A fire department pumper arrives new from the factory perfectly capable of flowing its rated pump capacity. Sometimes, the fire department choses to affix various intake fittings that in the end actually reduce the pumper's flow capability because of restricted orifices in the fittings. This situation becomes most problematic when choosing to leave the fittings in place during drafting operations. Attaching a 30-degree turn down elbow (5"Storx x 6" NST) to a pumper's suction inlet might be a great idea to speed up supply line operations, but it also could be a bad idea if that fitting is left in place for drafting.
While delivering one of our rural water supply operations seminars in New Hampshire earlier this year, one of our website members, DC Matt Cole of the Chichester FD provided two samples of intake adaptors with markedly different orifice sizes. Looking at the two fittings, we clearly expect some flow restriction to occur. How much? Well... we can only determine that through a flow test. Thus, if you operate with external fittings on your pumper's intakes, leave them in place during your next annual pump service test so that you can quantify their capabilities.