Solenoid Valves

Solenoid Valve -  Controlling Water Flow

Water or General Purpose solenoid valves normally of Brass Construction with NBR (Nitrile Buna Rubber) seals are ideal for ambient temperature mains water applications. However these are not suitable for Pure Water, Demineralised Water and Reverse Osmosis water which require a more specialised solenoid control valve.

Typically solenoid valves for controlling water will be 2/2 way (ie. 1 inlet 1 outlet with open or closed function), ideal for general water On OFF control. There are 3 main function types of water solenoid valve, miniature direct acting, general purpose assisted lift or servo assisted.

Miniature Direct Acting Water Solenoid Valves.

Miniature Brass water solenoid valves are typically direct acting and compact. The schematic on the left shows that the solenoid valve armature rests over the orifice or flow path and is directly controlling the ON OFF flow function of the solenoid valve. As there is no diaphragm involved the flow will be restricted according to the orifice size typically between 1.0mm and 8.0mm depending on water solenoid valve specifications. As these miniature water solenoid valves are direct acting they do not reply on system pressure differences to operate making them ideal for low flow, small, vacuum, medium and higher pressure systems up to 150 bar. Port sizes from 1/8 to 3/8 port.

Assisted Lift or Hung Diaphragm Water Solenoid Valves.

As you can see from the schematic on the left the internal solenoid valve diaphragm is attached or hung from the solenoid armature assembly. In essence it is forced or mechanically attached to assist lift. This means that regardless of pressure differential (pressure difference between inlet and outlet ports) this design of water solenoid valve will positively open and close making it ideal for low pressure, closed loop, gravity fed and water suction systems.

The picture on the right is typical for this design of brass water solenoid valve with coil mounted centrally over the body.

Sizes typically 3/8 to 2" BSP or Flange, Pressure vacuum to 10 or 16 Bar or more depending on water solenoid valve specifications

Servo Assisted or Floating Diaphragm Water Solenoid Valves.

As you can see from the schematic on the left the internal solenoid valve diaphragm is not attached to the solenoid armature but in essence it is floating, and requires pressure assistance to operate. This means that a pressure differential (pressure difference between inlet and outlet ports) is required for this design of water solenoid valve that is controlled by a pilot (servo assistance) circuit. The solenoid coil is mounted over the outlet port and when opened vents the pressure above the diaphragm downstream allowing inlet pressure to to lift the diaphragm and open the water solenoid valve allowing flow. When the pilot circuit closes the inlet pressure builds above the diaphragm forcing it closed making it ideal for medium to high pressure, open to atmosphere and pump fed systems.

The picture on the right is typical for this design of brass water solenoid valve with coil mounted over outlet port.

Sizes typically 3/8 to 3" BSP or flange, pressure 0.5 minimum differential to 50 bar or more depending on water solenoid valve specifications.

Some water control applications require high flow large bore control valves with flanged ends. Typically these will operate utilising the servo or pressure differential method being the least expensive design. Due to the large size the internals are not flexible diaphragm but a much more robust piston design with u Ring Sealing. Diaphragm design is fine with smaller solenoid valves but as the surface area increases the kg per square CM loading increases beyond that at which an elastomer diaphragm can cope.

Sizes Typically Flange PN16 from DN50 to DN500, pressure 0.3 minimum to 16 Bar. 

Plastic Solenoid Valves for water applications.

There are a vast range of plastic solenoid valves suitable for water applications. These range from Nylon appliance solenoid valves, POM or Delrin solenoid valves and Nylon body general purpose solenoid valves.

Typical Nylon appliance water solenoid valves come with 3/4 BSP male inlet threads suitable for industry standard water hoses as found on washing machines and dish washers. These can be straight inlet outlet or 90 degree outlet pointing down with options for single, double, triple or quad outlets with 10.5 mm or 12.5 mm hose tail or push in fitting and a range of control voltages from 12 volt DC (Direct Current) to 240 volt 50/60 Hz AC (Alternating Current).

 

Basic Nylon 2/2 way water solenoid valve series available from 3/4 to 2" thread.

Pressure ratings from 0.2 to 10 bar, manual over ride as standard and with flow control too, making this design ideal for simple cost effective ON/OFF water control.

NB Valve is plastic and unlike Brass water solenoid valves will need to be treated with care during installation and use. 

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