A label is the cheapest and the most easily neglected part of a machine. A label that states clearly the earthing and the overpressure action gives the operator a basis for judgement before an accident happens; a label that is missing or out of date is the same as no label at all. There are several points on the machine that have to be labelled, and specific things each label has to state. They are described below in three groups.
The first label: earthing and equipotential bonding
This machine takes a three-phase 380V / 50Hz supply and has a total power of 72 + 5 kW; the cabinet also contains the heating circuit and the pump starting equipment, and during maintenance the hand comes into contact with the metal parts of the cabinet, with the pipework and with the valves on it at the same time. The earthing label has to state the position of the earthing point and its purpose, and that the enclosure and the pipework are at the same potential. Phase loss and phase sequence protection are standard on this machine, and they deal with the power supply side: with the phase sequence wrong the motor runs in reverse, and with a phase lost the motor keeps running undervoltage, which burns the windings. Neither of those two protections replaces the earthing; the labelling and the wiring each have to be done properly.
The second label: overpressure and automatic shutdown
The overpressure alarm with shutdown is the last action in the safety chain of the machine: when the pressure exceeds the set value the audible and visual alarm comes first, and the control system then cuts the power and stops the machine. The label has to state two things: what the alarm and the shutdown each do, and who to call and in what order to reset once they have occurred. Do not reset and start up straight after the overpressure protection has operated — overpressure usually has a cause, such as a blocked filter element, a valve closed in error or pressure trapped on the oil inlet side. Remove the cause before resetting, otherwise the same thing happens again.
The third label: high temperature
The heating temperature control range is 45–80 °C, with the upper limit pulled down to 70 °C when the water content is high. When the tank surface temperature is running near the upper limit, the temperature close to the tank wall is well above the ambient temperature, so there is a burn risk whenever a hand touches the tank, the pipework or the flanges during maintenance. The high temperature label has to give the highest temperature that can be reached and the positions where it applies, for example the tank, the pipework and the flanges, rather than a general caution about hot surfaces.
| Label | What it has to state | How it is used on site |
|---|---|---|
| Earthing and equipotential bonding | The position of the earthing point and the scope of its effect | Check it before wiring and confirm continuity once after earthing |
| Overpressure protection | The sequence of the alarm and the shutdown, and the reset method | Find the cause after it operates, then reset |
| High temperature | The highest temperature that can be reached and the positions where it applies | After shutdown, wait for the machine to cool down before touching the tank and the flanges |
| Rotating and moving parts | The moving parts such as the pump shaft and the fan | Before maintenance, confirm that the machine has come to a complete stop and is disconnected from the supply |
| Electrical data | Three-phase 380V / 50Hz, total power 72 + 5 kW | Check the distribution capacity and the switch rating before the machine is brought in |
The labels themselves have to be maintained
- The labels are part of the machine documentation; the serial number, the model and the date of manufacture belong on the same set of labels and should not be torn off individually after delivery.
- A label covered by oil or moved to a different position has to be restored; the position is easier to overlook than the content.
- If new connections, a new heating method or a changed temperature control range are added on site, the labels concerned have to be changed with them, and the change goes into the handover record.
- The content of the labels has to match the technical documents and the parameter tables; where the three do not agree, the actual configuration of the machine is the reference and the other two are revised at the same time.
- When replacing a label, do not write on the machine with a marker pen in place of a proper label, because oil and abrasion make the writing illegible very quickly.
A label is the only instruction manual on the machine that does not speak. What it has to say should be settled before delivery, rather than added after something has gone wrong on site.
