Hi, I'm trying to get my head around what's required to install a semi pumped system with a Rayburn Royal. I'm likely going to fit a high output boiler into it for a start, in case someone pipes up with "forget it" I've got a garage full of logs and some, plus a Rayburn in there.
Anyway I'm studying this diagram and trying to be sure of how a gravity check valve works. The pipes from boiler to/from the cylinder I understand they're 28mm. I take it the pipework for the two heating legs ought to be 22mm with 15mm teeing off to radiators and a 22mm check valve must obviously be for water to flow in the direction towards the radiators.
How does it work though? Is it simply that the pump creates the necessary 'draw'(what would that be properly called) required for the valve port to open, while gravity alone would not have sufficient pressure to push the spring loaded device and allow water to pass? I can understand a zone valve better, along with the pump being controlled by stats.
Is a gravity check valve something unique or simply a bog standard single check valve? Clearly it's the cheaper option from a zone valve.