Solenoid Valve Media
There are many types of gases and liquids that a solenoid valves is used to control and as a result a vast range of types of solenoid valve have evolved to accommodate the specific properties of these gases and liquids. The parts of the valve component that come into contact with the controlled media need to be resilient to the potential corrosive effects of that media. Various valve seals and associated components must also be carefully chosen for this same reason.
Solenoid Valves for Water
Solenoid valves for mains water and WRAS approved and certified solenoid valves for drinking water (potable water) are typically either brass or plastic bodied 2/2 way normally closed. i.e. 2 ports inlet and outlet with 2 positions either open (allowing water flow) or closed (no water flow allowed). When choosing a water solenoid valve you must consider the key control elements such as port connection size 1/4", 3/8", 1/2", 3/4",1",11/4", 11/2", 2" or more and type BSP, NPT of Flange, water minimum and maximum pressure such as mains 3 to 5 bar water pressure to open outlet, mains water pressure in a closed loop pumped system or simply a gravity fed system, control voltage 12vdc, 24vdc, 24vac, 110vac or 230vac and function 2 port (in/out) normally closed (failsafe closed power to open) or normally open (failsafe open power to close) or 3 port diverting valve. If you peak to a good supplier or stockist of water solenoid valves you will need this information to make sure you are supplied with the correct valve for the application.
Brass solenoid valves have the benefit of being a more robust and reliable are better suited to industrial and commercial water applications where the solenoid valve will be under constant use, exposed or just simply in applications where the cost of break down would be inhibitive. Typical applications would be mains water inlet control, water header tank refill systems, gravity fed water systems, water fountains, water process systems, water cooling systems and commercial or industrial washing machine applications to name but a few.
Plastic solenoid valves, on the other hand are typically less expensive and fall into two main categories.
Water appliance valves as used for water inlet control for domestic washing machines, dish washers, water facets, drinking water dispensers. Designed to be energised open for short periods of time typically a maximum of 2 minutes followed with a minimum cooling off period of 3 minutes. The reason for the cooling off period is that the solenoid coil or coil, pack when energised will become hot, there will be some thermal heat transfer into the water and a minimal loss into the ambient air but if powered for more than 3 minutes will start to cook and fill finally fail. Typical sizes from 1/4", 3/8", 1/2" and 3/4" with options for 10mm and 12mm hose barb to fit rubber outlet hose, with options for single, double and triple water outlets. Most voltages are available from 12volts, 24 volts, 110volts and 230 volts AC 50/60 Hz or DC direct current, protection is typically IPXX with exposed electrical faston tags, pressure range 0.2 to 10 Bar, orifice 11.0mm with NBR sealing.
Agricultural nylon bodied water solenoid valves which are more robust than appliance valves but still less expensive than Brass versions. The glass reinforced nylon body is well able to work up to 10 bar water pressure, and in some models is available with a manual flow adjustment knob and a manual over ride facility so the solenoid valve may be manually opened with the need for electrical supply. The quality range of plastic water valve will be fitted with an industrial standard IP65 Class F 100% duty rated solenoid coil which can be powered ON 24/7 without concern for over heating. Most voltages are available from 12vAC, 24vAC, 48vAC, 110vAC 230vAC and 380vAC or 12vDC, 24vDC, 48vDC, 110vDC and 220vDC, pressure range 0.3 to 10 bar, seals typically reinforced NBR, typical port sizes 1/2", 3/4",1",11/2" and 2" BSP thread.
Solenoid Valves for Steam
Solenoid valves designed for steam and hot water applications have an arduous tasks of not only having to cope with the aggressive nature of pressurised steam but also the high temperature of steam media. Solenoid valves for steam applications will typically have either a Brass or Bronze body with options for stainless steel and in most cases the seals will be PTFE. PTFE has great chemical resistance and can cope with heat very well up to a maximum of +250 degrees centigrade but has the disadvantage of being a hard non pliable material unlike softer elastomer seals and will cause sealing problems if the steam media contains any debris a particles which would become caught between the PTFE seal and the solenoid valve internal sealing face. There is no simple solution around this sealing issue, some specialised elastomer seals such as Kalrez are available but the costs are quite inhibitive and in most cases push the cost of a solenoid valve outside of budget, so fitting a simple Y type filter strainer in-front of the solenoid valve (up-steam) is the best solution.
