Solenoid Valve Coils.
A solenoid valve coil
is designed to convert electrical energy into lateral motion. The coil
usually consists of copper wire wound around a hollow bobine or tube, so
when electric current flows through the coil, a magnetic field is
generated. By placing a solenoid valve coil over a ferromagnetic core
(usually magnetic 430F stainless steel armature) the magnetic field
generated causes the plunger to slide further up towards the magnetic
field (into the coil) thus allowing an opening to be created. This in
turn can be utilised to either to control direct acting solenoid valves,
Assisted Lift Solenoid Valves or Servo/ Pressure Assisted solenoid
valves.
Solenoid valve coils come in a huge range of sizes, voltages, IP
protection levels, temperature ratings and power levels.
Care needs to
be taken when replacing solenoid valve coils because all these factors
must be considered.
Solenoid Coil Sizing.
When measuring a coil, you need to measure accurately the internal
diameter of the coil (as above). Some solenoid coils may be fitted with a top plate
with a reduced diameter to aid secure fitment to the armature / core
tube. Then the depth of the internal core needs to be measured. If this
matches up, you are at the first step of finding the right coil.
Helpful hint - when buying solenoid valve coils, try to replace according to brand.
Solenoid Coil Voltages.
Coils are manufactured for specific voltages, it is very rare that a
coil will work on more than 1 voltage, whether it be AC or DC. There are
some instances of "Dual voltage coils" which can work on for example
12vDC or 24vAC, 48vDC or 24vAC but these are quite rare and this cannot
be relied on to overcome spares shortfall's.
Helpful hint - check your supply voltage rather than guessing or trying to read the coil voltage.
Solenoid Coil Temperature Ratings.
Coil winding's have several temperature classes and are usually
designed depending on the media, ambient temperatures and duty cycle
(duty cycle being the power on time and power off cool downtime) as all
coils generate heat when energised a bit like a light bulb the more
power they consume the hotter they will get.
Standard coils are
available for insulation classes E, F and H. The insulation class determines the coil’s maximum operating temperature for a specific life expectancy:-
Class H: 30 000 hours-Class F: 20 000 hours
Class F coils
are rated to 155°C, basically the copper wire windings can withstand a
working temperature up to but not exceeding 155°C. These are the most
common form of solenoid coil used in the pneumatic industry and are ideally suited to working ambient
temperatures up to 20°C and media up to 100°C.
Class H coils
are rated to 180°C, basically the copper wire windings can withstand a
working temperature up to but not exceeding 180°C. These are the most
common form of solenoid coil for higher temperature applications such as steam or hot oil with working ambient
temperatures up to 50°C and media up to 180°C.
Class N coils
are rated to 200°C, basically the copper wire windings can withstand a
working temperature up to but not exceeding 200°C. These are the most
common form of solenoid coil for extreme applications such as super heated steam and ambient
temperatures up to 80°C and media up to 200°C.
Helpful hint - replace brand like for like if experiencing short solenoid coil life, check supply voltage and application temperature parameters and make sure none of the internals where the coil sits are stuck or contaminated.
Power Levels for solenoid coils
Solenoid coils come in a range of power levels, DC coils are measured
in Watts, AC coils measured in VA (Volt Amps) and will have a higher
Inrush current and lower Holding Current. It is a bit like weight lifting,
lifting a weight requires more energy than holding it up with arms locked.
Helpful hint Watts = Volts x Amps.
You need to pay attention to the power ratings, underrated coils
will over load and burn out and too higher power rating may well do the
same.
Helpful hint - try to stay with the same power level unless the coil
fails quickly then check voltage supply and current availability then if
need be consult your supplier.
Solenoid Coil IP Protection Levels
Solenoid coils come with a wide range of IP (Ingress Protection)
ratings according to general protection and Dust and Water Ingress.
Please find below a basic IP Protection chart.

Some examples of standard solenoid coil types are shown below.
Standard DIN 43650B IP65 Rated coil Rectangular DIN connector required
8/11mm bore 22mm wide various power levels from 1 to 7 Watts.
Usually used on Small Miniature solenoid valves and primarily in the pneumatic industry.
Standard DIN 43650A IP65 Rated coil Square DIN connector required
14.6mm bore 30mm wide various power levels from 1 to 15 Watts.
Usually used on general purpose solenoid valves.
Standard DIN 43650A IP65 Rated coil Square DIN connector required
14.6mm bore 36mm wide various power levels from 15 to 18.5 Watts.
Usually used on general purpose solenoid valves.
Typical Italian Standard coil DIN 43650A IP65 Rated Square DIN connector required
13.5 mm bore 30mm wide various power levels from 8 to 10 Watts.
Usually used on Small Miniature solenoid valves and primarily in the pneumatic industry.
Typical Italian High Power coil DIN 43650A IP65 Rated Square DIN connector required
13.5 mm bore 36mm wide various power levels from 14 to 20 Watts.
Usually used on Small Miniature solenoid valves and primarily in the pneumatic industry.
Typical Italian Very High Power coil DIN 43650A IP65 Rated Square DIN connector required
13.5 to 16.0 mm bore 37.5mm wide various power levels from 26+ Watts.
Usually used on large solenoid valves and primarily in the hydraulics industry.
ATEX encapsulated EExmIIT4 IP65 Solenoid Coil
8/11mm bore 22mm wide various power levels from 3.8 to 5.1 Watts.
Usually used on Small Miniature solenoid valves and primarily in the pneumatic industry.
Fitted with 3 meter 3 core cable but can be found with 5 meter or terminal junction box.
ATEX encapsulated EExmIIT4 IP65 Solenoid Coil
10/14.6mm bore 36mm wide various power levels from 8.5 to 10.1 Watts.
Usually used on standard hazardous area solenoid valves and primarily in the Oil and Gas and Food Industries
Fitted with 3 meter 3 core cable but can be found with 5 meter or terminal junction box.
Typical American or Asian IP54 coil with 30 cm flying lead no DIN connector required
8 to 16.0 mm bore various widths various power levels from 8 to 26 Watts.
Usually used on large imported non European solenoid valves.
Why do solenoid coils burn out?
Solenoid coils are designed to convert electrical energy into
mechanical movement by means of a magnet field, which means as they
consume power like a light bulb for example they will become hot, and the
higher the wattage or power consumption or the longer they are switched
ON the hotter they can become.
If the coil becomes too hot or above its temperature rating (copper
winding class rating) the copper or insulating material can fail to
short circuit.
Other reasons include high media or ambient temperatures
preventing the coil from cooling sufficiently, water ingress between
armature and coil or if the coil is removed whilst energised!!
Why does a coil get burnt when removed from valve?
This is because with AC 50/60Hz coils you are reducing the impedance
or resistance of the coil, as the shading ring within the armature or
stem generates resistance within the coil. By removing the coil whilst
powered the resistance is reduced thus the power consumption can easily
increase above the coil winding class limits causing over heating.