Effect of Low Starting Voltage on the Required Water Pressure
Effect of Low Starting Voltage on the Required Water Pressure
(OP)
Can any mechanical engineer tell me what would be the effect (if any) of low starting voltage of an electric fire pump on the required water pressure? As you may know, the motor torque will drop in a squared amount as the voltage drops. Do you compensate for the drop in the initial water pressure drop? Any input in this matter is appreciated.





RE: Effect of Low Starting Voltage on the Required Water Pressure
Make sure you meet the voltage drop requirements of NEC 695.7.
RE: Effect of Low Starting Voltage on the Required Water Pressure
Low voltage will increase acceleration time at the very least.
As peebee said, fire pumps require special consideration and the applicable Codes give little flexibility for creative engineering.
RE: Effect of Low Starting Voltage on the Required Water Pressure
Yes, it will take a little longer this way for the water to get up to pressure. But even with full-voltage starting, there's a finite period of time required for the water to ramp up to pressure. They're both OK, and no, you don't need to compensate for that ramp-up time by any other means with either starter.
RE: Effect of Low Starting Voltage on the Required Water Pressure
Also, after reviewing the UL standard used for listing of controllers (UL 218), you will find out that the standard (and its listing)does not evaluate the effect of a voltage drop on the controller and it's impact on the fire pump motor. I imagine the reason is that the listing only looks at the controller as a stand-alone equipment rather than its role in a mechanical system.
RE: Effect of Low Starting Voltage on the Required Water Pressure
You mentioned soft-start -- if you're talking about a solid-state soft motor controller, I don't believe such controllers are listed for use with fire pumps, but I could be wrong. If anyone knows otherwise, please clue me in. I believe most reduced-voltage fire pump starters are autotransformer type or some other "old-fashioned" induction type. Anyone who's ever used a computer realizes that the last thing we need is a digital control system in charge of life safety equipment (how many people will I piss off with that one?!?). KISS (Keep It Simple Stupid) is the name of the game in life safety.
RE: Effect of Low Starting Voltage on the Required Water Pressure
1. Firetrol, INC
2. Hubbell Industrial Controls, INC
3. Joslyn Clark Controls, INC
4. Master Control Systems, INC
RE: Effect of Low Starting Voltage on the Required Water Pressure
RE: Effect of Low Starting Voltage on the Required Water Pressure
As far as I understand (I am not a mechanical engineer) the water line is constantly under water pressure. The reason for using the fire pump is to make sure that the required discharge pressure at the last sprinkler head is not less than a specified value (I guess 65 PSI). You may want to use the analogy of comparing the fire pump system to that of an electrical distribution system. Under all conditions of operation there is a set magnitude of voltage present at an electrical service (like the water pressure at the pump), upon turning on an equipment (activation of a sprinkler head) there would be voltage drop in the line ( drop in the water pressure due to discharge and flow resistance), if the voltage magnitude is below the rating of the equipment, it may not operate (lack of water pressure would not provide the required water coverage).
So, if we don't have enough water pressure (i.e., low voltage to begin with), would there be a problem or would they blame it on the electrical designer that did not give them the required torque as they thought it should have been there to begin with?