Heat - steam is very hot by nature and standard solenoid valves will not cope with this extreme heat which is why a steam rated solenoid valve not only have steam compatible sealing but also a high temperature rated solenoid coil fitted, typically either a Class H or Class N coil. A temperature Class H coil is designed to work up to +185 centigrade or steam up to 10 bar, where as a Class N coil is designed to work up to +200 centigrade or 12 bar steam. Steam temperatures typically relate directly to pressure so the higher the steam pressure the higher the steam temperature will be, which can be seen and read from a steam pressure to temperature graph.
Solenoid Valves for Air
Solenoid valves for air and pneumatic applications are available in a variety of functions and operation, either 2/2 way general purpose, 3/2 diverting for actuated valve and basic air cylinder control, 5/2 and 5/3 way with single or double coil combinations designed for air actuated pneumatic automation systems. Air solenoid valves are typically brass for 2/2 and 3/2 way or die cast aluminium for 3/2, 5/2 and 5/3 way applications and are fitted with NBR elastomer sealing as standard.
Solenoid Valves for Inert Gas
Solenoid valves work well for the ON/OFF open and closed flow control for most clean inert or noble gases at ambient temperature i.e. -20C to +60C, such as nitrogen, helium, neon, xenon, krypton, argon, oxygen* and most atmospheric gases and compressed air. Typically brass solenoid valves with standard NBR sealing are fine so long as the maximum permitted pressure ratings are followed and in the case of pressure / pilot assisted solenoid valves that the minimum pressure differential is maintained. Keep in mind that compressed gases will become significantly cold if allowed to expand as this draws heat and for liquid gas applications you will require a cryogenic rated solenoid valve to cope with temperatures down to -200C.
When dealing with oxygen users must we aware that oxygen can be extremely hazardous, valves must be degreased so be completely oil and grease and combustible contaminants. Also rapid opening of a valve can cause generate high temperatures by adiabatic compression and friction caused by metal to metal components can cause hot spots or potential ignition points for one of the materials. Oxygen valve sealing by FKM or NBR sealing is acceptable for normal ambient temperature conditions. For applications for solenoid actuated valves for oxygen over 40 bar, specialist high pressure oxygen rated solenoid valves must be used.
Solenoid Valves for Natural Gas
Solenoid controlled valves are commonly used for the on/off flow control Natural mains gas, town gas, LPG (Liquid Petroleum Gas) and Bio-gas applications, however users need to be careful that they choose the correct gas safe and EN161 certified valve designed for the application in hand. Safety shut off gas solenoid valves to be used on natural gas lines must be EN161 gas approved and installed by a Gas Safe Registered installer which replaces the old original Gorgi registered scheme that now void.
Natural gas is typically supplied at very low pressures typically 100 to 200 millibar and a gas approved safety shut off valve must be able to offer 100% shut off and sealing at these low pressures, and still provide the required flow with very little pressure drop and loss of gas flow. Port sizes range from 1/8" to 2" BSP thread with flanged PN16 options typically available from DN65 to DN300, beyond this gas valves from DN350 upwards will be actuated by electric motor or pumped hydraulic system just because of the weight / mass of the internal components to be safely controlled.
LPG solenoid valves can have different pressure parameters to natural gas solenoid valves, as LPG is typically supplied from high pressure LPG canisters and pressurised bottles (bottled gas), so users need to be sure what pressure needs to be controlled i.e. what is the gas outlet pressure setting if there is a gas pressure regulator (pressure reducing valve) or if the pressure is unregulated and supplied at high pressure. Typically a brass solenoid valve with NBR sealing will suffice so long as the chosen LPG solenoid valve meets the pressure, flow and function application criteria.
Bio-gas applications require a more specialist solenoid control valve as this biofuel has been produced from the bacterial breakdown of organic matter such as manure, general waste, plant and vegetable material, sewage, green and food waste in the absence of oxygen. There will be a small amount typically 1% of some more challenging gases such as hydrogen sulphide, moisture and siloxanes. Keep in mind that when hydrogen sulphide (h2S) meets moisture (water H20) the combination will generate Sulphuric acid (H2SO4). The main bulk of the gases produced from inside this oxygen free biogas fermentation system are 60% methane and 39% carbon dioxide, which can be combusted or oxidised when mixed with oxygen as a fuel as a renewable energy source for heating or compressed (CNG - compressed natural gas) for motor vehicles.
