Zone valve ratings and demo

hot_rod

On the spec sheet of any zone valve notice a number of pressure ratings.

The static pressure is basically the fill pressure of the hydronic system. Or main line water pressure in a potable water application. That could be 150- 200 psi or more

The maximum shutoff pressure, ∆P is the dynamic or flowing pressure the valve can shut -off. In a hydronic system this is the pressure the circulator develops, aka head. The pressure added to the fill pressure that the valves need to close off against.

This Caleffi 7.5 Cv valve has a 20 psi (∆P) shutoff. Different brands, different models will have different shut off capability.

A common HW 8 Cv valve shows an 8 psi shut-off number. Higher Cv will have lower shut-off pressure.

The next demo will be a HW valve test with one spring removed. Will it take the shut-off pressure down to 4 psi? 1/2 the valves rated close-off. If so, even the smallest of circulators could push flow past it.

I get some videos posted of the valves in operation.

So a spring return zone valve manufacturer needs to juggle the close off pressure, which is directly related to the spring force, against the close off speed.

Lower spring tension slows the valve close off, but you also need adequate close off, shut off pressure or you get unwanted "ghost" flow.

A system with a high head circ may be better served with a lower Cv zone valve. The Caleffi 1 Cv will close off 75 psi, for example. See the example of a 1, 3.5 and 7.5 Cv zone valve, the opening in the valve is the difference. Smaller hole= easier to close off flow.