Everything you need to know about Solenoid Valves part 2

Everything You Need To Know About Solenoid Valves - Part 2

In the following article you will find the second part of the basics about solenoid valves. Click here, if you missed the first part.

NUMBER OF WAYS

2 Ways

The solenoid valves have two ports (one inlet, one outlet) and only one orifice (seat) allowing the fluid control.

• 1 inlet port (P)
• 1 outlet port (A)

3 Ways

These solenoid valves have three ports (typically one inlet, one outlet and one exhaust) and two orifices (seats) allowing the fluid control.

• 1 inlet port (P)
• 1 outlet port (A)
• 1 exhaust port (R)
• Typical application: to operate a single acting cylinder
  
  

• 1 inlet port (P)
• 2 outlet port (A1, A2)
• Typical application: to select or divert flow
  
  

• 2 inlet port (P1, P2)
• 1 outlet port (A)
• Typical application: to mix two fluids

4 and 5 Ways

This solenoid valve is the functional combination of two 3 way valves. It includes generally 4 or 5 connection ports according to its design. The term 4 way or 5 way refers to the number of ports.

• 1 inlet port (P)
• 2 outlet ports (A1, A2)
• 1 or 2 exhaust ports (R1, R2)

FUNCTION

Digital solenoid valves operate on an all-or-nothing principle. They therefore possess two distinct states, which are (1) - when the coil is activated by an electrical current, and (2) - when the valve is resting (without electricity). Valve functions are defined from the resting position.

The solenoid valves direct acting or pilot operated may have two functions:

Normally Closed (NC)
A solenoid valve is normally closed (abbreviated - NC) if no flow cross the valve in its resting position (with no current on the solenoid contacts).

Please note that in the case of 3-way solenoid valves, port A is open to port R which, for example, enables the valve’s single-action cylinder to be exhausted to atmosphere.

Normally Open (NO)
A solenoid valve is said to be “normally open” (abbreviated NO) when it enables fluid to pass in its resting position (with no current on the solenoid contacts).

A specific choice of entry ports can change a valve’s function. However, since balanced-force calculations take rebound effects, coil effects and the effects of pressure exerted on the seal into account, the performance of an NC valve fitted in an NO position would be reduced. In this configuration it would be better to choose a universal solenoid valve.

Universal (UNI)
A solenoid valve is said to be “universal” (abbreviated UNI) when it enables several different functions as a result of specific orifice connections. Universal solenoid valves are specially dimensioned for giving optimum performance in all configurations.

Latch or Bistable
We manufacture solenoid valves designed for applications where reduced energy consumption is the determining factor. For these applications a short electrical impulse enables the solenoid valve to be opened or closed, and thanks to the residual effects of a permanent magnet this is sufficient for maintaining the valve in a particular working position with no electrical energy consumption.

A short impulse of inverted polarity ensures the valve’s return to its previous position. Electrical power consumption and heating are almost negligible.

ACTION - OPERATING MECHANISM

Direct acting
The magnetic plunger (orange) is acting directly on the valve seal to open or close the valve orifice depending upon whether the solenoid is energized or de-energized. The pressure and flow of this type of solenoid valve depend directly on the orifice size and the coil (yellow) power. Its function is not dependent upon line pressure or flow rate.

Pilot Operated
This type is designed to permit a high flow rate at high pressure not depending directly upon the coil power. The plunger is acting on a pilot orifice to close or open it, depending upon whether the solenoid is energized or de-energized, thus permitting to pressurize or to release pressure in the pilot chamber.

A 2/2 way solenoid valve is equipped with a diaphragm (3) in which there is one bleed orifice (4), and one pilot orifice (1). When the solenoid is energized, it opens the pilot orifice and releases pressure from the pilot chamber (2). This results in overpressure in the bottom of the diaphragm which is lifted by the line pressure opening the main orifice.

When the solenoid is de-energized, the pilot orifice (1) is closed and full line pressure is applied in the pilot chamber (2) through the bleed orifice (4) , thereby providing a seating force for tight closure. This type of solenoid valve requires a minimum operating differential pressure. We also produce pilot operated solenoid valves with a diaphragm mechanically connected to the plunger which may operate from zero up to its maximum pressure service. See all figures showing the various designs of solenoid valves direct and pilot operated as well as the different types of connections in order to obtain the functions as described above.

THE kv-VALUE

The valve dimensions will highly depend on the desired flow rate of your system. Therefore, it is very important to determine the flow coefficient (kv-value) at the beginning of the selection process. Valve manufacturers specify this kv-value, which describes the relationship between the pressure loss across a specific orifice and the respective flow rate. The kv is calculated as the amount of water at 20°C in litres per minute which flows through the valve at a pressure drop of 1 bar. It defines the flow when the valve is 100% open. The higher the kv-value, the higher the flow with the same pressure drop. Higher kv values are typically reached by increasing the orifice diameter and / or the plunger stroke.

Mathematically it can be described at:

with: Q = Flow; ρ = density of medium;  = pressure differential

We offer a practical Flow calculator (link) for this purpose. The values calculated in this way serve as a reference point for selecting the right valve for your application.

HOW TO SELECT THE RIGHT VALVE

Valve function (3/2, 2/2, Normally open, Normally Closed), medium type, space available, flow and pressure rates are typically the first steps towards selecting the right valve. We highly recommend a complete analysis of several additional factors including:

• Environmental (temperature, humidity, exposure to vibration)
• Electrical requirements (available voltage and power)
• Usage (life cycles, operating frequency)
• Regulatory requirements / Protection Class
• Specific needs such as response time or leak rate
• …

In order to make sure all factors are considered, feel free to contact our knowledgeable team who will guide you to select the most appropriate solution given your application requirements.