Safety gas valves are also available with manual reset devises, as opposed to standard solenoid valves or auto reset gas shut off valves that simply open or close according to the electrical power supplied. In this case a manual reset gas safety shut off valve it will have a manual lever or mechanical control device that has to be used to mechanically open the valve to allow gas flow, the solenoid when energised is only used to keep the valve in the open position. In large gas applications such as industrial and commercial gas boilers and gas powered furnaces there will be two gas solenoid valves, a small pilot flame solenoid valve and the larger manual reset gas solenoid valve. If electrical power is lost and regained or during the initial start-up process only the small pilot flame shut off solenoid valve can open to allow a small amount of gas to be ignited. When this small pilot flame has been confirmed the main large gas valve can be manually lifted into the open position by an engineer. In this way no large quantities of raw unburnt gas be allowed to flow and generate a very hazardous potentially explosive environment.
Solenoid control valves for aggressive and corrosive media.
Solenoid valves can be used for very aggressive and corrosive media such as acids and alkali's will typically be made from various grades of plastics such as PVC, PP, PVDF or PTFE and on occasion 316 stainless steel. These special application solenoid valves will have an isolating diaphragm or dry armature deign so that the media passing through the valve can only come into contact with the valve body and seal and is prevented from reaching the armature and tube assembly where lesser grades of stainless steel would be corroded.
Sealing materials for aggressive media valves will be typically a choice of NBR, EPDM, FKM or PTFE with some special quite expensive options such as Kalrez, FFKM or Rulon.
Typical media used for this application include Sulphuric Acid (H₂SO₄), Hydrochloric Acid (HCL), Nitric Acid (HNO₃), Hydrogen Sulphate (HSO₄), Phosphoric Acid (H₃PO₄), Hydroflouric Acid (HF), Formic Acid (HCO₂H), Benzoic Acid (C₆H₅CO₂H), Acetic Acid (CH₃CO₂H), Carbonic Acid (H2CO₃), Hydrogen Sulphide (H₂S), Hydochlorus Acid (HCLO), Ammonium ion (NH₄), Hydrocyanic Acid (HCN), Hydrogen Carbonate (HCO₃), Hydrogen Phosphate (HPO₄) and even Pure Water (H₂O).
Solenoid Valves for High Viscosity Fluids
Solenoid valves are available for high viscosity fluids or think glutanous liquids such as most mineral and vegatable oils, olive oil, castor oil, sour cream, liquid fats, thick hydrocarbons, syrup, corn oil, honey, coconut oil, ink, sesame seed oil, palm oil, linseed oil, molten chocolate, sauces and peanut butter.
In the solenoid valve world a high viscosity liquid would be any liquid with a measured viscosity over 50 centistokes. Solenoid controlled valves for liquids exceeding 50 CST are available such as direct acting solenoid valves that are without blockable internal pilot circuits or diaphragms or coaxial solenoid valves that operate a stainless steel tube laterally and air operated valves such as angle seat piston globe valves and of course pneumatically actuated coaxial valves.
Another solution for the control of thick liquids are motorised ball, gate, buuterfly and globe valves but unlike solenoid valves will require several seconds to actuate into position.
Solenoid Valves for Low Viscosity Fluids
Most general purpose or mainline solenoid valve will cope with any chemically pressure or temperature compatible liquid under 50 CST as this liquid is thin enough not to clogg or block any small pilot pressure control holes or circuits within the solenoid controlled valve.
This would include most gases such as compressed air, vacuum, nitrogen, argon, helium, carbon dioxide and oxygen etc but also low viscosity fluids such as sea water, salt water, ro water, pure water, demin water, mains water, potable drinking water, vinegar, acetic acid, alcohols, acetone, bromine, crude oil, diesel fuel, formic acid, fuel oil, gasoline, glycol, petrol, aviation fuels, kerosine and final effluent water.