4. Pressure Reducing Valve or Pressure Regulator
PRESSURE REGULATORS - MODEL APR
If the sample is to be measured at atmospheric pressure then valve 4A should be fitted and 4B omitted from the system. If the sample is to be measured at full line pressure and the exhaust vented to atmosphere then valve 4B should be fitted and 4A omitted from the system. If measurements are to be taken at less than full line pressure and the sample is to be returned to a part of the main line or vent, which is at a pressure higher than atmospheric, and the input to that line needs a controlled pressure, then both valves 4A and 4B should be fitted.