A couple other things we might want to be aware of is the governing system's reaction to the filling of a tank while set in the pressure mode as opposed to RPM. Not an issue with the older style PRV... but newer governors can be finnicky.
Kuh could probably explain the dynamics better- but when you open an otherwised closed circuit (or at least a "controlled open" circuit) by opening the tank fill / recirc valve ceompletely, you're essentially creating a loop that can't be pressurized efficiently. If the tank fill is opened too much, this will cause the governor to react by increasing RPM (as if another discharge was open). Of course, the truck is just going to keep increasing RPM until the pressure balances out- and that could take a lot of revolutions because you created a wide open loop!
I got into the habit of switching over to RPM for the short time it takes for me to fill up the tank. I'm paying attention to the gauges anyways, so I can keep a pretty close eye on things if pressures start to change.
Alternatively, don't open the tank fill too far and you should be able to avoid this problem. Kind of tough to "tickle" the valve when operating at higher pressures.
I also didn't see any mention of foam- I know in some cases folks still batch mix their tanks as necessary in older trucks. Also, round the pump foam proportioners can have some pretty unpredictable results with recirc. You'll know if you have erred if you see the water tank that used to be half full or less is suddenly full (with no incoming water) and bubbles lifting your top fill cover up.
Of course, an additional concern with the governor in pressure mode is that flowing bubbles is going to be causing some really tough pressure problems that could cause the engine to run away again. We use the Husky 30 and 300 from Pierce and have been reasonably satisfied with their performance. The injectors are at each discharge just before the connection to the hose so it won't allow for you to recirc solution. In one case there was an actuator that wasn't closing properly and we were having a number of problems with foam entering in the water tank and falling victim to the bubble buffet.
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04-10-2009, 09:09 PM #21
Last edited by Eno305; 04-11-2009 at 10:18 AM.Ian "Eno" McLeod
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