Like Offroad, I've installed numerous ones of them myself, several of the last ones were a different make other than Roda, basically were some kind of copy still utilizing the swinging hockey puck type valve. The newer ones available now are electric controlled, these are the ones Offroad referred to having the butteryfly valve, and are much more compact. Brother showed me his on his new vac truck he rigged up, have to admit, those newer ones are pretty slick compared to the older Roda.
As far as installing it, it is desired to install it in the intake air stream as close as possible to the intake manifold, preferably right before it. The idea being, if and when it is tripped, any hoses between it and the manifold are going to be collapsing, and it is possible even when clamped properly to pull a hose right off, rendering the system useless. There is incredible suction created when activated at high speed. Any I installed, most the air valve or cable to activate it, was installed as that it could be reached from the ground reaching thru the door. Not sure if this is an actual requirement or not, but its a good idea IMO.
I have never actually had to use one for its intended purpose, used to be commonplace to have demonstrate you had one and actually prove it worked when first pulling on a lease. As mentioned, the older ones were known to occasionally trip, usually with the unintentional help of the driver, I couldn't say how many times I got called out to travel to a dead truck on the side of the highway, tip the hood, reach up in the dark and pull the lever till it clicked then tell the driver "try it now". Guess that says something about the caliber of the modern truck driver
