When calibrating or testing a gauge or transducer with a pneumatic pressure controller you should protect the controller from any liquid contaminants that may be present in these devices under test (DUT). A block and bleed valve (BBV) in-line with a coalescing filter is a good way to do that.
The potential flow of containments is from the DUT to the controller. A BBV and a coalescing filter, oriented as observed in the diagram above, will to work to avoid contamination. The BBV can be used to purge the bulk of liquid from the DUT. The coalescing filter is really a backup to remove any residual liquid that may be present even after the initial purge and can separate entrained liquid droplets from gas flowing in the direction of the controller. The next procedure was created to prevent damage to a pneumatic pressure controller from a contaminated DUT.
Purge the DUT of liquid containments
Before connecting the DUT to the system, remove just as much liquid as possible from the DUT.
With the controller power off and both the block and bleed valve closed, connect the machine as shown above.
Use the controller to apply a pressure close to the full scale pressure of the DUT.
pressure gauge 10 bar to pressurize the DUT (note: the gas will flow in direction of the controller to the DUT ? high pressure to low pressure).
After the system is pressurized close the block valve.
Open the bleed valve and detoxify the system to atmospheric pressure. Take notice of the sump to see if any liquid is purged.
Close the bleed valve.
Repeat steps 3 to 7 until no more liquid is observed appearing out of the system.
With the block and the bleed valves securely closed, vent the controller.
After completion of the above procedure it should now be safe to calibrate the DUT. To calibrate, open the block valve and close the bleed valve. The coalescing filter will coalesce (join together) any liquid droplets that could still be within the gas, and gravity will draw the liquid to underneath of the filter housing. diaphragm seal may also remove particles bigger than the specified size. ไดอะแฟรม computerized or manual valve could be attached to underneath of the filter housing to periodically drain any liquid which has accumulated.
Note:
1. The coalescing filter will not protect against a large slug of liquid that fills the housing and is forced through the filter membrane or liquid vapor.
2. The gas used to calibrate the DUT can flow in either direction within this system.
3. You will see a pressure drop over the filter in the flowing condition; at steady state pressure there is absolutely no pressure drop.