Model Selection

With your requirements and budget unchanged, our team of experts may give a better adaptation solution, choose the most practical product model, the performance of the combined components will be more efficient, and the cost will be more economical.

In particular, the component combination of some projects is more complicated, and it will involve several types of interdisciplinary knowledge. Generally, a single technical staff cannot master such comprehensive knowledge, but our expert team is composed of several inter-departmental engineers. 

So, whether it's the performance results of a single product or the cost-effectiveness of the combination as a whole, our team of experts may know more.

How to select a suitable solenoid valve?

In selecting a solenoid valve, a number of operating and physical parameters must be considered. The operating parameters include opening pressure, flow, pressure drop, temperature and maximum pressure the solenoid valve may experience. The physical parameters are pipe size and type of fluid. 

1.    PRESSURES

MAXIMUM OPERATING PRESSURE DIFFERENTIAL –MOPD (PS)

When the solenoid valve is closed, the supply pressure is present at the inlet port only. This is the pressure the solenoid valve has to open against. In other words, this is the pressure the electrical solenoid has to overcome to open the solenoid valve and allows flow to occur. This pressure is called Maximum Operating Pressure Differential (PS) or simply “MOPD” in our catalogue. The value given in the catalogue must be equal to or greater than the maximum pressure at the supply port at which the solenoid valve must open. Note it is not always the same for different types of fluid and that AC solenoid valves usually have higher pressure ratings than DC solenoid valves.

Strictly speaking, the MOPD is the maximum pressure drop across the solenoid valve when the solenoid valve is closed. If there is a pressure at the outlet port when the solenoid valve has to open, this could be subtracted from the inlet pressure to arrive at the MOPD. However , if at some time a zero pressureis present at the outlet, the solenoid valve will have to open at the pressure at the inlet which may be too high, causing possible coil burnout on an AC source. Therefore , the supply pressure is considered as the MOPD in conservative designs.

MINIMUM OEPRATING PRESSURE DIFFERENTIAL

Once the solenoid valve has opened, the pressure conditions may change. A pressure is present at the solenoid valve outlet. This pressure may be negligible as when the solenoid valve is filling a tank, or it could be quite high when the solenoid valve supplies a spray nozzle. In some cases, the pressure at the supply and outlet will be the same when a cylinder has moved and we have in effect a dead-end load. When the pressures are equal, the fluid has ceased to flow.

If we call the supply port pressure P1 and the outlet port pressure P2, The pressure drop across the solenoid valve is P1-P2.We also call this the pressure differential (△P)across the solenoid valve.

Example: if P1 was 10 bar and P2 was practically zero, which would be the case if water was flowing out of the solenoid valve into a tank, the pressure drop or differential would be △P=P1-P2; that is  10-0=10 bar.

Now: if P2 was 9bar due to a nozzle

△P would equal 10-9=1 bar

(The minimum operating pressure differential is the minimum pressure drop that will exist across the solenoid valve when there is flow).

In selecting a solenoid valve, check if a minimum operating pressure differential column is applicable to the solenoid valve you are considering. If there is no column or the number in the column is zero, the solenoid valve will remain open even if the pressures at the inlet and outlet are the same. If there is such a column, make sure that the minimum pressure drop in the system never gets below the figure shown or the solenoid valve will throttle , causing fluctuation in flow.

MAX.ALLOWABLE PRESSURE

(According to EN764)

The maximum allowable pressure is the maximum line or system pressure the solenoid valve can be subjected to in normal service. Due to limitations on the maximum pressure test we can conduct on our production test stands, the figures shown may be conservative. If higher safe working pressures are required, Pls. contact with us.

Pressures up to the maximum allowable pressure can occur when the solenoid valve is open or closed and may damage the solenoid valve internal parts if exceeding the MOPD.

PROOF PRESSURE

2.    TEMPERATURES

Normal ambient temperature

The normal ambient temperature is assumed to be in accordance with standard conditions as specified in ISO 554

Ambient temperature: 20 ℃

Ambient pressure: 1013mbar

Relative humidity: 65%

Maximum ambient temperature (TS)

The  maximum ambient temperature listed (20 ℃) is based on test conditions to determine safe limits for coil insulation. The temperature is determined under continuously energized conditions and with maximum fluid temperatures (as listed) existing in the solenoid valve. In many applications the existing specific conditions will permit use at higher ambient temperatures. In addition, modifications to standard constructions are available which can extend the maximum ambient temperature limitation to 80℃ or more.

Minimum ambient temperature

The minimum ambient temperature of a solenoid valve is greatly affected by application and construction.

Damage may occur when liquids solidify above the specified minimum temperature.

Special constructions are available for lower temperature, Pls. contact us freely.

