium to flow through. A two-way, normally closed solenoid valve is opened and closed through the use of a plunger, which is raised and lowered by the energizing and de-energizing of a solenoid. The magnetic field created by the solenoid’s coil turns the valve’s stop into an electromagnet, attracting and raising the stainless steel plunger. A corresponding spring then compresses as the orifice opens. Upon de-energizing, the magnetic field is discontinued and the spring retracts, forcing the plunger back onto the orifice and shutting off flow.
Solenoid valves are used in the water cycling and chemical processing of paper. They are typically best used for functions “upstream” from the paper product due to the debris that is usually “downstream” in this type of application. They are also used in conjunction with control valves, air accumulators, air and hydraulic presses, and rollers to actuate the predictable, repetitive functioning of the system. In these applications, air or water is the medium cycling through the solenoid valve, while chemical or pulp media are transported through the larger components. Because solenoid valves are electromechanical, they can also function as an emergency shut-off mechanism for the system.
Repair vs. replace
One must consider the valve itself as well as the application to make this decision. Certain types of solenoid valves are so simple in design and construction that replacement is the most cost-effective solution. For high-end designs where the interaction of components is critical, where the materials of construction are exotic and expensive, or where the unit has been custom-designed for the application, the cost of replacement may be significantly greater than that of maintenance. Solenoid valve maintenance typically only includes the replacement of rubber parts and springs. So, if the remaining parts show wear or are damaged, it is time for a replacement.
Solenoid valve maintenance
Maintenance of a solenoid valve involves replacing worn components and ensuring that parts are clean and free of debris. As with any mechanical apparatus, proper and proactive maintenance and care of a solenoid valve can extend product life and ensure predictable operation.
Replacement part kits for solenoid valves can be purchased from the manufacturer. These will typically contain replacement O-rings, springs, a plunger, and possibly diaphragms, pistons and a host of related components. Be sure that the replacement kit is appropriate for the particular valve.
Here are the basic steps for solenoid valve maintenance:
First, disconnect the power source and depressurize the system. Likewise, handle the unit with the precautions necessary for the fluid controlled therein.
Inspect the coil for cracks in the encapsulation. In wet or humid environments, these can lead to moisture penetrating the coil, resulting in valve failure.
Connections to the coil should also be checked for damage or corrosion. Never power up an AC coil without ensuring that the coil is properly installed on the valve’s sleeve or stem. The resulting high inrush of current will likely result in a coil burn-out.
When the coil is removed, the remaining unit is the pressure vessel. The sleeve will have a feature to accept a sleeve removal tool, usually a wrench. Never remove the sleeve by clamping onto the sleeve tube, as this may cause the tube to dent or bend.
Removal of the sleeve from the valve body will expose the internal components of the valve operator. This includes the plunger with a seal, the plunger return spring, an O-ring, the sleeve, and operator body. These should be examined for damage and replaced as needed.
The seals may exhibit swelling, cracking or general deterioration. The spring should be inspected for worn or broken coils. The body orifice may be nicked or the crest may be worn. The top of the plunger and the inside of the sleeve may show wear as well.
For more complex solenoid valve types utilizing diaphragms, pistons, spools and levers, specific manufacturer’s instructions must always be followed.
Once all necessary parts are replaced and any build-up is removed from the valve, reassemble the pressure vessel according to manufacturer directions and reattach the coil. Then, reinstall the newly-assembled valve back into the application. Power to the valve should not be reengaged until it is confirmed that all parts are correctly installed.
The solenoid valve manufacturer is always the best source of knowledge on a particular product. The manufacturer’s engineers are trained to not only understand the ins and outs of the company’s product offering, but also the products’ operation in applications across all customer industries. So, specific questions regarding when to repair or replace a solenoid valve or how to properly maintain it are best addressed specifically with the manufacturer.”
Design Engineer Bryan Alfano has been with Parker Fluid Control Division of New Britain, Connecticut for three years. For more information on Parker Fluid Control Division’s products or to locate the nearest distributor, call (860) 827-2300 or visit www.parker.com/skinner.
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