In addition to the consideration of media, the working pressure, or pressure differential that will be applied to the solenoid valve must also be taken into account. This working pressure will also impact on the requirements of the control electronics (the solenoid) as well as the internal components of the valve that ultimately control the flow of the media
Solenoid valves designed for vacuum applications must be zero rated i.e. must be able to work with vacuum or from 0 pressure and can typically be either direct acting or assisted lift and do not reply on positive pressure differentials. Vacuum itself is not aggressive so either a brass, stainless steel, aluminium or on some instances plastic bodied solenoid valve can be used, but the elastomer seal will need to be NBR, as EPDM or FKM have a tendency to stick and PTFE offers poor sealing qualities. Vacuum solenoid valves can be 2/2 way or 3/2 way and are available in a range of port sizes from threaded BSP or NPT from 1/8" to 2" or flanged PN16 or ANSI150Lb from DN10 through to DN300 in size. When choosing a solenoid valve to control vacuum please be sure to check it is suitable for a vacuum application, in some instances a vacuum or suction rated solenoid valve will offer degrees of applied vacuum measured in Torr, Pa or mm Hg that they can control. Typical applications for vacuum solenoid valves would be vacuum lifting equipment, vacuum handling equipment, suction systems, vacuum packing systems or vacuum pick and place machines.
Solenoid valves designed for low pressure, gravity fed and closed circuit pumped systems will need to be what we call zero rated and can be either assisted lift (hung diaphragm / kick pilot) or direct acting (spool valve), in this way the low pressure solenoid valve does not rely or require any guaranteed pressure difference to operate as the opening and closing function of the valve is directly or assisted from the valve armature movement caused by the electro magnetic coil. Low pressure solenoid valves are available in brass, stainless steel, aluminium and most plastics to suit most low pressure applications.
High pressure solenoid actuated valves are specifically designed for high pressure applications, with a far more robust body, core tube, seal and usually a more powerful electro magnet. High pressure applications need to be dealt with care and careful consideration to the maximum and minimum pressures, required flow, materials of construction, chemical comparability, function, size and control voltage. Pressure is the key element, as the forces generated by high pressures can be considerable as the applied forces generated push against all the components of the valve and body. Even at a reasonably high 50 bar pressure the solenoid valve is having to control 50 pounds of force (22.7 Kg) for every square inch, or 50Kg for every cm2. In the case of a 100 bar rated solenoid valve this equates to 100 Kg force to every square cm, 200 bar 200kg force to every cm2 and so on. Typically high pressure solenoid valves are made from strong stainless steel but in some cases such as high pressure miniature solenoid valves they can be brass bodied with stainless steel internals.
High pressure solenoid control valves are available in both 2/2 and 3/2 way format, with either direct acting function (zero rated) as found with most small compact miniature valves however in the case of standard high pressure solenoid actuated valves these will typically be pressure or servo pilot assisted that utilise and simply control the pressure differential to lift the valve into the open of closed position, thus requiring a smaller less energy consuming electromagnet and are found in sizes 1/2" to 2" and upwards. There are some direct acting high pressure solenoid valve available but these solenoid coils can consume upwards of 100 to 200 watts of electrical power.