NFPA 20, 10.10.12.1 requires an electric VFD fire pump controller to be set to lock out pump shaft critical speeds supplied by the pump OEM on vertical turbines. That probably should have applied to multistage, long shaft horizontals also like the 5 stage Peerless TUT fire pumps. VFDs typically have three to five "skip or jump" speed settings for this.

The pressure limiting controls on diesel engines appear to be an all mechanical (hydraulic, pilot actuated like a main relief valve) positioner fastened to the existing engines governor speed lever controls. There does not appear to be anything mentioned that I found in the literature that says you can do the same with skip speeds. The only way that I know would be an electronic positoner, the standard engine governor cannot be substituted for a electronic one per NFPA 20.

Does anyone know if these engines have the same ability as the VFDs or are people being careful not to put them on vertical pumps? I don't readily see where this is covered anywhere unless I overlooked something.

Meant to say TUTF, F as in fire pump version.

Jim,

Did this "fall through the cracks?"

Mike,

NFPA 20 2010: 7.5.1.6.3 addresses the requirement of the pump to perform "a complete mass elastic torsional analysis" on VFD applications for turbines. IS it getting done? ... I dunno, my pricing is always too high...

Tom,

The pump people have the critical speeds to give to the controller people to set the VFDs with. The unknown issue is - do the "variable speed" fire engines have the ability to program them out like the electric VFDs do? There is no mention of this in the governor requirements under NFPA 20, 11.2.4.3.1.

The largest majority of verticals here in Texas are found all over in the industrial locations, pulling from pits and are all diesel engine driven. I've never come across one of the variable speed engines but looked at the piping drawings on one as mentioned above.

It doesn't look like anything was done about the horizontals. I've personally witnessed a single stage rotating assy. "wobble" all over the place on a Schenk balancer coming down from full RPMs. This Schenk is a "soft-pedistal" balancer with rollers suspended on leaf springs.

NFPA 20, 7.5.1.6.3 was primarily for the pumps fixed operating speed design, +/- 25%. NFPA 20, 10.10.12.1 may require at least three separate speeds to be obtained.