Theratherm setup bypass

Installing a bypass allows you to isolate the pool heat pump in winter while still allowing water to circulate around the pool water circuit to prevent freezing. The bypass can also be used to adjust the water flow through the heat pump by slightly opening or closing the bypass valve.

[@tasmedic]

Interesting Could you please explain why you're closing off some of the flow OUT of the heat pump? I'd have thought that if you closed that at all, there would be a chance of increasing the pressure inside the unit to unsafe levels. Isn't it best to leave out the valve on the output altogether and simply fit a check valve and 3-way joint there instead, then control the bypass with the single 3-way valve on the input? Is there something wrong with doing as I suggest? I do "get" the idea of being able to drain the item for the winter, but if that is the only reason for the output valve, best leave it wide open when the pump is running, yes? Thanks