I have a fairly oddball situation and have racked my brain over it for a while now. The situation is thus. 1.5 hp motor. It feeds a pump. This pump in turn feeds water to a waterjet cutter. The purpose of the 1.5 hp pump is to feed clean water into the waterjet. However, the waterjet does not always need the 1gpm of water the pump supplies - for instance when it is traversing it will shut off the high pressure valve, so water use drops to 0.
The decision tree is thus:
Option 1 - Leave the 1.5 hp motor running constantly. Do nothing. Constantly run water from the pump and at times water would not flow. This is bad for seals, etc. There is a chiller in play to avoid excess heat build up but it still seems like a bad idea.
Option 2 - Leave the 1.5 hp motor running constantly. Flow restriction via a pressure compensating orifice on the outlet. This would feed up to 1 gpm to the high pressure pump and then dump the rest back to recirculate. This is obviously a fairly easy solution.
Option 3 - Do not run the 1.5 hp motor constantly. Tap into the solenoid that triggers the nozzle (thus starting a demand for water) and also tie in one of those 20+ gallon well water tanks that supplies pressurized water and allows well pumps to "rest" and not run constantly when you only need a half gallon of water. When the pressure of this tank drops to a set amount, run the 1.5 hp pump and cut it off when the pressure reaches another set level. Simple, right?
Here is the question. I know inrush currents can be 3 - 5 times (or more) of the FLA. This is a 3 phase 480V motor (although I don't know if that makes a difference here). Would it be wiser from a total cost to run perspective to turn the motor off when not needed and then turn it back on to recharge the holding tank or would it be wiser to just run the pump constantly, probably under option 2 so the seal life is maximized? I suppose the size of the pressure holding tank comes into play. Assume the waterjet cuts 80% of the time and traverses 20% of the time. It may be as high as 90/10.
We have some large 5 hp blowers that when you close the blast gate on, pull nearly no amperage draw. My understanding is that it is more economical to leave it running but not under load than to start the entire motor again (momentum - a motor already started needs a lot of power to start up but not much to maintain running).
Anybody care to chime in with some practical considerations or issues I have possibly not addressed? Short of putting an amp meter on the motor, I don't have a clear answer what is "best" in terms of lowest cost to run over time.
The decision tree is thus:
Option 1 - Leave the 1.5 hp motor running constantly. Do nothing. Constantly run water from the pump and at times water would not flow. This is bad for seals, etc. There is a chiller in play to avoid excess heat build up but it still seems like a bad idea.
Option 2 - Leave the 1.5 hp motor running constantly. Flow restriction via a pressure compensating orifice on the outlet. This would feed up to 1 gpm to the high pressure pump and then dump the rest back to recirculate. This is obviously a fairly easy solution.
Option 3 - Do not run the 1.5 hp motor constantly. Tap into the solenoid that triggers the nozzle (thus starting a demand for water) and also tie in one of those 20+ gallon well water tanks that supplies pressurized water and allows well pumps to "rest" and not run constantly when you only need a half gallon of water. When the pressure of this tank drops to a set amount, run the 1.5 hp pump and cut it off when the pressure reaches another set level. Simple, right?
Here is the question. I know inrush currents can be 3 - 5 times (or more) of the FLA. This is a 3 phase 480V motor (although I don't know if that makes a difference here). Would it be wiser from a total cost to run perspective to turn the motor off when not needed and then turn it back on to recharge the holding tank or would it be wiser to just run the pump constantly, probably under option 2 so the seal life is maximized? I suppose the size of the pressure holding tank comes into play. Assume the waterjet cuts 80% of the time and traverses 20% of the time. It may be as high as 90/10.
We have some large 5 hp blowers that when you close the blast gate on, pull nearly no amperage draw. My understanding is that it is more economical to leave it running but not under load than to start the entire motor again (momentum - a motor already started needs a lot of power to start up but not much to maintain running).
Anybody care to chime in with some practical considerations or issues I have possibly not addressed? Short of putting an amp meter on the motor, I don't have a clear answer what is "best" in terms of lowest cost to run over time.