The chill system I am working with here consists of three 1985 Mc 048s with the evaporators in series. Yeah, I know, but that's the way it is. Single pass evaps.
I was called upon to investigate why there is excessive DP across the first two evaps, but not the third. No problem, I thought to myself, this should be simple. I'll just use one gauge to measure pressures in and out at each evap. The gauge ports are all within two feet or so of the inlets and outlets.
No pete ports, just places for gauges that can be valved off from the system.
First I verified the report, and yes it is true. One PACO pump drives the loop, and the nameplate is 460 GPM @ 75'. The DP on the third one matches the original install DP specs and is at almost twice the nameplate GPM of the pump. The pump is currently running at almost 100' of head, so unless I'm losing my mind, it's actual flow should be considerably less that the 460 GPM @ 75' figure on the nameplate. The DP on the first two evaps is almost twice the original spec.
The next thing I did was to open up the evap inlet of the first unit. I expected some sort of restriction, like half full of crap, from what I saw on the pump head and the first two barrel DPs. But it's clean as a whistle. The inlet and outlet are 8 inch, and it's necked down to 6 inch within inches of either end of all three evaps.
So, after all this, I have to assume, at this point, anyway, that either there is a restriction I haven't found yet, or the pump has had the impeller replaced with a higher GPM impeller. Even that doesn't make sense to me.
The only other thing I can think of is the six inch piping, and that doesn't really add up, either.
So I left there today talking to myself but at least I wasn't saying "Huh?"
Any wild guesses, word of wisdom, and even ridicule would be appreciated greatly at this point. I'll be back there tomorrow to put the piping back together and get the system running, even with the mysterious DP numbers.
My credibility and sanity are both coming into question here.