motor torque vs. pump torque requirements
I'd like to learn more about motor torque vs. pump torque. anyone know any good publications to read?
Cameron Hydraulic Data has all sorts of useful information.
+1 on Eric's response to what you probably meant ... but assuming direct coupled, pump torque IS motor torque.
Originally Posted by Designer69
What the book will give you is a guideline to understand, with centrifugal pumps, the relationships among construction, pressure, and flow. The impact of fluid characteristics will be addressed.
George thanks for the replay, btw you hit the nail in the head for what I was asking.
I already purchased the book, but more specifically...
if I have a direct coupled motor/pump then you are saying the pump and motor will have the same torque characteristics.
so the pump manufacturer's torque-speed curve should match the motor manufacturer's torque-speed curve?
What George was saying is that the torque coming out of the motor must equal the torque absorbed by the pump, at the operating point.
The over-all torque characteristic of the motor must be different than that of the pump, otherwise the system could never accelerate up to the operating point. At start the motor must produce more torque than the pump consumes.
If you overlap a graph of the motor torque characteristic and the pump torque characteristic, the operating point will be at the intersection of the two. If there are multiple intersections, then there are multiple possible operating points.
Minor edits to a great explanation.
Originally Posted by winnie
Also just to be clear, the concept of multiple intersections would only come into play if you were selecting a pump/motor size without yet knowing the head and/or pressure. Once you know that for an application, i.e. once someone has already selected the right pump for the job, there will only be one torque requirement curve for it and so only one intersection.
On this graph, the pump torque requirement curve is the dotted line near the bottom. The motor would be selected so that at slip speed, it is supplying as much or more torque as the pump required, which happens at about 97% speed here.
wow this is great stuff. question.. The motor is spinning the pump as soon as it is started (throughout starting torque and breakdown torque) What is it that makes the operating point different?
also is there a book specifically on this stuff, really interesting.
First, there are a whole set of motor speed curves that are similar for a particular motor but vary as the supply voltage changes. These are not what the motor produces at steady-state, but rather are the limit capability of the motor at a specific supply voltage.
Second, in the illustration by Jraef the motor never had a steady-state torque load above the curve higher than its limit.
During acceleration of the motor from 0 RPM to its steady-state speed the motor torque limit curve would be followed in some manner close to what is on the graph. Inertia plus friction plus the pump load is what the motor torque is driving as it accelerates to the steady-state speed. So inertia and very little friction is the difference between the pump curve and the motor limit curve.
The accelerating force (torque) has an odd shape.
Remember that the sum of the forces is always zero. In this case part of that sum is the force to accelerate the mass.
Pump torque Vs Motor torque
After selecting the pump its torque speed characteristics should be sent to a motor manufacturer or supplier to quote for a suitable motor for that particular application.