If you got a solar heating system and the non-return valve needs replacement (salt water shorten the lifespan)...

If the non-return valve is made of a BRASS material, a PVC version is available.
The Brass valve = ± R210 and the PVC valve = ±R20

The system showing the brass valve position

The old Brass non return valve

The new PVC non-return valve

The Old BRASS valve.

The new PVC valve.

 

How the PVC valve fits inside the water feed pipes

The PVC valve fitting into the adapter

The PVC valve fits into the water feed line.

The valve fitting into the adapter