How to install the compressor shaft displacement probe? Issues to note during installation

This is how we do it: after testing the displacement probe with TK-3, we determine a working voltage within a linear range; generally, 10V is used as the zero voltage (this applies to Bentley’s products; I haven’t used other brands). When installing the probe on the compressor, insert it carefully until the output voltage of the transmitter reaches 10V, at which point stop inserting it. Then secure the back cap of the probe, and if the voltage remains stable when measured again, that’s fine.

To monitor the axial position of the compressor rotor and alert the user when necessary, an axial displacement sensor is installed in the compressor. This sensor operates on the principle of eddy currents and is mounted on the side of the thrust bearing. If the thrust bearing fails to function or the shaft displacement exceeds the set alarm value, the shaft displacement sensor will also trigger an alarm; if it exceeds the shutdown value, the compressor’s drive motor can shut down automatically. Four vibration probes are installed in each cylinder of the compressor, two on each side at a 90-degree angle to one another. These probes operate based on the eddy current principle; if the vibration of the compressor rotor exceeds the set alarm threshold, the vibration probes will trigger an alarm. If the vibration levels exceed the shutdown threshold, the compressor’s drive motor can shut down automatically. In the latter case, a time delay is used by the relay to ensure that short-term vibration peaks during compressor startup do not cause an accidental shutdown.

How to install the displacement probe is not a problem for the instrument. On the contrary, before installation it is essential to clarify at least the following issues first: 1. Shaft alignment: After the unit is installed, the data regarding the shaft alignment is very important; it must be determined through repeated and precise measurements by maintenance personnel, as it forms the basis for the installation of the probes. If this data is incorrect, everything that follows loses its meaning. This critical parameter of serial data must be confirmed simultaneously by the maintenance team, the instrumentation department, and the process engineering team; if necessary, this confirmation process should also be supervised by the higher-level management authorities. 2. Which end the shaft is directed to: the zero position is determined. When installing the probe, the instrument operator must be clear as to which end the shaft has been directed to – that is, whether it has been directed to the main thrust end or the auxiliary thrust end – this must be absolutely clear. Only in this way can the zero point position be determined. 3. How many probes are there: There’s no need to explain this; it’s obvious. 4. Displacement interlock logic: Before installing the probe, it is essential to have a thorough understanding of the displacement interlock logic, including whether there are backups available and whether it involves single-point or multi-point interlocking. 5. Proper handling of the above points is very useful for future maintenance, as it can help avoid mistakes. The summary above may not be comprehensive, and we hope everyone will actively participate.

One more thing to add: ensure proper sealing at the installation site to prevent oil leakage

Our facility recently encountered a situation where the shaft of the high-pressure water pump experienced a displacement that exceeded the interlock threshold, causing the pump to shut down automatically. In this case, either of the two displacement sensors detecting such a displacement would trigger the shutdown once the value exceeded the threshold for 3 seconds. When installing the probes, we worked together with the mechanical staff. They specified that the maximum allowable gap was 500; they pushed the shaft towards the main thrust position, and we installed the probe at the value of 250 as indicated by the upper-level monitoring system. After fixing the probe in place, they pushed the shaft towards the secondary thrust position, and the probe then showed a value of -250. The readings from both probes were pretty similar. However, as soon as the machine is started, the displacement measurement reaches the alarm value and fluctuates around that level; the measured value gradually increases until the machine shuts down due to interlock protection. We have tried this more than 3 times, each time reducing the positive value to within the allowable range, down to 100, but the machine still shuts down after running for a little over an hour. Today, with the supervision and assistance of management and other staff, we adjusted the settings again, and we will try to start the machine again next Monday. I would like to ask those with experience: why does the rotor always move in the direction of thrust during startup? The maximum measured value for thrust is 250. I seek advice from experienced technicians.

What is the main shaft and what is the auxiliary shaft? We use Hangqi turbines; during maintenance, I saw the technicians pulling them back and forth. How is the clearance between them calculated? Could you explain it with an example?

The steam turbines in Hangzhou are relatively small units, used for waste heat boilers!

Regarding what the original poster said, actually installing a displacement probe is quite simple: 1. Obtain a probe that has passed the quality checks; 2. Have the mechanical team determine the maximum amount of movement of the shaft, and position the shaft in the middle; 3. The technician then installs the probe and adjusts the gap between the probe and the shaft. Once the voltage at this gap reaches the zero voltage level, the probe is fixed in place. (I have used both Bently and Pallis probes, and the zero voltage for both was 10V.) Note that the gap may change when fixing the probe, and it usually takes several adjustments to get it properly fixed.

The issue on the 6th floor is indeed quite profound and meaningful; I hope more people will pay attention to it