Festo Valves, Valve Terminals and CPX, New Zealand

Festo / Valves, valve terminals and CPX

Press the manual override on the valve. If the cylinder moves, the pneumatics are fine and you have an electrical fault. If it does not, the problem is air, the valve or the cylinder. That one test costs nothing and it splits the fault in half.

Valve terminals are where pneumatic and electrical faults get confused with each other, and where a cheap part regularly gets replaced by an expensive assembly.

Request a quote

The manual override is the best diagnostic on the machine

Worth doing before anything else.

Every Festo solenoid valve has a manual override, a small button or screw on the pilot end that shifts the spool without electrical power.

Press the override and	Conclusion
The cylinder moves normally	Air, valve and cylinder are all fine. The fault is the coil or the signal
The cylinder moves slowly or weakly	Air supply, exhaust restriction, or the cylinder
Nothing happens	No air at the valve, a jammed spool, or the cylinder

That splits a pneumatic fault from an electrical one in seconds, and it decides whether you are ordering a coil or looking at the machine.

The latching override causes its own faults

Overrides come in two kinds. A non-detenting one springs back when released. A detenting one latches when turned and stays there.

A latching override left engaged holds the valve permanently shifted. The machine then behaves as though an output is stuck on, the PLC output tests fine, and the fault survives every electrical check because it is mechanical.

So on an output that appears stuck on: look at the override on that valve. Somebody used it during a fault or a set-up and it never got released.

Valve function is a safety decision, not a size

The most important content on this page, because a wrong substitution changes what the machine does when things go wrong.

Single against double solenoid

	Single solenoid	Double solenoid
Coils	One, with a return spring	Two
When power is removed	Returns to its spring position	Stays exactly where it was
On an emergency stop	Cylinder returns	Cylinder holds position

These are not interchangeable and the difference only shows up when the machine stops. Fitting a single solenoid valve where a double one was means a cylinder that used to hold position now drives home the moment power is lost, and vice versa.

Either behaviour can be the correct one. Which is correct for a given axis was decided when the machine was designed, and on a guarded or clamping application it is part of the safety design.

The three centre positions on a 5/3

Centre type	With both coils off, the cylinder
Closed centre	Holds, with air trapped both sides
Open or exhausted centre	Goes limp. Free to be pushed
Pressurised centre	Pressure both sides. Stiff but movable

Three valves that look the same and behave completely differently at rest. On a vertical axis, an exhausted centre means the load drops and a closed centre means it holds.

So the function code is not a detail. Send the full type code and, if the axis is vertical or guarded, tell us. Whether a substitution is acceptable on a safety-related function belongs with whoever holds the machine's safety assessment.

You do not replace the terminal to replace a valve

Worth stating plainly, because people quote whole assemblies unnecessarily.

A valve terminal is a manifold carrying individual valve slices, and the slices come off individually.

What failed	What you need
One valve not shifting	A coil, or one valve slice
One valve leaking internally	That slice
Electrical fault on one position	Coil, or the electrical module driving it
Manifold cracked or seals blown throughout	The manifold
Network node failed	The bus node only

The whole terminal is rarely the answer. Send a photo and we will quote the part that failed.

Blanking plates matter

An empty valve position on a manifold needs a blanking plate. Taking a valve off and leaving the position open vents the manifold and the whole terminal loses pressure.

That sounds obvious and it is a very common cause of a machine that stopped working entirely after somebody removed one faulty valve. Keep a blanking plate with the spares.

How the terminal is wired changes everything

The electrical side comes in distinct arrangements, and identifying yours decides what a replacement involves.

Arrangement	What it means
Multi-pin	One plug with individual wires per valve. No configuration to lose
Integrated fieldbus node	The terminal joins the network directly
CPX	A modular electrical system. Bus node plus I/O modules plus the valve interface
AS-Interface	Two wire network, addressed per node

A multi-pin terminal is the easy case. Replace the valve, plug it in, done.

A networked terminal is not, because the node carries an address and a configuration, and that is the next section.

CPX is where the configuration lives

CPX is the electrical half of a Festo terminal: a bus node, optional I/O modules, and the interface to the pneumatic side. It is a modular system in its own right.

Part	Function
Bus node	Determines the protocol. A different node is a different network
I/O modules	Digital and analogue inputs and outputs on the terminal itself
Pneumatic interface	Drives the valve coils
End plates	Supply connections, and where the power comes in

Before removing a bus node, record its address and any switch settings, and photograph it. A replacement arrives at defaults, and a correct node at the wrong address is invisible to the PLC.

The module order matters too. The controller's configuration expects a particular arrangement of modules along the terminal, so a module fitted in a different position faults even though it is the right part.

Two power supplies, and the failure nobody expects

The best fault-finding fact on this page.

A CPX terminal is typically fed by more than one supply: one for the electronics and one for the valves and outputs. They are separately fused and separately terminated.

If this drops	You see
Electronics supply	The node goes dark. The PLC reports it missing
Valve and output supply	The node is healthy, the network is fine, and nothing moves

That second row is the one that wastes a shift. Everything reports normal, the PLC sees the terminal, the outputs turn on in the program, and no valve operates. People start replacing valves.

So on a terminal where nothing works but communications are healthy, check the valve supply voltage and its fuse first. CPX usually reports an undervoltage diagnostic for exactly this, which is worth reading if you can get at it.

