Solenoid Valves for Water

Working Pressure

System working pressures for water solenoid valves. Mains water is typically 2 or 3 bar, but in some areas such as in Cornwall the pressures are pumped and can exceed 10 bar, which can can problems when using plastic solenoid valves that typically are limited to a maximum working pressure of 10 Bar, unlike Brass or Stainless Steel solenoid valves that typically work up to 15 bar or more.

Flow requirements for water solenoid valves

It is good practice to check the flow required for the application and check this against the CV or Kv flow coefficient of the solenoid valve to be used. If the valve is too small the system will starve of water and the water may well travel excessively fast to achieve the desired flow potentially causing water hammer in the pipework. The other way around can be that the solenoid valve is too big for the required application, which not only increases cost but can when using a pressure assisted solenoid valve (also known as servo assisted solenoid valve) cause a very annoying chattering noise when energised open (allowing flow). This is caused by the fact that a pressure assisted solenoid valve requires a pressure differential to open or close, but when the solenoid valve is open it allows flow faster than the system demand and which generates a back pressure cancelling the pressure differential thus closing the solenoid valve. The instant the solenoid valve is forced closed by the back pressure, a pressure difference is generated as demand now exceeds supply which allows the solenoid valve to open again and this cycle repeats until the solenoid valve is switched off or the demand for water stops.

Temperature of water solenoid valves.

Typical water solenoid valves will have NBR seals that are rated between 60 and 80°C, whereas EPDM can typically withstand temperatures up to 150°C. If higher temperatures are required it is wise to use the correct steam rated solenoid valve, which should have PTFE seals and an H or N rated high temperature coil designed to resist the heat of the application.

Hard Water and issues with Calcium deposits from Water.

Solenoid valves are ideal for the ON/OFF flow control of water, but water will carry varying amounts of deposits including minerals, particles are calcium. As you know if you look inside your kettle, dishwasher or washing machine, central heating system you will find lime-scale, a hard off white chalky deposit that is typically Calcium. A solenoid valve when energised produces heat, and if energised for typically more than 20 minutes will reach its maximum temperature which can be anywhere up to 120 degrees centigrade. The electrical energy is used to generate a magnetic field to operate the solenoid valve but even a 10-watt coil will generate heat. This heat builds and can only disperse through the ambient environment, the metal pipe and the media flowing through it. However the coil or heat source is typically fitted onto the core tube, which is in itself a dead end and will see very limited flow.

In hard water areas over time this will cause a solenoid valve armature to fill with lime scale deposits and finally it will stick and fail. This is usually followed by the solenoid coil burning out especially if it is 50/60Hz AC coil, as it will stay in what we call the inrush state i.e. trying to move or lift the armature, and because the armature will not move the coil will over heat. Typically engineers replace the coil and then complain as this also failed within hours.

There are 2 solutions to this problem, the easy solution is to fit a valve that will not suffer from lime-scale, but lime scale will still build up in the system over time and cause blockages and issues in the remaining system at some point in time. The intelligent solution is to fit a water softener, this will remove the lime-scale from the water, allowing the solenoid valves, pipework and other process systems to run cleanly and effectively well into the future.

Environmental and Hazardous Area issues for water solenoid valves.

Typical water applications are well suited for Brass or even Plastic solenoid valves, but if food or chemical processing systems either the system or the environment are cleaned using corrosive anti bacterial chemicals which can make Brass or plastic solenoid valves unsuitable, so stainless steel solenoid valves need to be used. In some instances in processing of animal feed, sugar or flour for example there can be a build up of potentially explosive dusts in the atmosphere. In these instances the area will have a hazardous area rating and a solenoid valve with ATEX hazardous area certification will be required, either EEx m II T4 or EEx d II C T6 for example.

Water solenoid valves operation.

Weather it is a plastic, brass or stainless steel solenoid valve there are typically two different solenoid valve methods of operation, see below.

Assisted Lift water solenoid valves

Assisted lift, direct acting or hung diaphragm solenoid valves do not require a pressure differential to operate i.e. a pressure difference between the inlet and outlet ports and are ideally suited for most mains water applications, offering high flow rates. No consideration needs to be given to pressure differential and engineers can fit these solenoid valves in the safe knowledge of a positive opening and closing function regardless of system pressures. These are ideal for low pressure, vacuum, gravity fed and closed loop systems however typically they can operate up to 10 bar or more.

Helpful hint: Coil typically mounted centrally. Typical pressure ranges: 0 to 10 Bar. Typical sizes ranges : 3/8 to 2" thread and flange DN10 to DN300

Servo Assisted water solenoid valves.

Pressure assisted or floating diaphragm solenoid valves for water require a pressure difference between the inlet and outlet ports to open and close. These are ideal for most mains water supply because they provide a high flow rate and typically mains water will supply sufficient pressure differentials for operation. These are ideal for open to atmosphere tank refill systems and systems that will offer the required pressure differential. Another benefit is that this design of water solenoid valve is typically less expensive than as assisted lift deign.

Helpful hint: Coil typically mounted over outlet port.Typical pressure ranges: 0.5 to 10 Bar Typical sizes ranges : 3/8 to 3" thread and flange DN10 to DN 500

Published: 19-11-2015 Author: Mike Freye Category: Water