• Initially set up a system (MS Word document)
• Change temperature control settings
  – press the “index” button until the display alternates between “sp” (meaning set point) and a number (whatever the current set point is); it probably only will need to be pressed once
  – adjust to the desired set point using the up and down arrows
  – press “enter” to accept the new set point (important!)
• Isolate leaking valve (if low pressure test indicates that a valve is leaking)
  – best to avoid doing this procedure during cal cycle
  – use PC208 to bring up graph of pressure as a function of time, on a scale in which the leak is apparent
  – manually close all valves using switches on relay controller
  – close the main tank valves on all the tanks
  – starting at one end, remove tubing leading into enclosure for each tank (one at a time), observing the pressure change; the pressure will cease to increase when the line leading to the tank with the leaking valve is removed
  – reattach all tubing, return switches on relay controller to automatic, and open the main tank valves on all the tanks
• Change leaking valve
  – unscrew screws on leaking valve
  – remove wiring unit from leaking valve by pinching
  – attach wiring unit to new valve
  – attach new valve to manifold using screws
• Replace pump
  – Make sure to replace clear Bevaline tubing (Failure to do so will cause large leaks not detected by pressure tests!)
• Leak test regulators
  – Open tank
  – Adjust delivery pressure to around 10 psi
  – Close delivery pressure
  – Close tank
  (If there is a leak, the delivery pressure will decrease fairly quickly, but the tank pressure needs to show no change over several hours.)

Note:  Volume of 1/8″ OD (0.085″ ID) stainless steel tubing / length = V/l = 3.7 cc/m
Volume of 1/4″ OD Synflex tubing is about 14.6 cc/m. (March 2011)

Note:  When we had a valve leaking at a rate of 1 kPa/min with 40 ppm difference between the target and (leaking) cal gas, the error noticeable in the target tank was ~0.5 ppm.  So error induced by leak rate of 0.05 kPa/min is ~0.03 ppm (depending on difference between leaking gas and sample).

Note:  Nafion driers require over 8 hours to sufficiently dry (figure)