GENERAL INFORMATION ABOUT SOLENOID VALVES

1. Solenoid valve assembly and terminology

DIRECT ACTING SOLENOID VALVE

1. Solenoid coil
2. Solenoid base (or shaft)
3. Core
4. Spring
5. Disc seal
6. Valve body

DIAPHRAGM OR PISTON VALVE

1. Solenoid coil
2. Solenoid base (or shaft)
3. Core
4. Spring
5. Disc seal
6. Valve body
7. Diaphragm or piston 8. Spring
9. Bleed (or pilot) orifice
10. Valve bonnet


2. Function modes

2/2 CLOSED WHEN DE-ENERGISED (NC) DIRECT ACTING



When the coil is energised the valve opens. The valve does not require minimum operating pressure differential. Maximum operating pressure depends on the orifice diameter and coil power. Due to the coil power limitations high flow rates cannot be achieved.



3/2 CLOSED WHEN DE-ENERGISED (NC) DIRECT ACTING



Valve function similar to 2/2 NC, only with 3 ports that allow 2 ways simultaneously: one open and the other closed. 3/2 valves are often used as cylinder actuators. The same valve also allows NO function when properly connected.



2/2 CLOSED WHEN DE-ENERGISED (NC) PILOT OPERATED



Valve orifice is closed by a diaphragm or a piston. A bypass connects the chamber above the diaphragm/piston and valve outlet. Bypass is closed by a solenoid core and opens when coil is energized. When this occurs, the pressure above the diaphragm/piston drops and the flow through the valve is established.
This principle of operation requires pressure difference between the valve inlet and outlet and is therefore not applicable at pressures near 0 bar.



2/2 CLOSED WHEN DE-ENERGISED (NC) COMBINED OPERATION



Principle of operation combines direct acting and pilot. Valve diaphragm or piston is attached to the solenoid core and no pressure difference is required. This principle allows high flow rate at pressure near 0 bar.



3. Materials used

The choice of materials used in JAKŠA solenoid valves depends on the type of fluid to be controlled.
Valve bodies
• machined brass (CuZn39Pb3), optionally nickelised
• thermoplasts (Polyamide or Polypropylene)
• stainless steel (AISI 303/1.4305, AISI 304/1.4301 or AISI 316L/1.4404)

Seals - diaphragms
The choice of sealing material depends on mechanical, thermal and chemical requirements. NBR is the standard material for use with neutral chemically fluids at temperatures up to 90°C. At higher temperatures, EPDM, FPM and PTFE can be used. In some cases (high temperature and high cycling rate) stainless steel can also be used.

Characteristics of sealing materials:

NBR (Nitrile butadiene rubber)
• high mechanical durability
• resistant to oil and grease
• tight shut-off
• temperature range: -20°C (-40°C) to +90°C
• fluids: water, fuel, mineral oil, air, argon, town gas, methane, propane, buthane

EPDM (Ethylene propylene diene monomer rubber)
• resistant to acids and lyes of medium concentration
non-resistant to oil
• tight shut-off
• temperature range: -20°C to +130°C
• fluids: hot water, wet steam, ozone, ethylene and methylene, alcohol, acids and lyes

FPM (Fluorinated propylene monomer)
• excellent chemical resistance
• mechanical durability lower than NBR or EPDM
• tight shut-off
• temperature range: -40°C to +200°C
• fluids: hot and oiled air, acids, lyes and other fluids that do not allow use of NBR or EPDM

PTFE (Polytetrafluoroethylene)
• resistant to almost all chemicals
non-resilient, slight leakage on valve seat may be expected at low pressures
• temperature range: -200°C to +250°C
• fluids: various chemicals, refrigerants, ammonia, dry steam

PA (Polyamide, 30% glass-fiber reinforced)
non-resilient, slight leakage on valve seat may be expected at low pressures
• good chemical resistance, particularly to fuels, lubricants, solvents and cleaning agents
• temperature range: -40°C to +160°C (+180°C short term)

PU (Polyurethane)
• not suitable for water and other liquids due to cavitation
• elastic material with hardness of 90 Sh A and tight shut-off
• temperature range: -60°C to +70°C
• fluids: air (dry or oiled), grease

PEEK (Polyether ether ketone)
• excellent hardness and wear resistance
• easily machinable, with excellent surface finish
non-resilient, slight leakage on valve seat may be expected at low pressures
• temperature range: -50°C to +250°C
• fluids: mostly liquid

4. Electrical characteristics

• All solenoids are designed for continuous duty (ED100%).
• Exceptions are marked on individual solenoid or valve types.
• Wire insulation is class H (180 or 200°C).
• Voltage tolerance is ±10% at AC and ±5% at DC.
• Power consumption is stated in watts (W) and equals:
• the product of measured DC voltage and current
• the product of measured AC voltage and current multiplied by 0.6


Thermal conditions
After the solenoid has been energized for a period of time the temperature of the winding rises. Amount of heating is affected by ambient and fluid temperature. In extreme cases the overheating causes damage to the wire insulation and the solenoid becomes defective. Special solenoids for extreme thermal conditions are also available.

Electrical protection - IP rating
Apart from standard solenoids, original explosion- and waterproof types are also available, thus allowing the use of solenoid valves in practically any environment. Standard solenoids are encapsulated in special thermoplastic resin which prevents the intrusion of damp and protects the winding from mechanical damage.

Explosionproof solenoids are encapsulated in epoxy resin. Basic IP rating for a solenoid is IP00, whereas IP65 can be achieved with properly fitted plug.
TM35k type solenoid with IP67 rating is designed for extremely damp ambients (also water immersion).

5. Flow rate and kv value

Flow rate of any given valve depends on valve size, type of fluid and the pressure which forces the fluid through the valve. Kv value is given for each valve type in the table. With known parameters the flow rate can be calculated according to the following formula:


Q......flow rate [l/min]
Kv.....value given in the table for each valve type
Δp....difference between inlet and outlet pressure [bar]
p1.....pressure measured at valve inlet [bar]
p2.....pressure measured at valve outlet [bar]
ρ......specific mass of fluid [kg/dm3] (equals 1 for tap water)

Kv value is approximately the same for tap water and other fluids (e.g. oil) of viscosity not exceeding 21mm2/s. At higher viscosity a correction of Kv value is required.

6. Pressure rating

Maximum operating pressure differential is the maximum difference between valve inlet and outlet pressures at which the valve will still reliably operate. Values in tables (with tolerance ± 10%) are given at ambient and coil temperature 22°C.

Minimum operating pressure differential is the minimum difference between valve inlet and outlet pressures at which the valve will still reliably OPEN. If required pressure difference is not achieved the valve will not open when activated.

Maximum static pressure is the highest fluid pressure endured by valve body and internal parts without damage.

7. Installation and recommendations

JAKŠA solenoid valves can be installed horizontally or vertically. Upright coil position is recommended to avoid accumulation of impurities in pilot which may result in faulty operation.
Before installation it is highly recommended to clean the pipeline to minimize the amount of impurities in fluid. It is also necessary to install a strainer (40 µm mesh recommended) in front of the valve.
AC coils should not be connected to the electrical circuit unless fitted properly on the stem as this will result in coil burning. In very damp ambients the use of special coil sealing sets or TM35k type coil is necessary (available from your supplier).