pump question?
pump question?
(OP)
hello , new to forum , not an engineer , just a wrench puller .i would like some one to explain something to me about a single stage ansi pump . if i have to pumps in parallel , only using one pump at a time . both pumps identical , suction size,discharge size, same impeller size . one pump has a electric motor with a 200 hp rating and the other has an electric motor with a 400 hp rating , both motors run the same rpm . what happens to the flow or head between the two ? only running one pump at a time .





RE: pump question?
RE: pump question?
RE: pump question?
RE: pump question?
RE: pump question?
Assume you have truck and a small car. If you drive both with same constant speed, the much higher power of the truck does not make a difference. Not the best comparison but I cannot think of any better at the moment.
RE: pump question?
Ted
RE: pump question?
If the actual load is closer to 200 hp, then a fairly small increase in either flow rate or discharge pressure will tend to slow the motor down (decreasing the hp available to do work, and decreasing the flow rate through the pump). With the 400 hp motor, there is room to increase current (and therefore hp) to prevent the motor from slowing down with increased load.
David
RE: pump question?
Ted
RE: pump question?
Regards,
SNORGY.
RE: pump question?
RE: pump question?
Your example simply assumed a set of conditions far from any interesting boundary. The OP never mentioned where on the pump curve they were operating. You can assume 100 hp and system load and discuss what (doesn't) happen as you swap pumps. I chose to assume a point closer to a limit because I found it more interesting.
The universe that I live in is really short on systems with a "constant system load". If the OP has such a system and it is operating far from the hp limit of the 200 hp motor then I would be surprised that they had installed the second pump with a 400 hp motor. But people surprise me all the time.
David
RE: pump question?
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: pump question?
RE: pump question?
Re the last para of your first post of 14 Jan.
Increase in the load of a pump, will always increase the power draw from the motor,with reduction in speed due increase in slippage with a corresponding increase in the motor current even if the motor was already operating at it rated power.The motor will just being over loaded and burn out the insulation eventually if allow to run for extended period of time. The time take to cause damage is depending on how much is the over load, the ambient temp.and the insulation material rating.
RE: pump question?
Try www.mcnallyinstitute.com & www.pump-zone.com for more technical papers on pumps.
By the way banshee33 enough of the 'just a wrench puller". We are all part of teams bringing together systems and keeping them working. I have learnt a heck of a lot of stuff from guys on the tools. Even started there myself as a spotty 15 yo. My Dad was an electrical fitter and he taught me heaps. He had no academic training but started a factory during WWII injection moulding toys.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/
RE: pump question?
Depending on how they use electricity, electric utility customers are charged for different electric services. Along with a basic customer charge – which is a set fee paid monthly or seasonally – most customers pay for the energy they use (measured in kilowatt-hours, abbreviated kWh).
Larger users of electricity are also charged for something called demand (measured in kilowatts, abbreviated kW).
The demand charge is typically based on the largest motor in the facility.
Example: A customer runs a 400 horsepower (hp) pump for only five hours during July:
Demand Charge = 400 hp x .746 kW/hp x $8.03/kW = $2,396.15
Energy Charge = 400 hp x .746 kW/hp x 5 Hr x $0.034/kWh = $50.73
The demand charge will be a large part of the bill if the facility uses a lot of power over a short period of time, and a smaller part of the bill if the customer uses power at a more or less constant rate throughout the month.
The demand charge may be enough to buy a smaller motor.
The "Demand" charge is a premium price you pay to guarantee that all of the power your business needs will be there when you need it.
RE: pump question?
In your specific calculated scenario, I think that would force me to switch to IC engine.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: pump question?
RE: pump question?
The utility representative walks through the facility and sets the demand charge for the largest motor in the facility.
RE: pump question?
David
RE: pump question?
Most of the motor to load efficiency curves I've seen are more or less flat to 50-60% load and head downhill fast from there. I idealized the curves to a straight line from 0,0 to 75% eff at 50% load, 90% eff at 60% load to 94% eff for a new hi eff motor at full load. And you might also get 105% efficency at 110% load ... believe it or not.
bimr, david.. Thx
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso