Do you have any suggestions for a motor and a variable speed drive combination for a pump for a domestic shower?

We already have a fixed speed AC motor as a pump, but now  we want to do variable speed drive.
(so people can have variable pressure shower water, as they choose)
Our fixed speed motor has a fan, so we cannot use this motor with a variable speed set-up, as the fan would spin too slowly at the lower pumping settings.

We also want to do it cheaply, so am i right in saying that we are looking at a thyristor drive?

We are thinking of say a 3-speed drive, or in fact we may consider a more widely variable speed drive, if its not too expensive.

I believe Triac drives are out becuase of the non-symetric nature of triacs.(?)

I think Grundfos is big in the residential and commercial water supply/distribution systems.  They have pumps with integrated motor/VFD packages that might be a better solution for what you're wanting.

You will not be able to speed up the pump using a VFD.  So if the pump is not large enough for the shower now, you need a larger pump.  Then variable pressure for the shower would only require a pressure reducing valve.

As I envision your pumping arrangement, you have a booster pump (assumed to be centrifugal) in line with the shower head, and are looking for an adjustable boost pressure above the incoming line pressure.

It doesn't sound like you need a feedback loop or inherent pressure regulation; just an adjustable boost above baseline.

It seems to me that a series AC brush motor (think of an electric drill motor) might be the least costly and most effective way to accomplish this.  The AC brush motor can be controlled by a simple voltage chopper (think of the trigger on your variable speed drill) and is inherently a varying speed motor which would seem to want to develop a relatively constant torque above the float speed (as determined by the baseline flow) of the impeller.

Cumulative run times would not seem to be overly large so that brush life should not be an issue.  Above all, AC series brush motors (and controllers) can be very inexpensive, ase well as having what seems to be desireable characteristics for you application.

That motor shows to come only in single phase.  As Davidbeach says, you need a three phase motor to work with a VFD.  And as LionelHutz says, you will need a VFD to vary the voltage and frequency to control the speed.  I think the VFD will make more noise than restricting the flow with a valve.  In my experience pumps seem to run more quite when the flow is restricted.  You could test this by simply installing a ball valve on the discharge of the pump.  Have someone manually control the ball valve to maintain a steady pressure in the shower.  If it works as I believe it will, then a good control valve will be even more quite than the ball valve.

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