Water Filter Changing Instructions

The goal is to provide filtered house water to the three diffractometer heat exchangers ("A,B", "C" and "D") with sufficient flow to carry away the heat from the X-ray tubes. Clean water filters are essential to maintaining a constant source of X-rays for an experiment and to preserving the life of the X-ray tube and generator. Note the sequence of events: dirty water filters --> reduced tap water flow through heat exchanger --> reduced heat exchanger heat removing capacity --> increased temperature of circulating water --> circulating pump(s) stop --> X-ray generator turned off.

Recent experience indicates that the water filters last about 1 month with the refrigerated heat exchanger ("D") and a week or two with the ambient heat exchangers ("A,B", "C"). The filters are arranged in parallel with a pair of valves to isolate each one; the procedure for a pair of filters for a given heat exchanger is (starting with two new filters and all valves closed):

• open both valves for one filter allowing water to flow through only one filter
• after one week ("A,B", "C") or one month ("D") open both valves for the second filter allowing water to flow through both filters
• after one week ("A,B", "C") or one month ("D") change both filters:
  • close both valves for one filter
  • place a bucket beneath the filter housing (to catch any drips)
  • use custom wrench to loosen filter housing
  • unscrew filter housing
  • decant excess water from filter housing into bucket
  • take filter housing with filter to large trash can
  • remove filter element from filter housing:
    • place two fingers into hole in filter element
    • spread fingers apart (to grip filter element from inside)
    • lift filter element out of filter housing
    • discard filter element into large trash can
  • rinse out filter housing in sink
  • get new filter element from shelf over "D" heat exchanger
  • ensure "O"-ring in filter housing is properly seated in groove
  • place new filter element into filter housing ensuring that hole in the filter element fits around the short centering tube in bottom of filter housing
  • fit filter element around short centering tube in filter housing base
  • screw filter housing onto its base
  • hand tighten filter housing
  • slowly open supply valve while watching thread area of filter housing for leaks; if leaks are found:
    • close supply valve, briefly open and then close other valve
    • cautiously tighten filter housing using custom wrench
    • check for leaks (and cautiously tighten filter housing and re-check for leaks, repeatedly, until no leaks
  • "burp" the water line of trapped air by opening supply valve and then briefly opening other valve and closing it and waiting a few seconds, repeatedly, until all air bubbles have passed through the filters and into the drain
  • close both valves
  • repeat this procedure for the other filter
  • leave both valves open for one filter, both closed for the other filter

Note that it is especially bad when the X-ray generator is turned off because of dirty water filters as the hot X-ray tube, which was running at full normal power levels and was experiencing only minimal cooling from the higher temperature circulating water, suddenly has NO cooling water flowing past its hot anode. These are the conditions (hot X-ray tube, no cooling water flow, and THEN the X-rays are turned off) which can result in a perforated/melted anode and an X-ray tube full of water!