The diagnostics are worth reading

CPX reports faults over the network per position, including short circuits, open circuits and supply problems. So the terminal frequently knows which coil has failed.

Whether the PLC program surfaces that to the operator is another matter, but the information is there. If your integrator mapped the diagnostics, use them. If not, that is worth adding next time the program is opened.

Pilot air, and valves that shift unreliably

Underdiagnosed, and it produces intermittent faults that look electrical.

A solenoid valve does not shift the main spool directly. A small pilot valve does, using air.

Point	Detail
Minimum operating pressure	Below it, the spool will not shift reliably
Internal pilot	Pilot air taken from the main supply. The usual arrangement
External pilot	A separate pilot line. Needed at low pressure or on vacuum work

So a machine running at reduced pressure can have valves that work sometimes. The coil is fine, the signal is fine, and there is not enough pressure to move the spool.

And internal against external pilot is part of the terminal specification. A replacement configured the other way will behave oddly and it is not a faulty part.

If a machine has been turned down to save air or to be gentler on product, tell us. That changes what will work.

Check the silencer

Cheap, ignored, and it slows a whole machine.

Exhaust air leaves through a silencer, and silencers block up with oil, dust and moisture from the ring main.

Symptom	Cause
Everything on one terminal got slower	Blocked silencer, creating back pressure
Cylinders return sluggishly	Same, or restricted exhaust
Terminal noisier than it was	Silencer degraded or missing

A whole machine gradually slowing down is a classic blocked exhaust. It gets attributed to worn cylinders, and the fix is a part that costs almost nothing.

Ask for silencers with any valve order. They are consumables.

Terminals are built to order

Worth knowing before you send us a single number.

A valve terminal is configured, so the number on it may describe an assembly rather than a stock item. That configuration has to be broken back down into its parts to be quoted or rebuilt.

What we need is a photo of the whole terminal, front on, including both end plates and the bus node, plus the type codes off the individual slices if they are readable.

That is genuinely faster and more reliable than a parts list, and it lets us see the arrangement rather than infer it.

Before ordering

Symptom	Check first
One valve will not operate	Manual override, then the coil and its signal
Comms healthy, nothing moves	The valve supply and its fuse. A separate supply
Output appears stuck on	A latched manual override
Valves shift intermittently	Supply pressure against minimum operating pressure
Whole terminal got slower	Blocked silencer
Terminal dead after a valve was removed	Missing blanking plate
New node fitted, PLC cannot see it	Address and switch settings
Cylinder behaves differently on e-stop	Single against double solenoid, or the centre position

What to send us

A photo of the whole terminal, including both end plates and the bus node.

The type code off the individual valve slice, if that is what failed.

The coil voltage.

What network it is on, if it is networked.

Whether the axis is vertical, clamping or guarded. That affects which valve function is acceptable.

The supply pressure the machine actually runs at.

What the symptom is, and what the manual override did.

What we can supply

Individual valves. CPE, VUVG, VUVS and the MFH generation, in the function and voltage variants.

Valve slices. For CPV, VTUG, VTSA and MPA terminals, supplied singly.

Coils. Matched to the valve family, in the voltages and connector types.

CPX parts. Bus nodes, I/O modules, end plates and interfaces.

Manifolds and terminals. Built to your configuration where a whole assembly genuinely is the answer.

Consumables. Silencers, blanking plates, seals and fittings.

A sensible valve terminal spares holding

Item	Why
Coils in the voltage you run	The part that wears out
One valve slice per function you use	Far cheaper than a terminal, and usually two or three functions cover a machine
A blanking plate	Costs almost nothing and prevents a total stoppage
Silencers	Consumable, and a blocked one slows the whole machine
Spare fuse for the valve supply	The failure that looks like everything else

None of that is expensive and between them they cover most of what stops a valve terminal. A bus node is worth holding only on a critical machine.

We buy Festo valve terminals

Complete terminals from decommissioned lines are worth having, and a terminal with its bus node and end plates intact is worth considerably more than loose slices.

Keep the node with the manifold and leave the slices in place. See Sell To Us.

Common questions

Can you get a part that is not listed on your site?
Usually. The site shows what we hold, not what we can source.

Do I need to replace the whole terminal?
Almost never. Slices, coils and nodes are individually replaceable.

My valve will not operate.
Press the manual override. If the cylinder moves, it is electrical and probably the coil.

The network sees the terminal but nothing moves.
Check the valve supply and its fuse. It is a separate supply from the electronics.

An output seems stuck on.
Look for a latched manual override on that valve.

Can I fit a single solenoid valve instead of a double?
Not without changing what the machine does when power is lost. A single returns on spring, a double holds position.

The whole machine has got slower.
Check the silencers before anything else.

What is the lead time?
Ex stock items ship the next working day within New Zealand. We give you a firm lead time with the quote.

Do you quote in NZD?
Yes, in NZD including GST for New Zealand customers.

Send us a photo of the terminal

Front on, both end plates, and tell us what the manual override did. Those two things answer most of what we need to know. Quotes in NZD including GST.

Request a quote

Industech is an independent supplier of new, surplus and used industrial automation equipment. We are not an authorised distributor of, approved by, sanctioned by, or affiliated with Festo. Festo, CPX, CPV, VTSA, VTUG and MPA are trademarks of Festo SE & Co KG. AS-Interface is a trademark of AS-International Association. All trademarks, brand names and type codes are the property of their respective owners and are used here for identification purposes only.