Double Diaphragm Seals With Diaphragm Monitoring System

Unforeseen process disturbances can damage or even destroy the isolating diaphragm. If a seal with only one diaphragm is used, then the fill fluid will find its way into the process. As the process operators are not warned of diaphragm failure, large amounts of product can be contaminated. Therefore the process operators are required to remove all pressure-measuring instruments from the process after every batch to check the diaphragm for possible damage. If no failure of the diaphragm has occurred, only then can the product batch be released for further processing. On the other hand, in the case of diaphragm failure, the contaminated batches have to be quarantined or discarded. Because of the time delays, unplanned shutdowns and product contamination due to failure of the diaphragm in single diaphragm seals, a more advanced design was required to avoid all these problems. Therefore, a double-diaphragm seal annex diaphragm break-monitoring system has been developed.

In a double-diaphragm seal, the space between the two diaphragms is evacuated, and in this manner a vacuum is created between the two diaphragms (Fig. 7.90). The pressure in this space is continuously monitored with a pressure gauge, pressure switch, or pressure transmitter (Fig. 7.91). If for any reason the primary diaphragm fails, the vacuum is compromised (so, pressure increases), and the monitoring system alerts the process operators by giving a visual, acoustic, or electrical warning. Although the wetted

(A) Double-diaphragm seal

FIGURE 7.90 (A) Double-diaphragm seal: vacuum is created between two intact diaphragms.

The pressure in this space is continuously monitored with a pressure gauge, pressure switch, or pressure transmitter. (B) Wetted diaphragm breaks but the second still forms a reliable seal for the process. The space between the two diaphragms is no longer under vacuum. The monitoring system alerts the process operators by giving a visual, acoustic, or electrical warning. Courtesy of WIKA Alexander Wiegand SE & Co. KG.

Diaphragm monitoring system

FIGURE 7.91 Diaphragm monitoring system. With regular on-site inspection, a pressure gauge with green-red display will be sufficient to detect failure of the diaphragm in contact with the process. When the pointer goes in the red (right corner of the diaphragm monitoring device), the operator knows that the diaphragm in contact with the process is broken. Courtesy of WIKA Alexander Wiegand SE & Co. KG.

diaphragm is damaged, the second still forms a reliable seal to the process and maintains the pressure monitoring until the damage has been rectified. So, there is no need to stop the process immediately to make repairs. As the process integrity is not affected when the first layer of protection (wetted diaphragm) fails, the food manufacturer is not required to stop immediately. Using a double-diaphragm system can thus prevent unplanned shutdowns.

Calibration of Pressure Gauges and Pressure Sensors

Pressure gauges and pressure sensors require scheduled, periodic maintenance, and/or recalibration. Pressure transducers can be recalibrated in a calibration laboratory or online.

 
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