Most booster pumps provide high pressure at low flow rates, typically 50 PSI at 12 GPM, while a dual-speed pump typically has its low speed at half of the high-speed RPM rate. The GPM varies roughly with the RPM so your high speed flow rate will probably be 50 GPM or more so your low speed may be 25 GPM or so. That's much greater than what the booster pump needs (the booster pump taps into a branch from the output of the main pump).
So your booster pump should run fine with a 2-speed pump set at low speed. It will, however, cut down your flow output through the returns, but that shouldn't be a problem since the water is just being redirected into your pressure-side cleaner.
Richard
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