An automatic pump restart can be part of pressure control. An active low-vacuum warning is not permission to carry on lifting. Check the actual machine instructions, required indication and current fault condition.
What the changing number means
On a gauge-pressure display, −75 → −65 kPa means the vacuum has become weaker: pressure has moved closer to atmospheric pressure. The signed number increases, but the pressure difference available for suction decreases. These numbers explain direction; they are not universal operating limits.
Observed behaviour | Interpretation | Customer action |
|---|---|---|
Pump stops at the required condition, then restarts as pressure changes | This can be the intended pressure-controlled cycle | Compare with the documented machine behaviour. Record the readings and whether an alarm accompanies it. |
Alarm remains active or returns during a lift | Required vacuum or warning conditions need investigation | Follow the machine’s safe-response procedure; do not complete another lift just because the pump runs. |
Starts become more frequent than before | Contact, leakage, supply, configuration or control behaviour may have changed | Record what changed and use the contact/air-path checks. Frequency alone does not prove pump failure. |
Green display or OUT1 indicator is on | A configured display/output state | Do not treat colour or OUT1 alone as a lifting-ready signal. Confirm what it controls on this machine. |
Why not set every machine to −65 / −75 kPa?
A supplied service note shows this pair, but does not establish the full range of machine models to which it applies. Other equipment instructions describe different control arrangements. A pressure-switch manual also contains component defaults, which are not the completed machine’s commissioned settings.
Identify the machine serial number, installed switch, output mode and approved settings together. Changing a threshold can make an alarm disappear without correcting a leak or restoring lifting capability. Do not copy a demonstration value, reset the switch or change output logic to silence a warning.
Only reaching about −66 kPa at a high-altitude site
A supplied customer exchange records a site at about 2,500 m and a report of approximately −66 kPa against a −75 kPa target. This is an investigation example, not a validated correction or proof that the pump was faulty.
At higher altitude, local atmospheric pressure is lower. NASA’s standard-atmosphere model gives roughly 75 kPa absolute pressure near 2,500 m. Actual weather and site conditions vary. A gauge vacuum near −75 kPa would then approach the local physical limit, leaving very little absolute pressure. This explains why a sea-level target can be unsuitable; it does not establish a safe alternative threshold or payload.
Record the site altitude, gauge units, machine/pump identification and the reading reached. Supply checks under operation belong to a qualified technician. Site-specific suitability and any setting or load change require the machine supplier’s assessment. Do not simply lower the alarm setting until it stops.
NASA atmospheric-pressure model
What to record before changing anything
Record the reading when the pump stops, when it restarts, and when the warning appears; include units and whether the load was supported. Use existing observations only—do not induce a loaded fault for a recording. Add the switch nameplate and any change of workpiece or site.
Prepare a useful service record · Identify your pressure switch