Piston detectors for monitoring the progressive metering device
Piston detectors or cycle switches are used in central lubrication systems to monitor the correct functioning of the metering device. The function of the metering device is essential for the correct dosing of the lubricant and should be monitored continuously. A distinction must be made between main and secondary distributors. Main distributors are placed hydraulically after the pump to distribute the volume flow of lubricant to the secondary lines or directly to the lubrication points. Auxiliary distributors are used in complex systems to further distribute the mass flow of oil or fat. In progressive systems from SKF, for example, up to 150 lubrication points can be supplied with lubricant in succession.
There are a few points to consider when choosing the right piston detector. First, the type of lubrication system plays a role. Progressive central lubrication systems work differently from circulation systems, which is why the control of the metering device must be adjusted accordingly. It is also important to note which type of metering device is used. While progressive metering devices supply the lubrication points with lubricant one after the other, the volume flow in single-line systems is divided simultaneously at time-dependent intervals.
Piston detectors in progressive central lubrication systems
Cycle indicators like the model of the type VPx-ZY are suitable for progressive metering devices in the SKF ProFlex system and monitor the correct function with the help of an indicator pin. This pin is attached to the piston bore of the first or last disc on the manifold and registers each cycle by moving in and out once. If the metering device is not working properly, for example because it is blocked, the piston detector will no longer move. With progressive systems, stroke control is comparatively simple because the lubricant is distributed one after the other and only a single piston needs to be monitored.
The 177-300-09x cycle indicators are also used in progressive lubrication systems and act as NC contacts with NC contacts. The proximity switches work with an operating voltage of 10 to 26 V DC and can be loaded with up to 100 mA current. Thanks to the robust construction, the piston detector can be used at pressures of up to 350 bar and in a temperature range from -25 to +80°C. The model is available in two and three-pole versions. With the VP-ZYS models, cycle switches with built-in microswitches are also available. These are equipped with a changeover contact and work with a nominal voltage of 230 V.
SKF metering devices with a monitor are used for SGA and SG metering devices in two-line centralized lubrication systems. These record the movement of the dosing piston and send an output signal using a potential-free relay connector.
Electrical pressure switches can also be used to monitor the metering device function. These are equipped with an overpressure safety device with a rupture disc and give a visual or acoustic signal when a certain pressure is exceeded or automatically switch off the system.