There are a number of possible causes that can result in a Distribution Leak error while calibrating the Whole Body Plethysmograph. However, the most likely cause will be the variable valves that control the bias air flow through the chambers. Potentially these valves can become contaminated due to particles in the chambers being drawn into the system while in pull bias flow mode.
During calibration, the system is pressurized such that air bubbles can be seen coming from the center tube within the calibrator. This pressure is then held for a few seconds to establish that there are no leaks. If the water level rises from the bottom of the tube by 1 cm while the pressure is being held then a Distribution Leak error will be displayed.
If any site valve does not close properly, air will escape from the associated bias flow port, through the in-line filter and out through the animal chamber. To test which port is leaking it is necessary to block the port to see if the Distribution Leak error disappears. There are a number of ways this can be done; a simple solution is to use the in-line filters supplied with the WBP system and seal one end. Below, the tubes have been sealed with silicone sealant. Any filter can be used, even old ones as no air will pass through them during calibration.
The first step in testing is to make sure that the tubing and connections to the calibrator are secure. Connect an animal chamber to site one and plug the remaining ports using the above filters, calibrate site one. If the calibration completes successfully we know that site one is working correctly and the leak must be in one of the remaining ports. Now plug site one, connect the animal chamber to site two and calibrate that site, leaving the remaining ports still plugged. Continue to test all sites until the Distribution Leak error appears, the site where the chamber is connected will have a faulty valve.
If when calibrating the first site the Distribution Leak message appears, you should plug that site and continue to test all the others as there may be more than one faulty site/valve. If the Distribution Leak error appears when all individual sites are tested it means either that all valves are faulty (unlikely) or that there is a leak elsewhere. In this case contact DSI support for further assistance.
Solution: Valve replacement
Having removed the top cover of the WBP controller the yellow variable control valves can be seen mounted on top of the distribution manifold. Site 4 is difficult to see as it is obscured by the gas inlet valves and tubing.
The valves are relatively easy to replace, they are secured by two screws and are supplied with the necessary connector. Care should be taken to ensure that the two small O rings are correctly positioned between the valve and the manifold when refitting. Replacement valves can be ordered using part number, 601-4002-001.