WFI Loop Pressure Control Solved
Russ Bailey
A large pharmaceutical manufacturer needed to control 40 psi back pressure on a 3" WFI loop with 14 user drops. The loop had to maintain constant flow from the pumps and discharge to a spray ball in the return tank. It was decided that a back pressure control valve be located at the end of the loop close to the spray ball discharge to maintain the required velocity. The spray ball, however, created a rangeability problem for the back pressure control valve. At higher flows through the back pressure valve, the spray ball would create higher head pressures requiring even a larger CV from the control valve. The opposite was true under lower flow rates, essentially exaggerating the already demanding turndown requirements.
A Sanitary Jordan Control Valve was originally considered for this application; but in addition to a large turndown, speed of response time was also needed. Past experience in a similar system showed that the 14 user locations created rapid pressure changes that a conventional control valve could not keep up with leading to erratic control.
A Jordan 3" Mark 95 self operated back pressure regulator was ultimately selected for the application. The angle body design allowed it to be mounted directly on top of the tanks and response time was instantaneous. The Jordan sizing program and new droop calculation program provided very specific numbers for every scenario. This program shows exactly how much offset the valve would provide under various operating conditions rather than just an estimate. The system provided very stable control well within the pressure ranges that were needed and turned out to be less costly as well.
|
