Solenoid Valve Coils: 12/24 V DC and 110/220 V AC Replacement Coils

A solenoid valve consists of two parts: the body that directs the oil or air, and the electromagnet — the coil — that moves the spool inside it. The coil is the part of the valve that talks to the electrical system, and it is the part that fails most often. That is why it is sold separately: the body may be sound while the coil has burnt out, or a machine may have been moved to a different supply voltage so that only the coil needs changing.

Ordering a replacement coil calls for three pieces of information. First, voltage and current type: 12 V DC and 24 V DC on mobile machinery and PLC-controlled circuits, 110 V AC and 220 V AC in fixed industrial plant. Fitting a coil of the wrong voltage burns it out in seconds; putting 220 V on a 24 V coil is the most common and most expensive of these mistakes.

Second, the diameter and height of the bore that sits over the valve pin. Stock covers Ø9, Ø10, 13, 14.85, 16, 21.1, 23.2, 26.2 and 31.6 mm. This dimension is printed in the product name in millimetres and governs fit regardless of brand — coils of the same size from different makers will usually interchange. On modular hydraulic valves the size is quoted by valve size directly: NG06 (Cetop 3) valves take 23.2 mm class coils, NG10 (Cetop 5) valves take the 31.6 mm class.

Third, power and protection rating. AC coils are rated in VA, DC coils in W (18 VA, 28 W and so on). Coils rated IP65 withstand dust and water jets; that rating should be insisted on outdoors and on machines that are washed down. Connector type should also be stated when ordering; some coils come with an LED connector fitted.

The two most common causes of a burnt coil are a spool jammed by dirt in the body, and a supply voltage that runs persistently high. When the spool sticks, the coil converts the load it cannot move into heat and the winding cooks. For that reason, when coils burn one after another the culprit is usually not the coil but a valve body that needs cleaning.