A manifold puts several valves on one common air supply and one common exhaust. A valve island adds electrical connection, so one cable carries the signals for every valve on the block. Both trade flexibility for tidiness, and both introduce a single point of failure that a machine with individually mounted valves does not have.
This guide covers when centralising pays, what it costs in response time, how to size the supply, and the failure modes that only appear on a manifold.
What you gain and what you give up
Gains
- One supply connection and one exhaust connection instead of one pair per valve.
- One electrical connector or fieldbus node instead of a cable per valve.
- Less tubing, fewer fittings, fewer leak paths, a smaller cabinet.
- Faster assembly and much faster fault-finding, because everything is in one place.
Costs
- All valves share a supply. A restriction upstream affects every actuator on the block.
- All valves share an exhaust. Simultaneous operations interfere with each other.
- A longer tube run from valve to cylinder, because the valve is no longer at the actuator.
- Loss of one block can stop the whole machine.
The longer tube run is the one people underestimate. A valve mounted at the cylinder empties a short line; a valve on a manifold two metres away has to fill and empty two metres of tubing on every stroke. That costs cycle time and air.
When to centralise and when not to
Centralise when the machine has many valves doing similar work at moderate speed, when the cabinet layout matters, when the machine is built in series and assembly time is a cost, or when a fieldbus is already in the design.
Keep valves at the actuator when cycle time is critical and the tube run would be long, when one cylinder needs a much larger valve than the rest, when the actuator is far from the cabinet, or when a failure must be contained to one function.
Most real machines end up mixed: a valve island for the routine motions, and individually mounted valves for the two or three that need speed or size.
Sizing the supply: add up the simultaneous demand
The common supply must carry the peak simultaneous flow, not the sum of every valve on the block and not the demand of one.
Work it out in three steps:
- List the valves that can operate at the same instant in the worst case of the cycle. On most machines that is a handful, not all of them.
- Add their flow requirements at the pressure they run at.
- Size the supply port and the feed line to that total, with margin.
A manifold fed through the same tube size as a single valve will sag whenever two actuators move together, and the symptom is a machine whose timing shifts depending on what else is happening. It is one of the more frustrating faults to chase, because each function tests correctly on its own.
For blocks with a genuinely high total demand, manifolds with a supply feed at both ends solve the pressure gradient along the block that otherwise starves the far end.
The shared exhaust, and why it bites
Exhaust is the half of the circuit that gets forgotten. On a manifold, every valve exhausts into a common gallery.
Two consequences:
Back pressure from a neighbour. When several cylinders exhaust simultaneously, pressure in the gallery rises and the cylinders decelerate. Speed control that was set with one cylinder moving is wrong when three move together.
Silencer restriction. A common exhaust usually ends in a single silencer, which is the whole block's bottleneck. Silencers clog with oil and dust. A manifold that has slowed progressively over months usually has a silencer that has stopped being a silencer and started being a throttle.
Where interference matters, specify a manifold with separate exhaust ports per valve or per section, and give the heavy consumers their own outlet.
Electrical connection
Multipole. One multi-way connector, one cable to the cabinet, wired to the PLC output card. Simple, cheap, and the wiring is fixed at build time.
Fieldbus node. The block carries a bus interface and joins the machine network. Fewer wires again, diagnostics per valve, and valves can be addressed in software. It costs more and it ties the block to a protocol.
For a machine built once, multipole is usually enough. For a machine built repeatedly, or one where diagnostics matter, the fieldbus pays back in commissioning and downtime.
Failure modes that only exist on a block
- Seal between block sections. Sub-base manifolds are assembled from sections with seals between them. A seal that has been disturbed during a valve change leaks internally, and the symptom is a valve that operates weakly for no visible reason.
- Blanking plate missing. Every unused station needs its blanking plate. An open station is a permanent, sizeable leak straight to atmosphere.
- Wrong valve function in a station. A 5/2 and a 5/3 valve can be mechanically interchangeable on the same sub-base. Fitting the wrong one gives a machine that behaves almost correctly.
- Pilot air starvation. Many valves take their pilot supply internally from the main supply. If main pressure sags below the valve's minimum pilot pressure, the valve stops switching reliably while the gauge still reads a plausible number. Where supply pressure is low or varies, specify external pilot supply.
A specification checklist
- Which functions go on the block and which stay at the actuator.
- Peak simultaneous flow, and the supply port and feed line sized to it.
- Feed from both ends where the block is long or demand is high.
- Exhaust arrangement: common gallery, or separated where cross-interference matters.
- Silencer sizing, and a replacement interval that someone owns.
- Electrical: multipole or fieldbus, decided on build volume and diagnostic needs.
- Blanking plates for every unused station, ordered with the block.
- Pilot supply: internal, or external where main pressure is low or unstable.
- Spare stations, because a machine always grows.