Vacuum systems fail slowly. A leak opens by a fraction of a millimetre, a filter loads by a gram, a cup hardens over months — and the machine keeps running, slightly worse each week, until one day it stops picking reliably and the operator reports that the vacuum has “gone”.

Treating vacuum as a system rather than as a component is what prevents that. This article sets out what to measure, how often, and what the numbers mean.

The Short Answer

Four measurements, taken on a schedule, characterise the entire vacuum circuit: vacuum at the cup face, time to reach vacuum, filter differential pressure, and resistance to ground where static is a concern.

A monthly campaign of these four readings on each machine takes under thirty minutes and answers most questions that would otherwise consume a shift of fault-finding. Their value is not in any single reading but in the trend: a vacuum that has fallen from 0.55 to 0.50 bar over three months is telling you something that a single out-of-spec reading cannot.

The target values for most case erectors are 0.4 to 0.6 bar below atmospheric at the cup face, with the full vacuum developed in under one second.

How the Vacuum Circuit Is Built

Understanding the architecture makes diagnosis possible, because each element produces a distinguishable symptom.

The generator. An ejector or a vacuum pump. An ejector is simple and has no moving parts other than the air supply valve; a pump gives steadier vacuum and lower air consumption but has vanes or seals that wear.

The filter. Between the generator and the cups, protecting the generator from board dust. On recycled board this element loads quickly, sometimes within days.

The valve. Controls vacuum to the cups, and in a demand-controlled system opens only during the pick window. Valve timing errors produce symptoms that look like capacity problems.

The manifold. Distributes vacuum to multiple cups. A leaking manifold gasket affects all cups equally, which makes it a distinctive fault: every cup weakens at once.

The hoses. Flexible connections to the moving picking head, and the place where most leaks originate, because flexing is what opens cracks.

The cups. The final interface. Cup condition affects the seal; cup geometry affects whether the seal survives a flexible blank.

The Four Measurements

Vacuum at the Cup Face

This is the reading that matters, and it is the one most often taken in the wrong place. A gauge at the pump measures the generator’s capability, not the vacuum at the blank. A tee’d gauge at the cup measures what the blank actually receives.

Measure with the cup sealed against a flat plate, so that the machine’s sealing is not part of the reading. Then measure again with a blank in place. The difference between the two figures is the seal quality, and it is the single most informative number in the system.

Time to Reach Vacuum

A healthy circuit reaches specification in well under a second. A circuit that reaches the right final value slowly has a restriction or a degraded generator, and the fault will appear as intermittent pick failures at high case rates rather than as steady weakness.

Measure by watching the gauge while sealing and releasing the cup, and time the rise. A stopwatch is adequate; a logging gauge is better.

Filter Differential

Measure immediately upstream and downstream of the element. A differential above 0.05 bar indicates a restriction worth addressing. On recycled board, check weekly; on virgin board, monthly.

Resistance to Ground

Only relevant where static is controlled, but worth measuring on any machine handling low-humidity board. The dissipative band is 10^4 to 10^9 ohm to ground. A reading above that band means the path is not draining charge; below it means the discharge itself may be damaging.

Component Life and Service Intervals

The hoses row deserves emphasis. Replacing one hose when it fails is the standard practice and the wrong one, because hoses age together. A set replacement at a fixed interval costs less than three individual failures and three line stops.

Building a Vacuum Trend Record

The record is what converts maintenance from reactive to predictive, and it takes one row per machine per month.

What to record: machine identifier and date, vacuum at the cup face against a sealed plate, vacuum with a blank in place, time to reach vacuum, filter differential, and any cup change since the last reading.

What the trend tells you:

Vacuum sealed-plate falling, vacuum with blank steady. The generator or the circuit is degrading. Time-to-vacuum will usually fall first.

Vacuum sealed-plate steady, vacuum with blank falling. The seal is degrading — cup wear, or a change in blank surface.

Both falling together. A circuit leak, most likely a hose or the manifold gasket.

Time-to-vacuum lengthening with a steady final value. A generator losing capacity or a valve opening slowly.

Differential rising while vacuum holds. The filter is loading and will become the constraint shortly.

Each of these patterns has a different cause, and the trend distinguishes them without needing to dismantle anything. Recording templates for this kind of trend log are available through our support section.

Leak Survey

Air leaks in a vacuum circuit are not the same as leaks in a compressed air line, and they behave differently: a vacuum leak draws air in rather than letting it out, so it is silent and cannot be found by listening.

The practical methods are these.

Isolation test. Plug the cups and measure the vacuum the generator can hold. If it cannot reach specification with no load, the leak is in the circuit.

Section testing. Isolate the circuit in sections — generator to filter, filter to valve, valve to manifold, manifold to head — and measure each. This localises a leak without dismantling the whole circuit.

Ultrasonic detection. An ultrasonic detector can locate a vacuum leak by the noise of air entering, and the method works well on hoses behind guards.

Soap solution. Effective but slow, and it must be applied along the whole circuit, not only at joints. It also introduces moisture, which should be dried afterwards.

Alarms and the Vacuum Circuit

E-14 Air Pressure Low is the alarm that points outside the machine. When it appears, the cause is usually the plant air system rather than the erector, and adjusting the machine will not help. Check the compressor and the distribution network first.

Maintenance Rhythm

Every shift — listen for leaks around the picking head, check the local filter drain, and confirm the first picks of the shift are single and clean.

Every week — clean the vacuum filter element, inspect cups for glazing and cracking, check hoses at their flexing points, and verify the vacuum reading against specification.

Every month — take the four measurements and record them as a trend; inspect the manifold gasket; check cup mount springs or cushions for fatigue.

Every quarter — replace any hose showing surface cracking, measure filter differential, and inspect the generator for contamination from oil carry-over.

Annually — replace the full hose set, replace or assess cups against a wear standard, service or replace the ejector, and re-baseline pick reliability across the board grades actually run.

FAQ

Why is my vacuum reading good at the pump but poor at the cup?
Because something between them is losing vacuum — a loaded filter, a leaking hose or a leaking manifold gasket. Measure in sections to localise it.

How often should suction cups be replaced?
Plan on 12 months or 2 to 3 million picks. On recycled board, in dusty conditions or in a cold room, inspect monthly and expect a shorter life.

Can I find a vacuum leak by listening?
No. A vacuum leak draws air in, so it is silent. Use isolation, section testing or an ultrasonic detector.

Is a vacuum pump better than an ejector?
A pump gives steadier vacuum and lower air consumption; an ejector is simpler and has fewer wearing parts. The choice depends on duty cycle and on whether the plant air system is already at capacity. Which configurations a given machine carries is listed in our product range, and standard board and cup questions are answered in our FAQ.

Tracking down a slow vacuum decline? Send your machine model, current vacuum readings, filter differential and cup age to [email protected] or WhatsApp +86 13681839278. Our engineers will identify the degrading element and recommend a service plan within 24 hours.