Solar pool heaters can have many different types of valves and it can get confusing, here is a run down of the different types and their functions.
Figure 1. Example manual pool heating system plumbing diagram
Figure 2. Example independent pool heating system plumbing diagram
Pump Non-return (17)
For an independent type system (or booster type, see different system set ups page) - there should either be a separate non-return valve (17) (with 6mm hole drilled in the flap) after the pump or the pump itself has an integrated non-return flap installed on the outlet. The function of this non-return is important. It prevents water from gushing down as the pump stops and potentially undoing the rotor by spinning it backwards. This valve should be non-perfectly sealing and should allow drain back to the pool. All solar pool heating systems are called drain back type systems (although not all water will drain from them).
Vacuum Release Valve (7)
Solar pool heater must have a vacuum release valve (7) installed on or just off the roof. As the pump stops and the system wants to drain back, the function of this valve is to open on negative pressure and allow air to enter the collectors so that the weight of the water pulling internally on system components does not internally crush collectors and PVC piping up on the roof. A system will not last long if this critical valve was not installed.
3-Way Ball Valve (9)
For manual systems there is a 3-way ball valve (9) installed on the main filter line, the purpose of this valve is to divert water up to the solar collectors. This valve can be manual or it can be motorized and controlled by a specialized controller. It is good practice to have a stop installed on the valve, to make sure it cannot open past a certain point so as not to over-pressurize collectors.
Ball Break Valve (16)
Pressure Limiting Valve
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