solenoid valve

Design Terminology
Continuous Duty — A rating given to a valve that can be energized continuously without overheating.
Correction Factor — A mathematical relationship related to a fluid’s specific gravity used to convert specific flows from a standard media to the media in question.
Current drain — The amount of current (expressed in amperes) that flows through the coil of a solenoid valve when it is energized.
Cv Factor — A mathematical factor that represents the quantity of water, in gallons per minute, that will pass through a valve with a 1 psi pressure drop across the valve.
Flow — Movement of fluid created by a pressure differential.
Flow Capacity — The quantity of fluid that will pass through a valve under a given set of temperature and pressure conditions.
Manual Stem — A mechanical device that permits the manual opening or closing of a valve in the case of emergency or power failure. A manual stem is available on all normally closed valves.
Maximum Operating Pressure Differential (MOPD) — The maximum pressure difference between the inlet and outlet pressures of the valve must not be exceeded, allowing the solenoid to operate in both the energized and de-energized positions.
Minimum Operating Pressure Differential — The minimum pressure difference between the inlet and outlet pressures required for proper operation. This minimum operating pressure differential must be maintained throughout the operating cycle of pilot operated valves to assure proper shifting from the closed position to the open position and visa versa. In the absence of the minimum operating pressure, the valve may close or will not fully open.
Orifice — The main opening through which fluid flows.
Safe Working Pressure — The maximum pressure a valve may be exposed to without experiencing any damage. The valve does not have to be operable at this pressure, but merely withstand the pressure without damage.

Solenoid valves are also characterized by how they operate. A small solenoid can generate a limited force. If that force is sufficient to open and close the valve, then a direct acting solenoid valve is possible. An approximate relationship between the required solenoid force Fs, the fluid pressure P, and the orifice area A for a direct acting solenoid value is:[3]

Where d is the orifice diameter. A typical solenoid force might be 15 N (3.4 lbf). An application might be a low pressure (e.g., 10 psi (69 kPa)) gas with a small orifice diameter (e.g., 3⁄8 in (9.5 mm) for an orifice area of 0.11 in2 (7.1×10−5 m2) and approximate force of 1.1 lbf (4.9 N)).

The solenoid valve (small black box at the top of the photo) with input air line (small green tube) used to actuate a larger rack and pinion actuator (gray box) which controls the water pipe valve.
When high pressures and large orifices are encountered, then high forces are required. To generate those forces, an internally pilotedsolenoid valve design may be possible.

Valve Selection Criteria

The following factors are important in making the right commercial and technical choice:
– Valve actuation · solenoid · pressure · proportional · motorised – Number of ways · 2/2 Valve · 3/2 Valve – Switching function · normally closed (NC) · normally open (NO) –
Connection size · flow rate · kv (flow coefficient) value – Type of connection · threaded · flanged · weld ends – Working pressure · upstream of valve · downstream of valve · differential pressure · vacuum – Process fluid · neutral to aggressive · gas to liquid · filtered to contaminated – Fluid temperature · range from – to + °C – Ambient temperature · range from – to + °C · ambient atmosphere – Solenoid power supply · voltage · frequency – Protection classification · IP · EEx – Control fluid supply · control fluid · control pressure · temperature of control fluid from – to + °C · ambient temperature from – to + °C – Accessories and options – Safety requirements · TÜV approval/test certificates · specific certifications

