Checking protections of the main air compressors

Greetings! I continue to write articles on checking the protection of various mechanisms on a ship and this time we will consider the compressors of the starting air of the main engine. Usually, they are of no interest to inspectors, but there are exceptions.

In this article, we will consider the main protections of the main air compressors that directly concern electricians. Let's take Japanese TANABE compressors as an example.

What protections do the main air compressors have?

LO Low pressure - low oil pressure in the compressor. This protection stops the air compressor due to low oil pressure in the system. In our case, if the pressure is below one bar, the compressor shuts down.

Danfoss low oil pressure switch

To check, simply close the valve on the pressure switch and release the pressure from the sensor. For a more accurate check, you can use a calibrator (pressure pliers), set the pressure on the pressure switch to 1 kg (bar).

Checking the pressure switch with a calibrator (pressure pliers)

Video of checking the pressure sensor (pressure switch) with a calibrator

Video of checking the pressure sensor (pressure switch) with a calibrator

Air High Temperature - high air temperature in the compressor. This protection stops the compressor due to high air temperature. To check, heat the capillary with a calibrator to a temperature of 90 °C, the protection will be triggered, which will stop the compressor. When the temperature drops to 80 °C (differential 10 °C) and below, the compressor can be started. If you only need to check the protection circuit and it does not matter at what temperature, you can activate the test on the thermostat.

Compressor pressure and temperature sensors

Test on Danfoss thermostat

Danfoss thermostat

Checking thermostats with a calibrator

Video of checking a temperature sensor (thermostat) with a calibrator

Thermal protection - thermal protection of the electric motor. Stops the compressor electric motor in case of current overload. To activate, press or pull the "Test" button on the thermal relay.

Compressor control panels

Compressor control panel (thermal relay)

Danfoss air pressure sensors (pressure switches) for controlling automatic operation of compressors

4-20 mA transmitter for transmitting air pressure readings in the reservoir to AMS

Safety valves - safety valves on starting air reservoirs, as well as on compressors. These protections do not concern the electrician, but are very important, so it is worth knowing about them too. To check the safety valve on the starting air reservoir, it is necessary to start the compressor in manual mode and fill the pressure in the cylinder to 29.5 - 30 kilograms (bars). The safety valve will “blow up” and release excess air pressure.

Starting air reservoirs

Starting air reservoirs and safety valves

Safety valve

Video of compressors in operation

Video of compressors in operation

Thus, we have considered the main critical protections of the main air compressors. These protections must be checked at least once every three months according to PMS, and also be able to quickly demonstrate to inspectors.

If you need an electrical circuit diagram of this air compressor, then write in the comments to the article and I will post it as a separate file.

By the way, if you need instructions for the compressors that were discussed in this article (or any others, for example, GEA Bock, Atlas Copco, Deno, Sauer or BITZER), then all this can be found in our closed telegram channel Marine Engineering Manuals.

If you have any questions about the main air compressors or have something to share, please write in the comments to this article.

Thank you for your attention! I hope this article was useful for you!