Danfoss produces four kinds of solenoid valves:
Direct-operated valves (or pilot valves) are relatively simple valves. Ideal for autoclaves, boilers, compressors, printing machines, and water treatment, these valves are available in limited sizes and capacities and operate from zero bar differential pressure.
Direct servo-operated valves are used for larger capacities such as commercial dish washers, dry cleaning machines, and high pressure cleaners. They consist of a main servo part with a diaphragm and pilot part. The valves require a minimum differential pressure for the diaphragm to open and close correctly; pressure above and below the diaphragm is equalised by a hole in the diaphragm.
Direct servo-operated valves with assisted lift are ideal for conditions where there is a risk of zero, low or unknown differential pressures. The armature is connected to the diaphragm by a spring that allows the valve to operate like a direct valve for low differential pressures and a servo valve for higher differential pressures. This valve type is suitable for closed water/heating systems, and safety fuel shut-offs.
Indirect servo-operated valves are for larger capacities than direct operated and direct servo-operated valves and most suited where damping water hammer is required. The pressure above and below the diaphragm is equalised by a separate channel unit with filter protection. This valve is typically used for commercial dish washers, compressors and water treatment.
To make sure you choose the right valve for your needs, you must also consider:
• Media characteristics and temperature
• Risk of water hammer
• Coil supply (voltage, frequency, power)
• Ambient temperature
• Valve cycles and frequency of opening and closing
Taking these features and parameters into account will help ensure that you make the optimal Danfoss solenoid valve choice, every time.
By Tom Jensen, Lead Technical Service Engineer