Rosemount 400A running with “odd” pressure settings

Some of the activities that we perform on your analyzer include replacing the restrictors (and/or capillary).  We’ve adopted the “Teledyne API” method of installing good restrictors but not ‘exact’ restrictors.  By that I mean, we buy restrictors that meet a small tolerance range, but each restrictor behaves just a little different from the other.  So rather than toss out restrictors that are not EXACTLY on target, we install them in your analyzer, adjust the upstream source pressure to achieve the desired results, and then create a label (or placard) that says what pressures we tuned the analyzer to.

Let’s do a “for instance” discussion.  So, under the old way of thinking, the 400A had to run at 15 psig for air, and 25 psig for fuel.  When it wouldn’t light or stay lit at 25 psig fuel, you blamed the restrictor(s) (logically), and ordered a new one for about $500.  Under “our” way (the Teledyne API way), your analyzer can operate at any pressure that works easily with the physical characteristics of the restrictor that is installed.  AND, we’ll give you assistance to adjust the baseline pressure when the restrictor begins to show signs of fouling.  Case in point:

  • Your 400A needs to be serviced
  • You send it to RIGAS for repair / overhaul
  • We find that:
    • the air restrictor flows weak at 400 cc/min @ 15 psig but flows at specification at 18 psig . . . we’re not going to replace this working restrictor
    • the fuel restrictor flow weak at 60 cc/min @ 25 psig but flows at specification at 30 psig . . .  this is the top end of your pressure gauge so we need to replace the restrictor
  • We install a new fuel restrictor that performs nicely at 20 psig
  • We calibration your analyzer at these new pressure values:
    • air = 18 psig
    • fuel = 20 psig
  • we affix our calibration sticker
  • we affix our optimized pressure settings sticker (that says that these numbers override the OEM’s numbers from the manual)
  • We send your analyzer back to you . . . and it performs marvelously for five to ten years

During those five to ten years, your restrictors are going to age (i.e., foul; flow less at a given pressure); you don’t need to send the analyzer in for servicing, just do this:

  • add a little air if necessary
  • add a little fuel if necessary
    • on this one, look at burner temperature.  We usually find that 60 to 120 mV on the Flame Temperature signal works best.  60mV is hot but not too hot.  120mV is a somewhat cool flame temperature but not too cool.
    • And if you’re wondering, the flame safety circuits (some call it “flame confirmation”) trip at 1000mV as it heats up and 1200mV as it cools down

Keywords: Rosemount 400A troubleshooting