Maximum fluid temperature (TS)

The maximum fluid temperature listed is valid for an ambient temperature of 20 ℃and 100% RD (Relative Duty Time). In case of higher fluid temperature, refer to 

3.    VISCOSITY

Viscosity is the resistance of a fluid to flow, due to internal friction. Viscosity affects the flow rate of a solenoid valve considerably and the flow factor is reduced when viscous fluids are to pass the solenoid valve.

There are two types of viscosity:

a) dynamic viscosity, expressed in Pa.s (Pascal seconds) or Poises

b) kinematic viscosity, which is the ratio between dynamic viscosity and density of the fluid

4.    RESPONSE TIMES:

This is the time-lapse after energizing (or de-energizing) a solenoid valve until the outlet pressure reaches a specific percentage of its maximum steady value, the outlet being connected to a circuit having specified flow parameters.

Response time depend on 5 factors:

-       Kind of electrical supply: AC or DC

-       Fluid handled by the solenoid valve, viscosity and pressure level

-       Type of operation: direct or pilot operated

-       Size of the moving parts of the solenoid valve mechanism

-       Circuit in which the time is measured

Approximate values for AC solenoid valves on air service under average conditions are:

a) small direct acting solenoid valves: 5 – 25ms

b) large direct acting solenoid valves: 20 – 40ms

c) internal pilot operated solenoid valves:

 1) small diaphragm type: 15  - 60ms

2) large diaphragm type: 40 - 120ms

3) small piston type: 75 - 100ms

4) large piston type: 100 - 1000ms

Generally speaking, operation on liquid media will have the following effects:

a) small direct acting solenoid valves ±20-30% higher

b) large direct acting and internally pilot operated solenoid valves: dependent on size 50-150% higher

Response time on DC operation is approximately 60% higher than on AC operation.

Consult us if response time is a critical factor.

The ratings below are associated with the speed of response of self-contained pilot operated solenoid valves, using the flowing stream as the operating

Excellent:                      0 to 500 SSU

Good:                          500 to 1000 SSU

Satisfactory:                1000 to 2000 SSU

Fair:            ;   ;             2000 to 5000 SSU

Unsatisfactory:              above 5000 SSU

Normally a solenoid valve application that falls into the fair category performs or responses very slow with regulating pilots such as pressure reducing, back pressure or pressure relief. A solenoid on-off solenoid valve will perform satisfactorily provided an overrun can be compensated for.

Electrically operated directional control solenoid valves

The switching time of an electrically operated directional control solenoid valve is the time which elapses between the closing or opening of the electric circuit and the instant when the pressure at the outlet port reached 50% of its maximum value , the outlet port being blocked at the solenoid valve body or at the sub-plate if the solenoid valve is mounted on a sub-plate.

Electric (direct operated)

The switching threshold of a direct electrically operated solenoid valve is the limiting value of the electric voltage, rising or falling, which causes or allows “switching”, i.e . the complete transition from an initial to a final state under the normal operating conditions foreseen by the manufacturer (no oscillation, correct sealing，normal flow values, etc).

Electric (pilot operated)

Here consider only the case where the medium causing switching is compressed air coming either from the main inlet port or from an external auxiliary port.

The switching threshold of an electric pilot operated solenoid valve is the joint effect of two limiting values , rising or falling ;on the one hand the signal pressure and on the other the signal voltage , which cause or allow “switching” , i.e. the complete transition from an initial to a final state under the normal operating conditions foreseen by the manufacturer (no oscillation , correct sealing, normal flow values etc.).

SOLENOID VALVE SEAT TIGHTNESS:

Solenoid valve seat tightness or leakage depends on the type of solenoid valve, used sealing materials trim and medium.

Although it is expected that a big orifice piston solenoid valve with high DURO disc will show some more leakage flow than a simple core-disc execution with soft resilient. To establish practical test leakage flow rates for the solenoid valve the following 3 groups(categories) are applicable for all solenoid valve types and / or sizes.

1) Leakage flow <0.24N dm3/h within the specified pressure range of the solenoid valve product (all resilient disc, diaphragm or poppet closing members such as NBR, FPM, EPDM, TPE, UR, etc.).

2) Leaking flow <0.084N m3/h within the specified pressure range of the solenoid valve product (all non-resilient disc or other closing members such as PTFE, reinforced PTFE, metal, POM, etc.).

3) Leakage flow for “Gas Approved solenoid valves” see table below

DEGREES OF PROTECTION PROVIDED BY ELECTRICAL ENCLOSURES ( IP CODE)

(according to standard EN60529 and IEC529)

The code letters IP (Ingress Protection) followed by 2 characteristic numerals: e.g. IP65.The first figure indicates the degree of protection of the energized parts and internal moving parts against ingress of solid foreign objects. The second figure indicates the degree of protection against ingress of water with harmful effects.