Positive Displacement Pumps on DC- Selection, Design Considerations

[stabmaster]

I am trying to find the appropriate pump for my design. Simply, there is a hot water storage vessel open to atmosphere.
The water may be from 65-90C.
The elevation before the pump is 5 feet.
The elevation after the pump is 15 feet.
The required flowrate is from 0.5-10 GPM.
The return path is open and it drains down by gravity.

I am using a 0-90VDC motor on a variable speed drive. The water is pumped through solar thermal collectors on top of a structure. The flowrate depends on the temperature differential, attempting to maintain a setpoint by PID. When temperature differential is minimal, the DC motor reverses, draining the fluid (water) from the circuit.

My questions relate to the pump itself.
Is a rotary vane the most appropriate design?
The other option seems to be the internal gear.

The problem with most of these rotary vanes are that they are generally light duty, not rated for continuous.

Over the average day, there is a possibility of perhaps 12 hours of continuous operation. The speed will vary, but this is the only moving part in our system; therefore, we want to have a robust solution, even if it were to cost extra.

Further consideration: the controller that I am developing will calculate the diff. temperature and the flow rate based on the output to the variable speed drive. If the flowrate/pump speed relation is well established, the major source of error may be the reduction of efficiency of the motor due to wear over the years. Does this sound reasonable? I would like to select a pump which wears very little.

It appears that start-up is a big issue with pumps on a/c motors. Is there any design considerations in terms of starting the pump on a dc motor? I plan to pump water through the circuit to the maximum rate for 5 minutes on start-up, before the PID control begins.

 

[stabmaster]

I'm lost on finding the pump. There are too many out there, and no review site or comparison chart. No one source for many manufacturers. Is there a good, reliable, cost effective, quiet, reversible positive displacement pump?

 

[ScottyUK]

Taking a step back, is there a specific reason you are using a 90V DC motor instead of a standard AC machine? AC motors are capable of pretty much everything a DC machine is capable of except in the most demanding servo environments, and are both cheaper and more robust than an equivalent DC design.

If you used an AC motor with variable speed drive you will find most drives have a PID loop built in.

I'm also surprised by choice of a PD pump but I'll let the pump experts comment on that.


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Sometimes I only open my mouth to swap feet...

 

[Artisi]

Is the to use a DC motor necessary, if not why are you trying to re-invent the wheel.

There are a number of manufactureres who can supply pumps and controllers for this application with millions of units in the field and a vast history of experience.

 

[BigInch]

Perhaps an adjacent PV array powers the motor, but in that case, would not a 48 VDC max be easier to handle? Over 48 VDC, switching starts to get into the heavier duty range ... and a bit expensive for my pocket.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com