How restrictive are fill valves?

[Grenage]

Our cold water tank isn't large enough for the power shower; I was going to add an additional tank, join with two 22mm links and move the fill/overflow to the second tank.

Would adding a second fill valve (off the 15mm feed) increase the flow to the existing tank? I can't imagine they are that restrictive but thought I'd check before doing the work.

 

[Madrab]

All depends on available mains flow and pressure, that will dictate whether there is a drop off in delivery when more than one fill valve is running at the same time. Is your mains pressure and flow suitable as the cold input needs to be able to at least match the outflow to both the cold feed and the feed to the HW cylinder.

When setting up tandem cisterns you need to set it up correctly to ensure proper flow through both cisterns. The overflow, any vent, and the fill valve(s) should be on one cistern with the other cistern providing all the system feeds to promote proper circulation. 2 x 22mm links, upper and lower promote better circulation but isn't really required unless the cisterns are large with a high output, one lower 22mm connection should be more than adequate.

Don't forget to consider the added weight of a 2nd cistern to the ceiling joists.

 

[Grenage]

Thanks madrab. I'll stick a jug under the inlet and see how much I get in a minute, then compare that to the garden tap. If it's a lot more then I'll look at a second inlet.

The existing tank isn't over a wall, the additional tank won't be either. I was going to put some 2x4 along several adjacent joists (that aren't supporting tank 1) and place tank 2 on those. If the tank is the same size or smaller then it should be fine.