Is my solenoid Valve Rusty?


Recently we found rust in the solenoid valve tube and plunger. But the funny thing is we did not find any rust before. Does different batch of this stainless steel can give different properties? If yes, what can we do to check it?

This is quite typical for valve tubes made from 303 stainless steel, which are a high sulphur free machining grade stainless. You may be having a sulphide problem and not a rusting problem at all. Sulphides will bloom to the surface when exposed to moisture and look very similar to rust. Try soaking the part in 10% NaOH (Sodium Hydroxide) overnight and see if it goes away. If it does go away or wipes off it is sulphides, not rust. If it was rust or chemical attack, then when you clean the metal surface, you will see pitting in the metal surface after cleaning or wiping.

Solenoid valves can get rusty and stop working.

Usually the signs are that the valve is typically in the energised position for long periods of time and then fails to return to the failsafe position when power is removed.

As 90% of solenoid valves purchased are normally closed, the valve will stick in the open position and will cause the solenoid coil to overheat and burn out, especially AC 50/60Hz voltages, as the coil will stay in the higher wattage inrush position.

When you dismantle the solenoid valve, you will see clear signs of rust build up on the armature assembly inside the core tube where the solenoid coil is mounted. However, if you are using a quality solenoid valve with the correct grade of stainless steel internal parts you will find that the rust deposits will wipe away with a damp cloth leaving a shiny stainless steel surface without the signs of pitting and corrosion. Without pitting or corrosion, the rust has only accumulated here from the water passing through and has simply been trapped by the solenoid magnetic field.

You will typically find various degrees of rust particles even in mains water supply lines, depending on location and the age or type of supply pipeline. However, in many cases, the rust or metal particulates have either been generated from other water process equipment upstream or from metal debris left inside the pipework during the installation process. Keep in mind that initial installation work pipelines have threads cut into them, metal dust from grinding, cutting and fabricating can remain inside the equipment and if it has not been cleaned before being installed will end up being flushed downstream and magnetically trapped by any solenoid operated valve. 

Helpful hint: Avoid pouring neat cleaning chemicals into new pipework systems even if water is added behind it, as this concentrated cleaning solution will cause corrosion downstream, as it can become trapped in dead end lines, crevices, solenoid core tubes etc, which will remain stagnant for some time then you will probably find the internal parts are pitted and corroded.

Best option is to water down the chemicals to the correct dilution then immediately flush the system with clean water, operate all the valves several times to ensure any chemicals are flushed free as much as possible. If you don't have a power supply to operate the valves, you can buy a solenoid valve commissioning magnet or permanent magnet to do the job.

You can prevent rust particles in the system by cleaning the process pipework and equipment before installing, installing quality equipment that does not contain ANY rust generating materials and by fitting a magnetic descale unit upstream.

Water Hardness the affects on Solenoid Valves.

Hard water under a threshold of 20-25 French degrees the valve should not be affected by scale build ups provided that the system undergoes regular servicing. Nickel plated bodies and covers offer a better resistance but the best solution would be a motor actuated ball valve. If you are aware of possible scale build ups then you should have equipped the plant with a  water softening system, since water treatment is the only solution to be recommended when solenoid valves are to be used. 

French degrees (°f) (shares symbol with degree Fahrenheit, but in lower case) - conversion to mg/L calcium: divide by 0.25One degree French corresponds to one part calcium carbonate in 100,000 parts of water.