One of the most labor intensive maintenance efforts in a plant relates to the figurative care and feeding of pH and ORP probes and other electrochemical sensors. While many such probes are touted as “rugged,” they are actually quite delicate. Advertisements tout their rugged build quality, often suggesting that they have been “beefed up” by wrapping a “tougher” pH measurement element in a strong, protective housing.
While this may help with handling in transit and on site, the measurement method is still identical, but the supposedly tougher pH measurement elements often result in reduced sensitivity and slower response to parameter changes.
Toughness aside, no electrochemical sensor can report accurate measurements if it is covered in gunk and grime, but traditional cleaning approaches are time intensive and costly.
It’s a common task to remove and clean probes in industrial installations. This may be done on a preventative schedule basis, or only when the measurement is “acting up,” but the cleaning process is largely the same.
First, the plant control room must be informed that the measurement point is going offline. The process flow, or sample line from the main flow, is then shut off and isolated so the technician can physically remove the probe and carefully clean it.
In hazardous applications, protective clothing is needed, often including disposable gloves. Once cleaned, the probe is reinstalled and the measurement brought back on line by reinsertion into the process. But this takes time, and the process of uninstallation, cleaning and reinstallation can cause damage to the probe itself.
A safer and more efficient method of keeping the measurement on line is to install an automatic retractor and cleaning system.
Retracting and cleaning a probe by hand must be performed as infrequently as possible, due to downtime and the potential for equipment damage. However, a retractor can operate frequently—as often as every 15 minutes, if necessary!—to keep the probe clean and in operating condition.
Automatic retraction systems can work in conjunction with a probe’s electronic unit to provide seamless measurement to a remote control system. In addition to providing a more reliable measurement, the useful measuring life of the probe is extended, and the probe is protected from potential handling damage.
At the very least, a manual extractor can provide a safe and efficient means to pull the probe out of the process.
Exner Process Equipment manufactures a wide range of automatic and manual probe retractors that can be used in process conditions both benign and aggressive.
Typically installed directly on process vessels or into piping, the Exner EXtract series use either a pneumatic or manual rotary action actuator to insert the sensor into the process medium and retract it back into an integral cleaning chamber within the assembly. When retracted, the mechanism isolates the probe from the process fluid. In manual retractors, a safety interlock engages at each end of its travel to prevent further movement without depression of an “insert” or “retract” button on the housing. On automatic units, there are pneumatic and optional electrical feedback switches to indicate position. Whether automatic or manual, the insertion mechanism cannot be operated when no sensor is installed, and it is impossible to uninstall any probe while in the inserted position.
All EXtract housings have inlet/outlet fittings for cleaning and rinsing of the installed sensor when retracted from the process. Calibration solutions can also be introduced to the housing while the probe is retracted, allowing for in situ calibration and standardization of the sensor, all without interrupting process flow.
Advantages of Exner Extract Retractable Housings
- Greater reliability and confidence in the measurement
- Protects technicians from process material contact, with no need for additional PPE
- Dramatically reduces maintenance time
- Prolongs sensor life
- Manual or automatic operation versions
- Operate without process line shut down
- Integrated process scraper cleans probe as it is retracted
- Manual unit has position locking system with indicators
- No way to uninstall probe when inserted into process
- Automatic safety lock while sensor is removed
- Optional electrical position feedback switches
- Operates safely under high process pressures
- Immersion lengths up to 107mm
- Suitable for use in hazardous areas
- Wide variety of process connections
- Up to 16 bar / 230 psi and 140°C / 285°F
