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Solenoid Valve Guide: Part 2

You can read part 1 of this guide here

Solenoid Valve Guide: Part 2

In part 1 of this guide, we went through some of the operating features of different solenoid valve variations such as; 2 way or 3 way and the 3 different variants. We also discussed the Basic operating principles of these valves.

In this part we are going to be discussing:

Technical data and special features.

Technical information and valve installation:

Following on from some of the valve selection information in part 1, we are going to be a bit more detailed about some of the things needed for the correct valve selection:

The following points should be considered to ensure a correct choice of valve:

Connections and nominal diameters;

Threaded connections are either “G” – inches (ISO 228) or metric. Nominal diameters (DN) are expressed in millimetres and correspond to the diameter of the valves main orifice.

Potential questions;

How large does the valve need to be?
What orifice size is needed?
What connections are being used?

Pressure (units of measurement);

The SI of pressure is the pascal (Pa), defined as 1 newton of force per square metre (1 N/m2).
As Pa is such a small unit, the kPa (1 kilonewton/m2) or MPa (1 Meganewton/m2) tend to be more appropriate to fluid engineering.

However, the most popular metric unit used to measure the pressure in the fluid engineering field is the bar, which is equal to 105 N/m2 and approximates to 1 atmosphere.
Other units often include lb/in2 (PSI), kg/cm2, atm in H2O (atmosphere) and mm Hg. Conversion factors are readily available from many sources.

Potential questions;

How much pressure is in the system/pipework?
Can the valve handle the pressure?

Flow;

The flow is the quantity of fluid that passes through the valve’s main orifice which has the nominal diameter (DN) sown in the tables.

The flow is given with a constant Kv value (according to VDI/VDE 2173) that shows how many litres of water, at a temperature of 20°C, flow through the valve in one minute with a pressure difference of one bar across the valve.

To determine the flow at higher pressures, multiply the Kv value by the square root of the differential pressure. Flow values shown in the selection tables are subject to a tolerance of ± 15%.

Potential questions;

What is the flow rate?
Will the solenoid valve be suitable for this?

- These three subjects are something for both parties to consider.

If the customer is able to provide a full specification or as much information as they can regarding the spec, it will make it easier to choose the correct valve for the application.

The person providing the solution also has to consider these specifications because the valve has to be suitable and perform well in the application. Making sure that all of the specifications fit the application and the requirements provided by the customer.

Performance details;

Performance (OPD);

Pressure values given through technical data or specification sheets are the max values expressed in relative bar with no pressure at the outlet.

For 3/2-way solenoid valves, the pressure range can vary when used in other functions or systems.

The maximum pressure (PN) that the valve can bear is generally equal to 1.5 times the maximum value of the operating pressure differential (OPD).

Absolute pressure (bar a)

This is the pressure measured from the datum of a perfect vacuum: i.e. a perfect vacuum has a pressure of 0 bar a.

Gauge pressure (bar g)

This is the pressure measured from the datum of the atmospheric pressure. Although in reality, the atmospheric pressure will depend upon the climate and the height above sea level, a generally accepted value of 1.013 bar a (1 atm) is often used.

This is the average pressure exerted by the air of the earth’s atmosphere at sea level.

Gauge pressure = absolute pressure – Atmospheric pressure.

Pressure above atmospheric will always yield a positive gauge pressure. Conversely, a vacuum or negative pressure is the pressure below that of the atmosphere. A pressure of -1 bar g corresponds closely to a perfect vacuum.

Differential pressure;

This is simply the difference between two pressures.

When specifying a differential pressure, it is not necessary to use the suffixes ‘g’ or ‘a’ to denote either gauge pressure or absolute pressure respectively, as the pressure datum point becomes irrelevant.
Therefore, the difference between two pressures will have the same value whether these pressures are measured in gauge pressure or absolute pressure, as long as the two pressures are measured from the same datum.

Viscosity;

The viscosity of a fluid (liquid or gas) is its resistance to flow freely in a duct.

This phenomenon is also called internal friction and depends on the existing cohesion forces among the fluid molecules.

The viscosity of liquids decreases as the temperature rises; the viscosity of gases grows if the volume does not change.

According to the International System of Units (SI), the physical quantities are: force F – in Newton N, distance H – in meters M, area A – in square meters m2, speed u – in meters per second m/s, the unit of measurement of the dynamic viscosity is Pascal per second (Pa·s) or Newton multiplied by second per square meter (N·s/m2).

Dividing the dynamic viscosity of the liquid by its density, you can obtain the kinetic viscosity. Its unit of measurement is expressed in square meter per second (m2/s).

1 St = 1·10-4 m2/s or 10.000 St =1 m2/s

As well as the additional unit centistokes cSt.

1 cSt = 1·10-2 St

Valve installation;

To ensure proper valve function please observe the following instructions;

Water hammer or fluid hammer;

Water hammer (or, more generally, fluid hammer) is a pressure surge or wave resulting when a fluid (usually a liquid but sometimes also a gas) in motion is forced to stop or change direction suddenly (momentum change).

Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe. It may also be known as hydraulic shock.

When using liquid fluids water-hammer can occur at a pressure of 6 relative bar or higher.
This pressure wave can cause major problems, from noise and vibration to pipe collapse.

It is possible to reduce the effects of the water hammer pulses with accumulators and other features.

Mitigating measures:

- Air vessels

Typically have an air cushion above the fluid level, which may be regulated or separated by a bladder.
Sizes of air vessels may be up to hundreds of cubic meters on large pipelines.
They come in many shapes, sizes and configurations. Such vessels often are called accumulators or expansion tanks.

