Solenoid Valve Types Explained: 3/2, 5/2 and 5/3 Valves for Pneumatic Systems

A solenoid valve is the part that tells a pneumatic cylinder when to move. Choosing the wrong type is a common reason for a cylinder that will not return, a machine that stops dead on power failure, or a valve that is too small to move the load fast enough. This guide explains the common solenoid valve types, shows how to read designations such as 3/2, 5/2 and 5/3, and lists what to check before you buy. Valve definitions are taken from Festo's own data sheet and from Wikipedia, both listed at the end.

What a solenoid valve does in a pneumatic circuit

According to Wikipedia, a solenoid valve is an electromechanically operated valve used to regulate the flow of liquids or gases. In fluid power systems, solenoid valves control cylinders, fluid power motors or larger industrial valves. The concept is also recorded in Wikidata (Q1430621).

In practice, a controller (a PLC or a relay) sends an electrical signal to a coil. The coil moves the valve, and compressed air is sent to one side of a cylinder or the other. When the signal stops, the valve either goes back to its rest position or stays where it is, depending on its type.

Solenoid valve types: reading 3/2, 5/2 and 5/3 designations

A designation such as 5/2 has two numbers.

• The first number is the number of ports the valve connects. A 3-way valve has three ports, and a 5-way valve has five.
• The second number is the number of switching positions. A 3/2 or 5/2 valve has two positions, and a 5/3 valve has three.

Festo's data sheet shows how the ports are numbered on a 5-way valve: port 1 is the air supply, ports 2 and 4 are the outlets to the cylinder, ports 3 and 5 are exhausts, and 12/14 and 82/84 are the pilot air supply and pilot exhaust.

3/2 valves: single-acting cylinders, normally closed and normally open

A 3/2 valve connects one working port to either the supply or the exhaust. Wikipedia describes a 3-way valve as connecting one port to either of two others, typically a supply port and an exhaust port. That is exactly what a single-acting cylinder needs: air goes in to push the rod out, and the same port exhausts so the spring can push it back.

Festo's data sheet gives the rest position with a letter:

• C: normally closed. With the coil off, the working port is not supplied with air.
• U: normally open. With the coil off, the working port is supplied with air.
• H: two 3/2 valves in one housing, one normally closed and one normally open.

Choose normally closed when the cylinder should be relaxed on power failure, and normally open when it should stay pressurised.

5/2 valves: double-acting cylinders, single and double solenoid

A 5/2 valve has two outlets, one for each side of a double-acting cylinder. In one position, air goes to the outstroke side and the other side exhausts. In the other position it is the reverse. There are two common versions:

• Single solenoid (monostable). One coil moves the valve and a spring, or compressed air acting as a spring, returns it. When power is lost, the valve returns to its rest position and the cylinder goes back.
• Double solenoid (bistable). Two coils, one for each position. Wikipedia notes that more complex valves may have two or more coils to move a spool valve. With no return spring, the valve normally stays where it was last switched until the opposite coil is energised, so the cylinder holds its position when power is lost.

Festo's data sheet lists both single and double solenoid versions of its VUVG range and gives a "memory stability" entry for each, so check that line for the exact valve you plan to buy.

5/3 valves: three positions

A 5/3 valve adds a centre position, which is useful when you want to stop a cylinder part-way or hold it free. The Festo data sheet lists three versions, named by the state in the centre position:

• 5/3C, normally closed. All ports are blocked in the centre position, which holds the cylinder where it is.
• 5/3E, normally exhausted. The working ports vent in the centre position, so the cylinder can be moved by hand.
• 5/3U, normally open. Festo's footnote for U is "normally open". Look at the circuit symbol on the data sheet to see exactly which ports are connected in the centre position.

Direct-acting and pilot-operated valves

Valves also differ in how the coil moves the main spool.

• Direct-acting valves use the coil to move the valve directly. Wikipedia gives response times of 5 to 10 ms for them.
• Pilot-operated valves use a small coil to send air to a larger spool. Wikipedia gives 15 to 150 ms and notes that they need a sufficient pressure difference between input and output.

Festo's data sheet for its VUVG sub-base valves lists the type of control as "piloted" and the design as a piston spool valve. Because a piloted valve uses air to move the spool, a small coil, listed at 1 W on that data sheet, can control a large flow.

Selection checklist

Work through these points before you order a valve.

• Cylinder type: single-acting needs a 3/2 valve, and double-acting needs a 5/2 or 5/3 valve.
• Failure behaviour: decide what the cylinder should do when power is lost, then choose single solenoid (return), double solenoid (hold) or a 5/3 centre position.
• Flow: the valve must be large enough for the cylinder to reach the speed you need. Take the flow value from the data sheet of the exact valve.
• Port size: match the ports to your tubing and fittings, and to the manifold rail if you use one.
• Voltage: Festo's data sheet lists 5, 12 and 24 V DC for the VUVG range. 24 V DC is the usual industrial supply, but check your control cabinet.
• Mounting: single valve, sub-base, or a manifold rail that serves several valves.
• Air quality: the data sheet specifies filtered compressed air with 40 µm filtration, lubricated or unlubricated. Use a filter before the valve.

Where to buy Festo solenoid valves in Delhi NCR

Multiweld Engineering is an authorised distributor of Festo and supplies Festo solenoid valves from our Delhi NCR stock, together with cylinders, FRL units, tubing and fittings. Our warehouse is at Kherki Daula (Wikidata Q6401350) in Gurgaon (Wikidata Q238508), close to the industrial town of Manesar (Wikidata Q3273362). We deliver to businesses in Delhi in one day.

The table shows driving distance and typical drive time from the Kherki Daula warehouse to the main industrial areas we serve. The figures come from OpenStreetMap routing with no live traffic, so peak-hour trips will take longer.

Tell us the valve code, or the cylinder and the voltage you use, and we will confirm the right product. You can contact us for a quote.

About the maker: Festo is a German automation company headquartered in Esslingen am Neckar (Wikipedia, Wikidata Q657230). Product data sheets and catalogues are on the official site, festo.com.

Sources and references

• Solenoid valve, Wikipedia and Wikidata Q1430621
• Festo solenoid valves VUVG, catalogue data sheet (PDF, edition 2010/02)
• Festo official website, Festo on Wikipedia and Wikidata Q657230
• Distances and drive times: OpenStreetMap data, routed with OSRM, measured from Kherki Daula (Wikidata Q6401350)
• Places: Gurgaon, Manesar, Sohna, Dharuhera, Bhiwadi, Faridabad, Noida, Ghaziabad, Greater Noida and Connaught Place, New Delhi

Data sheets are revised from time to time, so check the current Festo catalogue before you specify a valve.