Materials – Seals

Material selection Information about the concentration, temperature and the degree of contamination of the fluid is important in making the right choice of materials. Further criteria are the operating pressure and maximum flow rate. Besides extreme temperatures, pressures and flow rates must be taken into consideration when choosing a material.
NBR Nitrile Butadiene Rubber Standard flexible material for neutral fluids such as air, water, and oil. Good resistance to mechanical loads. Temperature range depending on working conditions from -10 to +90 °C.
HNBR Hydrogenated Nitrile Rubber Similar in many features to NBR. Particularly suitable for hot water and steam. Temperature range depending on working conditions from -20 to +150 °C.
EPDM Ethylene Propylene Diene Monomer Rubber Resistant to alkalis and acids of mid-range concentration, water, hot water and steam. Not resistant to oils and greases. Temperature range depending on working conditions from -20 to +130 °C.
FPM Fluorocarbon Rubber A highly temperature and weatherproof elastomer. Suitable for many acids, bases, fuels and oils (including synthetic).Not resistant to steam. Temperature range depending on working conditions from -10 to +180 °C.
CR Polychloroprene Rubber Similar in many features to NBR. Particularly suitable for most refrigerants. Temperature range depending on working conditions from -20 to +90 °C.
PTFE Polytetrafluoroethene A duroplastic, not a flexible material and therefore not suitable for the conventional diaphragms (separating membranes are possible). Resistance is almost universal in the temperature ranges from -20 to +200 °C. Valve bodies and internal parts are also made of this material.
FFPM Perfluoride Elastomer A flexible material with the same resistance as PTFE and excellent sealing qualities. Temperature range depending on working conditions from -30 to +200 °C.
TPE Thermoplastic elastomers Very durable yet flexible over a wide temperature range. Resist oils, grease, many solvents and weathering.

Materials – Polymers

Material selection The design of the valve is decided by the application, with the materials’ ability to resist the operating fluid constituting an important factor. Information about the concentration, temperature and the degree of contamination of the fluid is important in making the right choice of materials. Further criteria are the operating pressure and maximum flow rate. All of the materials used for the bodies, seals, solenoids, etc. Plastics for valve bodies
PVC Polyvinyl Chloride Resistant to most acids, alkalis, salt solutions and organic solutions; miscible with water. Not resistant to aromatic and chlorinated hydrocarbons.
PVDF Polyvinylidene Fluoride Suitable for nearly all aggressive fluids in the temperature range from -20 to +100 °C.
PFA Perfluoralkoxy As resistant as PVDF but in a higher temperature range from -20 to +150 °C.
PP Polypropylene Resistant to aqueous solutions of acids, alkalis and salts, depending on concentration and temperature.
POM Polyoxymethylene A material with a high degree of hardness and low water absorption. Not suitable for bases, acids or oxidising agents.
PA Polyamid Suitable for all neutral fluids and gases
PPS Polyphenylene Sulfide Suitable for all neutral fluids and gases.

Materials – Metals

Material selection Information about the concentration, temperature and the degree of contamination of the fluid is important in making the right choice of materials. Further criteria are the operating pressure and maximum flow rate.
Brass (Ms 58) Has many applications, not suitable for aggressive and ammoniacal fluids.
Brass (CuZn36Pb2As) Suitable in agressive fluids and seawater.
Grey cast iron (G 1/4-25) Mainly for flanged valve bodies up to PN 16,the temperature range is limited, suitable for neutral fluids.
Spheroidal cast iron (GGG-40.3) Mainly for flanged valve bodies up to PN 16, suitable for neutral fluids.
Cast steel (GS-C 25) Mainly for flanged valve bodies up to PN 40,high temperature range, suitable for neutral fluids.
Gun metal (Rg 5) (CuSn 5 ZnPb) Seawater, mildly aggressive water or steam.
Cast stainless steel (G-X 7 CrNiMo 18 10) Austenitic high-alloy steel for aggressive fluids.
Stainless steel – Ingot material (X 10 CrNiMoTi 18 10) Austenitic high-alloy steel for aggressive fluids.
Stainless steel (X 5 CrNi 18 9) Low-alloy austenitic stainless steel for valve’s internal parts.
Stainless steel (X 12 CrMo S 17) – Corrosion-resistant magnetisable stainless steel, not suitable aggressive fluids or seawater. – Sandvik Stainless steel 1802. – Magnetic stainless steel, suitable for aggressive fluids.
Aluminum (AlSi 8 Cu 3) Aluminum die casting for bodies up to PN 16, suitable for neutral fluids.