- Water hammer arrestors

Are hydropneumatic devices similar to shock absorbers that can be installed between the water pipe and the machine to absorb the shock and stop the banging.
Safety;

This product is not a safety device and must not be used as a sole device to prevent the over-pressure of some parts of the plant or the containment of dangerous fluids.

Always connect the coil’s earth terminal to ground to ensure the safety of the user and installation. The coil provides the basic insulation only. Install the product in a protected place to prevent electric shocks.

The coil should not be energised if it is not fitted onto a valve or without a plunger inside the valve, as it would overheat and get damaged. Do not touch the energised coil; risk of high temperature.

Do not use the tubes for conveying fluid to ground electrical devices.

Before disconnecting or disassembling the valve, make sure that there is no pressure inside the tubing or the valve itself.

Accidental shocks due to fall or collision may damage the operator and/or the integrity of the coil encapsulation thus causing malfunctions such as loss of insulation, seizure of the moving parts and overheating.

Installation;

Check for the operating conditions on the product label and on the technical documents.

Check for compatibility between medium and valve materials. In case of doubt, please contact the manufacturer.

Keep the valve operator in a vertical position, facing upwards. This prevents limescale or dirt particles in the operator tube which could restrict the armature or create excessive noise whilst operating.

Whilst tightening or unscrewing the valve must be held or revolved around only and exclusively by the hexagon or the frameset (in order to avoid damage to its components such as the coil, armature tube, etc.).

The recommended tightening torque of the coil nut is 0.5 Nm maximum, a higher torque may cause damage to the valve armature tube.
The recommended tightening torque of the connector screw is 0.5 Nm maximum, a higher torque may cause an excessive yield stress with consequent damages to the coil rivet and/or plastic encapsulation.

Connections;

To ensure that the solenoid valve works properly, do not connect to pipework with an internal diameter less than the nominal diameter (DN) of the valve. Clean all pipework before connection to the solenoid valve: care should be taken to prevent foreign bodies – dirt or material chips – from entering the valve during the assembly phase.

Use suitable seal material on the valve threads. Where liquid sealants are used, it is important to prevent them from entering the valve and blocking the movement.

Flow direction;

Respect the direction of flow across the valve, shown with an arrow or by numbers on the valve body, depending on the model type.

Filtration:

If the fluid contains dirt particles it is necessary to install a filter upstream of the solenoid valve.
Dirt is the most frequent cause of malfunction.

Environment:

Coils fitted with suitable connectors have a protection class of IP65.
However, it is advisable not to use the solenoid valve outside or in very damp conditions without adequate protection. This could require building an enclosure for the valve to be placed in.

Provide sufficient ventilation for the solenoid valve.

During continuous service, the coil of the solenoid valve becomes very hot and should not be touched.

Coil power supply;

It is important that the exact voltage and frequency of the coil is used for the valve to operate correctly.

Provided the coil is fitted correctly on the operator and that the armature is not obstructed, the valve can be operated for an indefinite time within the temperature limitations indicated. All solenoid valves have a copper shading ring to reduce vibrations caused by alternating currents.

Remark: The same valve fitted with coils of different power may have different pressure ratings than standard combinations indicated in Technical information or specification sheets. (e.g. UL coils or high-power coils).
Media and ambient temperatures;

Temperature limits for the media in the datasheets and should be used as a guide to valve selection. Normally the maximum ambient temperature can reach +50°C for solenoid valves with coils in class “F”, +70°C for class “H”.

For applications outside these limits please contact our technical department.

General purpose solenoid valves;
Solenoid valves shown throughout this guide, either normally closed or normally open, are intended to control the flow of fluids and cannot be used as safety valves.

Benefits of M&M International Solenoid Valves;

M&M Contact Us

Robust construction for industrial applications featuring stainless steel orifice on most models – High reliability – long life.

Stainless steel operators with low residual magnetism according to 1.4105 EN 10088 (AISI 430F) – Corrosion resistant – High performance.

High-quality seal materials – NBR, FKM, EPDM, PTFE, Sigodur (filled PTFE), Ruby, Kalrez – High compatibility with a wide range of media.

Fully interchangeable coils with a wide range of AC and DC voltages – High flexibility with reduced stock.

Coil orientation possible through 360° - Simple and quick installation.

Coils tested 100% in compliance with the current EC directives, compliance to RoHS directive and to relevant international standards upon request – (certification pics)

Development and realisation of special projects – Customer tailored solutions.

Optional features;

Manual override (M)

Normally closed direct acting and pilot operated solenoid valves can be supplied with a manual override which allows the valve to be opened independently of electrical current.

This allows for the operation to be dictated by hand, interrupting the operating cycle of the electrified solenoid valve and coil.

Manual override can be beneficial in the case of a power cut, where the valve may be stuck in a certain position, open or closed, and it is required to change.

Waterhammer Control (v)

Pilot operated solenoid valves (only versions specified in each datasheet) can be supplied with a system that regulates the closing speed of the diaphragm in order to control waterhammer.

The seal closing speed is operated by the adjusting screw: by screwing it clockwise (in the “+” direction) when using liquid, the valve will close slower reducing any waterhammer effect that may occur in the solenoid valve and the upstream pipes.

In the case of larger valves (1 ¼”, 1 ½” and 2”), please adjust the anti-waterhammer screw to ensure that the valve closes as slowly as possible in order to avoid causing any damage that may affect the functioning of the equipment and valve due to the waterhammer effect.


Read Part 3

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