Maintenance
Figure 4 . Sectional drawing of a proximity switch on a spring loaded valve .
individual components , leaky and destroyed valve disks , and valve seats getting damaged from chattering . Valve chattering describes the rapid , repetitive opening and closing of a breather valve . It occurs when a valve disk oscillates between its open and closed positions due to fluctuating fluid pressure or flow conditions in the system . Proper breather valve design , sizing , and control are crucial in preventing valve chatter and ensuring smooth and reliable operation of the system . Another cause could be a valve getting stuck in the open position due to pressure surges or improper commissioning , where transport locks have not been removed . Additionally , heavy contamination can hinder proper valve closure . The presence of polymerising substances in the application can lead to deposit formation or sticking on the valve disk . This , in turn , may increase the set pressure for weight-loaded valves and delay the opening , posing a threat to the system ’ s safety . To counteract these challenges , we recommend the use of proximity switches for valves . These systems enable real-time monitoring of the valve ’ s status during operation , providing valuable insights into their performance and conditions . In general , each valve requires an increase in pressure above the set pressure to achieve full opening , with the valve disk always guided during the process . As the valve opens , the valve disk and valve spindle move upwards . Once the highest point of the spindle reaches the position monitoring system ( located outside the valve body in the case of weight-loaded valves ), the proximity switch emits a signal indicating that the valve has opened and is now in the open position . If the pressure drops , the valve closes again when the closing pressure is reached . The valve disk descend onto the valve seat and the valve spindle moves away from the proximity switch , and again , the signal is emitted that the valve is now closed . These proximity switches are used with both weight and spring-loaded valves and can also be used in ATEX zones . The difference in
Figure 5 . KITO ( R ) EFA-Det4-IIA-300 / 150-1,2-T , detonation arrester ( type 4 ) with differential pressure measurement system .
position monitoring between weight-loaded and spring-loaded valves lies in the placement of the proximity switch . In case of the spring-loaded valve , the proximity switch is not mounted on top of the spindle ; instead , it is positioned at the lowest point of the spring inside the spring housing .
The challenge of monitoring flame arresters
Contamination and subsequent clogging of the flame arrester is a potential cause of failure , leading to an increase in pressure drop . To obtain real-time information on the degree of clogging inside the flame arrester , we recommend utilising a differential pressure measurement system . The pressure transducers are mounted on both sides of each half of the device , both before and after the actual flame arrestor unit . Upon installation , the pressure loss is measured under clean conditions . Subsequently , if the pressure loss increases due to clogging , the differential pressure measurement will detect and record the rise in pressure drop . A maximum pressure drop must be defined by the operator . Once this limit is reached , the flame arrester should be cleaned to ensure proper functionality and safety . Another danger arises from the possibility of short time ( stabilised burning for a specific period of time ) or endurance burning ( stabilised burning for an unlimited period of time ) that can occur in certain systems ( e . g ., vapor combusting systems , flare and incineration systems and burners ). Regular approvals in the area of deflagration for in-line deflagration- and detonation arresters of type 4 ( according to EN ISO 16852 ) are covering stabilised burning for a short time period ( called burn time ) of one minute . If this burn time is exceeded , the flame arrester can no longer provide protection . The heat input into the flame arrester becomes too high , causing it to heat up and reach the auto-ignition temperature of the substance on the protected side of the device ( the side where the system to be protected is located ). This leads to the mixture igniting by itself without
Figure 6 . KITO ( R ) EFA-Det4-IIA-300 / 150-1,2-T , detonation arrester ( type 4 ) with temperature sensor .
any external ignition spark . If , during the safety assessment , it is determined that short time burning with a burn time exceeding one minute or an endurance burning may occur , temperature sensors must be employed to detect potential fires . The temperature sensor should be installed on the unprotected side of the device , where the flame is suspected to emerge or where the ignition source is present . In addition , a name plate is essential to ensure that the flame arrester is installed correctly in the pipeline . This prevents the possibility of installing it the wrong way around , which could lead to the temperature sensor being accidentally placed on the protected side . Such an error would result in delayed flame detection , potentially exceeding the allowed burn time and causing the flame arrester to fail . Bidirectional flame arresters cannot be used symmetrically for any longer in case the short time burning only functions from one direction or is actively monitored with a temperature sensor when a corresponding risk assessment requires it . A second factor to consider is the response time of the temperature sensor . The temperature sensor ( s ) must be integrated into the process control system of the plant so that when the sensor detects a critical temperature rise , countermeasures can be automatically initiated . According to the standard , the temperature sensor has a window of 0,5 x burn time of the device , 30 seconds in this case , to emit a signal . However , in practice , the signal is often emitted much faster than this timeframe . Countermeasures must be taken automatically within the remaining burn time , at latest when the burn time ends , such as shutting off the fuel supply , inerting with air , steam , nitrogen , or other substances , or rerouting the stream as well as shutting off the pipeline completely . In demanding applications , intelligent measurement technology for safety devices can not only minimise maintenance intervals , maximise system availability but also prevent unplanned downtimes . This enables operators to plan maintenance work over long term and carry it out cost-effectively .
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