I gotta say i find the, what I call 'high tech' questions about c/h systems and alike fascinating even if at times the info flies over my head ! My questions are going to be considerably lower tech but I need to understand the basics before I get into the hunkier stuff !

My first dim question is ..
What IS the difference between service, isolation and check valves ? The Screwfix catalogue lists all three and they all look the same to me in that there is a ball assembly screw thing to stop water flow. Is there a difference in the diameter of the insides allowing less or more flow ?

Short and to the point. Excellent. Thank you thescruff.